Hans Brix

Abstract: The effects of inorganic nitrogen (N) source (NH4+, NO3- or both) on growth, biomass allocation, photosynthesis, N uptake rate, nitrate reductase activity and mineral composition of Canna indica were studied in hydroponic culture. The relative growth rates (0.05-0.06 g g(-1) d(-1)), biomass allocation and plant morphology of C. indica were indifferent to N nutrition. However, NH4+ fed plants had higher concentrations of N in the tissues, lower concentrations of mineral cations and higher contents of chlorophylls in the leaves compared to NO3- fed plants suggesting a slight advantage of NH4+ nutrition. The NO3- fed plants had lower light-saturated rates of photosynthesis (22.5 mu mol m(-2) s(-1)) than NH4+ and NH4+/NO3- fed plants (24.4-25.6 mu mol m(-2) s(-1)) when expressed per unit leaf area, but similar rates when expressed on a chlorophyll basis. Maximum uptake rates (V-max) of NO3- did not differ between treatments (24-35 mu mol N g(-1) root DW h(-1)), but V-max for NH4+ was highest in NH4+ fed plants (81 mu mol N g(-1) root DW h(-1)), intermediate in the NH4NO3 fed plants (52 mu mol N g(-1) root DW h(-1)), and lowest in the NO3- fed plants (28 mu mol N g(-1) root DW h(-1)). Nitrate reductase activity (NRA) was highest in leaves and was induced by NO3- in the culture solutions corresponding to the pattern seen in fast growing terrestrial species. Plants fed with only NO3- had high NRA (22 and 8 mu mol NO2- g(-1) DW h(-1) in leaves and roots, respectively) whereas NRA in NH4+ fed plants was close to zero. Plants supplied with both forms of N had intermediate NRA suggesting that C indica takes up and assimilate NO3- in the presence of NH4+. Our results show that C indica is relatively indifferent to inorganic IN source, which together with its high growth rate contributes to explain the occurrence of this species in flooded wetland soils as well as on terrestrial soils. Furthermore, it is concluded that C. indica is suitable for use in different types of constructed wetlands. (C) 2009 Elsevier B.V. All rights reserved.

Abstract:

Abstract: Application of low doses of alum to treatment wetlands to reduce elevated outflow winter phosphorus concentrations were tested in mesocosms vegetated with either Typha domingensis, Schoenoplectus californicus, or submerged aquatic vegetation (SAV) (Najas guadalupensis-dominated). Alum was pumped to experimental units at a rate of 0.91 g Al m(-2) d(-1) and water quality monitored for 3 months. The alum application significantly improved the outflow water quality and overall the growth of the plants was unaffected by the alum application. Biomass and growth varied between species and through time, but no significant effects of alum application were detected. The concentrations of nutrients and mineral elements in the aboveground tissues differed between species and over time, but only the concentration of Al in plant tissue was increased by alum additions. The concentration of Al was 50-fold higher in alum-treated SAV as compared to the control, and in Typha and Schoenoplectus the concentrations were 4- and 2-fold, higher, respectively. The N/P ratios in the plant tissues were low (<10) suggesting that their growth and biomass was limited by nitrogen. The research suggests that a continuous or seasonal low-dosage alum application to treatment wetlands provides an effective tool to maintain discharge concentrations within permitted values during the inefficient winter treatment times. We suggest that the use of alum should be restricted to treatment wetland areas dominated by emergent vegetation as the effects of the elevated Al concentrations in SAV needs further study. (C) 2010 Elsevier Ltd. All rights reserved.

Abstract: In the Florida Everglades, the expansion of cattail (Typha domingensis) into areas once dominated by sawgrass (Cladium jamaicense) has been attributed to altered hydrology and phosphorus (P) enrichment. The objective of this study was to quantify the interactive effects of P availability and soil redox potential (Eh) on the growth and nutrient responses of Typha, which may help to explain its expansion. The study examined the growth and nutrient responses of Typha to the interactive effects of P availability (10, 80 and 500 mu g P L-1) and Eh level (-150, +150 and +600 mV). Plants were grown hydroponically in a factorial experiment using titanium (Ti3+) citrate as a redox buffer. Relative growth rate, elongation, root-supported tissue/root ratio, leaf length, lateral root length and biomass, as well as tissue nutrient concentrations, were all adversely affected by low Eh conditions. P availability compensated for the negative effect of low Eh for all these variables except that low P stimulated root length and nutrient use efficiency. The most growth-promoting treatment combination was 500 mu g P L-1/ + 600 mV. These results, plus previous data on Cladium responses to P/Eh combinations, document that high P availability and low Eh should benefit Typha more than Cladium as the growth and tissue nutrients of the former species responded more to excess P, even under highly reduced conditions. Therefore, the interactive effects of P enrichment and Eh appear to be linked to the expansion of Typha in the Everglades Water Conservation Area 2A, where both low Eh and enhanced phosphate availability have co-occurred during recent decades.

Abstract: The treatment capacity of constructed wetlands is expected to be high in tropical areas because of the warm temperatures and the associated higher rates of microbial activity. A pilot scale horizontal subsurface flow constructed wetland system filled with river sand and planted with Phragmites vallatoria (L) Veldkamp was set up in the southern part of Vietnam to assess the treatment capacity and the removal rate kinetics under tropical conditions. The system received municipal wastewater at four hydraulic loading rates (HLRs) of 31, 62, 104 and 146 mm day(-1). Removals of TSS, BOD5 and COD were efficient at all HLRs with mean removal rates of 86-95%, 65-83% and 57-84%, respectively. Removals of N and P decreased with HLRs and were: NH4-N 0-91%; TN 16-84% and TP 72-99%. First-order area-based removal rate constants (k, m year(-1)) estimated from sampling along the length of the wetland from inlet to outlet at the four HLRs were in the range of 25-95 (BOD5), 22-30 (COD), 31-115 (TSS), 5-24 (TN and TKN) and 41-84 (TP) at background concentrations (C*) of 5. 10, 0, 1.5 and 0 mg L-1, respectively. The estimated k-values should not be used for design purposes, as site-specific differences and stochastic variability can be high. However, the study shows that domestic wastewater can be treated in horizontal subsurface flow constructed wetland systems to meet even the most stringent Vietnamese standards for discharge into surface waters. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: Background: Cattail (Typha domingensis) has been spreading in phosphorus (P) enriched areas of the oligotrophic Florida Everglades at the expense of sawgrass (Cladium mariscus spp. jamaicense). Abundant evidence in the literature explains how the opportunistic features of Typha might lead to a complete dominance in P-enriched areas. Less clear is how Typha can grow and acquire P at extremely low P levels, which prevail in the unimpacted areas of the Everglades. Results: Apparent P uptake kinetics were measured for intact plants of Cladium and Typha acclimated to low and high P at two levels of oxygen in hydroponic culture. The saturated rate of P uptake was higher in Typha than in Cladium and higher in low-P acclimated plants than in high-P acclimated plants. The affinity for P uptake was twofold higher in Typha than in Cladium, and two- to three-fold higher for low-P acclimated plants compared to high-P acclimated plants. As Cladium had a greater proportion of its biomass allocated to roots, the overall uptake capacity of the two species at high P did not differ. At low P availability, Typha increased biomass allocation to roots more than Cladium. Both species also adjusted their P uptake kinetics, but Typha more so than Cladium. The adjustment of the P uptake system and increased biomass allocation to roots resulted in a five-fold higher uptake per plant for Cladium and a ten-fold higher uptake for Typha. Conclusions: Both Cladium and Typha adjust P uptake kinetics in relation to plant demand when P availability is high. When P concentrations are low, however, Typha adjusts P uptake kinetics and also increases allocation to roots more so than Cladium, thereby improving both efficiency and capacity of P uptake. Cladium has less need to adjust P uptake kinetics because it is already efficient at acquiring P from peat soils (e.g., through secretion of phosphatases, symbiosis with arbuscular mycorrhizal fungi, nutrient conservation growth traits). Thus, although Cladium and Typha have qualitatively similar strategies to improve P-uptake efficiency and capacity under low P-conditions, Typha shows a quantitatively greater response, possibly due to a lesser expression of these mechanisms than Cladium. This difference between the two species helps to explain why an opportunistic species such as Typha is able to grow side by side with Cladium in the P-deficient Everglades.

Abstract: Constructed wetlands have a good potential for wastewater treatment in developing countries due to the simple operation and low implementation costs. Ornamental plants like Canna and Heliconia are used in the wetlands to increase their aesthetic value and these two species were compared in this study. Six pilot scale horizontal subsurface flow constructed wetland units were constructed at the Asian Institute of Technology (AIT) campus in Bangkok, Thailand, of which three were planted with Heliconia psittacorum L.f. x H. Spathocircinata (Aristeguieta) and three with Canna x generalis L. Bailey. The beds were loaded with domestic wastewater in four trials with hydraulic loading rates ranging from 55 to 440 mm d(-1) corresponding to nominal detention times between 12h and 4 days. Both plant species grew well in the systems and especially Canna had high growth rates (3100 +/- 470 g DW m(-2) yr(-1)) compared to Heliconia (550 +/- 90 g DW m(-2) yr(-1)). TSS mass removal rates were very high with efficiencies >88% even at hydraulic loading rates of 440 mm d(-1). COD mass removal rates varied between 42 and 83% depending on the loading rates. The removal rate constants for COD as fitted by the first-order k-C-center dot model were estimated to be 0.283 and 0.271 m d(-1) for Canna and Heliconia beds, respectively (C-center dot = 28.1 and 26.7 mg l(-1)). Removals of nitrogen (N) and phosphorus (P) were low compared to the loading rates, but removal of total-N was higher in the beds planted with Canna than in beds with Heliconia because of the higher growth rate of Canna. it is concluded that ornamental species like Canna and Heliconia can be used to enhance the aesthetic appearance and hence the public acceptance of wastewater treatment systems in tropical climates. Canna is the preferred species from a treatment perspective because of its more vigorous growth, but since Heliconia has an economic potential as cut flowers may be preferred in many cases. (C) 2008 Elsevier B.V All rights reserved.

Abstract: Occurrence and removal efficiencies of 13 pharmaceuticals and personal care products (PPCPs) as well as BOD5, TSS and NH4+ were evaluated for the first time in thirteen onsite household secondary wastewater treatment systems, including two compact biofilters followed by Filtralite-P filter units, two biological sand filters, five horizontal subsurface flow and four vertical flow constructed wetlands. As expected, all systems removed TSS and BOD5 efficiently (>95% removal). The PPCP removal efficiencies exceeded 80% with the exception of carbamazepine, diclofenac and ketoprofen because of their more recalcitrant characteristics. Despite no statistical differences in the PPCP removal were observed between the different systems evaluated, the vegetated vertical flow constructed wetlands which had unsaturated flow and hence better oxygenation, appeared consistently to perform better in terms of PPCP removal efficiency. The combined effects of vegetation and unsaturated water flow provide a higher tolerance to variations in loading rate and a consistent removal rate. (C) 2008 Elsevier Ltd. All rights reserved.

Abstract: In this study we assessed the growth, morphological responses, and N uptake kinetics of Salvinia natans when supplied with nitrogen as NO3-, NH4+, or both at equimolar concentrations (500 mu M). Plants supplied with only NO3- had lower growth rates (0.17 +/- 0.01 g g(-1) d(-1)), shorter roots, smaller leaves with less chlorophyll than plants supplied with NH4+ alone or in combination with NO3- (RGR = 0.28 +/- 0.01 g g(-1) d(-1)). Ammonium was the preferred form of N taken up. The maximal rate of NH4+ uptake (V-max) was 6-14 times higher than the maximal uptake rate of NO3- and the minimum concentration for uptake (C-min) was lower for NH4+ than for NO3-. Plants supplied with NO3- had elevated nitrate reductase activity (NRA) particularly in the roots showing that NO3- was primarily reduced in the roots, but NRA levels were generally low (< 4 mu mol NO2- g(-1) DW h(-1)). Under natural growth conditions NH4+ is probably the main N source for S. natans, but plants probably also exploit NO3- when NH4+ concentrations are low. This is suggested based on the observation that the plants maintain high NRA in the roots at relatively high NH4+ levels in the water, even though the uptake capacity for NO3- is reduced under these conditions. (c) 2008 Elsevier B.V. All rights reserved.

Abstract: A large variety of aquatic animals was found to emit the potent greenhouse gas nitrous oxide when nitrate was present in the environment. The emission was ascribed to denitrification by ingested bacteria in the anoxic animal gut, and the exceptionally high N2O-to-N-2 production ratio suggested delayed induction of the last step of denitrification. Filter- and deposit-feeding animal species showed the highest rates of nitrous oxide emission and predators the lowest, probably reflecting the different amounts of denitrifying bacteria in the diet. We estimate that nitrous oxide emission by aquatic animals is quantitatively important in nitrate-rich aquatic environments like freshwater, coastal marine, and deep-sea ecosystems. The contribution of this source to overall nitrous oxide emission from aquatic environments might further increase because of the projected increase of nitrate availability in tropical regions and the numeric dominance of filter- and deposit-feeders in eutrophic ecosystems.

Abstract: Osmotic and ion-specific effects of NaCl and Na2SO4 on Phragmites australis (Cav.) Trin ex. Steud. were investigated in a laboratory experiment by examining effects of iso-osmotic solutions of NaCl and Na2SO4 on growth, osmolality of cell sap, proline content, elemental composition and gas exchange. Plants were supplied with a control standard nutrient solution (Psi = -0.09 MPa) or solutions of NaCl or Na2SO4 at water potentials of -0.50, -1.09 or -1.74 MPa. Salt treatments increased root concentrations of Na and S or Cl, whereas P. australis had efficient mechanisms for exclusion of Na and S and partly Cl ions from the leaves. Incomplete exclusion of Cl from the leaves may affect aboveground biomass production, which was significantly more reduced by NaCl than Na2SO4. Stomatal conductance was negatively influenced by decreasing water potentials caused by NaCl or Na2SO4, implying that a non-significant photosynthetic depression observed in plants grown at -1.74 MPa was mainly due to osmotically induced stomatal closure. This was supported by decreasing internal CO2 concentrations. Saline conditions increased the intrinsic water use efficiency and did not alter photosynthetic parameters derived from light response curves, supporting the assumption of a well-functioning CO2 utilization in salt stressed plants. The leaf proline concentration increased equally in NaCl and Na2SO4-treated plants, and may play an important role as a compatible organic solute. P. australis possesses a range of mechanisms conferring tolerance to both NaCl and Na2SO4 stress and except in terms of growth the phytotoxicity of NaCl and Na2SO4 are comparable. (c) 2008 Elsevier B.V. All rights reserved.

