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Teresa Elena Vegas Vlarrúbia

Aggregate Professor
Dep. Ecology, Fac. Biology,
Univ. of Barcelona
Av. Diagonal 645, Ramon Margalef bulding
08028 Barcelona

Journal articles

Sandra Nogue, Valentí Rull, Teresa Vegas-Vilarrúbia (2013)  Elevational gradients in the neotropical table mountains: patterns of endemism and implications for conservation   Biological Conservation  
Abstract: Aim The aim of the present study was to describe the diversity patterns along elevational gradients that are crucial for conservation management and for understanding diversification processes in montane environments. This article analyses the distributional range and elevation patterns of endemic and nonendemic (NE) vascular plants living on a unique set of Neotropical table mountains (tepuis). To investigate the potential causes of the high degree of diversity and endemism we tested the role of elevation, area and the middomain effect (MDE). We also aimed to discuss the origin of the current tepuian biota. Location The Guayana Highlands (northern South America). Emphasis is placed on the mountaintops above 1500 m elevation, which form the highly biodiverse Pantepui biogeographical province. Methods We examined the distribution patterns of vascular plant species richness in relation to elevation, area, and the MDE using generalized additive models. We used Range Model for the MDE. Results We found that regional endemics richness show a hump-shaped curve in relation to elevation. Single-tepui endemics (STE) increase with elevation, whereas NE and total species richness decrease. Area and MDE influence this pattern for Pantepui and STE, but not for NE. We also observed that the spatial distribution of endemic richness displays a left-skewed distribution pattern due to the dominance of STE. Main conclusions Our results demonstrate that a combination of elevation, area and MDE provide a basic explanation for the diversity of vascular plants in Pantepui. In addition, the present study indicates that maxima of STE are located at the highest altitudes, where the possibility of biotic connection (via migration) and gene flux has been minimal, even during glacial phases when most migration pathways amongst the tepui mountains were open. We also suggest that climatic filtering due to the extreme conditions atop the tepuis and low dispersal capacity stand out as the main drivers of the decline in NE species richness with elevation.
Notes: in press
Ana Moreno, Ana Pérez, Jaime Frigola, Vanesa Nieto-Moreno, Marta Rodrigo-Gámiz, Belén Martrat, Penélope González-Sampériz, Mario Morellón, Celia Martín-Puertas, Juan Pablo Corella, Ánchel Belmonte, Carlos Sancho, Isabel Cacho, Gemma Herrera, Miquel Canals, Joan O Grimalt, Francisco Jiménez-Espejo, Francisca Martínez-Ruiz, Teresa Vegas-Vilarrúbia, Blas L Valero-Garcés (2012)  Moisture fluctuations reconstructed from paleoclimate archives in the Iberian Peninsula region: is there a common pattern during the Medieval Climate Anomaly?   Quaternary Science Reviews 43: 16-32  
Abstract: Selected multi-proxy and accurately dated marine and terrestrial records covering the past 2000 years in the Iberian Peninsula (IP) facilitated a comprehensive regional paleoclimate reconstruction for the Medieval Climate Anomaly (MCA: 900e1300 AD). The sequences enabled an integrated approach to land esea comparisons and, despite local differences and some minor chronological inconsistencies, presented clear evidence that the MCA was a dry period in the Mediterranean IP. It was a period characterized by decreased lake levels, more xerophytic and heliophytic vegetation, a low frequency of floods, major Saharan eolian fluxes, and less fluvial input to marine basins. In contrast, reconstruction based on sequences from the Atlantic Ocean side of the peninsula indicated increased humidity. The data highlight the unique characteristics of the MCA relative to earlier (the Dark Ages, DA: ca 500e900 years AD) and subsequent (the Little Ice Age, LIA: 1300e1850 years AD) colder periods. The reconstruction supports the hypothesis of Trouet et al. (2009), that a persistent positive mode of the North Atlantic Oscillation (NAO) dominated the MCA.
T Vegas-Vilarrúbia, J Sigró, S Giralt (2012)  El Niño-Southern oscillation events affect river nitrate concentratioms in a Mediterranean river.   Science of the Total Environment 426: 446-453  
Abstract: The causes of interannual nitrate variability in rivers remain uncertain, but extreme climatic events have been suggested as drivers of large nitrate inputs to rivers. Based on a 24-year data set (1983-2006), we suggest that El Niño-Southern Oscillation (ENSO) can affect nitrate behaviour in a seasonal extra-tropical stream of the Llobregat basin (NE Iberian Peninsula), located thousands of kilometres away from the ENSO oscillating system via atmospheric teleconnections. Two commonly used indices, the Southern Oscillation Index (SOI) and the self-calibrating -Palmer Drought Severity Index (scPDSI) showed highly significant correlations with nitrate concentrations, which recurrently increased during La Niña phases, coinciding with severe droughts.
Notes: in press
T Vegas-Vilarrúbia, S Nogué, V Rull (2012)  Global warming, habitat shifts and potential refugia for biodiversity conservation in the neotropical Guayana Highlands. (in press).   Biological Conservation.  
Abstract: Current global average temperatures are 2ºC cooler than during the last interglacial period. The expected increase in temperature during the 21st century will be most stressful for cold-adapted and stenothermic mountain species, forcing them to migrate upwards, and eventually to concentrate into either large areas with favourable climates (refugia) or small stands under locally favourable microclimates (microrefugia). We investigate potential refugia in the neotropical Guayana Highlands mountain biome (Pantepui), consisting of ~50 isolated table mountains (tepuis), to develop strategies for conserving biodiversity during future global warming. We predict the amount of loss of altitudinal habitats of endemic vascular flora of 26 tepuis and evaluate potential threats to these taxa with respect to species extinction, habitat loss, habitat connectivity and the degree of isolation. We compare past, present and future Pantepui landscape configurations through fragmentation analysis and identify potential in situ refugia. Spatial analysis forecasts more species isolation and declining biodiversity at the end of this century relative to current and past levels. Habitats are predicted to experience >80% loss, with the disappearance of 38 habitat patches. One large patch (Chimantá massif) accounts for 46% of the predicted remaining habitat. This patch can be considered a potential refugium for future vascular flora, as it is predicted to contain some present-day resistant species from lower altitudinal levels and other species eventually persisting in microrefugia. The easternmost Pantepui district, containing the Chimantá massif and other tepuis, seems to be the most suitable for the application of in situ conservation strategies
Notes: in press
M Morellón, A Pérez-Sanz, J P Corella, U Büntge, J Catalán, P González-Sampériz, J J González-Trueba, J A López-Sáez, A Moreno, S Pla-Rabes, M Á Saz-Sánchez, P Scussolini, E Serrano, F Steinhilbe, V Stefanova, T Vegas-Vilarrúbia, B Valero-Garcés (2012)  A multi-proxy perspective on millennium-long climate variability in the Southern Pyrenees.   Climate of the Past 8: 683-700  
Abstract: This paper reviews multi-proxy paleoclimatic reconstructions with robust age-control derived from lacustrine,dendrochronological and geomorphological records and characterizes the main environmental changes that occurred in the Southern Pyrenees during the last millennium. Warmer and relatively arid conditions prevailed during the Medieval Climate Anomaly (MCA, ca. 900â1300 AD), with a significant development of xerophytes and Mediterranean vegetation and limited deciduous tree formations (mesophytes). The Little Ice Age (LIA, 1300â1800 AD) was generally colder and moister, with an expansion of deciduous taxa and cold-adapted montane conifers. Two major phases occurred within this period: (i) a transition MCAâLIA, characterized by fluctuating, moist conditions and relatively cold temperatures (ca. 1300 and 1600 AD); and (ii) a second period, characterized by the coldest and most humid conditions, coinciding with maximum (recent) glacier advances (ca. 1600â1800 AD). Glaciers retreated after the LIA when warmer and more arid conditions dominated, interrupted by a short-living cooling episode during the late 19th to early 20th centuries. Some records suggest a response to solar activitywith colder and slightly moister conditions during solar minima. Centennial-scale hydrological fluctuations arein phase with reconstructions of NAO variability, which appears to be one of the main climate mechanisms influencing rainfall variations in the region during the last millennium.
