Abstract: This paper reports chamber measurements of ecosystem respiration (ER) from reed canary grass (Phalaris arundinacea L.) (RCG) cultivation made during 2004 and 2005 and respiration rates from an adjacent, bare peat extraction site. Annually, the RCG site released 1465 g in 2004 and 1968 g CO2 m(-2) in 2005. The peat extraction site, however, emitted 498 g in 2004 and 264 g CO2 m(-2) in 2005. Heterotrophic respiration accounted for about 45% of the RCG ER. Temperature explained 75-88% of the variation in 2005 RCG heterotrophic respiration. Autotrophic respiration was the dominant component of ER and it followed a similar seasonal pattern as the living (green) biomass. RCG heterotrophic respiration was related to soil temperature in interaction with soil volumetric water content and seasonal rainfall distribution. It explained 79 and 47% of the variation in the bare soil respiration from the peat extraction site during 2004 and 2005 snow free periods, respectively. Compared to other ecosystems, emissions from RCG were lower indicating that the RCG is a promising after use option in organic soils.
Abstract: Liming is a common management practice used to achieve optimum pH for plant growth in agricultural soils. Addition of lime to the soil, however, may Cause CO2 release when the carbonates in lime dissolve in water. Although lime may thereby constitute a significant carbon source, especially under acidic soil conditions, experimental data on the CO2 release are lacking so far. We conducted a split-plot experiment within a cut-away peatland cultivated with a bioenergy crop (reed canary grass, Phalaris arundinacea L) with lime and fertilizer treatments to determine effects of lime on the CO2 emissions from soil and to better understand mechanisms underlying liming effects. Carbon dioxide release was measured over two growing seasons in the field after liming, and complementary laboratory studies were conducted. To differentiate CO2 derived from lime and biotic respiration the delta C-13 of CO2 released was determined and the two-pool mixing model was applied. The results showed that lime may contribute significantly to CO2 release from the soil. In the laboratory, more than 50% of CO2 release was attributable to lime-carbonates during short-term incubation. Lime-derived CO2 emissions were much lower in the field, and were only detected during the first (2-4) months after the application. However, a maximum of 12% of monthly CO2 emissions from the cultivated peatland originated from the lime. Biotic respiration rates were similar in limed and unlimed soils, suggesting that higher pH did not, at least in the short-term, increase carbon losses from cultivated peat soils. Additional fertilization and acidification did not contribute to further CO2 release from the lime. According to our first estimations about one sixth of the lime applied would be released as CO2 from the managed peatland, with all lime-derived emissions occurring during the first year of application (equivalent to about 4.6% of the total annual CO2 losses from the soil in the first year). This suggests that the mass-balance approach as proposed by the IPCC Tier 1 methodology, which assumes that all carbon in lime ends up as CO2 in the atmosphere, overestimates the emissions from lime. Our study further shows that there is a great risk to overestimate heterotrophic microbial activity in limed soils by measuring the CO2 release without separating abiotic and biotic CO2 production. (C) 2008 Elsevier Ltd. All rights reserved.
Abstract: This paper summarises the results of several research groups participating in the research programme "Greenhouse Impacts of the use of Peat and Peatlands in Finland", and presents emission factors for peat-atmosphere fluxes of CO2, CH4, and N2O, filling gaps in knowledge concerning the afforestation of organic croplands and cutaways, and improves the emission assessment of peatlands drained for forestry. Forest drainage may result in net binding of soil carbon or net release, depending on site characteristics and the tree stand. Use of peatlands for agriculture (48-4821 g CO2-eq. m(-2) a(-1)), even after the cultivation has ceased, or for milled peat harvesting (1948-2478 g CO2-eq. m(-2) a(-1)) can cause the highest overall emissions. Extremely high CO2 emissions are possible from peat harvesting areas during wet and warm summers. Afforestation of those peatlands abandoned from cultivation or peat harvesting can reduce the warming impact at least during the first tree generation. Heterotrophic soil respiration may have a systematic south-north difference in temperature response. More data must be collected before the information on peatland forest soil CO 2 emissions can be adapted for different climatic regions in Finland. A test of the model DNDC against measured data showed that DNDC has to be developed further before it can be used in estimating N2O emissions from boreal peatlands.