Abstract: The ability of vertical flow (VF) constructed wetland systems to treat high-strength (ca. 300 mg L-1 of COD and ca. 300 mg L-1 total-nitrogen) wastewater under tropical climatic conditions was studied during a S-month period. Nine 0.8-m diameter experimental VF units (depth 0.6 m) were used: three units were planted with Typha angustifolia L., another three units were planted with Cyperus involucratus Rottb and three units were unplanted. Each set of units were operated at hydraulic loading rates (HLRs) of 20, 50 and 80 mm d(-1). Cyperus produced more shoots and biomass than the Typha, which was probably stressed because of lack of water. The high evapotranspirative water loss from the Cyperus systems resulted in higher effluent concentrations of COD and total-P, but the mass removal of COD did not differ significantly between planted and unplanted systems. Average mass removal rates of COD, TKN and total-P at a HLR of 80 mm d(-1) were 17.8, 15.4 and 0.69 g m(-2) d(-1). The first-order removal rate constants at a HLR of 80 mm d-1 for COD, TKN and total-P were 49.8, 30.1 and 13.5 In year(-1), respectively, which is in the higher range of k-values reported in the literature. The oxygen transfer rates were ca. 80 g m(-2) d(-1) in the planted systems as opposed to ca. 60 g m(-1) d(-1) in the unplanted systems. The number of Nitrosomonas was two to three orders of magnitude higher in the planted systems compared to the unplanted systems. Planted systems thus had significantly higher removal rates of nitrogen and phosphor-us, higher oxygen transfer rates, and higher quantities of ammonia-oxidizing bacteria. None of the systems did, however, fully nitrify the wastewater, even at low loading rates. The vertical filters did not provide sufficient contact time between the wastewater and the biofilm on the gravel medium of the filters probably because of the shallow bed depth (0.6 m) and the coarse texture of the gravel. It is concluded that vertical flow constructed wetland systems have a high capacity to treat high-strength wastewater in tropical climates. The gravel and sand matrix of the vertical filter must, however, be designed in a way so that the pulse-loaded wastewater can pass through the filter medium at a speed that will allow the water to drain before the next dose arrives whilst at the same time holding the water back long enough to allow sufficient contact with the biofilm on the filter medium. (C) 2008 Elsevier B.V. All rights reserved.

Abstract: Preference for NH4+ or NO3- nutrition by the perennial legume Sesbania sesban (L.) Merr. was assessed by supplying plants with NH4+ and NO3- alone or mixed at equal concentrations (0.5 mM) in hydroponic culture. In addition, growth responses of S. sesban to NH4+ and NO3- nutrition and the effects on root nodulation and nutrient and mineral composition of the plant tissues were evaluated in a hydroponic setup at a range of external concentration of NH4+ and NO3- (0, 0.1, 0.2, 0.5, 2 and 5 mM). Seedlings of S. sesban grew equally well when Supplied with either NH4+ or NO3- alone or mixed and had high relative growth rates (RGRs) ranging between 0.19 and 0.21 d(-1). When larger plants of S. sesban were supplied with NH4+ or NO3- alone, the RGRs and shoot elongation rates were not affected by the external concentration of inorganic N. At external N concentrations up to 0.5 mM nodulation occurred and contributed to the N nutrition through fixation of gaseous N-2 from the atmosphere. For both NH4+ and NO3--fed plants the N concentration in the plant tissues, particularly water-extractable NO3-, increased at high supply concentrations, and concentrations of mineral cations generally decreased. It is concluded that S. sesban can grow without an external inorganic N supply by fixing atmospheric N-2 gas via root nodules. Also, S. sesban grows well on both NH4+ and NO3- as the external N source and the plant can tolerate relatively high concentrations of NH4+. This wide ecological amplitude concerning N nutrition makes S. sesban very useful as a N-2-fixing fallow crop in N deficient areas and also a candidate species for use in constructed wetland systems for the treatment of NH4+ rich waters. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: Four different pilot-scale treatment units were constructed to compare the feasibility of treating domestic wastewater in the City of Heraklio, Crete, Greece: (a) a free water surface (FWS) wetland system, (b) a horizontal subsurface flow (HSF) wetland system, (c) a rotating biological contactor (RBC). and (d) a packed bed filter (PBF). All units operated in parallel at various hydraulic loading rates (HLR) ranging from 50% to 175% of designed operating HLR. The study was conducted during an 8 month period and showed that COD removal efficiency of HSF was comparable (> 75%) to that of RBC and PBF, whereas that of the FWS system was only 57%. Average nutrient removal efficiencies for FWS, HSF, RBC and PBF were 6%, 21%, 40% and 43%, respectively for total nitrogen and 21%, 39%, 41% and 42%, respectively for total phosphorus. Removals of total coliforms were lowest in FWS and PBF (1.3 log units) and higher in HSF and RBC (2.3 to 2.6 log units). HSF showed slightly lower but comparable effluent quality to that of RBC and PBF systems, but the construction cost and energy requirements for this system are significantly lower. Overall the final decision for the best non-conventional wastewater treatment system depends on the construction and operation cost, the area demand and the required quality of effluent. (C) 2009 Published by Elsevier B.V.

Abstract: The startup of a wet retention pond designed for extended stormwater treatment was monitored by more than one year of continual measurement of hydraulic parameters, nutrients and quality parameters in the pond itself (pH, temperature, dissolved oxygen, turbidity). The data revealed that photosynthesis played an important role for dissolved oxygen and pH for most of the year. Another important observation was that the pond behaved more like a completely mixed reactor than like a plug flow reactor-even though the length to width ratio was as high as 4.5:1. The pond was equipped with sand filters and sorption filters whereby very good nutrient removal efficiencies were achieved.

Abstract: The ability of Salvinia natans (L.) All. to tolerate growth in oxic, hypoxic and anoxic nutrient solutions when Supplied with either NH4+ or NO3- were studied in the laboratory to test the hypothesis that inorganic N-source affects the response of the plants to O-2 deprivation. The relative growth rate (RGR) was significantly reduced in the anoxic treatment, but in the hypoxic treatment RGR was only slightly affected. The NH4+ fed plants generally had a higher shoot to root ratio than the NO3- fed plants, and highest in the anoxic treatment. Plants had more roots and larger leaves when supplied with NH4+ as compared with NO3-, particularly in the oxic treatment, and root length was most affected by O-2 deprivation for NO3- fed plants. Cell walls in the endodermis, the bundle sheath and the cortex adjacent to endodermis developed thickened sclerenchymatous walls when deprived of O-2, and more so in plants supplied with NO3-. Plants lost chlorophylls, had lower rates of photosynthetic electron transport (ETRmax) and lower quantum yields (Fv/Fm ratios) when grown in anoxic solutions, and the negative effects were mildest for NO3- fed plants suggesting that NO3- may be used as an alternative e(-)-acceptor in non-cyclic electron transport in the chloroplasts. Overall S. natans grew best on NH4+, but it also grew well on NO3-, and the O-2 stress symptoms differed somewhat between NH4+ fed and NO3- fed plants. However, because N-form itself significantly influenced morphology and cell metabolism, it was impossible to conclusively identify the role of N-form for the O-2 stress reactions. S. natans is not well-adapted to grow in O-2 deficient waters and will not tolerate completely anoxic conditions as will prevail in waters receiving high loadings of organic pollutants such as livestock wastewater. (c) 2009 Elsevier B.V. All rights reserved.

Abstract: The effects of NaCl salinity on growth, morphology and photosynthesis of Salvinia natans (L.) All. were investigated by growing plants in a growth chamber at NaCl concentrations of 0, 50, 100 and 150 mM. The relative growth rates were high (ca. 0.3 d(-1)) at salinities up to 50 mM and decreased to less than 0.2 d(-1) at higher salinities, but plants produced smaller and thicker leaves and had shorter stems and roots, probably imposed by the osmotic stress and lowered turgor pressure restricting cell expansion. Na+ concentrations in the plant tissue only increased three-fold, but uptake of K+ was reduced, resulting in very high Na+/K+ ratios at high salinities, indicating that S. natans lacks mechanisms to maintain ionic homeostasis in the cells. The contents of proline in the plant tissue increased at high salinity, but concentrations were very low (<0.1 mu mol g(-1) FW), indicating a limited capacity of S. natans to synthesize proline as a compatible compound. The potential photochemical efficiency of PSII (F-v/F-m) of S. natans remained unchanged at 50 mM NaCl but was reduced at higher salinities, and the photosynthetic capacity (ETRmax) was significantly reduced at 50 mM NaCl and higher. It is concluded that S. natans is a salt-sensitive species lacking physiological measures to cope with exposure to high NaCl salinity. At low salinities salts are taken up and accumulate in old leaves. and high growth rates are maintained because new leaves are produced at a higher rate than for plants not exposed to salt. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: Many plants develop toxicity symptoms and have reduced growth rates when supplied with ammonium (NH4+) as the only source of inorganic nitrogen. In the present study, the growth, morphology, NH4+ uptake kinetics and mineral concentrations in the tissues of the free-floating aquatic plant Salvinia natans (water fern) supplied exclusively with NH4+-N at concentrations of 0.25-15 mM were investigated. S. natans grew well, with relative growth rates of c. 0.25 g g(-1) d(-1) at external NH4+ concentrations up to 5 mM, but at higher levels growth was suppressed and the plants had small leaves and short roots with stunted growth. The high-affinity transport system (HATS) that mediate NH4+ uptake at dilute NH4+ levels was downregulated at high NH4+ concentrations with lower velocities of maximum uptake (V-max) and higher half-saturation constants (K-1/2). High NH4+ levels also barely affected the concentrations of mineral cations and anions in the plant tissue. It is concluded that S. natans can be characterized as NH4+-tolerant in line with a number of other species of wetland plants as growth was unaffected at NH4+ concentrations as high as S mM and as symptoms of toxicity at higher concentrations were relatively mild. Depolarization of the plasma membrane to the equilibrium potential for NH4+ at high external concentrations may be a mechanism used by the plant to avoid excessive futile transmembrane cycling. S. natans is tolerant to the high NH4+ levels that prevail in domestic and agricultural wastewaters, and the inherent high growth rate and the ease of biomass harvesting make S. natans a primary candidate for use in constructed wetland systems for the treatment of various types of nitrogen-rich wastewaters. (C) 2008 Elsevier B.V. All rights reserved.

Abstract: The ability to cope with NH4+-N was studied in the littoral helophytes Phragmites australis and Glyceria maxima, species commonly occupying fertile habitats rich in NH4+ and often used in artificial wetlands. In the present study, Glyceria growth rate was reduced by 16% at 179 mu M NH4+-N, and the biomass production was reduced by 47% at 3700 mu M NH4+-N compared to NO3--N. Similar responses were not found in Phragmites. The amounts (mg g(-1) dry wt) of starch and total non-structural carbohydrates (TNC) in rhizomes were significantly lower in NH4+ (8.9; 12.2 starch; 20.1; 41.9 TNC) compared to NO3- treated plants (28.0; 15.6 starch; 58.5; 56.3 TNC) in Phragmites and Glyceria, respectively. In addition, Glyceria showed lower amounts (mg g(-1) dry wt) of soluble sugars, TNC, K+, and Mg2+ in roots under NH4+ (5.6; 14.3; 20.6; 1.9) compared to NO3- nutrition (11.6; 19.9; 37.9; 2.9, for soluble sugars, TNC, K+, and Mg2+, respectively), while root internal levels of NH4+ and Ca-2(+) (0.29; 4.6 mg g(-1) dry wt, mean of both treatments) were only slightly affected. In Phragmites, no changes in soluble sugars, TNC, Ca2+, K+, and Mg2+ contents of roots (7.3; 14.9; 5.1; 17.3; 2.6 mg g(-1) dry wt, means of both treatments) were found in response to treatments. The results, therefore, indicate a more pronounced tolerance towards high NH4+ supply in Phragmites compared to Glyceria, although the former may be susceptible to starch exhaustion in NH4+-N nutrition. In contrast, Glyceria's ability to colonize fertile habitats rich in NH4+ is probably related to the avoidance strategy due to shallow rooting or to the previously described ability to cope with high NH4+ levels when P availability is high and NO3- is also provided. (c) 2007 Elsevier B.V. All rights reserved.

Abstract: Genetic diversity, population structure and interrelationships were investigated in eight populations of the common reed, Phragmites australis, in the Po Plain, Italy, by means of amplified fragments length polymorphisms (AFLPs) and random amplified polymorphic DNAs (RAPDs). Patterns of genetic diversity were analysed in relation to size, age and degree of human impact in the wetlands and compared with that of a distant population in Romania. Genetic distances between Po Plain clones and geographically distant clones were measured to determine the geographical extent of the gene pool. Nearly all populations studied are polyclonal and little correlation was found between genetic diversity and size, age and degree of human impact on the wetlands. One large (86 ha) monoclonal stand occurred in an old wetland with rather stable environmental conditions over a long time period, whereas polyclonal stands were younger and characterized by disturbance. On the interpopulation level it was not possible to differentiate between Po Plain populations and the Romanian population, indicating that a very extensive gene pool exists in Europe, to which both Po Plain and Romanian populations belong. There is however a certain degree of genetic structure among the populations that is not correlated with geographic distance, but is most likely related to P. australis colonization dynamics. A significant "stepwise" increase in average genetic distances was observed between clones >500 and > 1500 km distant suggesting some kind of genetic pattern on a very large scale. Based on these results, P. australis populations in Europe could be considered members of a single meta-population. (c) 2007 Elsevier B.V. All rights reserved.