J P Corella, A Brauer, Mangili Cl, V Rull, T Vegas-Vilarrrúbia, MorellónM, B Valero-Garcés (2012)  Recent climate changes vs. human activities in Mediterranean mountains: the 1.5 ka varved record of Lake Montcortès (southern Pyrenees, NE Spain) . (in press)   Quaternary Research  
Abstract: The karstic Lake Montcortès sedimentary sequence (42º 19´ N, 0º 59´ E; 1027 m a.s.l., Pre-Pyrenean Range) constitutes the first continuous, high-resolution, multi-proxy varved record in northern Spain for the last 1548 years. The robust age model is based on absolute varve chronology. Sediments are constituted of biogenic varves composed of calcite, organic matter and detrital laminae with intercalated turbidite layers. Variations in calcite layer thickness and internal sub-layering, and frequency and thickness of detrital layers reflect the interplay of anthropogenic activities and climatic changes in the catchment. Geochemical and sedimentological proxies highlight two main periods of high human pressure in the lake catchment during the Medieval Ages and the 19th century. The sedimentary record of Lake Montcortès shows two different patterns of climate - land use interactions controlling landscape dynamics in Mediterranean mid mountain areas. In pre-industrial times, during favourable (warm) climate conditions like the MCA, population and, consequently, land use increased while during colder conditions (e.g. LIA), population and farming activities decreased. After the onset of the industrialization, the relationship between climate and human activities progressively decoupled; population dynamics and subsequent landscape modifications, therefore, were mostly determined by socio-economic factors.
Notes: in press
E Montoya, V Rull, Vegas-Vilarrúbia (2012)  Non-pollen palynomorph studies in the Neotropics: the case of Venezuela.   Review of Palaeobotany and Palynology. 186: 12. 102–130  
Abstract: This paper summarises the NPP studies developed so far in a wide range of environments from Venezuelan lowlands, midlands and highlands, as an example of a growing discipline in a Neotropical area. The studies discussed include both modern analogues from surface sediments and Late Quaternary sequences combining pollen and spores with NPP analyses. Emphasis is placed on the utility of NPP as palaeoecological indicators both individually and collectively (NPP assemblages), as well as in combination with other proxies. The main advantages of using NPP instead of only pollen and spores are highlighted using case studies as examples. Among them, the occurrence of NPP in samples barren for pollen and spores, the independent indicator nature of NPP, and their capacity to reveal previously unnoticed environmental shifts (notably those related to local conditions), are emphasised. The main results obtained in all these analyses are discussed in the frame of several areas of the NPP study that are considered crucial (methods, taxonomy, indicator value and statistical treatment). Some ideas for future developments are proposed in each of these areas, and the need for closer collaboration among NPP specialists is strengthened, in a way towards unification and standardisation
E Safont, T Vegas -Vilarrúbia, Rull (2012)  Use of Environmental Impact Assessment (EIA) tools to set priorities and optimize strategies in biodiversity conservation.   Biological Conservation 149: 113-121  
Abstract: Pantepui is a biogeographical province composed of a group of approximately 50 tabular mountain summits, or tepuis, in the southeast of Venezuela. This region, also known as Guayana Highlands (GH), lies between 1500 and 3014 m elevation and has an approximate extension of 6000 km2. The summits of the tepuis are characterized by exceptional vascular plant diversity and high endemism. However, it is expected that ongoing global warming will produce upward displacements of summit taxa, which may cause the extinction of certain species due to habitat loss. This study assessed the potential extinction risk of the >600 Pantepui endemic vascular plant species during the 21st century due to global warming, revealing that 30â50% of endemic species would lose their habitat by the end of this century. In light of these results, prioritization of threatened species for conservation purposes became necessary. This was achieved through the calculation of an Environmental Impact Value (EIV) for each species, and a subsequent division of these species into priority categories, which should be used in a chronological sequence to guide decision-making and future research aimed at establishing the most suitable conservation strategies. A number of in situ and ex situ conservation alternatives were discussed. In situ conservation by means of designating protected areas does not appear a viable option because of the upward habitat displacement involved in this case. Conversely, seed banks, living plant collections and managed relocation were suggested in this chronological order to preserve the species studied here
E Montoya, V Rull, N D Stansell, B W Bird, S Nogué, T Vegas-Vilarrúbia, M B Abbott, W A Díaz (2011)  Vegetation changes in the Neotropical Gran Sabana (Venezuela) around the Younger Dryas chron   Journal of Quaternary Science 26: 2. 207–218  
Abstract: The occurrence of the Younger Dryas cold reversal in northern South America midlands and lowlands remains controversial. We present a palaeoecological analysis of a Late Glacial lacustrine section from a midland lake (Lake Chonita, 4.6501 8N, 61.0157 8W, 884m elevation) located in the Venezuelan Gran Sabana, based on physical and biological proxies. The sediments were mostly barren from 15.3 to 12.7 k cal a BP, probably due to poor preservation. A ligneous community with no clear modern analogues was dominant from 12.7 to 11.7 k cal a BP (Younger Dryas chronozone). At present, similar shrublands are situated around 200m elevation above the lake, suggesting a cooling-driven downward shift in vegetation during that period. The interval from 11.7 to 10.6 k cal a BP is marked by a dramatic replacement of the shrubland by savannas and a conspicuous increase in fire incidence. The intensification of local and regional fires at this interval could have played a role in the vegetation shift. A change to wetter, and probably warmer, conditions is deduced after 11.7 k cal a BP, coinciding with the early Holocene warming. These results support the hypothesis of a mixed origin (climate and fire) of the Gran Sabana savannas, and highlight the climatic instability of the Neotropics during the Late Glacial.