Abstract: Heterotrophic soil respiration (CO 2 efflux from the decomposition of peat and root litter) in three forestry-drained peatlands with different site types and with a large climatic gradient from the hemi-boreal (central Estonia) to south (southern Finland) and north boreal (northern Finland) conditions was studied. Instantaneous fluxes varied between 0 and 1.3 g CO2-C m(-2) h(-1), and annual fluxes between 248 and 515 g CO2-C m(-2) a(-1). Variation in the annual fluxes among site types was studied only in the south-boreal site where we found a clear increase from nutrient-poor to nutrient-rich site types. More than half of the within-site variation was temporal and explained by soil surface (-5 cm) temperature (T5). The response of soil respiration to T5 varied between the sites; the most northerly site had the highest response to T5 and the most southerly the lowest. This trend further resulted in increased annual fluxes towards north. This unexpected result is hypothesised to be related to differences in site factors like substrate quality, nutrient status and hydrology but also to temperature acclimation, i.e., adaptation of decomposer populations to different climates.
Abstract: Closed (non-steady state) chambers are widely used for quantifying carbon dioxide (CO2) fluxes between soils or low-stature canopies and the atmosphere. It is well recognised that covering a soil or vegetation by a closed chamber inherently disturbs the natural CO2 fluxes by altering the concentration gradients between the soil, the vegetation and the overlying air. Thus, the driving factors of CO2 fluxes are not constant during the closed chamber experiment, and no linear increase or decrease of CO2 concentration over time within the chamber headspace can be expected. Nevertheless, linear regression has been applied for calculating CO2 fluxes in many recent, partly influential, studies. This approach has been justified by keeping the closure time short and assuming the concentration change over time to be in the linear range. Here, we test if the application of linear regression is really appropriate for estimating CO2 fluxes using closed chambers over short closure times and if the application of nonlinear regression is necessary. We developed a nonlinear exponential regression model from diffusion and photosynthesis theory. This exponential model was tested with four different datasets of CO2 flux measurements (total number: 1764) conducted at three peatlands sites in Finland and a tundra site in Siberia. Thorough analyses of residuals demonstrated that linear regression was frequently not appropriate for the determination of CO2 fluxes by closed-chamber methods, even if closure times were kept short. The developed exponential model was well suited for nonlinear regression of the concentration over time c(t) evolution in the chamber headspace and estimation of the initial CO2 fluxes at closure time for the majority of experiments. However, a rather large percentage of the exponential regression functions showed curvatures not consistent with the theoretical model which is considered to be caused by violations of the underlying model assumptions. Especially the effects of turbulence and pressure disturbances by the chamber deployment are suspected to have caused unexplainable curvatures. CO2 flux estimates by linear regression can be as low as 40% of the flux estimates of exponential regression for closure times of only two minutes. The degree of underestimation increased with increasing CO2 flux strength and was dependent on soil and vegetation conditions which can disturb not only the quantitative but also the qualitative evaluation of CO2 flux dynamics. The underestimation effect by linear regression was observed to be different for CO2 uptake and release situations which can lead to stronger bias in the daily, seasonal and annual CO2 balances than in the individual fluxes. To avoid serious bias of CO2 flux estimates based on closed chamber experiments, we suggest further tests using published datasets and recommend the use of nonlinear regression models for future closed chamber studies.
Abstract: The purpose of this paper is to introduce the gas exchange measurement and flux calculation methods commonly used in the projects of the programme "Greenhouse gas emissions from the use of peat and peatlands in Finland". The methods include measurements of instantaneous fluxes of CO2, CH4 and N2O made at the ecosystem-atmosphere boundary using closed chamber, and whole ecosystem fluxes of the gases using micrometeorological EC tower extending above the canopy, and the integration of seasonal and annual fluxes. In addition, tools developed for gap filling of missing weather records, and generating complete weather patterns for the key environmental controls of the gas fluxes are introduced. Derivation of emission factors from the collected gas fluxes, capable of reproducing the dynamic, climate dependent nature is outlined.
Abstract: This study was conducted to improve the estimates of C gas fluxes in boreal ombrotrophic and minerotrophic mires used in the lifecycle analysis of peat energy. We reviewed literature and collected field data from two new sites in southern Finland. In the literature, annual estimates of net CO2 exchange varied from -85 to +67 g C m(-2) a(-1) for ombrotrophic mires and from -101 to +98 g C m(-2) a(-1) for minerotrophic mires. Correspondingly, net CH, flux estimates varied from less than -1 up to -16 g C m(-2) a(-1) and from less than -1 up to -42 g C m(-2) a(-1) for ombrotrophic and minerotrophic mires, respectively. Negative values indicate net efflux from the ecosystem. The modelling of C gas fluxes for the 30 simulated years clearly highlighted the need for long-term records of multiple environmental factors from the same sites, and the need for a number of improvements in the modelling of fluxes, as well as the environmental conditions driving C fluxes. The reduction of uncertainty in the background values of lifecycle analyses requires more detailed knowledge of the mire types used for peat harvesting and long-term field measurements combined with the developed process models and meteorological information. The use of C gas fluxes in pristine mires as a background for anthropogenic emissions is, however, only one option. Another option could be to consider anthropogenic emissions from the use of peat energy as such.