Abstract: Growth and nutrient responses of Rhynchospora tracyi (Tracy's beak-rush), a wet prairie species in the Florida Everglades, to redox intensity and phosphate availability were examined under controlled redox intensities (Eh: -150, +150, and +600 mV) and phosphate levels (P: 10, 80, and 500 mu g P l(-1)) for 60 days. Root length, total biomass, and photosynthesis of R. tracyi were higher at Eh(+600) than at Eh(-150). Growth variables (e.g., shoot length, biomass, relative growth rate, and root porosity) significantly increased with phosphate availability, while R. tracyi allocated more biomass to shoots and rhizomes than to roots at the higher P levels. Tissue P concentration increased 5-6 times when phosphate availability increased from 10 mu g P l(-1) to 500 mu g P l(-1), while P use efficiency and molar N:P ratio significantly decreased with P availability. Net P accumulation was significantly higher at P-500 than at P-10 across the three redox intensities. Tissue N concentration was significantly higher at Eh(+600) than at Eh(-150), and higher at P-500 than at P-10. In terms of plant performance at the three redox intensities, we conclude that R. tracyi is not well-adapted to strongly reduced conditions that would result from lengthened hydroperiods. Altered hydroperiods may be a major reason why wet prairie species, such as R. tracyi, have decreased in abundance in some areas of the Everglades.

Abstract: Herbarium collections are a valuable source of genetic information. Even though the DNA obtained from the specimens is often highly fragmented and present in small quantities, it has been successfully used particularly for DNA sequencing and microsatellite analysis. The present study shows that the quality is often sufficient for use also for AFLPs. With this technique, a considerable number of DNA fragments with unknown sequence from the entire genome of the plant are amplified, often with the purpose of phylogeographic studies or analyses of interrelationships of closely related species. In order to avoid the effects of potential artefacts resulting from DNA degradation, such as "false polymorphisms", it is suggested that fresh samples should always be included for comparison, and that AFLP chromatograms based on herbarium specimens should be included in analyses only when they contain AFLP fragments monomorphic among the fresh samples, and when signal quality is comparable to that of fresh samples.

Abstract: The germination of Sesbania sesban seeds was studied under controlled environmental conditions. Interactive effects of temperature and light, effects of salinity and effects of different pre-treatments of seeds were studied. Sesbania seeds were placed in Petri dishes with filtration paper and the germination and radical development followed during seven day periods. The seeds generally germinated within one or two days. There was no difference in percent germination between dark and light treatments, but the development of radical length was significantly influenced by both light conditions and temperature. Germination was highest at 30 and 37 (degrees) under barC (up to 85%) but seeds also germinated readily at 22 (degrees) under barC. No germination was observed at low (5 and 13 (degrees) under bar) and high (45 (degrees) under barC) temperatures. Salinities up to 100 mM NaCl (5.8 ppt) did not influence the germination percentage, but at 200 and 250 mM germination was reduced to 29 and 17% respectively. Pre-treatment of seeds in hot water, sulphuric acid or calcium sulphate had only minor effect on germination rate. The results are consistent with S. sesban being an opportunistic tropical wetland species capable of establishing itself in a wide range of environmental conditions.

Abstract: Phragmites australis (Cav.) Trin. ex Steud. is virtually cosmopolitan and shows substantial variation in euploidy level and morphology. The aim of this study was to assess clone-specific differences in morphological, anatomical, physiological and biochemical traits of P. australis as affected by the geographic origin, the euploidy level (4x, 6x, 8x and 12x), and to assess differences between native and introduced clones in North America. Growth, morphology, photosynthetic characteristics, photosynthetic pigments and enzymes were measured on 11 geographically distinct clones propagated in a common environment in Denmark. Any differences between the measured parameters were caused by genetic differences between clones. Overall, the largest differences between clones were found in ontogeny, shoot morphology and leaf anatomy. The North Swedish clone was adapted to short growing seasons and sprouted very early in the spring but senesced early in July. In contrast, clones from southern regions were adapted to warmer and longer growing seasons and failed to complete the whole growth-cycle in Denmark. Some clones from oceanic habitats with climatic conditions that do not differ much from conditions at the Danish growth site did flower in the common environment. The octoploid genotype in general had larger dimensions of leaves, taller and thicker shoots and larger cell sizes than did the hexaploid and tetraploid clones. The dodecaploid clone was neither bigger than the octoploid, nor significantly different from tetraploid and hexaploid clones in most of the morphological characters observed. Stomatal density decreased with increasing ploidy level, while length of guard cells increased. Tetraploid clones generally had morphometric dimensions, similar to hexaploids. Hence, polyploidy did not always result in an increase in plant size, probably because the number of cell divisions during development is reduced. Four North American clones were included in the study. The clone from the Atlantic Coast and the supposed invasive European clone resembled each other. The Gulf Coast clone differed from the rest of the clones in having leaf characters resembling Phragmites mauritianus Kunth. Thus, morphological characters are not unmistakable parameters that can be used to discriminate between introduced and native clones. The physiological and biochemical processes also differed between clones, but these processes showed considerable phenotypic plasticity and were therefore very difficult to evaluate conclusively. It is concluded that P. australis is a species with very high genetic variability which is augmented by its cosmopolitan distribution, clonal growth form and the large variation in chromosome numbers. It is therefore not surprising that large genetically determined differences in ontogeny, shoot morphology and leaf anatomy occur between clones. (c) 2006 Elsevier B.V. All rights reserved.

Abstract: Removal efficiencies and elimination kinetics of 13 pharmaceuticals and personal care products (PPCPs) and BOD5, TSS, and ammonium were evaluated in a pilot vertical subsurface-flow constructed wetland (VFCW) and compared with those obtained by a sand filter. On the basis of the observed removals, the PPCPs studied were grouped in relation to their removal efficiency into (i) PPCPs very efficiently removed, that is, >95% removal in one of the systems (caffeine, salicylic acid, methyl dihydrojasmonate, CA-ibuprofen, hydrocinnamic acid, oxybenzone, ibuprofen, OH-ibuprofen); (ii) PPCPs moderately removed, with removals between 70 and 90% in the two systems (naproxen, diclofenac, galaxolide, and tonalide); and finally (iii) PPCPs poorly removed, with elimination rates of <30% (carbamazepine). At design hydraulic loading rate (HLR) the planted VFCW and the nonplanted SF exhibited similar PPCP removal efficiencies, but the VFCW was less sensitive to removal decline in overloading conditions (up to 2 times the design HLR). Moreover, under a clogging simulation, the HLR and the presence of vegetation were some of the key aspects affecting the PPCPs, BOD5, and ammonium removal from domestic wastewater. The VFCW evaluated was more efficient in terms of removal efficiency and loading rate for most of the PPCPs studied in comparison to constructed wetlands of other configurations (i.e., horizontal subsurface flow) and SF (nonplanted). The shorter hydraulic residence time (a few hours) in VFCW compared to that in other CW configurations ranging from days to weeks makes VFCWs a very appropriate wastewater treatment option in space-limited areas.

Abstract: Luronium natans (L.) Rafin. is a very rare macrophyte even though it has the ability to grow in a wide variety of habitat types. Previous studies leave two possibilities for this pattern: the species has a poor ability to disperse and establish or it is unable to grow and develop a sustainable population after colonization. Experiments on establishment of shoots, seed bank dynamics, seed germination and genetic analysis (AFLP) were conducted to establish whether L. natans disperse to new habitats within hydrologically linked water systems by means of vegetative shoots or by seeds. Shoots had high ability to establish by roots (52% in autumn shoots), but only when subjected to water depths < 4 cm. Seeds of L natans has a high germinate rate (mean of 51-60%), and the density of seeds in the seed bank ranged from 635 to 3354 m(-2) during a year. Analysis of the genetic diversity showed that samples could be differentiated to individuals with higher diversity between populations than within population. Low ability of shoots to establish if not subjected to low water depth, high germination rate of seeds, substantial seed bank and a high genetic diversity all indicate that most colonization events depend on sexual reproduction. Genetic diversity in L. natans seems to depend on habitat type and management. Habitats subjected to high water velocities or management with weed cutting generally have a lower genetic diversity (5-6%) than habitats subjected to dredging (11 %), indicating that the latter habitats favor sexual reproduction. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: Within the genus Phragmites (Poaceae), the species P. australis (the common reed) is virtually cosmopolitan, and shows considerable variation in ploidy level and morphology. Genetic variation in Phragmites was studied using AFLPs, and analysed with parsimony and distance methods. Groups of P. australis strongly supported in the analyses include one that comprises all South American clones, a distinct group from the US Gulf Coast, and a group of E. Asian and Australian octoploids. Among the other species, the paleotropical P. vallatoria is supported as monophyletic and most closely related to the paraphyletic P. mauritianus and to the Gulf Coast and S. American groups. The E. Asian species P. japonicus is closely related to a group of P. australis clones mostly from central North America. Tetraploidy predominates in the genus, and optimisation of chromosome numbers onto the phylogeny shows that higher ploidy levels have evolved many times.

Abstract: The effect of NH4+/NO3- availability on nitrate reductase (NR) activity in Phragmites australis and Glyceria maxima was studied in sand and water cultures with the goal to characterise the relationship between NR activity and NO3- availability in the rhizosphere and to describe the extent to which NH4+ suppresses the utilization of NO3- in wetland plants. The NR activity data showed that both wetland helophytes are able to utilize NO3-. This finding was further supported by sufficient growth observed under the strict NO3- nutrition. The distribution of NR activity within plant tissues differed between species. Phraginites was proved to be preferential leaf NO3- reducer with high NR activity in leaves (NRmax > 6.5 mu mol NO2- g dry wt(-1) h(-1)) under all N treatments, and therefore Phraginites seems to be good indicator of NO3- availability in flooded sediment. In the case of Glyceria the contribution of roots to plant NO3- reduction was higher, especially in sand culture. Glyceria also tended to accumulate NO3- in non-reduced form, showing generally lower leaf NR activity levels. Thus, the NR activity does not necessarily correspond with plant ability to take up NO3- and grow under NO3--N source. Moreover, the species differed significantly in the content of compounds interfering with NR activity estimation. Glyceria, but not Phragmites, contained cyanogenic glycosides releasing cyanide, the potent NR inhibitor. It clearly shows that the use of NR activity as a marker of NO3- utilization in individual plant species is impossible without the precise method optimisation. (c) 2004 Elsevier B.V. All rights reserved.

Abstract: A recently constructed wetland, located in the Venice lagoon watershed, was monitored to investigate growth dynamics, nutrient and heavy metal shoot accumulation of the two dominating macrophytes: Phragmites australis and Bolboschoenus maritimus. Investigations were conducted over a vegetative season at three locations with different distance to the inlet point to assess effects on vegetation. The distance from the inlet did not affect either shoot biomass or nutrients (N, P, K and Na) and heavy metals (Cr, Ni, Cu and Zn) shoot content. With the exception of Na, nutrient and heavy metal concentrations were higher in shoots of P. australis than in B. maritimus. Heavy metal concentration in the incoming water and in the soil was not correlated to the plant content of either species. Shoot heavy metal concentrations were similar to those reported in the current literature, but accumulation generally increased towards the end of the growing season. (c) 2006 Elsevier Ltd. All rights reserved.

Abstract: A new type of rhizotron is described that facilitates the study of root growth of inundated wetland plants. This rhizotron provides: (1) non-destructive root morphometric measurements during an experiment, (2) rhizotron-specific independent experimental units, (3) a water level of up to 45 cm above the soil surface, (4) easy access for planting, and (5) the ability to harvest at multiple soil depths. A removable back allows easy access for planting and harvesting at multiple soil depths. A gasket ensures a watertight seal. Detailed methods of construction allow researchers to construct and use similar rhizotrons for experimental research. Advantages and disadvantages of the new rhizotron type are discussed. Using the new rhizotron construction, growth response of the Cyperaceae species Eleocharis cellulosa and Rhynchospora tracyi from the Florida Everglades under different water levels and phosphate availabilities were investigated. Destructive and non-destructive analysis of development of above- and belowground biomass for the two species demonstrates that the two species differ in their response to alterations in water level, but show similarities in their response to phosphorus availability. While E cellulosa showed larger increases in root density, root biomass, total shoot length, and shoot biomass with rising water level, the opposite was the case in R. tracyi. Both species produced more aboveground biomass with increasing phosphorus availability. Only E. cellulosa showed an increase in root density and a root biomass increase with high phosphorus availability. In R. tracyi, there was no significant increase in root biomass and root density with high phosphorus availability. (c) 2006 Elsevier GmbH. All rights reserved.

Abstract: 1. Litronium natans is a rare macrophyte that seems to be disappearing from lakes and rivers throughout its distribution area. In Denmark L. natans is most often found in man-made canals and ditches, and its presence seems to be favoured by regular physical disturbance. Hence, management by cutting presents a possible method of preserving the few remaining populations of L. natans in Denmark and throughout its distribution area. 2. The objective of this study was to elucidate the effect of different weed cutting frequencies on L. natans in order to propose recommendations for management with weed cutting for future conservation of L. natans. 3. Three reaches of a river with L. natans were Subjected to the following weed cutting frequencies: no cutting, twice per year, and four times per year, and the cover of L. natans and of other plants was monitored from June 2003 to October 2004. 4. L. natans developed highest cover when subjected to weed cutting four times per year, but the frequency of flowering was then very low, resulting in a reduction in sexual reproduction, which could lead to a lower genetic diversity and possibly fatal effects in the long term. At a cutting frequency of twice per year L. natans was able to maintain healthy and sexually reproducing populations. 5. Future management in canals should consist of weed cutting once or twice per year to prevent a population from being outcompeted by other species and to secure production of flowers and seeds. Alternatively, high frequencies of weed cutting could be performed in order to suppress competitive species, but should then be accompanied by a weed cutting-free zone where flowering can Occur. Copyright (c) 2006 John Wiley & Sons, Ltd.