E Safont, V Rull, T Vegas-Vilarrúbia, S Nogué (2011)  L´escalfament global i l’extinció de les plantes: un exemple tropical. (Calentamiento global y extinción de plantas: un ejemplo tropical).   Atzavara 20: 29-42  
Abstract: Global warminG and plant extinction: a tropical example. â Pantepui is a phytogeographical province made up of a group of approximately 50 tabular mountain summits or tepuis in southeast Venezuela. This region lies between 1500 and 3014 m a.s.l and covers an approximate area of 6000 km2. Its pristine state of conservation is remarkable. The summits of the tepuis contain an excep- tional level of vascular plant diversity, including 2446 known species, of which 771 are endemic to Pantepui. It is expected that the ongoing effects of global warming will produce upward displace- ments of summit taxa, which could result in the extinction of certain species due to habitat loss. This study is an assessment of the potential extinction risk during the 21st century due to global warming. In order to determine those species that will potentially become extinct during each time frame (2011-2030, 2046-2065 and 2080-2099), we used Altitudinal Range Displacement (ARD) analysis and different scenarios to forecast expected temperatures, as predicted by the Intergov- ernmental Panel on Climate Change (IPCC). The ARD results revealed that at least 169, and up to 321, endemic species would lose their habitat by the end of this century based on the more con- servative and pessimistic scenarios, respectively. In light of these results, a number of in situ and ex situ conservation alternatives are discussed. In situ conservation by means of protected areas does not appear be a viable option because of the upward habitat displacement that would occur. Conversely, ex situ conservation techniques (seed or pollen banks, in vitro culture, collections un- der cultivation, etc.) have great potential to preserve the species discussed herein.
Notes: pdf upon request
A Moreno, M Morellón, C Martín-Puertas, J Frigola, M Canals, I Cacho, P Corella, A Pérez, A Belmonte, T Vegas-Vilarrúbia, P González-Sampériz, B L Valero-Garcés (2011)  Was there a common hydrological pattern in the Iberian Peninsula region during the Medieval Climate Anomaly?   PAGES news 19: 1. 16-18  
Abstract: Climate variability reconstructions for the last millennium from several Iberian lake and marine records shed light on the spatial and temporal hydroclimate and associated climate mechanisms during the Medieval Climate Anomaly.
T Vegas-Vilarrúbia, V Rull, E Montoya, E Safont (2011)  Quaternary palaeoecology and nature conservation: a general review with examples from the neotropics   Quaternar Science Reviews 30: 2361-2388  
Abstract: Palaeoecology, as an ecological discipline, is able to provide relevant inputs for conservation science and ecosystem management, especially for issues involving long-term processes, such as ecological succession, migration, adaptation, microevolution, and extinction. This use of palaeoecology has been noted for several decades, and it has become widely accepted, especially in the frame of ongoing and near-future global warming and its potential biotic consequences. Selected palaeoecological insights of interest for conservation include the following: 1) species respond in an individualistic manner to environmental changes that lead to changes in community composition, suggesting that future ecosystems would have no modern analogues; 2) in the short-term, acclimation is more likely a response of species that are expected to persist in the face of global warming, but the possibility of evolutionary change linked to the existence of pre-adapted genomes cannot be dismissed; 3) species unable to acclimate or adapt to new conditions should migrate or become extinct, which has been observed in past records; 4) current extinction estimates for the near-future should be revised in light of palaeoecological information, which shows that spatial reorganisations and persistence in suitable microrefugia have been more common than extinction during the Quaternary; 5) biotic responses to environmental changes do not necessarily follow the rules of equilibrium dynamics but depend on complex and non-linear processes that lead to unexpected âsurprisesâ, which are favoured by the occurrence of thresholds and amplifying positive feedbacks; 6) threshold responses can cause the movement of ecosystems among several potentially stable states depending on their resilience, or the persistence of transient states; 7) species and their communities have responded to environmental changes in a heterogeneous fashion according to the local and regional features, which is crucial for present and future management policies; 8) the global warming that occurred at the end of the Younger Drays cold reversal (ca. 13.0 to 11.5 cal kyr BP) took place at similar rates and magnitudes compared to the global warming projected for the 21st century, thus becoming a powerful past analogue for prediction modelling; 9) environmental changes have acted upon ecosystems in an indirect way by modifying human behaviour and activities that, in turn, have had the potential of changing the environment and enhancing the disturbance effects by synergistic processes involving positive feedbacks; 10) the collapse of past civilisations under climate stress has been chiefly the result of inadequate management procedures and weaknesses in social organisation, which would be a warning for the present uncontrolled growth of human population, the consequent overexploitation of natural resources, and the continuous increase of greenhouse-gas emissions; 11) the impact of fire as a decisive ecological agent has increased since the rise of humans, especially during the last millennia, but anthropic fires were not dominant over natural fires until the 19th century; 12) fire has been an essential element in the development and ecological dynamics of many ecosystems, and it has significantly affected the worldwide biome distribution; 13) climate-fire-human synergies that amplify the effects of climate, or fire alone, have been important in the shaping of modern landscapes. These general paleoecological observations and others that have emerged from case studies of particular problems can improve the preservation of biodiversity and ecosystem functions. Nature conservation requires the full consideration of palaeoecological knowledge in an ecological context, along with the synergistic cooperation of palaeoecologists with neoecologists, anthropologists, and conservation scientists.
Notes: invited paper
P Scussolini, T Vegas-Vilarrúbia, V Rull, P Corella, B Valero-Garcés, J Gomà (2011)  Mid-late Holocene climate change and human impact based on diatoms, algae and aquatic vegetation pollen from Lake Montcortès (NE Iberian Peninsula).   Journal of Paleolimnology 46: 369-385  
Abstract: During the middle and late Holocene, the Iberian Peninsula underwent large climatic and hydrologic changes, but the temporal resolution and regional distribution of available palaeoenvironmental records is still insufficient for a comprehensive assessment of the regional variability. The high sedimentation rate in karstic, meromictic Montcortès Lake (Catalan pre-Pyrenees) allows for a high-resolution reconstruction of the regional palaeoecology over the last 5,340 years using diatom analysis, aquatic pollen, sedimentological data, and historic documentary records. Results show marked fluctuations in diatom species assemblage composition, mainly between dominant Cyclotella taxa and small Fragilariales. We suggest that the conspicuous alternation between Cyclotella comta and C. cyclopuncta reflects changes in trophic state, while the succession of centric and pennate species most likely reflects changes in the hydrology of the lake. The diatom assemblages were used to identify six main phases: 1) high productivity and likely lower lake levels before 2,350 BC, 2) lower lake levels and a strong arid phase between 2,350 and 1,850 BC, 3) lake level increase between 1,850 and 850 BC, 4) relatively high lake level with fluctuating conditions during the Iberian and Roman Epochs (650BC-350 AD), 5) lower lake levels, unfavourable conditions for diatom preservation, eutrophication and erosion triggered by increased human activities in the watershed during Medieval Climate Anomaly (900-1300 AD), and 6) relatively higher lake levels during the LIA (1380-1850 AD) and afterwards. The combined study of diatoms, algae and pollen provides a detailed reconstruction of past climate, which refines understanding of regional environmental variability and interactions between climate and socio-economic conditions in the Pyrenees.