Abstract: The effects of land-use and land-use change on soil greenhouse gas (GHG) fluxes are of concern due to Kyoto Protocol requirements. To quantify the soil GHG-fluxes of afforested organic soils in Finland, chamber measurements of soil CO2, CH4 and N2O fluxes were made during the years 2002 to 2005 on twelve organic soil cropland and six cutaway peatland sites afforested 9 to 35 years ago. The annual soil CO2 effluxes were statistically modelled using soil temperature as the driving variable and the annual CH4 and N2O fluxes were estimated using the average fluxes during the measurement period. Soil CO2 effluxes on afforested organic soil croplands varied from 207 to 539 g CO (2)-C m(-2) a-(1) and on cutaway peatlands from 276 to 479 g CO2-C m(-2) a(-1). Both the afforested organic soil cropland and cutaway peadand sites acted mainly as small sinks for CH 4; the annual flux ranged from -0.32 to 0.61 g CH4-C m(-2). Afforested organic croplands emitted more N2O (from 0. 1 to over 3.0 g N2O-N m(-2) a(-1)) than cutaway peatland sites (from 0.01 to 0.48 g N2O-N m(-2) a(-1)). Due to the decrease in soil CO2 efflux, and no change in CH4 and N2O fluxes, afforestation of organic croplands appears to decrease the greenhouse impact of these lands.
Abstract: Hydrology controls the physical, chemical and biological processes in peatlands and hence could be the most important process regulating their function, development and characteristic biogeochemistry. Models describing hydrological processes and soil heat exchange phenomena are an important tool in understanding the peatland biogeochemical cycles of C and N. Presented in this paper is a peat soil climate model that uses weather data, mire site and peat characteristics as input data. The model is related to the heterogeneous peat characteristics (e.g. bulk density, degree of humification, remains of Sphagnum, Carex, Eriophorum and woody tissues), which in turn vary with depth. Evapotranspiration is related to weather parameters and tree stand characteristics. The model simulations were validated against the observed data collected during 1993 and 1994 growing seasons at a fen and bog sites at the Lakkasuo mire complex located in central Finland. The observed and simulated day-to-day variations in water table levels and soil temperatures during both seasons appeared overall to be in phase. As the model lacks the data needed to characterize the peat matrix hysteresis, the model was found lacking in response to wetting and drying cycles. The mean differences between simulated and observed water table levels during 1994 were -0.3 +/- 1.3 and -0.5 +/- 2.3 cm for the fen and bog sites, respectively. The model was found to be sensitive to mire surface characteristics and evapotranspiration, particularly for the bog site with an unsaturated zone deeper than at the fen. The absolute mean differences between the simulated and measured peat temperatures from 5 to 150 cm, were less than 1.0 degrees C with a maximal standard deviation of 1.6 degrees C. The model deviations for the upper layers showed larger variations compared to deeper layers, implying a greater accuracy in defining the lower boundary of the thermal regime within the peat column. (c) 2005 Published by Elsevier B.V.
Abstract: Rice-wheat rotations, practised in 12.5 million ha in Indo-Gangetic Plain region (IGPR), are the most important production system for food security of south Asian countries. Recent reports, however, indicate that the system is under production fatigue as yields have started declining due to continuous rice-wheat cultivation. We analysed the yield trends and effect of fertiliser NPK application, alone or in combination with farmyard manure (FYM), green manure (GM) or wheat crop residue (CR) incorporation, on the changes in soil organic carbon (OC) and available NPK contents. Data of a long-term experiment conducted at six locations in the IGPR and at one location in the Central Highlands and Plateau region of India, adjacent to IGPR, revealed that yields of rice and wheat were constantly greater in all the years when complete doses of NPK were applied through fertilisers, or 50% dose of NPK were applied through fertilisers along with organic materials compared to that in unfertilised-control. At Ludhiana and Pantnagar, where yield levels during initial years of the experiment were relatively high, a declining trend in yield was observed over years in all the treatments. At other locations, rice or wheat yield trends in the treatments receiving complete doses of fertiliser NPK were generally not significant, but in the treatments having fertiliser + manure combination, positive and significant trends in yield of rice were observed. Linear regressions fitted to pooled data across the locations revealed highly significant (p < 0.01) annual increase in yield of rice with integrated supply of nutrients through fertilisers and manures, indicating thereby the advantage of combined use of manures plus fertilisers over fertilisers alone in sustaining crop yields. Soil OC decreased over time at locations where the OC content was greater than 6.5 g kg(-1) at the start of the long-term experiment, but increased at locations having initially low (<5.0 g kg(-1)) OC content. Available P content increased with P additions through fertilisers or manures at four locations. Temporal changes in available P content, however, appeared to have depended on the changes in soil OC. Despite annual K additions at recommended rates through fertilisers and at more than the recommended rates through organic manures, available K content decreased due to continuous cropping at five locations. (C) 2000 Published by Elsevier Science B.V.