Abstract: The water stress tolerance of Phragmites australis (Cav.) Trin ex. Steud. grown in the laboratory were investigated by examining effects of different levels of imposed water deficits on growth, photosynthesis and various physiological traits related to water stress. Individual plants were grown under conditions of unrestricted water supply and compared with groups of plants receiving 60, 30, 15 or 5% of previous daily water requirements, respectively. Water deficit was found to reduce the leaf area and the leaf biomass per plant due to decreased production of new leaves, increased leaf shedding and reduced average leaf size. Leaf production and leaf expansion growth were very sensitive to water availability and were reduced when plants were Subjected to fairly mild water deficit. Osmolality in sap expressed from leaves and the concentration of proline in leaves were only significantly increased in severely stressed plants, indicating that osmotic adjustment was of minor importance until a critical stress level was reached. Photosynthetic parameters were rather Unaffected until the water availability was very low and led to the assertion that reduced CO2 assimilation was mainly due to stomatal Closure and not biochemical changes. Water stress had no effect on the activity of Rubisco. The CO2 assimilation rate and stomatal conductance decreased in such a way that the intrinsic water use efficiency (A/g(s)) increased, indicating efficient CO2 utilization in water stressed plants. The apparent quantum yield (phi i) was reduced in leaves of the most stressed plants, probably due to a decrease in the CO2 molar fraction in the chloroplasts following stomatal closure. The initial response of P. australis to water deficit is a reduction in leaf area, the remaining leaves staying physiological rather well functioning until they are severely stressed. A high intrinsic water use efficiency and the ability to maintain some capacity for photosynthesis under severe water stress can undoubtedly contribute to the survival of P australis under dry conditions. Taken together with its well-developed adaptations to flooding, P australis seems very well adapted to grow in wetland areas with a widely fluctuating hydroperiod. P. australis grows very well in rather deep water, but can also tolerate extensive periods of drought with reduced availability of water. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: The effects of NH4+ or NO3- on growth, resource allocation and nitrogen (N) uptake kinetics of two common helophytes Phragmites australis (Cav.) Trin. ex Steudel and Glyceria maxima (Hartm.) Holmb. were studied in semi steady-state hydroponic cultures. At a steady-state nitrogen availability of 34 mu M the growth rate of Phragmites was not affected by the N form (mean RGR = 35.4 mg g(-1) d(-1)), whereas the growth rate of Glyceria was 16% higher in NH4+-N cultures than in NO3--N cultures (mean= 66.7 and 57.4 mg g-1 d(-1) of NH4+ and NO3- treated plants, respectively). Phragmites and Glyceria had higher S/R ratio in NH4- cultures than in NO3- cultures, 123.5 and 129.7%, respectively. Species differed in the nitrogen utilisation. In Glyceria, the relative tissue N content was higher than in Phragmites and was increased in NH4+ treated plants by 16%. The tissue NH4+ concentration (mean = 1.6 mu mol g fresh wt(-1)) was not affected by N treatment, whereas NO3- contents were higher in NO3- (mean = 1.5 mu mol g fresh wt(-1)) than in NH4+ (mean = 0.4 mu mol g fresh wt(-1)) treated plants. In Phragmites, NH4+ (mean = 1.6 mu mol g fresh wt(-1)) and NO3- (mean = 0.2 mu mol g fresh wt(-1)) contents were not affected by the N regime. Species did not differ in NH4+ (mean = 56.5 mu mol g(-1) root dry wt h(-1)) and NO3- (mean = 34.5 mu mol g(-1) root dry wt h(-1)) maximum uptake rates (V-max), and V for NH4+ uptake was not affected by N treatment. The uptake rate of NO3- was low in NH4+ treated plants, and an induction phase for NO3- was observed in NH4+ treated Phragmites but not in Glyceria. Phragmites had low K (mean = 4.5 mu M) and high affinity (10.31 g(-1) root dry wt h(-1)) for both ions compared to Glyceria (K-m = 6.3 mu M, affinity = 8.01 g(-1)root dry wt h(-1)). The results showed different plasticity of Phragmites and Glyceria toward N source. The positive response to NH4+-N source may participates in the observed success of Glyceria at NH4+ rich sites, although other factors have to be considered. Higher plasticity of Phragmites toward low nutrient availability may favour this species at oligotrophic sites. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: It is widely documented that vertical flow constructed wetlands are efficient for producing well nitrified effluent. However, because the treated effluent is oxygen saturated and has a low availability of carbon, the removal of total nitrogen is limited. We hypothesize that by recycling the fully nitrified effluent to the pretreatment unit and the sedimentation tank (where conditions are favorable for denitrification) the removal of total nitrogen from the wastewater can be enhanced. In order to assess the effects of recycling volumes, we monitored the nitrogen removal in an experimental vertical flow constructed wetland, consisting of a 2 m 3 sedimentation tank, two vertical flow beds of 10 and 5 m 2, and the necessary pumping equipment and controllers to manage the loading and recycling volumes. The system was loaded with approximately 0.5 m(3) d(-1), and the recycling volumes evaluated were equal to the loading rate (100% recycling), as well as twice (200%) and three times (300%) the loading. The system produced a fully nitrified effluent independent of recycling rate. However, recycling increased removal of total-N in the system from ca. 1% removal when there was no recycling to 52%, 66%, and 68% removal with 100, 200, and 300% recycling, respectively. The optimal recycling rate seems to be 100-200%. At lower recycling rates, the removal of total-N was poor, and at higher recycling rates, the system became hydraulically overloaded, compromising both the denitrification capacity of the sedimentation tank and the nitrification capacity of the vertical bed.

Abstract: Removal of phosphorous in constructed wetlands is limited by the capacity of the media to adsorb, bind or precipitate the incoming P. To enhance P removal and the life span of constructed wetlands the approach might be to use natural sands rich in calcium or iron, to use an alternative 'artificial' medium with high P-binding capacity, or to establish external P-binding filters after the wetland. Our studies focused on the evaluation of calcium-rich materials potentially useful as P-binding media. The materials tested included calcite products, natural sands and seashells. Tests included assessment of physical and chemical properties of the materials, extractions in P-spiked water at different P concentrations to determine P-binding equilibrium isotherms, and column experiments, In addition, full-scale tests were performed with calcite in an external filter. The result showed that equilibrium isotherm is an indicator of the potential P-sorption capacity of the media, although the value is of limited application for the determination of the binding capacity in full-scale systems. The columns showed that the materials do bind phosphorus. However, the binding capacities are still insufficient for the establishment of external P-removal filter; the volumes of the filters would be too large to be of practical use.

Abstract: Phosphorus (P) availability limits plant growth in many ecosystems. The ability of plants to explore for soil P is often impaired by nonresource stressors. Understanding the effects of these stressors on P acquisition in oligotrophic environments is critical in predicting species dominance. Growth and nutrient responses of Eleocharis celhilosa to redox intensity and phosphate level were evaluated under three redox potentials (Eh) and three phosphate (PO4) levels (P). Although low Eh (-150 mV) decreased root length at low P, Eh did not affect shoot height, relative growth rate (RGR), shoot elongation, photosynthesis, or biomass of E. celhilosa. Low PO4 (10 mu g P P (.) L-1) strongly inhibited growth. Shoot height, RGR, elongation, photosynthesis, and biomass were lower at 10 mu g P (.) L-1 than at 80 or 500 mu g P (.) L-1. None of the growth variables, except the ratio of root-supported biomass to root biomass, significantly differed between the 80 and 500 mu g P (.) L-1 treatments. At low P, plants allocated relatively more biomass to roots than to shoots, compared to the medium and high P levels. Eleocharis cellulosa is well adapted to flooded conditions that lower soil Eh, and elevated PO4 levels, further promote its growth potential.

Abstract: Official guidelines for the on-site treatment of domestic sewage have recently been published by the Danish Ministry of Environment as a consequence of new treatment requirements for single houses and dwellings in rural areas. This paper summarises the guidelines for vertical constructed wetland systems (planted filter beds) that will fulfil demands of 95% removal of BOD and 90% nitrification. The system can be extended with chemical precipitation of phosphorus with aluminium polychloride in the sedimentation tank to meet requirements of 90% phosphorus removal. The necessary surface area of the filter bed is 3.2 m(2)/person equivalent and the effective filter depth is 1.0 m. The filter medium must be filtersand with a d(10) between 0.25 and 1.2 mm, a d(60) between I and 4 mm, and a uniformity coefficient (U = d(60)/d(10)) less than 3.5. The sewage is, after sedimentation, pulse-loaded onto the surface of the bed using pumping and a network of distribution pipes. The drainage layer in the bottom of the bed is passively aerated through vertical pipes extending into the atmosphere in order to improve oxygen transfer to the bed medium. Half of the nitrified effluent from the filter is recirculated to the first chamber of the sedimentation tank or to the pumping well in order to enhance denitrification and to stabilise the treatment performance of the system. A phosphorus removal system is installed in the sedimentation tank using a small dosing pump. The mixing of chemicals is obtained by a simple airlift pump, which also circulates water in the sedimentation tank. The vertical flow constructed wetland system is an attractive alternative to the common practice of soil infiltration and provides efficient treatment of sewage for discharge into the aquatic environment. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: Due to the increasing concern caused by the discharge of untreated wastewater from single households, the Danish EPA funded studies to develop a system which could comply with the current wastewater discharge limits, while maintaining low construction costs, and operating in an autonomous way. A compact vertical flow constructed wetland system serving a single household has been under constant sampling and the results provide valuable experience on the construction, operation and maintenance of this type of system. The compact vertical flow system consists of a sedimentation tank, a pumping well from which the water is pulse loaded onto a planted bed with a surface of about 3 m(2) per PE and a filter depth of ca. 1 m. The bed is filled with local filter sand and winter insulated with a layer of wood chips. The distribution system is installed on top of the bed, under the insulation, and operates under pressure to obtain an even distribution of the water. At the bottom of the bed the water is collected in drainage pipes which are connected to the atmosphere to enhance aeration. The bed is planted with Phragmites australis. Following the bed a P filtering unit containing calcite is installed. After the P filter a device in a splitting well allows the recycling of determined volumes of water to the sedimentation tank in order to improve removal of total nitrogen. The initial results show that the system can effectively meet the stringent Danish discharge standards while maintaining a small surface area per pe served. The construction costs are generally similar to that of constructions of soak-away systems. Initial experience with the external calcite-based P-filter unit which is included in the system was promising. Unfortunately, the commercial supplier of the calcite material can no longer deliver the material, and attempts to find alternative suppliers and/or materials have failed. The initial experiences from the system however gave valuable information on some construction and operations issues that improve the performance of vertical flow constructed wetland systems. In particular recycling within the system improves and stabilises performance.

Abstract: The Danish Ministry of Environment and Energy has passed new legislation that requires the wastewater from single houses and dwellings in rural areas to be treated adequately before discharge into the aquatic environment, Therefore official guidelines for a number of onsite treatment solutions have been produced. These include guidelines for soakaways, biological sand filters, technical systems as well as different types of constructed wetland systems. This paper summarises briefly the guidelines for horizontal flow constructed wetlands, vertical flow constructed wetlands, and willow systems with no outflow and with soil infiltration. There is still a lack of a compact onsite solution that will fulfil the treatment classes demanding 90% removal of phosphorus, Therefore work is presently being carried out to identify simpler and robust P-removal solutions.

Abstract: Root and shoot growth response of Eleocharis cellulosa and Rhynchospora tracyi, two wet prairie species from the Everglades, to water level and phosphate availability were examined in rhizotrons facilitating root growth analysis. Plants were cultivated in Everglades peat subjected to ambient (10 mug Pl(-1)) and high phosphorus (500 mug Pl(-1)) availability and three water levels (+45, +10 and -30 cm). Flooded conditions resulted in large increases in canopy height (from 60 to 80 cm), maximum shoot length (from 75 to 100 cm), and aboveground (from 8.5 to I I g), root (from 2.6 to 3.8 g), rhizome (from 1.1 to 1.6 g), and total (from 15 to 20 g) biomass in E cellulosa. Flooding also increased relative growth rate (RGR) in E. cellulosa from 0.012 to 0.016 g g(-1) per day and root densities at -10 cm, had no effect on shoot/root ratio, and root density at the 30 and 40 cm soil depths, but decreased relative biomass allocation to shoots from 0.77 to 0.73. In R. tracyi, flooded conditions resulted in an increase in shoot/root ratios from 5.1 to 6.7, and relative biomass allocation to shoots (from 0.75 to 0.81) as well as in canopy height (from 59 to 67 cm), had no effect on maximum shoot length, root porosity, aboveground biomass, rhizome and total biomass, but decreased root biomass (from 1.5 to 0.8 g), RGR of total biomass (from 0.017 to 0.014 g g(-1) per day), root density (from 22 to 6 at -10 cm) and relative biomass allocation to roots (from 0.06 to 0.04). High P-availability increased aboveground (+24%) and total biomass (+22%) and root density in both species (+60% in E. cellulosa and +80% in R. tracyi at -10 cm), but had no effect on canopy height, maximum shoot length, and root and rhizome biomass. In E. cellulosa, high P-availability increased RGR of total biomass from 0.012 to 0.016gg(-1) I per day, but did not influence shoot/root ratio and relative biomass allocation. High P-availability did not influence RGR of total biomass in R. tracyi, but increased shoot/root ratio from 4.3 to 6.6 and increased relative biomass allocation to shoots from 0.76 to 0.80. In E. cellulosa, flooding increased root porosity from 52 to 69%, but had no effect on shoot porosity. In R. tracyi, the opposite was the case (increase of shoot porosity from 19 to 29%). Neither root porosity nor shoot porosity was affected by high P-availability. The results indicate E. cellulosa is better adapted to higher water levels than R. tracyi. Consistently, E. cellulosa performed best under flooded conditions, while R. tracyi growth was better under drained conditions. Thus, the relative success of E. cellulosa and R. tracyi in the field may change with alterations in site hydrology and P-availability. (C) 2003 Elsevier B.V All rights reserved.