T Vegas-Vilarrúbia, F Baritto, P López, G Meleán, M E Ponce, L Mora, O Gómez (2010)  Tropical Histosols of the lower Orinoco Delta, features and preliminary quantification of their carbon storage   Geoderma 155: 280-288  
Abstract: Histosols are potentially important in the global carbon cycle, since they show significant carbon accumulation. Variations in Histosol featuresmay influence both vegetation types and carbon storage amounts and rates. In this paper, we compare Histosols of the Lower Orinoco River Delta by examining relationships among the vegetation communities they maintain and differences among organic and mineral layers. We preliminarily assess their potential organic carbon accumulation. Soil samples were collected from 227 sites and analyzed for soil texture, organic matter, pH, salinity, organic carbon, exchangeable cations, nutrients (P, N, K) and sulphate acid Histosols accounted for more than 80%, whilst Entisols represented 11.8% of the studied samples. The interdistributary peats may be ombrogenous, since they receive inorganic elements mainly by atmospheric deposition,whereas coastal and some riverine peats may be topogenous. Like other ombrogenous tropical peats, topsoils had higher levels of P, N, Ca and Mg than bottom soils. Total nitrogen suggested some degree of N deficiency due to extreme acidity. Total phosphorus was probably associated with humic and fulvic acids.When compared to otherombrogenous tropical peat soils, our total phosphorus values were higher,which is consistent with the younger age of the lower Orinoco Delta peat. The area showed potential sulphate acid soils. Estimations of organic carbon stored yielded 45.0â97.0 kgmâ2, similar to the range reported for other peatland soils of the world of similar age and accumulation rate. The study area contributed approximately 0.049 Gt to the global carbon storage in soils. Extrapolating from these results, the carbon storage of the study in the lower Orinoco Delta (roughly 7000 km2) is approximately 0.067 Gt in the first metre of soil. This is not a negligible contribution when compared with the 19.9 Gt of carbon in the first metre of soil of all tropical peatland soils (roughly 444,000 km2). When combined with the 150,000 km2 estimated for the Amazonia, the importance of neotropical peatlands as sinks or sources of carbon appears greater than previously thought.
M Morellon, B Valero-Garcés, T Vegas-Vilarrúbia, P González-Sampériz, O Romero, A Delgado-Huertas, P Mata, A Moreno, M Rico, P Corella (2009)  Lateglacial and Holocene palaeohydrology in the western Mediterranean region: The Lake Estanya record (NE Spain)   Quaternary Science Reviews 28: 2582–2599  
Abstract: The multi-proxy analysis of sediment cores recovered in karstic Lake Estanya (42020 N, 0320 E; 670 ma. s. l.,NE Spain), located in the transitional area between the humid Pyrenees and the semi-arid Central Ebro Basin,provides the first high-resolution, continuous sedimentary record in the region, extending back the last 21000years.The integrationof sedimentaryfacies,elementalandisotopicalgeochemistryandbiogenic silica,together with a robust age model based on 17 AMS radiocarbon dates, enables precise reconstruction of themain hydrological and environmental changes in the region during the last deglaciation. Arid conditions, represented by shallow lake levels, predominantly saline waters and reduced organic productivity occurred throughout the last glacial maximum (21â18 cal kyrs BP) and the lateglacial, reaching their maximum intensity during the period 18â14.5 cal kyrs BP (including Heinrich event 1) and the Younger Dryas (12.9â11.6 cal kyrs BP). Less saline conditions characterized the 14.5â12.6 cal kyrs BPperiod, suggesting higher effective moisture during the Bo¨ lling/Allerød. The onset of more humid conditions started at 9.4 cal kyrs, indicating a delayed hydrological response to the onset of the Holocene which is also documented in several sites of the Mediterranean Basin. Higher, although fluctuating, Holocene lake levels were punctuated by a mid Holocene arid period between 4.8 and 4.0 cal kyrs BP. A major lake-level rise occurred at 1.2 cal kyrs BP, conducive to the establishment of conditions similar to the present and interrupted by a last major water level drop, occurring around 800 cal yrs BP, which coincides with the Medieval Climate Anomaly. The main hydrological stages in Lake Estanya are in phase with most Western Mediterranean and North Atlantic continental and marine records, but our results also show similarities with other Iberian and northern African reconstructions, emphasizing peculiarities of palaeohydrological evolution of the Iberian Peninsula during the last deglaciation.
M Morellon, B Valero-Garcés, P González-Sampériz, T Vegas-Vilarrúbia, E Rubio, M Rieradevall, A Delgado-Huertas, P Mata, O Romero, D R Engstrom M Lopez-Vicente, A Navas, J Soto (2009)  Climate changes and human activities recorded in the sediments of Lake Estanya (NE Spain) during the Medieval Warm Period and Little Ice Age.   Journal of Paleolimnology  
Abstract: Multi-proxy study of short sediment cores recovered in small, karstic Lake Estanya (42020 N, 0320 E, 670 m.a.s.l.) in the Pre-Pyrenean Ranges (NE Spain) provides a detailed record of the complex environmental, hydrological and anthropogenic interactions occurring in the area since medieval times. The integration of sedimentary facies, elemental and isotopic geochemistry, and biological proxies (diatoms, chironomids and pollen), together with a robust chronological control, provided by AMS radiocarbon dating and 210Pb and 137Cs radiometric techniques, enabled precise reconstruction of the main phases of environmental change, associated with the Medieval Warm Period (MWP), the Little Ice Age (LIA) and the industrial era. Shallow lake levels and saline conditions with poor development of littoral environments prevailed during medieval times (1150â1300 AD). Generally higher water levels and more dilute waters occurred during the LIA (1300â 1850 AD), although this period shows a complex internal paleohydrological structure and is contemporaneous with a gradual increase of farming activity. Maximum lake levels and flooding of the current littoral shelf occurred during the nineteenth century, coinciding with the maximum expansion of agriculture in the area and prior to the last cold phase of the LIA. Finally, declining lake levels during the twentieth century, coinciding with a decrease in human pressure, are associated with warmer climate conditions. A strong link with solar irradiance is suggested by the coherence between periods of more positive water balance and phases of reduced solar activity. Changes in winter precipitation and dominance of NAO negative phases would be responsible for wet LIA conditions in western Mediterranean regions. The main environmental stages recorded in Lake Estanya are consistent with Western Mediterranean continental records, and show similarities with both Central and NE Iberian reconstructions, reflecting a strong climatic control of the hydrological and anthropogenic changes during the last 800 years.
S Nogué, V Rull, T Vegas-Vilarrúbia (2009)  Modeling biodiversity loss by global warming on Pantepui, northern South America: projected upward migration and potential habitat loss.   Climatic Change 94: 77-85  
Abstract: This work aims to estimate the potential effects of the global warming projected for the twenty-first century on the biodiversity of a remote and pristine region of the Neotropics called Pantepui. Habitat loss and fragmentation by upward migration of bioclimatic conditions is analyzed using Species-Area Relationships (SAR) and Altitudinal Range Displacement (ARD) analysis. The ARD is a tool that uses the present-day lapse rate to estimate the upward migration of the species based on the global warming predicted by the IPCC. The results show that around 80% of the vascular flora, ca. 1,700 species of which up to 400 would be Pantepui endemics, are threatened of extinction. These estimates should be considered preliminary, but the danger is real. Therefore, suitable conservation or mitigation strategies are needed.