Abstract: The spatial variability of turbulent flow statistics in the roughness sublayer (RSL) of a uniform even-aged 14 m (= h) tall loblolly pine forest was investigated experimentally. Using seven existing walkup towers at this stand, high frequency velocity, temperature, water vapour and carbon dioxide concentrations were measured at 15.5 m above the ground surface from October 6 to 10 in 1997. These seven towers were separated by at least 100 m from each other. The objective of this study was to examine whether single tower turbulence statistics measurements represent the flow properties of RSL turbulence above a uniform even-aged managed loblolly pine forest as a best-case scenario for natural forested ecosystems. From the intensive space-time series measurements, it was demonstrated that standard deviations of longitudinal and vertical velocities (sigma(u), sigma(w)) and temperature (sigma(T)) are more planar homogeneous than their vertical flux of momentum (u(*)(2)) and sensible heat (H) counterparts. Also, the measured H is more horizontally homogeneous when compared to fluxes of other scalar entities such as CO2 and water vapour. While the spatial variability in fluxes was significant (>15%), this unique data set confirmed that single tower measurements represent the 'canonical' structure of single-point RSL turbulence statistics, especially flux-variance relationships. Implications to extending the 'moving-equilibrium' hypothesis for RSL flows are discussed. The spatial variability in all RSL flow variables was not constant in time and varied strongly with spatially averaged friction velocity u(*), especially when u(*) was small. It is shown that flow properties derived from two-point temporal statistics such as correlation functions are more sensitive to local variability in leaf area density when compared to single point flow statistics. Specifically, that the local relationship between the reciprocal of the vertical velocity integral time scale (I-w) and the arrival frequency of organized structures ((u) over bar/h) predicted from a mixing-layer theory exhibited dependence on the local leaf area index. The broader implications of these findings to the measurement and modelling of RSL flows are also discussed.
Abstract: Methane flux was measured, employing the micrometeorological eddy correlation technique, during two growing seasons (1991 and 1992) in a peatland in Minnesota. As compared to 1991, the 1992 season was wetter and cooler Here we examine the seasonal distributions of CH4 flux and the relationship between concurrently measured CH4 and CO(2)fluxes. Midday CH4 flux was low (1.5 mg m(-2) h(-1)) during late May in both seasons. Subsequently, the flux ranged from 2.5 to 5.5 mg m(-2) h(-1) during early June to early July in both years. Methane flux peaked at 6.5 mg m(-2) h(-1) during mid July in 1991. The peak flux (8.0 mg m(-2) h(-1)) in 1992 occurred 3 weeks later. A sustained drop in water table during late July to late August in 1991 may have reduced the methane emission. During mid August-mid October in 1992, the water table was consistently high and the flux ranged from 2.0 to 3.0 mg m(-2) h(-1). As compared to 1991, CH4 flux during this time in 1992 was higher by about 1.0 mg m(-2) h(-1) because of the overriding influence of the water table. Integration over the growing season (late May to mid October), indicated that this ecosystem released approximately 10.4 and 11.5 g C m(-2) of CH4 in 1991 and 1992, respectively. We examined our concurrent measurements on methane flux and canopy photosynthesis under a variety of environmental conditions from different parts of the growing season. On a time scale of the entire season, the overall patterns of methane flux and canopy photosynthesis were similar in both years. Canopy photosynthesis, however, showed large day-to-day changes in response to variations in temperature and moisture. Corresponding changes in methane flux during these selected periods were relatively small. The slopes and correlation coefficients of linear regressions between methane flux and photosynthesis data varied widely. Accordingly, a close coupling between short-term (day to day) variations in methane flux and canopy photosynthesis was not evident.