Abstract: Internal pressurization and convective gas flow in emergent wetland plants is a function of the water vapour pressure deficit (WPD) and stomatal conductance (G(s)) separating the external atmosphere from the internal aerenchyma. We have compared the effects of WPD and G(s) under a range of light intensities on static pressures and convective flows in Phragmites australis, Typha orientalis and Baumea articulata. The capacity of the three species to generate flows per unit leaf area differed, being greatest in P. australis and lowest in B. articulata. In all three species, decreasing light intensity from full sunlight (2200 mumol m(-2) s(-1) photosynthetically active photon flux density (PPFD)) to < 200 and < 10 mumol m(-2) s(-1)PPFD caused immediate decreases in photosynthetic assimilation, followed by more gradual decreases in transpiration and G(s). However, internal pressures and flows in the two low light intensities remained similar to values recorded in full sunlight. WPD was more significantly related to pressures and flows in P. australis and T. orientalis than G(s). In B. articulata, pressures increased at low G(s) values but flow rates were unaffected, as predicted by earlier models describing pore size effects on pressures and flows. The data suggest that emergent macrophytes can maintain significant internal convection even at low light intensities, and this may be beneficial for nocturnal aeration, particularly in arid climates where the atmospheric humidity at night is low.

Abstract: Several European countries have produced guidelines for the construction of subsurface flow constructed wetland systems. No consensus has however been reached because the discharge requirements vary from country to country. The guidelines cannot be directly transferred to Denmark because of very stringent outlet requirements. In order to improve the knowledge on nitrification capacity of vertical flow systems and the potential to remove phosphorus in constructed wetlands, a number of studies were conducted in a five-year old constructed wetland system with a horizontal subsurface flow bed and a vertical flow bed, serving two small communities in Denmark. The experiments evaluated the nitrification activity in vertical flow systems as a function of area mass loading rate, loading frequency and temperature of treated, but not nitrified, effluent. The constructed wetland system used as basis for the experiments was, however, poorly suited for these experiments because of the restricted bed depth and other on-site problems with system design and wastewater composition. It was therefore not possible to establish the relationship between area loading rate and nitrification activity. However, the studies do indicate that frequent pulse loadings increase the nitrification rate. Furthermore, nitrification occurred even at 2degreesC. Thus, a pulse loaded vertical bed can sustain some nitrification activity even at very low water temperatures. The studies also documented that recycling of nitrified effluent water to the sedimentation tank increases the removal of total-nitrogen because of denitrification. It is concluded that constructed wetland systems with vertical non-saturated flow will be able to fulfil the most stringent treatment requirements imposed for on-site treatment of domestic sewage in rural areas. However, design and area demand is not yet fully established, and more work is needed to refine the removal process for phosphorus. A set of provisional guidelines for the design and construction of vertical flow systems is presented.

Abstract: The P-adsorption capacities of 13 Danish sands were studied by short-term isotherm batch experiments and related to the physico-chemical characteristics of the sands. The maximum P-adsorption capacities (Q) and P-binding energy constants (b) were calculated using the Langmuir-isotherm model. The Freundlich model was also used, but it was not useful for the description of adsorption phenomena per se since it fitted well P-removal data even if precipitation of P-salts occurred simultaneously. The Langmuir model described the data well (R-2 = 0.90 - 0.99) when precipitation of phosphates did not occur and seems therefore to be useful for describing the adsorption processes per se. The relationships between maximum sorption capacities and physico-chemical characteristics of the sands were investigated using classical univariate and partial least squares regression analyses. Among the physico-chemical properties of the sands, Ca and Mg content, grain size, porosity, bulk density and hydraulic conductivity were significantly related (P < 0.1) to the maximum adsorption capacity as estimated by the Langmuir model. Using the maximum P-adsorption capacities, it was estimated how long the P-removal can be sustained with the different sands in subsurface flow constructed reed beds. If the most efficient sand for P-adsorption was used, the adsorption capacity would be used up after about I year, while, for the less efficient sands, the P-retention would go on for about 2 months. This suggests that, in order to sustain a long-term P-removal in subsurface flow constructed reed beds, precipitation reactions of insoluble P-salts should be promoted. P-binding energy constants were not significantly related to the physico-chemical properties of the sands, except the Ca content, which showed, however, a low correlation coefficient. (C) 2003 Elsevier Science Ltd. All rights reserved.

Abstract: Expansion of Typha domingensis into areas previously dominated by Cladium jamaicense in the Florida Everglades has been linked to anthropogenic phosphorus (P) enrichment and increased hydroperiod. The principal stress factor for plants in flooded soils is biochemical reduction. the intensity of which is measured as redox potential (Eh), The objective of this study was to assess the growth response of C. jamaicense to Eh (-150, +150, and +600 mV) and P availability (10, 80, and 500 mug P/L). Plants were grown hydroponically in a factorial experiment using titanium (Ti3+) citrate as an Eh buffer. Treatment effects on growth, biomass partitioning, and tissue nutrients were recorded. Growth approximately doubled in response to a 50-fold increase in P availability. Low redox significantly reduced growth and tissue P concentration. While plant P concentrations increased 20-fold between the 10 and 500 mug P/L treatments. P concentrations were 50-100% higher at +600 mV than at -150 mV within each phosphate level. At high Eh, C. jamaicense appears well adapted to low nutrient environments because of its tow P requirement and high retention of acquired P. However. at low Eh the ability to acquire or conserve acquired P decreases and as a consequence, higher phosphate levels are required to sustain growth. Findings of this study indicate that young C. jamaicense exhibits low tolerance to strongly reducing conditions when phosphate is scarce.

Abstract: The removal of sanitary indicator bacteria (total coliforms, faecal coliforms, and faecal streptococci) was studied in an experimental constructed wetland system consisting of (1) a 2-m(3) three-chamber sedimentation tank, (2) a 5 m(2) vertical flow constructed wetland, (3) a filter-unit with calcite aimed at removing phosphorus, and (4) a 10 m(2) vertical flow constructed wetland. The indicator bacteria were enumerated before and after each unit of the wetland system during four monitoring episodes with different loading conditions. At a hydraulic loading rate of 520-1,370 mm/d, the first-stage vertical flow beds removed about 1.5 log-units of total coliforms, 1.7 log-units of faecal coliforms and 0.8 log-units of faecal streptococci. In the second stage bed receiving lower loadings both in term of concentration and quantity (260-690 mm/day), the eliminations were lower. It was not possible in the present study to identify any seasonal effects, but no measurements were done during summer. Recycling of treated effluent back to the sedimentation tank did not affect elimination. Area-based rate constants for the vertical flow wetland receiving effluent from the sedimentation tank averaged 3.2 m/d for total coliforms, 3.3 m/d for faecal coliforms and 2.1 m/d for faecal streptococci. The rate constants depended on loading rates. It is suggested that filtration is a major removal mechanism for bacterial indicator organisms in vertical flow constructed wetland systems.

Abstract: Laboratory studies have indicated that calcite may be used in separate, exchangeable filter units in a constructed wetland systems to remove phosphorus. Based on these studies we built a full-scale experimental constructed wetland with a calcite-based filter unit to study its performance, under real-life conditions. The system consists of a 2-m(3) sedimentation tank and two vertical flow constructed wetlands. The system has three 0.09 m(3) calcite filter-units to study phosphorus removal. The hydraulic loading rate varied between 1.7 and 6.2 m(3)/d. The residence time in filters ranged from 28 to 99 minutes. Overall the system removed 62 +/- 18% of phosphorus. The removal in the calcite filter was initially good, but after three months all P-filters were saturated. The calcite increased pH by approximately half a unit and released calcium. A total of about 2.2 kg P/m(3) calcite was removed by the filter. The first-stage bed receiving effluent from the sedimentation tank consistently removed phosphorus, whereas the second bed sometimes released phosphorus. The first order area-based removal rate constant for total-P in the vertical bed averaged 0.24 +/- 0.20 m/d and was highly dependent on the loading rate. This shows that first order removal kinetics do not satisfactorily describe removal of phosphorus in vertical flow constructed wetland systems with unsaturated flow.

Abstract: The NH4+ and NO3- uptake kinetics by Typha latifolia L. were studied after prolonged hydroponics growth at constant pH 3.5, 5.0, 6.5 or 7.0 and with NH4+ or NO3- as the sole N-source. In addition, the effects of pH and N source on H+ extrusion and adenine nucleotide content were examined. Typha latifolia was able to grow with both N sources at near neutral pH levels, but the plants had higher relative growth rates, higher tissue concentrations of the major nutrients, higher contents of adenine nucleotides, and higher affinity for uptake of inorganic nitrogen when grown on NH4+. Growth almost completely stopped at pH 3.5, irrespective of N source, probably as a consequence of pH effects on plasma membrane integrity and H+ influx into the root cells. Tissue concentrations of the major nutrients and adenine nucleotides were severely reduced at low pH, and the uptake capacity for inorganic nitrogen was low, and more so for NO3- fed than for NH4+-fed plants. The maximum uptake rate, V-max, was highest for NH4+ at pH 6.5 (30.9 mumol h(-1) g(-1) root dry weight) and for NO3- at pH 5.0 (31.7 mumol h(-1) g(-1) root dry weight), and less than 10% of these values at pH 3.5. The affinity for uptake as estimated by the half saturation constant, K-1/2, was lowest at low pH for NH4+ and at high pH for NO3-. The changes in V-max and K-1/2 were thus consistent with the theory of increasing competition between cations and H+ at low pH and between anions and OH- at high pH. C-min was independent of pH, but slightly higher for NO3- than for NH4+ (C-min(NH4+) similar to 0.8 mmol m(-3); C-min(NO3-) similar to 2.8 mmol m(-3)). The growth inhibition at low pH was probably due to a reduced nutrient uptake and a consequential limitation of growth by nutrient stress. Typha latifolia seems to be well adapted to growth in wetland soils where NH4+ is the prevailing nitrogen compound, but very low pH levels around the roots are very stressful for the plant. The common occurrence of T. latifolia in very acidic areas is probably only possible because of the plant's ability to modify pH-conditions in the rhizosphere.

Abstract: Activity of root phosphatase was examined in Cladium jamaicense (sawgrass) and Typha domingensis (cattail) grown under controlled conditions in Everglades peat with different inorganic P availabilities and flooding regimes. Cladium root phosphatase activity was significantly greater than for Typha when both were subjected to relatively low inorganic phosphorus concentrations (10 to 80 mug l(-1)) in the interstitial water, indicating a greater potential for Cladium to use organic phosphor-us compounds as a phosphate source. When inorganic phosphorus concentration was elevated (500 mug l(-1)), internal root phosphate concentrations increased and root phosphatase activities decreased in both species to similar levels. Thus, root phosphatase activity in these species is induced by low ambient inorganic phosphate concentrations. The relatively greater ability of Cladium to hydrolyze organic phosphorus compounds indicates that it is physiologically better adapted to peat-based, low inorganic phosphorus conditions and helps explain this species' historic dominance in peat-based Everglades soils.

Abstract: Phragmites australis is a cosmopolitan wetlands species occurring in a wide range of climatic habitats, It can be assumed that adaptations to climate have evolved to enable the synchronization of growth with the seasonality of the environment. To study these adaptations, European P. australis was collected in different geographic regions, and grown in common environments situated in the Czech Republic, Denmark and The Netherlands. Phragmites australis originating from higher latitudes showed higher relative length growth rates (RLGR), and flowered earlier in time than that from lower latitudes. Plants from Spain even continued growth until the first autumn frosts. When grown in the different common environments, population differences were found in RLGR, but no general trend was apparent. On average, shoots started to grow 2 weeks earlier in The Netherlands than in Denmark and 6 weeks earlier than in the Czech Republic. These differences could be largely related to lower spring temperatures in the latter two countries. When shoot-growth was plotted against the temperature sum, no differences in RLGR between Denmark and The Netherlands were apparent, whereas shoot-growth was slower in the Czech Republic. Results from a greenhouse experiment showed that seedlings from southern populations formed taller but fewer shoots and thicker but shorter rhizomes than those from northern populations, irrespective of total dry weight. They also allocated more dry matter to stems at the expense of leaves, whereas no differences in allocation to below-ground plant parts were found. It was concluded that populations of P. australis showed clinal variation in (i) the length of the growing season, (ii) time of flowering, and (iii) morphology and biomass allocation. These results are discussed with respect to the possible effects of global warming on population functioning. (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract: Four populations of Phragmites australis collected from geographically distinct areas in Europe were propagated in outdoor experimental plots at four sites with dissimilar climate (Denmark, The Netherlands, Spain and Czech Republic). During the second growing season the photosynthetic characteristics of Phragmites leaves were evaluated under controlled conditions for each site, each population, and their interaction, and related to tissue nutrient and pigment content. The light-saturated rate of photosynthesis (P-max), dark respiration rate (R-d), light compensation point (I-c), and apparent quantum efficiency (phi (i)) were significantly affected by growth site, whereas differences between populations were less pronounced. Plants grown in the more northerly climates appeared to be more photosynthetically limited through lower P-max values and lower phi (i) levels, reflecting phenotypic acclimation to the lower summer temperatures and irradiance levels at the northern growth sites. The higher P-max levels in the southern climate were correlated with higher nutrient levels in the tissue of leaves. The study shows that the four genetically distinct populations of P. australis exhibited high phenotypic plasticity in photosynthetic response to climatic change. The degree of photosynthetic plasticity within P. australis genotypes is large, and generally larger than the genetically determined differences between European populations. The results are discussed in relation to the prospected global climate change. (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract: Phragmites australis wetlands act as a sink for greenhouse gases by photosynthetic assimilation of carbon dioxide (CO2) from the atmosphere and sequestration of the organic matter produced in the wetland soil. The wetlands also act as a source for greenhouse gases by emission of sediment-produced methane (CH4) to the atmosphere. In P. australis wetlands, the dominant mechanism of CH4 release to the atmosphere is internal gas transport in the plants, primarily by pressurized convective gas flow. The time periods of carbon fixation and CH4 release therefore vary seasonally and diurnally. The balance between net CO2-assimilation and CH4 emission determines if a wetland can be regarded as a net sink or a net source of greenhouse gases, and hence, the function of the wetland in relation to global climate change. On an annual basis up to 15% of the net carbon fixed by the wetlands may be released to the atmosphere as CH4. Because of the different infrared absorption characteristics and atmospheric longevity of CH4 and CO2, the warming effect of CH4 in the atmosphere is about 21 times higher on a mass basis than CO2 over a 100-year timescale. Thus, the immediate carbon balance, coupled with the different physical characteristics of the two gases, would suggest that although some wetlands function as a net sink for CO. the wetlands still increase the greenhouse effect because of their release of CH4. However, the short adjustment time for CH4 in the atmosphere means that, over a longer time scale, the radiative forcing of CH4 is less relative to CO2 and the wetlands effectively become a sink for greenhouse gases. Wetlands may therefore be regarded as a source for greenhouse gases and so increase radiative forcing if evaluated on a short time scale (decades), but as a sink for greenhouse gases and thus attenuating radiative forcing if evaluated over longer time scales (>100 years). (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract: Sorption of P to the bed sand medium is a major removal mechanism for P in subsurface flow constructed reed beds. Selecting a sand medium with a high P-sorption capacity is therefore important to obtain a sustained P-removal. The objective of this study was to evaluate the P-removal capacities of 13 Danish sands and to relate the removal to their physico-chemical characteristics. The P-removal properties were evaluated in short-term isotherm batch-experiments as well as in 12-week percolation experiments mimicing the P-loading conditions in constructed reed bed systems. The P-removal properties of sands of different geographical origin varied considerably and the suitability of the sands for use as media in constructed reed beds thus differs. The P-removal capacity of some sands would be used up after only a few months in full-scale systems, whereas that of others would persist for a much longer time. The most important characteristic of the sands determining their P-removal capacity was their Ca-content. A high Ca content favours precipitation with P as sparingly soluble calcium phosphates particularly at the slightly alkaline conditions typical of domestic sewage. In situations where the wastewater to be treated is more acid, the contents of Fe and Al may be more important as the precipitation reactions with these ions are favoured at lower pH levels. The maximum P-sorption capacities estimated using the Langmuir-isotherm plots did not correspond to or correlate with the actual amount of P removed in the percolation columns. Hence, the Langmuir-isotherm does not estimate the P-removal capacities of sands. It is suggested that a suitable quick method of screening a selection of potential media for P-removal potential is to perform simple removal isotherm studies using water with a similar chemical composition as the wastewater to be treated. This method will not provide a direct estimate of the P-removal capacity that can be obtained in full-scale systems, but it is a means of comparing the relative performance of potential media. (C) 2001 Elsevier Science Ltd. All rights reserved.