Notes: Biodiversity loss, climate change, species-area relationship, Neotropic, habitat loss, upward migration
S Nogué, V Rull, E Montoya, O Huber, T Vegas-Vilarrúbia (2009)  Paleoecology of the Guayana Highlands (northern South America): Holocene pollen record from the Eruoda-tepui, in the Chimantá massif   Palaeogeography, Palaeoclimatology, Palaeoecology 281: 165-173  
Abstract: The previously recorded vegetation constancy during most of the Holocene, atop some summits of the Guayana tabular mountains (or tepuis), led to the hypotheses of either environmental stability or site insensitivity. As high-mountain biomes are considered to be especially well suited for recording past environmental changes, a palynological study on the uppermost summit of the Chimantá massif was designed to test its suitability for these purposes. A peat sequence was obtained spanning the last ~13.0 cal kyr BP, but an acceptable resolution for paleoecological reconstruction is available only for the last ~4000 years. Around 4.3 cal kyr BP, the modern vegetation was established and has remained virtually unchanged until today; minor paleoenvironmental changes recorded in other sequences around 2.5 cal kyr BP were not detected here. The main paleoclimatic trends are in good agreement with other neotropical records, especially from Lake Valencia and the Cariaco Basin. It is concluded that high-altitude tepuian sites are useful to record paleoenvironmental changes of moderate to high intensity but once a dense vegetation cover is established, gentle shifts remain hidden due to the capacity of plant communities to absorb the changes. The best sites for paleoecological research atop the tepuis are those lying on or near altitudinal ecotones, especially between the meadows and the paramoid shrublands (~2200 m elevation). Sites withinthe meadow domain, as most well-studied so far, are relatively insensitive to Holocene paleoenvironmental changes.
T Vegas-Vilarrúbia, F Baritto, G Melean (2008)  Critical examination of some common field tests to assess the acid-sulphate condition in soils   Soil use and Management 24: 1. 60-68  
Abstract: Acid-sulphate soils are of major environmental concern in many wetlands. Severe acidification episodes have occurred worldwide because of the oxidation of iron sulphides to sulphuric acid by human activities, and diverse techniques have been set up to determine the presence of acid-sulphate soils. This paper evaluates the usefulness of four common easy-to-apply field survey tests for potential acidsulphate diagnosis in some Histosols and Entisols in wetlands: incomplete oxidation by fast air-drying, incubation, fast oxidation with hydrogen peroxide, and the indirect determination of sulphide with lead acetate. Samples of 227 surface-organic and underlying mineral soils of poorly drained Histosols and Entisols of the Orinoco river delta plain were tested. Results showed that for highly organic samples the interpretation of results obtained from the acid-sulphate soil tests may be misleading, because they cannot be unambiguously related to the production of sulphuric acid derived from pyrite oxidation. Mineral samples yielded more reliable results. The incomplete oxidation by fast air-drying test did not induce significant acidification either in organic or in mineral samples; the final pH values were dependent on the original pH values. The fast oxidation with hydrogen peroxide test was effective with mineral samples. During the incubation test, the slower rate of pH decrease and the final values obtained with the organic samples suggested retardation in the rate and amount of acid generation by pyrite oxidation because of the concurrent oxygen consumption by organic matter and bacterial activity. The indirect determination of sulphide with lead acetate yielded only qualitative results in organic samples, but worked well in mineral samples, indicating a higher content of pyrite intermediates. Effective estimation of the actual presence and potential for acidification of soil is important, in order to avoid excessive or inappropriate amelioration techniques to prevent acid production.
T Vegas-Vilarrúbia, P López (2008)  Edaphic patterns as related to β-diversity in swamp forests and meadows of the lower Orinoco delta plain (Venezuela).   Wetlands 28: 616-631  
Abstract: In the Neotropics, differences in phytogeographic patterns and species richness respond nonrandomly to edaphic factors in many upland forests. However, whether wetland forests follow the same species differentiation patterns is not well known. In this paper we analyze the relationship among species occurrences and selected soil characteristics, particularly salinity and acidity, in several wetland plant communities. Plant specimens were collected and soil samples analyzed for exchangeable cations, chloride, and organic carbon. Statistical methods were applied to assess b-diversity and to detect relationships between patterns of floristic variation and spatial variations of the soil conditions. bdiversity was high among vegetation communities. Edaphic conditions were heterogeneous, and landward gradients were present only for salinity and some exchangeable bases. This resulted in a lack of a straightforward relationship of vegetation patterns to salinity. More than 30% of the reported species covaried with at least one of the three acidity-related variables, suggesting that some tolerance to deleterious effects of H+ and Al3+ at pH values , 4 is likely. Thus, in contrast to what we might expect in deltaic regions, acidity rather than salinity was the major factor driving species organization. However, variation of these soil characteristics taken together accounted for only 40% of floristic differences among communities.
V Rull, J A López-Sáez, T Vegas-Vilarrúbia (2008)  Contribution of non-pollen palynomorphs to the paleolimnological study of a high-altitude Andean lake (Laguna Verde Alta,Venezuela).   J Paleolimnol 40: 399-411  
Abstract: This paper evaluates the potential usefulness of non-pollen palynomorphs or NPPs (microfossils other than pollen and spores present in palynological preparations) contained in lake sediments in the paleolimnological reconstruction of high altitude environments ([4,000 m) from the Venezuelan Andes. A synthetic, quantitative approach is employed, instead of the classical analytical and mostly qualitative approach commonly used so far for NPPs. The main sources of variation are the PediastrumâBotryococcus alternation and the relationship between these two algae and animal remains such asAcari legs, postabdomina of Cladocera, mandibles of other invertebrates, and an unknown type called LVA-1. Other significant microfossils are remains of Rivularia-type and turbellarian oocytes,including Gyratrix. The sequence initiates around 15,000 calibrated years before present (cal BP) with the deglaciation of the lake catchment, high water levels and still cold climates. A phase of lower lake levels was recorded between about 12,000 and 6,000 cal BP. Temperatures increased by around 9,000 and 7,000 cal BP, and then decreased until 6,000 cal BP. Since that time, both lake levels and temperature increased again and stabilized at about 4,000 cal BP, when they reach modern-like values. These results show a good agreement with previous studies based on pollen, diatom and oxygen isotope analyses, and provide additional paleoecological information, as for example the possibility of a previously unrecorded Younger Dryas signal. The inclusion of quantitative NPP analysis in routine npaleolimnological studies using synthetic methods is thus recommended. Possible future improvements are suggested, mainly those related with the development and use of NPP modern analogs.
V Rull, T Vegas-Vilarrúbia, S Nogué, E Montoya, N Cañellas, A Lara (2007)  Quaternary paleoclimatology, neotropical biodiversity, and potential effects of global warming   Contributions to Science 3: 3. 407-415  
Abstract: The Quaternary paleoclimatic trends documented for the Northern Hemisphere also affected the neotropical region, and contributed to the shaping of its present-day biodiversity patterns. DNA molecular-clock studies on extant neotropical species have recorded a significant acceleration of speciation rates in the last 5 million years (my), coinciding with a marked Plio-Pleistocene global cooling. Furthermore, around half of the species studied originated during the last 2.6 my, in the frame of Pleistocene glaciations. The refuge hypothesis is considered inadequate for the Neotropics, and alternative diversification mechanisms linked to climate change are discussed herein. Among them, recurrent vertical migrations controlled by alternating glacial/interglacial climates, and the resulting connection and disconnection of lowland and highland biotas, have been considered important speciation factors. A significant number of endemic taxa from the neotropical highlands is potentially threatened of extinction by habitat loss/fragmentation, due to the global warming predicted by the end of the present century.