Abstract: Soil biogenic NOx emissions are an important part of the total global NOx budget. The objective of this study was to investigate the role of the soil NOx source in an urban-metropolitan area. We measured the emissions from soils within the urban-metropolitan land use area of Nashville, Tennessee, and surrounding Davidson County, to estimate the importance of this source in the overall NOx budget of Davidson County. Nashville is currently in nonattainment for ozone (O-3), and a State Implementation Plan (SIP) has been promulgated to help achieve compliance of the O-3 standard. Using geographic information systems imagery and aerial photographs, we determined the extent of urban-metropolitan soils within the Nashville area. Results indicated that 409 km(2), or approximately 34% of the county, was classified as residential or urban, with the predominant vegetation being grass (68%). The residential sector was the largest with 323 km(2), the urban area comprising 87 km(2), and a total area of 8 km(2) of golf courses. Soil NOx emission measurements were made in approximate proportion to the major land use types using static chamber techniques. Results indicated that urban-metropolitan soils were not an important source of soil NOw(x). Approximately 10 Mg NOx, or 0.003% of the total annual NOx budget of Davidson County, is estimated to be emitted by urban soils annually. Additionally, the remaining soil sources in the county, forests and agricultural land, contributed 179 Mg, or 0.66% of the total annual NOx budget. While soil NOx emissions were concluded to be a negligible component of the Davidson County budget, their contribution to the NOx budget of the surrounding four counties in the STP area was significant. Extrapolation of soil NOx emissions for three of the four counties within the SIP area indicated that soil biogenic NOx emissions contributed from 7.0 to 9.8% of the daily average NOx budget during the months of June through August. Because of the soil temperature dependence of soil NOx emissions, it was estimated that during the hottest July days the soil biogenic component could contribute over 17% of the total NOx in some SIP counties.
Abstract: Micrometeorological measurements of carbon dioxide exchange were made in an open peatland in north central Minnesota during two growing seasons (1991 and 1992). The vegetation at the site was dominated by Sphagnum papillosum, Scheuchzeria palustris, and Chamaedaphne calyculata. The objective of the study was to examine the diurnal and seasonal variations in canopy photosynthesis (P) and develop information on the net ecosystem CO2 exchange. The two seasons provided contrasting microclimatic conditions: as compared with 1991, the 1992 season was significantly wetter and cooler. Canopy photosynthesis was sensitive to changes in light, temperature, and moisture stress (as indicated by water table depth and atmospheric vapor pressure deficit). Under moderate conditions (temperature 18-28 degrees C, vapor pressure deficit 0.7-1.5 kPa, and water table near the surface) during the peak growth period, midday (averaged between 1000-1400 hours) P values ranged from 0.15 to 0.24 mg m(-2) s(-1). Under high-temperature (30 degrees-34 degrees C) and moisture stress (water table 0.16-0.23 m below the surface and vapor pressure deficit 2.2-3.0 kPa) conditions, midday P was reduced to about 0.03-0.06 mg m(-2) s(-1). There was a high degree of consistency in the values of P under similar conditions in the two seasons. Seasonally integrated values of the daily net ecosystem CO2 exchange indicated that the study site was a source of atmospheric CO2, releasing about 71 g C m(-2) over a 145-day period (May-October) in 1991. Over a similar period in 1992, however, this ecosystem was a sink for atmospheric CO2 with a net accumulation of about 32 g C m(-2). These results are consistent with previous investigations on CO2 exchange in other northern wetland sites during wet and dry periods.
Abstract: Methane flux was measured using the micrometeorological eddy correlation technique during 62 days in mid-May through mid-October 1991 in a peatland ecosystem in north central Minnesota. Application of this technique allows measurement of spatially integrated fluxes. The distribution of methane flux consisted of a gradual pattern with several episodic emissions superimposed. The gradual (nonepisodic) pattern of methane flux (daytime average) exhibited an increase from 30-120 mg m-2 d-1 in late May to early July to 125-160 mg m-2 d-1 in mid-July to mid-August and then a decline to 100-35 mg m-2 d-1 in early September to mid-October. Peat temperature (at 0.1 m depth) and water table depth accounted for about 70% of the variance in the methane flux data. The episodic emissions were associated with drops in atmospheric pressure and a declining water table. Generally, the hourly values of daytime methane flux were fairly stable, perhaps with a slight depression during the midday. However, on days with episodic emissions, the daytime methane flux had a peak during the midafternoon, and its pattern appeared to be similar to those of the standard deviation of atmospheric pressure fluctuations and mean horizontal wind velocity. The ratio of soil CO2 to methane fluxes (during nonepisodic emission periods) increased with increasing water table depth in a manner similar to that observed in a laboratory study of peat columns from different wetland types in Quebec. The annual methane emission for this ecosystem was estimated to be about 16-19.5 g m-2 yr-1.