Abstract:

Abstract: The effects of phosphorus (P) and oxygen availability on growth, biomass allocation and nutrient use efficiency in Cladium jamaicense Crantz and Typha domingensis Pers, were studied in a growth facility equipped with steady-state hydroponic rhizotrons. The treatments included four P concentrations (10, 40, 80 and 500 mug l(-1)) and two oxygen concentration (8.0 and < .5 mg O-2 l(-1)) in the culture solutions. In Cladium, no clear relationship was found between P availability and growth rate (19-37 mg g(-1) d(-1)), the above to below ground biomass ratio (A/B) (mean = 4.6), or nitrogen use efficiency (NUE) (mean = 72 g dry weight g(-1) N), However, the ratio between root supported tissue (leaves, rhizomes and ramets) and root biomass (SIR) (5.6-8) increased with P availability. In contrast, the growth rate (48-89 mg g(-1) d(-1)) and the biomass ratios A/B (2.4-6.1) and S/R (5.4-10.3) of Typha increased with P availability, while NUE (71-30 g dry weight g(-1) N) decreased. The proportion of root laterals was similar in the two species, but Typha had thinner root laterals (diameter = 186 mum) than Cladium (diameter = 438 mum) indicating a larger root surface area in Typha. The two species had a similar P use efficiency (PUE) at 10 mu gP1(-1) (mean = 1134g dry weight g(-1) P) and at 40 and 80 mu gP1(-1) (mean = 482 dry weight g(-1) P) but the Nm ratio indicated imbalances in nutrient uptake at a higher P concentration (40 mu gP1(-1)) in Typha than in Cladium (10 mu gP1(-1)). The two species had similar root specific P accumulation rate at the two lowest P levels, whereas Typha had 3-13-fold higher P uptake rates at the two highest P levels, indicating a higher nutrient uptake capacity in Typha. The experimental oxygen concentration in the rhizosphere had only limited effect on the growth of the two species and had little effect on biomass partitioning and nutrient use efficiency. The aerenchyma in these species was probably sufficient to maintain adequate root oxygenation under partially oxygen depleted conditions. Cladium had characteristics typical for plants from nutrient poor habitats, which included slow growth rate, low capacity for P uptake and relatively inflexible biomass partitioning in response to increased P availability. In contrast, Typha demonstrated a high degree of flexibility in growth, biomass partitioning, and nutrient accumulation to P availability, similar to species from nutrient rich habitats. Although the N/P ratio indicated that Typha was more nutrient stressed at the low P levels. Typha had a higher capacity for P uptake and was more competitive than Cladium at the applied P concentrations. (C) 2001 Elsevier Science B.V. All rights reserved.

Abstract: Lake Utterslev is situated in a densely built-up area of Copenhagen, and is heavily eutrophicated from combined sewer overflows, At the same time the lake suffers from lack of water. Therefore, a 5,000 m(2) vertical flow wetland system was constructed in 1998 to reduce the phosphorus discharge from combined sewer overflows without reducing the water supply to the lake. During dry periods the constructed wetland is used to remove phosphorus from the lake water. The system is designed as a 90 m diameter circular bed with a bed depth of c. 2 m. The system is isolated from the surroundings by a polyethylene membrane. The bed medium consists of a mixture of gravel and crushed marble, which has a high binding capacity for phosphorus. The bed is located within the natural littoral zone of the lake and is planted with common reed (Phragmites australis). The constructed wetland is intermittently loaded with combined sewer overflow water or lake water and, after percolation through the bed medium, the water is collected in a network of drainage pipes at the bottom of the bed and pumped to the lake. The fully automated loading cycle results in alternating wet and dry periods. During the initial two years of operation, the phosphorus removal for combined sewer overflows has been consistently high (94-99% of inflow concentrations). When loaded with lake water, the phosphorus removal has been high during summer (71-97%) and lower during winter (53-75%) partly because of lower inlet concentrations. Effluent phosphorus concentrations are consistently low (0.03-0.04 mg/L). Ammonium nitrogen is nitrified in the constructed wetland, and total suspended solids and COD are generally reduced to concentrations below 5 mg/L and 25 mg/L, respectively. The study documents that a subsurface flow constructed wetland system can be designed and operated to effectively remove phosphorus and other pollutants from combined sewer overflows and eutrophicated lake water.

Abstract: Sorption of phosphorus (P) to the bed sand medium is a major removal mechanism for P in subsurface flow constructed wetlands. Selecting a sand medium with a high P-sorption capacity is therefore important to obtain a sustained P-removal. The P-removal capacities of 13 Danish sands were evaluated and related to their physico-chemical characteristics. The P-removal properties of sands of different geographical origin varied considerably and the suitability of the sands for use as media in constructed reed beds thus differs. The P-sorption capacity of some sands would be used up after only a few months in full-scale systems, whereas that of others would subsist for a much longer time. The most important characteristic of the sands determining their P-sorption capacity was their Ca-content. Also the P-binding capacities of various artificial media were tested (light-expanded-clay-aggregates (LECA), crushed marble, diatomaceous earth, vermiculite and calcite). Particularly calcite and crushed marble were found to have high P-binding capacities. It is suggested that mixing one of these materials into the sand or gravel medium can significantly enhance the P-sorption capacity of the bed medium in a subsurface-flow constructed wetland system. It is also possible to construct a separate unit containing one of these artificial media. The media may then be replaced when the P-binding capacity is used up.

Abstract: A novel constructed wetland system has been developed to treat sewage, evaporate water and recycle nutrients from single households at sites where effluent standards are stringent and soil infiltration is not possible. Main attributes of the willow wastewater cleaning facilities are that the systems have zero discharge, the willows evapotranspire the water, and nutrients can be recycled via the willow biomass produced in the system. The willow wastewater cleaning facilities generally consist of c. 1.5 m deep high-density polyethylene-lined basins filled with soil and planted with clones of willow (Salix viminalis L.). The surface area of the systems depends on the amount and quality of the sewage to be treated and the local annual rainfall. For a single household the area needed typically is between 200-300 m(2). Settled sewage is dispersed underground into the bed under pressure. When correctly dimensioned, the willow will - on an annual basis - evapotranspire all water from the sewage and rain falling onto the system, and take up all nutrients and heavy metals from the sewage. The stems of the willows are harvested on a regular basis to remove nutrients and heavy metals and to stimulate the growth of the willows. Initial experiences from full-scale systems in Denmark show promising results.

Abstract: The germination requirements of Cladium jamaicense Crantz and Typha domingensis Pers. were studied under controlled conditions in the laboratory. Treatments included six temperature regimes, (constant temperatures of 15, 20, 25, 30 degrees C, and two fluctuating day : night temperature regimes of 25 : 10 degrees C and 30 : 20 degrees C), two light levels (14 : 10 h light : dark photoperiod and 24 h dark environment), two substrates (peat and water) and two O-2 levels (atmospheric and low (4.34%) O-2 concentration) using a complete randomized block design. The average incubation period needed for seeds to germinate was shorter for T. domingenesis (1.1-19.5 days) than for C. jamaicense (26-46 days) and the final germination percentage was higher for T. domingensis than for C. jamaicense (85 vs. 42 %). Cladium jamaicense only germinated with fluctuating temperatures whereas T. domingensis germinated at all temperature regimes. Light was required for T. domingensis seeds to germinate, whereas C. jamaicense could germinate at a reduced rate in the dark. Peat substrate had a positive effect on germination in both species. Peat substrate shortened the incubation period for seeds of both species, enhanced germination of T. domingensis, especially at low temperatures, and enhanced germination of C. jamaicense in the dark. Low oxygen availability did not influence the germination of C. jamaicense but enhanced germination of T. domingensis at low temperatures. Although the two species differ significantly in their germination requirements and responses to specific environmental conditions, germination of both these species was enhanced by environmental conditions typical of exposed water saturated mudflats or sediment surfaces. Typha domingensis produces a large number of small seeds, which do not germinate when covered by sediment. In contrast, C. jamaicense produces fewer and larger seeds, with resources able to support growth through a thin layer of sediment or detritus. (C)2000 Elsevier Science B.V. All rights reserved.

Abstract: The interactive effects of three levels of NH4-N (50, 500 and 1000 mu mol l(-1)) and two levels of phosphate (15 and 50 mu mol l(-1)) on growth, nutrient allocation and ammonium uptake kinetics by Phragmites australis (Cav.) Trin. ex Steudel were studied in hydroponic culture in the laboratory. Nitrogen level in the root solution significantly affected the relative growth rate of the plants, the rate being lower at low N (0.026 per day) than at intermediate (0.035 per day) and high N (0.037 per day), but phosphorus did not significantly affect growth. The N:P ratio in the root solution significantly affected the growth rate which was highest at N:P ratios between 10 and 33 on a molar basis. Nitrogen and phosphorus concentration in the plant tissues generally increased with N level in the root solution, but P level had no effect. Plant tissue N:P ratios (on a molar basis) varied between 13.5 in the stems to 28.0 in the leaves and were unaffected by the treatments. Ammonium uptake kinetics were unaffected by N treatment, but V-max was significantly affected by P treatment averaging (mean +/- 95% confidence limits (CL)) 151 +/- 44 mu molg(-1) root dry weight h(-1) in the low-P treatment and 229 +/- 70 mu mol g(-1) root dry weighth(-1) in the high-P treatment. The overall mean (+/-95% CL) NH4-N uptake kinetic parameters were: V-max = 190 +/- 20 mu mol g(-1) root dry weight h(-1); K-1/2 = 21.8 +/- 1.8 mu mol l(-1), and C-min = 1.2 +/- 0.2 mu mol l(-1). Mean (+/-SD) root respiration rate was 72 +/- 22 mu mol CO2 g(-1) dry weight h(-1) and was unaffected by the treatments. The results of the study support the general hypothesis that P. australis is well-adapted for growth in nutrient-rich habitats. However, P. australis is able to acclimate to low nutrient availability by increasing the affinity for ammonium uptake. (C) 1999 Elsevier Science B.V. All rights reserved.

Abstract: Spatial and seasonal variations in concentrations of lower organic acids in the sediments of stands of Phragmites australis (Cav.) Trin. ex Steud. were studied in wetlands in the Czech Republic (Rozmberk fishpond), Hungary (Lake Ferto and Kis-Balaton), and Denmark (Vejlerne Nature Reserve). Pore water concentrations of lactic, formic, acetic, propionic, butyric, oxalic, citric, tartaric, malic and fumaric acid were analysed by HPLC and shown to vary both qualitatively and quantitatively between sites. Acetic acid was prevalent at all sites, and dominated together with citric, malic, and tartaric acid at Rozmberk fishpond, with lactic and oxalic acid at Lake Ferto and Kis-Balaton, and with lactic and propionic acid at Vejlerne Nature Reserve. The maximum total concentrations of organic acids recorded were 2984 and 2215 mu mol l(-1) at a land and a deep-water site of Rozmberk fishpond, 1673 and 2216 mu mol l(-1) at a healthy and damaged stand of Lake Ferto, 1006 and 1642 mu mol l(-1) at a healthy and damaged stand of Kis-Balaton, and 570 and 223 mu mol l(-1) at a healthy reed stand and a lagoon at Vejlerne Nature Reserve, respectively. At Rozmberk fishpond the concentrations of lower organic acids were considered sufficiently high to diminish the plants vigour and possibly to induce die-back. At Lake Ferto and Kis-Balaton the organic acids are unlikely to have had a toxic effect on the reeds at the sampling time because of the relatively high pH (similar to 7) in these wetlands. However, because of the great spatial and seasonal variability in organic acid speciation and concentration, organic acid phytotoxity may affect the reed also at these sites. At Vejlerne Nature Reserve, the toxic effect on the reeds is unlikely because of consistently low concentrations of organic acids. (C) 1999 Elsevier Science B.V. All rights reserved.