M Vila-Escalé, T Vegas-Vilarrúbia, N Prat (2007)  Release of polycyclic aromatic compounds into a Mediterranean creek (Catalonia, NE Spain) after a forest fire   Water Research 41: 2171 2179  
Abstract: Wildfires produce polycyclic aromatic compounds (PACs), among which polycyclic aromatic hydrocarbons (PAHs) are of environmental concern. After a fire affecting a Mediterranean creek, we studied the distribution and short-term permanence of PACs and of 16 priority PAH pollutants in the aquatic environment. PACs were traced through absorbance and fluorescence emissions and organic carbon concentrations. PAHs were analysed by gas chromatography. High TOC/DOC concentrations and fluorescence/ absorbance values reflected abnormal inputs of fire-induced aromatic compounds. Their concentrations decreased gradually but showed sporadic peaks after precipitation. Fifteen months later, values still surpassed background levels. Initially concentrations of individual and total PAH species of the dissolved, particulate and sediment phases were increased. Then they fluctuated with new PAH inputs related with runoff, leaching and soil erosion following precipitation events. All PAH concentrations approached background levels 15 months after the fire, and never reached values of toxicological concern. However, some bioaccumulation may have occurred.
T Vegas-Vilarrúbia, M E Ponce, Oscar Gómez, L Mora (2007)  Wetland vegetation of the lower Orinoco delta plain (Venezuela): a preliminary approach.   Amazoniana XIX: 3/4. (3/4): 35-61  
Abstract: This is a preliminary study of the vegetation of a potential oil prospecting zone of remote areas of the Orinoco Delta. It aims to provide a scientific basis to delineate efficient conservation strategies. Flora, life and growth forms were examined along with ethnobotanical aspects, as there are three Warao Indian settlements in the area. Various vegetation patterns were identified from satellite images and aerial photographs: swamp and palm forests, mangroves, shrubland and meadows. The first vegetation map of the zone was elaborated (1:25.000). Over 500 botanic samples encompassing 77 families, 148 genera and 205 species were collected. Twenty-two families had 3 to 20 species, the remaining families had only one or two, being Orchidaceae, Araceae and Bromeliaceae the best represented ones. Endemic species known for the Venezuelan Guayana were not observed in the study area. A non-gramineous meadow, not reported before for the Venezuelan Guayana, combines three dominant species, the fern B. serrulatum and the cyperaceous herb Lagenocarpus guianensis. The main forest forming species showed morphological adaptations to flood and anoxic conditions, for which they are expected to be particularily sensitive to oil pollution. Around 40% of the plants species used by the Warao Indians in the study area are for medical purposes
V Rull, T Vegas-Vilarrúbia (2006)  Unexpected biodiversity loss under global warming in the neotropical Guayana Highlands: a preliminary appraisal.   Global Change Biology 11: 9-11  
Abstract: The fully vegetated summits of the table mountains that form the Guayana Highlands (GH), in northern South America, hold amazing biodiversity and endemism levels, and unique vegetation types. In spite of their present-day healthy appearance, their biota is seriously threatened of habitat loss by upward displacement, because of the projected warming for the end of this century. Available data are still insufficient for a definite assessment, but preliminary estimations based on representative endemic vascular plant species show that roughly one-tenth to one-third of them would loss their habitat with the 2â4 1C temperature increase predicted for the region by AD 2100. Given the underlying endemism, the eventual loss of biodiversity will be of global nature. Othermountain ranges around the world with similar characteristics of the GH, namely topographical isolation, high endemism and absence of nival stage because of the lower altitude, would be under similar unexpected risk, and should be urgently considered for conservation purposes.
V Rull, T Vegas-Vilarrúbia, S Nogué (2005)  Cambio climático y diversidad de la flora vascular en las montañas tabulares de Guayana   Orsis 20: 61-72.  
Abstract: Una de las posibles consecuencias del calentamiento global es la extinción de especies de alta montaña por migración ascendente de las condiciones ambientales y pérdida de hábitat, fenómeno que, por el momento, ha sido considerado únicamente en montañas templadas y boreales. Este trabajo analiza la misma situación en montañas tropicales y estima el grado de amenaza de la flora vascular de las cimas de las montañas neotropicales de Guayana, al norte de Sudamérica. Del estudio basado en una muestra de 83 especies, entre aproximadamente el 8 y el 33% de las mismas se encuentran en peligro de extinguirse debido a la desaparición de su hábitat. La mayoría de estas especies son endémicas de Guayana, por lo que su desaparición afectaría a la biodiversidad global. Among the potential consequences of the projected global warming on high-mountain environments is biodiversity loss by upward migration of environmental conditions and the consequent habitat vanishing for upland species. So far, such effect has been considered only for temperate and boreal mountain ranges. Here, the same situation is analysed on the neotropical Guayana mountains, in northern South America. A preliminary appraisal based on 83 species of vascular plants shows that 8-33% of them are threatened of extinction by habitat loss. Most are endemic, hence their disappearance would affect global biodiversity.
T Vegas-Vilarrúbia (2004)  Ecology of an isolated mangrove lagoon (Playa Medina, Venezuela) and its potential use as sewage pond.   Orsis 19: 101- 115  
Abstract: The present study focuses on the hydrochemical conditions of a coastal mangrove lagoon in Venezuela which is completely isolated from the sea, lacking any visible connections such as tidal channels, preventing in this way tidal flushing. These isolation conditions introduced important changes in vegetation, soil salinity and hydrology. The aim of this paper is to relate some of the effects of disconnection, with the potential use of the mangrove as a sewage pond for treated domestic wastewater. Available data are analyzed on soil properties, hydrochemistry and water level fluctuations of surface and groundwater, recorded through a whole hydrological year. Present day mangrove characteristics are examined through the scrutiny of recordable historical disturbances. Finally, the potential effect of treated wastewater to be supplied to the lagoon is estimated, on the basis of local climate trends. It is concluded that the present day surface water quality would be impaired, and the desalinization process of soil and groundwater accelerated. The annual volume of residual water to be supplied would equal a 20% increase in the local precipitation regime, supply that would deeply alter the existing flood/drought regime. It is suggested that recuperating the original mangrove connection to the sea through channel opening may alleviate the impact of wastewater discharge.