Abstract: Although soil organic matter decomposition is an important process determining nutrient transformations and availability in wetland ecosystems, few studies have attempted to assess which environmental factors are most important in controlling spatial differences in decomposition rates found along environmental gradients. Relative soil decomposition was determined in a Phragmites australis Cav. Trin ex Steudel dominated wetland in northern Jutland, Denmark along a natural salinity gradient, where nutrients, soil moisture, temperature and salinity among other factors also varied. Our objective was to identify which edaphic factors most limited rates of relative soil de composition, as evaluated by measuring cellulose decomposition with the cotton strip technique. Replicate cotton strips were placed at seven marsh sites along the salinity gradient, and soil and interstitial water samples were collected and analyzed for major macro- and micronutrients (NH4-N, NO3-N, P, PO4, K, Mg, Ca, Na, S, Fe, Mn, Zn, Cu, Mo, B, Si), pH, Eh, conductivity, temperature, and soluble sulfides. Cellulose decomposition, expressed as cotton tensile strength loss (CTSL) per day, decreased with increasing salinity, except at the highest salinity site where a significant increase occurred. Mean CTSL values, averaged for each marsh site, varied 3-fold from 1.8 to 5.5% loss per day. Principal component and multiple regression analyses were used to prioritize the importance of the various factors that might control this spatial difference in CTSL rates. Although soil conductivity (salinity) accounted for the large percentage (45%) of the variation in the environmental data, soil fertility- and soil reduction-associated variables explained the greatest percentage (56%) of the spatial variation in cellulose decomposition. Univariate correlation analyses supported the conclusion that soil fertility, primarily inorganic nitrogen and phosphorus, is the major environmental factor determining soil cellulose decomposition rates along this salinity gradient. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

Abstract: Effects on methanogenesis and CH4 emission of three water table positions, sediment composition and presence or absence of the emergent macrophyte Phragmites australis (Cav,) Trin. ex Steud. were studied in outdoor experimental mesocosms. Water table position significantly affected methanogenesis and CH4 emission, the rates being 40% and 60% lower, respectively, in vegetated organic sediments with a water table 22 cm below the surface as compared with vegetated inundated sediments. Due to the high water-holding capacity of organic sediments, rates of methanogenesis and CH4 emission in organic sediments with a water table 8 cm below the sediment surface were only slightly, but not statistically significantly different from rates in inundated sediments. Sandy sediments with water tables 8 cm below the sediment surface had very low methanogenic activity as compared with organic sediments (1 versus 55 mmol m(-2) per day). The presence of P. australis in inundated sediments attenuated the rate of methanogenesis by 27%, enhanced the proportion of CH4 oxidised from 7% to 18%, and as a result attenuated CH4 emission by 34%, In vegetated sediments CH4 emission peaked at midday and was lowest during the night and early morning in concert with the diurnal changes in internal convective flow in the plants. Internal gas transport through the plants accounted for 62% of the CH4 emitted from vegetated sediments while ebullition dominated in unvegetated sediment. (C) 1999 Elsevier Science B.V. All rights reserved.

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Abstract: A two-stage constructed wetland capable of removing TSS, BOD and Total-N, and providing nitrification is described. The system consists of a horizontal subsurface flow constructed wetland followed by an intermittently loaded vertical flow constructed wetland. Recirculation is included as an option to enhance total-N removal. The design guidelines presented are based on experiences from various constructed wetland systems as well as traditional trickling filter technologies. The experiences from the first systems constructed according to this design in Poland show excellent removal of TSS and BOD as well as efficient nitrification and total-P removal throughout the year. It is possible that future refinements of the dimensioning principles will result in smaller and thus less costly systems.

Abstract: The term 'green' is nowadays widely used (and misused) in connection with many types of technologies. If a technology is 'green' it usually means that the technology requires less non-renewable energy sources than other alternatives. However, other parameters need to be considered as well, such as sustainability, recycling potential, treatment capacity and potential, conservation of ecosystems, etc. In this paper the energy requirements and nutrient recycling potential of constructed wetlands and wastewater aquaculture facilities are compared with that of conventional wastewater treatment technologies. The energy requirements of constructed wetlands are very low, but if significant reuse of nutrients is included (aquaculture), the energy requirements increase significantly and usually beyond the energy equivalent of the biomass produced. This is especially true in cold temperate climates where the aquaculture systems need to be housed in heated greenhouses and artificial light must be provided to secure operation throughout the year. In countries where fresh water itself is a limiting resource and where the economic capability may limit the use of artificial fertilisers, the reuse potential of wastewater may be more important. The potential for sustainable cropping of the plant biomass is excellent in tropical wetlands as the plants have a high productivity and a continuous growing season. In order to evaluate in more detail the 'greenness' of the different wastewater treatment technologies, the life-cycle approach might be applied. However, because constructed wetlands, besides the water quality improvement function, perform a multitude of other functions such as biodiversity, habitat, climatic, hydrological and public use functions, methodologies need to be developed to evaluate these functions and to weigh them in relation to the water quality issues. (C) 1999 IAWQ Published by Elsevier Science Ltd. All rights reserved.

Abstract: A controlled environment system, termed the Phyto-Nutri-Tron (PNT), has Seen established to study whole plant ecophysiological responses to multiple environmental factors. The PNT is a computer-controlled highly flexible growth facility with independent control of the shoot and the root environment. The facility consists of two growth cabinets each containing four separate hydroponic growth systems. The growth cabinets can be used as assimilation chambers with individual control of temperature, humidity, light, CO2 and monitoring of O-2. The hydroponic growth systems are connected to nutrient supply units with disinfection systems and individual control of temperature, pH and oxygen. The ionic composition of the solutions has automated feedback control through a PO4 autoanalyzer and a flow injection analyzer which also analyzes NH4+, NO2- and NO3-. Other ions are automatically monitored by ICP-AES. The system has automated calibration procedures of the analytical equipment and prolonged studies of plant growth can be performed under constant environmental conditions. This paper describes the design and construction of the PNT, the results of a number of tests showing the degree of control of environmental factors and construction of the PNT, the results of a number of tests showing the degree of control of environmental factors and the results of a comparative study on NH4+ and NO3- uptake kinetics by Juncus effusus conducted in the PNT demonstrate the use of the PNT in ecophysiological studies. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract: Growth of Typha latifolia L. and its effects on sediment methanogenesis were examined in a natural organic sediment and a sediment enriched with acetate to a concentration of 25 mM in the interstitial water. The lower redox potential and higher oxygen demand of the acetate-enriched sediment did not significantly impede growth of T. latifolia despite some differences in growth pattern and root morphology. Plants grown in acetate-enriched sediment were ca. 15% shorter than plants grown in natural sediment, but the former produced more secondary shoots at earlier stages, which resulted in similar total biomasses after 7 weeks of growth in the two sediment types. Plants grown in acetate-enriched sediment had thicker and much shorter roots than plants grown in natural sediment. This difference did not significantly affect the release of oxygen from the roots when measured under laboratory conditions, which was 0.12-0.20 mmol O-2 g(-1) DW h(-1). Enrichment with acetate resulted in much higher sediment methanogenesis rates (643 vs. 90 nmol CH4 g(-1) sediment DW h(-1)). Growth of T. latifolia significantly reduced methanogenesis in both types of sediment, but the effect was twice as marked in the natural sediment (34%) as in the acetate-enriched sediment (18%), although in absolute terms the reduction was higher in the enriched sediment. The data suggest that this effect of plant growth was via root oxygen release and its effect on redox conditions. In the natural sediment, oxygen release resulted in a significantly higher redox potential and lower sediment oxygen demand, whereas there were no significant changes in the acetate-enriched sediment. The very high oxygen demand of this sediment probably masked the effect of root oxygen release so that a significant reduction in methanogenesis occurred without any significant increase in the redox potential. This demonstrates how root oxygen release from plants like T. latifolia can significantly alter rates of biogeochemical processes such as methanogenesis.

Abstract: Methanogenesis was measured during the summer of 1994, in sediment cores and bulk samples from a Phragmites australis wetland in northern Jutland, Denmark. We compared sediment from healthy reed and dying-back reed, and an open lagoon resulting from die-back. Cores revealed variability with depth and between sites, with the highest rates coinciding with layers of organic gyttja, and negligible methane production from the underlying sand base. Methanogenesis rates in the lagoon and die back sites were higher (up to 100-150 nmol h(-1) g(-1) dry wt. sediment) than in the healthy reed (50-80 nmol h(-1) g(-1)), with the highest rates being recorded from May to July. At these times, methanogenesis was markedly temperature limited; samples incubated at 30 degrees C a non-limiting temperature, gave rates as high as 200-400 nmol h(-1) g(-1) for the lagoon and die-back areas and 150 nmol h(-1) g(-1) for the healthy area. Addition of 8 mM acetate and H-2/CO2 headspace suggested that both acetate-fermenting and CO2-reducing bacteria were present. Acetate additions suggested some co-limitation by substrate availability, with acetate limitation occurring in the healthy site during July and in the die-back site during August. Lower rates during August, especially in the healthy area, were associated with low water levels which resulted in more oxidized sediments. The data reveal highly variable methanogenesis in the sediment which, when considered with sediment depths, indicates that sites of Phragmites die-back have significantly greater rates of anaerobic mineralization than surrounding healthy wetland, and may be intense sources of methane.

Abstract: In this study we examine the influence of temperature on growth, photosynthetic performance and acclimation of two submerged macrophyte species, Elodea canndensis L.C. Rich and Ranunculus aquatilis (L.) Wimmer. The plants were grown at 5, 10 and 15 degrees C and a photon flux density of 300 mu mol m(-2) s(-1) (PAR) in a medium with an alkalinity of 0.85 meg l(-1) bubbled with atmospheric air containing 400 ppm CO2. In general, growth rates of both species increased with temperature with a Q(10) varying from 2.3 to 3.5. An exception was Elodea at 5 degrees C, where growth was nearly arrested. Temperature effects on ambient rates of net photosynthesis and photosynthetic capacity followed the pattern observed for growth. Dark respiration was not suppressed for Elodea at 5 degrees C and both species had a Q(10) of 2.3. The light-use efficiency (alpha(I)) for photosynthesis declined with increasing growth temperature for Ranunculus. For Elodea no difference in alpha(I) was observed between 10 and 15 degrees C; at 5 degrees C, however, alpha(I) was reduced by about 30%. Both species acclimated to temperature as shown in a series of experiments in which the plants were exposed to a change in temperature. Acclimation was faster for shoots transferred from low to high temperature, where growth rates stabilised after a few days; for shoots transferred to low temperature growth rates still changed after 22 days. Although acclimation was evident, the changes in the metabolic apparatus were insufficient to balance effects of temperature. It is suggested that temperature may affect local distribution of the two species and their ability to grow in turbid or deep water.

Abstract: The larger aquatic plants growing in wetlands are usually called macrophytes. These include aquatic vascular plants, aquatic mosses and some larger algae. The presence or absence of aquatic macrophytes is one of the characteristics used to define wetlands, and as such macrophytes are an indispensable component of these ecosystems. As the most important removal processes in constructed treatment wetlands are based on physical and microbial processes, the role of the macrophytes in these has been questioned. This paper summarizes how macrophytes influence the treatment processes in wetlands. The most important functions of the macrophytes in relation to the treatment of wastewater are the physical effects the presence of the plants gives rise to. The macrophytes stabilise the surface of the beds, provide good conditions for physical filtration, prevent vertical flow systems from clogging, insulate the surface against frost during winter, and provide a huge surface area for attached microbial growth. Contrary to earlier belief, the growth of macrophytes does not increase the hydraulic conductivity of the substrate in soil-based subsurface flow constructed wetlands. The metabolism of the macrophytes affects the treatment processes to different extents depending on the type of the constructed wetland. Plant uptake of nutrients is only of quantitative importance in low-loaded systems (surface flow systems). Macrophyte mediated transfer of oxygen to the rhizosphere by leakage from roots increases aerobic degradation of organic matter and nitrification. The macrophytes have additional site-specific values by providing habitat for wildlife and making wastewater treatment systems aesthetically pleasing. (C) 1997 IAWQ.

Abstract: The ability of diffusive gas transport and pressurized, convective flow to satisfy internal oxygen demands was examined for an aquatic sedge, Eleocharis sphacelata R. Br.. Resistances to convection and diffusion through the plant were quantified from anatomical studies of the airspace dimensions, and these were used in mathematical models to calculate the fluxes required to satisfy oxygen demands measured in the tissue. The greatest resistance to diffusion in the underwater tissue was the submerged culm between the waterline and sediment surface (1560 Ms m(-3) per m culm length). Resistances of the nodal intercalary meristem (52 Ms m(-3)) and rhizome internode (34 Ms m(-3)) were minor. In contrast, resistances to convection were low in the culms (38 MPa s m(-3) per m culm length), and higher in the nodal meristems (93 MPa s m(-3)). The rhizome internodes had large cortical canals with a low convective resistance (0.75 MPa s m(-3)), and a parallel spongy pith with a very high resistance (518 MPa s m(-3)) that is probably short-circuited by convection. The resistance of the submerged culm means that diffusion is inadequate to satisfy oxygen demands in plants growing in > 10 cm of water, and that convection is therefore essential in the natural habitat of this species (water to c. 2 m depth). However, a convective oxygen influx as low as 2.8x10(-s) mol s(-1) per culm (equivalent to a gas flow rate of 3 mu l s(-1) per culm) could satisfy the entire oxygen demand of the underwater tissue; this value is well below actual rates. At this flow rate, the spongy pith in the rhizome would also remain aerobic: it has a low resistance to diffusion (73 Ms m(-3)) and could receive sufficient oxygen by diffusion from the node. The data agree well with previous empirical measurements of convection in this species and show that diffusion and convection are both important processes for its aeration.

Abstract: The Common Reed (Phragmites australis Cav. Trin. ex Steud.) possesses an outstanding capacity to vent its underground tissues by pressurized through-flow. Phragmites-dominated wetlands therefore potentially provide a significant source of trace gas emissions to the atmosphere. In this paper we present results of in situ studies on gas exchange through Phragmites, and evaluate various methodologies used for measuring gas transport and the fluxes they record. Gas exchange rates were related to atmospheric humidity, temperature and light. Green shoots were influx culms and dead culms and broken or damaged green shoots were efflux culms. Gas exchange through the plants fluctuated diurnally, with highest rates in the early afternoon (up to 11 l m(-2) h(-1)) and lowest rates during the night The net flux of O-2 to the below-ground tissues and sediment was up to 5.7 l m(-2) day(-1), and the net emissions of CO2 and CH4 up to 5.1 and 0.27 l m(-2) day(-1) respectively. Net gas exchange rates varied with season and sediment characteristics, being highest during hot and dry summer days, and on organic sediments with a high oxygen demand and high rates of microbial decomposition. Hence, the convective throughflow mechanism in Phragmites not only accelerates gas exchange between the sediment and the atmosphere, but the oxygen delivered through the plant may also affect the microbial processes in the sediment. Therefore, the role of the plants for rhizosphere oxidation and conveyers of gases should be further assessed in future studies. A comparison of current methods for measuring flow suggested that they need refining if they are to quantify gas exchange through Phragmites wetlands on a large scale or over longer time periods.

Abstract: 1. Growth, photosynthesis and root adenine nucleotides were compared in two wetland plants, Phalaris arundinacea and Glyceria maxima, grown in aerated, deoxygenated or reduced (redox potential = -250 mV) nutrient solutions, to test the hypothesis that the stress of de-oxygenated conditions is mild compared with that of naturally reducing sediments. 2. Relative growth rate (RGR) was not significantly different between plants in the aerated and de-oxygenated treatments. However, plants in the reducing treatment stopped growing and some lost mass (RGR negative). Differences in root porosity were not significant between treatments. 3. Rates of net photosynthesis in both species were stable in the de-oxygenated and aerated treatments, at 3-8 mu mol CO(2)m(-2)s(-1). However, net photosynthesis in the reducing treatment declined over 5 days, becoming negative in P. arundinacea and falling below 1 mu mol CO2 m(-2)s(-1) in G. maxima. 4. Concentrations of adenine nucleotides in the roots of both species were significantly but only slightly lower in the de-oxygenated treatment than in the aerated treatment (0.65 times as much ATP and 0.70-0.87 times as much total adenine nucleotides). However, nucleotide concentrations were much lower in the reducing treatment (0.10-0.19 times as much ATP and total adenine nucleotides as the aerated treatment). Both species tolerated the de-oxygenated treatment but were sensitive to the reducing treatment.

Abstract: The effects of solution pH on NH4+ uptake kinetics and net H+ extrusion by Typha latifolia L. were studied during short-term (days) and long-term (weeks) exposure to pH in the range of pH 3.5-8.0, The NH4+ uptake kinetics were estimated from depletion curves using a modified Michaelis-Menten model, T. latifolia was able to grow in solution culture with NH4+ as the sole N source and to withstand a low medium pH for short periods (days), With prolonged exposure (weeks) to pH 3.5, however, the plants showed severe symptoms of stress and stopped growing, The solution pH affected NH4+ uptake kinetics, The affinity for NH4+, as quantified by the half saturation constant (K-1/2) and C-min (the NH4+ concentration at which uptake ceases), decreased with pH. K-1/2 was increased from 7.1 to 19.2 mmol m(-3) and C-min from 2.0 to 5.7 mmol m(-3) by lowering the pH in steps from 8.0 to 3.5, V-max was, however, largely unaffected by pH (approximate to 22 mu mol h(-1) g(-1) root dry weight), Under prolonged exposure to constant pH, growth rates were highest at pH 5.0 and 6.5, At pH 8.0 growth was slightly depressed and at pH 3.5 growth completely stopped, NH4+ uptake kinetics were similar at pH 5.0, 6.5 and 8.0 whereas at pH 3.5 NH4+ uptake almost completely stopped, The ratio between net H+ extrusion and NH4+ uptake decreased significantly at low pH, The adverse effects of low pH on NH4+ uptake kinetics are probably a consequence of a reduced H+-ATPase activity and/or an increased re-entry of H+ at low pH, and the associated decrease in the electrochemical gradient across the plasma membranes of the root cells.

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Abstract: We studied the effects of oxygen (aerated versus O-2 depleted similar to 0.5 mg l(-1) O-2) and nitrate (none versus 10 mu mol l(-1)) on the ammonium uptake kinetics and adenylate pools in two wetland plants differing in their degree of flood tolerance (Phalaris arundinacea L. and Glyceria maxima (Hartm.) Holmb.). The study was performed as a random block design in a growth chamber. The NH4+-uptake kinetics were estimated by using a computerised nonlinear parameter estimation procedure to fit the differential farm of a modified Michaelis-Menten model to solution depletion curves. The uptake kinetics for NH4+ differed between the two species: V-max was significantly higher for P. arundinacea (24.7 to 29.6 mu mol h(-1) g(-1) root dry weight) than for G. maxima (4.6-10.3 mu mol h(-1) g(-1) root dry weight). The NH4+ concentration at which uptake ceases (C-min) was 0.2 to 0.5 mu mol l(-1) for P. arundinacea and significant higher (1.1-2.7 mu mol l(-1)) for G. maxima. K-m varied between 3.1 and 6.2 mu mol l(-1) for P. arundinacea, and 1.6 and 3.0 mu mol l(-1) for G. maxima. The different uptake kinetics of the two species reflect the different structure of their root systems: P. arundinacea has an extensive root system consisting of many thin roots whereas G. maxima has fewer but thicker roots. The uptake kinetics also suggest that P. arundinacea is adapted to growing at lower ambient NH4+ concentrations than G. maxima. Oxygen had no consistent effect on NH4+ uptake kinetics. However, the plants that had NO3- in the nutrient solution as well as NH4+ had slightly higher V-max values and lower C-min and K-m values than those without NO3-. Thus, both species were able to sustain their uptake characteristics at low external O-2 concentrations, probably because of internal aeration through the air-space tissue of the plants. Nitrate deprivation also lowered the energy charge ratio and adenine nucleotide content in roots. The roots recovered quickly from NO3- deprivation once NO3- was resupplied. The stresses imposed by partially O-2-depleted conditions and lack of nitrate were therefore relatively mild and reversible. It seems that the inherent aerenchyma development under aerated conditions in these species is sufficient to maintain adequate root oxygenation under partially O-2-depleted conditions.

Abstract: Macrophytes have several intrinsic properties that makes them an indispensable component of constructed wetlands. The most important functions of the macrophytes in relation to the treatment of wastewater are the physical effects brought about by the presence of the plants. The macrophytes stabilise the surface of the beds, provide good conditions for pbysical filtration, prevent vertical flow systems from clogging, insulate against frost during winter, and provide a huge surface area for attached microbial growth. Contrary to earlier belief, the growth of macrophytes does not increase the hydraulic conductivity of the substrate in soil-based subsurface flow constructed wetlands. The metabolism of the macrophytes affects the treatment processes to different extents depending on the design of the constructed wetland. Plant uptake of nutrients is only of quantitative importance in low-loaded systems (surface flow systems). Macrophyte-mediated transfer of oxygen to the rhizosphere by leakage from roots increases aerobic degradation of organic matter and nitrification. The macrophytes have additional site-specific values by providing habitat for wildlife and making wastewater treatment systems aesthetically pleasing.

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Abstract: The gas flow pathways within Typha latifolia L. and Typha angustifolia L. were evaluated by studying the internal pressurization and convective flow through individual leaves and the internal resistances to gas flow within the plants. Air enters the middle-aged leaves against a small pressure gradient by humidity-induced pressurization, is convected down the lacunae of the leaves to the rhizome, and from there is vented back to the atmosphere, through old or damaged leaves or through horizontal rhizomes to other shoots. A model was developed to analyze the gas flow pattern within the plants under different conditions. The analysis showed that the throughflow pattern is dynamic: leaves can be influx leaves under a certain set of conditions and efflux leaves under different conditions. The specific internal resistance to gas flow was generally low in leaves (less than 1 Pa s mm(-2)) and rhizomes (3 Pa s mm(-2)), and somewhat higher in junctions between leaves and rhizome (5-14 Pa a mm(-2)). T. angustifolia generally produced a greater leaf area specific convective flow rate (up to 31 mu l min(-1) cm(-2)) than T. latifolia (up to 11 mu l min(-1) cm(-2)). This greater ventilation capacity of T. angustifolia may be significant for its ability to grow in deeper water, and may contribute to the explanation of the depth distribution of the two species.

Abstract: The internal gas transport in the shoots of the cattails, Typha latifolia L. and Typha angustifolia L., occurs principally via pressurized convective throughflow of gases. Static pressure differentials of up to 350 Pa relative to ambient for T. latifolia and 570 Pa for T. angustifolia were found to be generated mainly by humidity-induced diffusion at ambient temperatures of 15-25 degrees C. Thermal transpiration did not contribute significantly to the internal pressurization. Convective gas flow rates of up to 8 cm(3) min(-1) for T. latifolia and 3.5 cm(3) min(-1) for T. angustifolia were recorded from cut rhizomes. Internal pressurization and convective throughflow rates were highest at high ambient temperature and low ambient relative humidity. Light did not affect pressurization in T. latifolia, whereas pressurization and convective gas flows were lower in the light than in the dark in T. angustifolia, probably as a consequence of stomatal movements. A layer of closely packed mesophyll cells located just below the palisade parenchyma of the leaves is probably the porous partition responsible for the pressurization, but stomata with tortuous pathways may also be involved. Under identical environmental conditions the ventilation capacity of T. angustifolia is about twice as high as that of T. latifolia indicating that root aeration of the former may be more efficient.

Abstract: During the last two decades the multiple functions and values of wetlands have been recognized not only by the scientists and managers working with wetlands, but also by the public. The ability of wetlands to transform and store organic matter has been exploited in constructed wetlands. This paper summarizes the state-of-the-art of the uses of constructed wetlands in water pollution control by reviewing the basics of the technology, the historical development, and the performance expectations with focus on the use of free water surface and subsurface flow constructed wetlands for municipal wastewater treatment. Performance data from a total of 104 subsurface flow systems and 70 free water surface flow systems are reviewed. The present state of knowledge is sufficient to apply constructed wetlands as a tool for improving water quality. The potential applications range from secondary treatment of municipal and various types of industrial wastewaters to polishing of tertiary treated waters and diffuse pollution. In many situations constructed wetlands is the only appropriate technology available. The treatment capacity of subsurface flow systems can be improved by selecting vertical flow systems with intermittent loading, by proper media selection, and by recycling of the wastewater. Further research is needed to help define and optimize engineering design criteria and the long-term performance capabilities and operational problems.

Abstract: Net oxygen exchange between entire root systems of the sedges Cyperus involucratus Rottb. and Eleocharis sphacelata R. Br. was measured in a bi-compartment apparatus, fitted with a polarographic oxygen electrode and a platinum wire electrode in the root chamber. The roots of both species consumed oxygen from water in the root chamber, with no net exchange when the oxygen partial pressure (pO(2)) in the chamber was zero. Rates of oxygen uptake by roots of intact plants were always lower than those of excised roots, suggesting a contribution by oxygen transport from the shoots to the root respiratory demand. The contribution of oxygen transported from the shoots increased with diminishing pO, in the root medium, approaching the total oxygen demand as pO(2) fell to zero. The roots released oxygen when titanium (III) citrate redox buffer (E(H) = -350 mV) was used in the root chamber to mimic the redox potential of natural sediments. Rates of oxygen release into the reduced solutions were 21 +/- 5 and 55 +/- 7 mu mol O-2 hr(-1) g(-1) root dry weight from C. involucratus and E. sphacelata, respectively, in the light, and 16 +/- 3 and 9 +/- 3 mu mol O-2 root dry weight in the dark (mean values +/- 1 standard deviation). These results suggest that an agitated body of water alone is not a suitable medium for measuring root oxygen release by entire root systems. A solution with a high oxygen demand is more appropriate.

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Abstract: Internal pressurization and convective through-flow are demonstrated to be common attributes of wetland plants with cylindrical culms or linear leaves. Eight of 14 species tested produced static internal gas pressure differentials of 200-1,300 Pa relative to ambient and internal convective airflows of 0.2 to > 10 cm3 min-1 culm-1, depending on species. Four species produced internal static pressure differentials of < 100 Pa. Two species did not pressurize. The driving forces are gradients in temperature and water vapor between the internal ps spaces of the plants and the ambient atmosphere (thermal transpiration and humidity-induced pressurization). A clear diel variation in pressurization and convective flow was observed; rates were highest in the afternoon and lowest at night, responding to ambient changes in light, temperature, and humidity. The resistance to airflow at the stem-rhizome junction was very high for some species, resulting in a low ability to convert internal pressurization into convective airflow through the rhizomes. Species with a high potential for internal pressurization and a low internal resistance to convective flow seem to have a competitive advantage over species that rely exclusively on diffusive gas transport, which allows them to grow in deeper waters.

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Abstract: Uptake of dissolved inorganic carbon (DIC) by roots and rhizomes of Phragmites australis (Cav.) Trin. ex Steudel and the subsequent internal transport and photosynthetic fixation were studied by adding C-14 labeled DIC to the rhizosphere interstitial water and then monitoring the C-14 activity in the interstitial water, the lacunal air and the different plant tissues over the following 70 h. Interstitial water (CO2)-C-14 diffused into the lacunae of the root system and upward within the hollow stems of the plant. The amount of C-14 in all parts of the plant increased with time. The concentration was highest in the basal parts of the plant and decreased with distance from the substrate. Culm nodes and internodes generally contained more C-14 than leaf sheaths and leaf laminae. The data suggest that sediment-derived carbon is predominantly transported via the lacunae to the aerial tissues as gaseous CO2 where it is fixed photosynthetically by green culms and leaf sheaths. Sediment-derived carbon constituted less than 1% of the amount of carbon fixed from the atmosphere by the aerial plant tissues. Apparently, the loss of root respiratory CO2 to the rhizosphere interstitial water quantitatively exceeded the root CO2 uptake. It is suggested that the utilization of sediment-derived carbon may be of significance for young sprouting shoots.

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