T Vegas-Vilarrúbia, V Rull (2002)  Natural and human disturbance history of the Playa Medina mangrove community (Eastern Venezuela).   Caribbean Journal of Science 38: 66 – 77  
Abstract: This paper reviews ecological and paleoecological information for a small isolated mangrove communtiy in NE Venezuela to explain its past and present features. Paleoecological data was provided by radiocarbon dating plus pollen and fossil wood analysis of samples from an 11 m deep boring section. Current data were obtained from vegetation characterization plus soil and hydrochemistry analysis. The oldest dated sediments are 6960 ± 70 14C years old. They were deposited on an extensive mangrove fringe dominated by Rhizophora sp. and Avicennia sp., and the sea-level was about 9 m below the present one. Relative sea level has experienced an average rise of about 13 cm/100 years, which disconnected this mangrove from adjacent communities. Avicennia disappeared and Rhizophora became the only dominant mangrove. Today, the mangrove community lies about 500 m inland, surficial hydrological connections to the sea are lacking, and the intermediate area is occupied by coconut plantations. Partial isolation from the sea has favored the existence of a seasonal low-salinity marsh, maintained by runoff and a marine groundwater wedge, which produce eutrophic water conditions and favor the establishment of continental and halophytic terrestrial vegetation. This mangrove community may disappear in a few decades if isolation and human disturbance continue.
T Vegas-Vilarrúbia (2000)  Zonation of an isolated mangrove community at Playa Medina, Venezuela. 8   Wetland Ecology and Management 8: 9 – 17  
Abstract: This study focuses on a mangrove system which is completely isolated from the sea, lacking any connecting tidal channels or creeks and far enough from the coastline to prevent tidal flushing. The reason why it has become isolated remains unclear. But it is obvious that this situation may have introduced important changes in soil salinity and hydrological patterns, which might be reflected in the present composition and zonation patterns of the mangrove community. Main findings of this study suggest that: (1) Plant species distribution is affected mainly by water logging and mineral content of soils. (2) Ground water is the only permanent supply of water and salts to the isolated mangrove. (3) Soils are subjected to different degrees of leaching of salts. (4) The K: Na ratios support that mangrove community is not subjected to salinity stress. (5) Continuous leaching of salts favor the advance of terrestrial non-halophytes plants.
V Rull, T Vegas-Vilarrúbia (2000)  Chrysophycean stomatocysts in a Caribbean mangrove.   Hydrobiologia 428: 145 – 150  
Abstract: A chrysophyte cyst assemblage from surface sediments of a tropical, brackish-water environment in the southern Caribbean coast is described and depicted. All the cysts are unornamented and relatively large. The taxonomic diversity is low, due probably to human disturbance or salinity stress. It is assumed that the chrysophyte taxa involved are salinity-tolerant, freshwater algae. This is the first record of chrysophyte cysts in mangrove environments, and extends the range of habitats in which they are commonly found.
V Rull, T Vegas-Vilarrúbia (1999)  Surface palynology of a small coastal basin from Venezuela and its potential paleoecological applications.   Micropaleontology 45: 365 – 393  
Abstract: The palynomorph content of surface samples from a sea-land transect in a small coastal basin was analysed, in order to characterise palynologically the sedimentary subenvironments and vegetation types. These results should provide the basis for the interpretation of further palaeoecological analyses on stratigraphical samples from the same site. The main vegetation types are mangroves, swamps, Cocos plantations and abandoned crops, arranged in a zonal pattern. All the palynomorph types found were recorded and counted, including pollen, fern and allied spores, fungi spores and unknown remains (probably algal material and animal parts). Both general and individual trends of these palynomorphs followed the main vegetation patterns, and both zonal sea-land arrangement of plant communities and their disturbance patterns were reproduced by them. Furthermore, particular types were found to be direct or indirect indicators of given plant zones and local disturbance. Detrended correspondence analysis allowed definition of the sedimentary attraction domains for the involved communities and ordination of both samples and palynomorphs with respect to them. The results are encouraging for palaeoecological studies, since the main key environmental and vegetational patterns are reflected by the palynomorphs of surface sediments. Limitations are also discussed.
V Rull, T Vegas-Vilarrúbia, N Espinoza de Pernia (1999)  Palynological Record of an Early-Mid -Holocene mangrove in eastern Venezuela. Implications for sea-level rise and disturbance history.   Journal of Coastal Research 15: 469 – 504  
Abstract: The purpose of the present report is to document the occurrence of a Holocene mangrove community on the southern Caribbean margin, and to build up a preliminary sea-level curve for Venezuela. This is accomplished through pollen analysis of a buried coastal peat layer at 9.4 m depth, as well as anatomical analysis and radiocarbon dating of an overlying wood fragment. The pollen assemblage from the peat layer is analogous to those found in present-day Caribbean mangroves. The wood comes from a 6,960±70 year old Rhizophora tree. This is used as evidence of a in situ mangrove community and, consequently, of the position of sea level at that time. A tentative curve for sea-level rise is presented, by compilation of radiocarbon dates on mangrove peats and corals. This study is a contribution to the evaluation of recent sea-level increase connected to the global warming, its main value being the possibility of recognizing the natural trend in sea-level rise, and separate it from the human-induced effect.
V Rull, T Vegas-Vilarrúbia (1998)  Palynomorphs other than pollen and fern spores in glacial sediments from the Venezuelan Andes   Boletín de la Sociedad Venezolana de Geólogos 23: 5-27  
Abstract: Abstract: The aims of the present study are to document the palynomorphs other than pollen and pteridophyte spores encountered in the Last Glacial alluvial and lacustrine sediments from the Venezuelan Andes, and to test their potential paleoecological and paleolimnological values using taonomic and statistical approaches. A total of 28 fungal spore types, 7 forms of remains of aquatic organisms, and 30 unidentified morphological classes are reported. Seven funagl spores forms follow the same stratigraphical trends as the pollen from páramo vegetation, suggesting that they are controlled by similar environmental (climatic?) factors, or that the parent fungi depend on these vegetation to develop. Five other forms show an inverse behaviour, their maximum coinciding with the minimum estimated temperatures, during the El Caballo stadial. It is proposed tentatively that these two fungal assemblages are inversely related to temperature, and could be used as paleoeclimatic indicators. Remains of aquatic organisms allowed following the local trends in water balance. A glacial paleolake with well-developed littoral communities existed in front of the terminal moraines before the stadial maximum. The subsequent incoming of a colder climate determined the impoverishment of shore communities and finally, their disappearance, so that during the stadial only cold-water tolerant plankton could develop in the lake. The lake dried out immediately after the stadial maximum. Seven unidentified forms follow the same trends as the littoral indicator remains, suggesting that they come from organisms of this habitat. Two other of these forms fit well with pelagic conditions, and two very similar to bryophyte spores are statistically associated to bog representatives. Proposed studies for the future are 1) a characterisation of modern sediments from different environments by their total fossil content, 2) increased documentation and identification of unknown forms by comparison with living material, and 3) macrofossil and geochemical analysis of both sediments and living material.
T Vegas-Vilarrúbia (1995)  Distribution of the phytoplankton from the Guri Reservoir (Venezuela).   Hydrobiologia 310 310: 33-46  
Abstract: The distribution of phytoplankton species of a tropical blackwater reservoir is discussed on the basis of spatial differences in water composition and of species abundance and diversity. Spatial heterogeneity in water composition identified three different environments within the reservoir itself: (1) strongly colored waters, high turbidity and iron concentrations at the inflow; (2) calcium enriched, nearly uncolored waters at El Pao Bay; (3) lightly colored water, higher transparency and a higher ratio monovalent to divalent cations in the main body of the reservoir. Three corresponding phytoplankton associations were found. Principal Component Analysis helped to explore the relationship of particular species with the abiotic factors. Among them, water color, turbidity, and mineralization proved to be determinant in habitat diversification.
T Vegas-Vilarrúbia (1994)  Water chemistry of the Guri reservoir (rainy season 1985). Relationships between humic color and aqueous iron and their limnological importance   Archiv für Hydrobiologie 132: 389-391  
Abstract: Abstract: The present work attempts to identify which factors regulate the metabolism and transport of elements of the Guri reservoir, a tropical blackwater man-made lake on the Caroní River (Venezuela). Two sampling stations were located on each of the inlet rivers, five in the reservoir and further five downstream of the dam. Variables measured were dissolved O2, conductivity, pH, temperature, turbidity, color, total suspended solids, chlorides, alkalinity, dissolved silicates and metals (Na, K, Ca, Mg, Fe). Humic color, aqueous iron and turbidity were well correlated and increased towards the bottom layers, suggesting co-accumulation of humic substances and iron. This might involve adsorption of aquatic humus with hydrous iron oxides, and might have an important influence on the phosphorus cycle by retaining otherwise available phosphorus. The Guri reservoir was undergoing intense oxygen consumption during the period of sampling due to oxidation of the recently flooded biomass. Nevertheless, waters leaving the reservoir suffered a reoxygenation process through natural mixing and partial overflow and excess waters that assures good water quality for future hydroelectrical uses downstream.
T Vegas-Vilarrúbia, M Cova (1993)  Estudio sobre la distribución y ecología de macrófitas acuáticas en el embalse de Guri.   Interciencia I8: 77 – 82  
Abstract: This study aims at inventoring macrophyte species (weeds) of the Guri reservoir (Venezuela) exaimining their spatial distribution and assessing their present state of development. We identified 14 families, 19 genera and 27 species. Among the 27 species only 3 were free-floating, the remaining ones were attached to the substrate. The variety of species and their spatial distribution suggested the comparison of sampling locations based on species composition. We used Jaccard's similarity index and clustering to build a dendrogram of hierachical classification. We also analyzed frequencies of coincidence of species to identify associations among them and found 7 associations of phytosociological value.
T Vegas-Vilarrúbia, A M Ibáñez, W Riehl (1993)  Aspects of the Phytoplankton of the Guri Reservoir, Venezuela, and the importance of its relationship with water chemistry.   Verh. Internat. Ver. Limnol. 25: 1295-1300  
Abstract: The Guri reservoir (Venezuela) is a large blackwater reservoir built by the damming up of the caroni river (1968) and was brought to its final elevation in 1986. It has an area of 43000 km2 , a water volume of 135 km3, a maximum depth of 130 m and a water retention time of 360 days. The present research is the first one after the guri reservoir has been filled up to 270 m a.s.l.. former limnological work has been carried out on previous stages of the reservoir. Further studies are urgently needed to establish a limnological baseline for future management. This work were studies the effect of impoundment on the phytoplankton communities and examines the relationship of phytoplanktonic species with the most variable chemical variables of the reservoir, in order to find out biological indicators of particular environmental conditions. In this context, emphasis was done on sampling collecting in areas of the reservoir receiving drainage from agriculture and gold mining activities. Quantitative phytoplankton and water samples were also taken following the former river axis. . Correlation of species with physical and chemical variables resulted to be an useful tool to study the affinity of species with a particular environment.
T Vegas-Vilarrúbia, R Herrera (1992)  Seasonal alternation of lentic / lotic conditions on a tropical floodplain lake in Venezuela.   Hydrobiologia 262: 43 – 55  
Abstract: We studied the changing hydrological conditions of a transient system at the Mapire River mouth(Orinoco) and their effect on hydrochemistry of the system at six locations. Subjected to strong annual waterlevel fluctuations, the Orinoco River acts as a dam to the Mapire River discharge, resulting in the formation of a standing lake-like waterbody that covers the gallery forest to the canopy for five to six months. The Mapire floodplain fills primarily with Mapire waters and only secondarily with Orinoco water. The latter enters into the Mapire basin, but mixing of both waters is poor, resulting in chemically and physically different waterlayers. A significant thermal stratification is observed. This transient lake reverts to flowing conditions during the dry season. The Mapire River mouth, therefore, behaves as a cyclic system in which lotic/lentic and terrestrial/aquatic conditions alternate seasonally. Some ecological implications are suggested and comparisons with similar systems are made.
T Vegas-Vilarrúbia, R Herrera (1992)  Effects of periodic flooding on the water chemistry and primary production of the Mapire system (Venezuela). 262: 31 -42.   Hydrobiologia 262: 31-42  
Abstract: The Mapire river mouth forms a complex floodplain system, where the river behaves as a river during the dry season, but changes to a transient lake which partially covers the inundation forest during the rainy season. Thus, we expected changes in water chemistry and a gradual increase of primary production during high waters. The system was sampled monthly for one year; two floodplain lakes were also studied for comparative purposes. Variations in the concentration of macro- and micronutrients occurred in a pulse-like manner andseemed to relate to mechanisms at work in the transient lake. Dissolved oxygen showed a stratification with low values at the bottom, but never reached anoxia. Net and gross primary production and respiration did not show any clear spatial pattern, reflecting a mosaic of different biochemical states within the transient lake. Heterotrophy tended to prevail in the transient lake, while autotrophy dominated floodplain lakes.
V Rull, T Vegas-Vilarrúbia (1991)  A palaeolimnological example of modulated succession from Southeast Venezuela, and its significance in Pleistocene Palaeoecology.   Current Research in the Pleistocene 8: 81 – 83  
Abstract: Most frequently, Pleistocene records are interpreted in paleoenvironmental terms. However, they may provide more information related with ecological succession. To exemplify this statement, we analyzed a recent pollen sequence from Lake Carinapay. The lake is shallow with well-developed macrophytes . The core studied (1.90 m) was subdivided from the top to the base. A surface sample represented the present-day conditions. Common methods of pollen analysis were used. Based on the variation of algal remains, we established a ratio (P/L) between plankton and littoral macrophytes to estimate the relative water level. The responses of macrophytic community were analyzed by defining assemblages through clustering of samples, according to the abundance of different genera. Six assemblages were obtained. A transfer matrix was built, and the probabilities of between stages moving were computed. Complexity, as measured by the Shannon-Weaver index of diversity was oscillating. The sequence studied did not show a directional auto organizational trend from simple to more complex seral stages - the classical concept of ecological succession. We assumed that oscillating external factors may have caused continuous reorganizations in the involved biocenose, leading to "modulated succession " patterns. This case study supports the unsuitability of the "climax" concept of Flenley, as well as the hypothesis of a maintained disequilibrium between environment and living communities.
T Vegas-Vilarrúbia, J Paolini, J García-Miragaya (1988)  Differentiation of some Venezuelan blackwater rivers based upon physic-chemical properties of their humic substances.   Biogeochemistry 6: 59-77  
Abstract: Abstract The dissolved humic substances of seven Venezuelan blackwater rivers, belonging to different tropical biogeographical regions, were analyzed. Fractionation using Sephadex gel together with an analysis of their fluorescence, absorbance and infrared spectral properties, showed differences between their humic substances. These differences were related to their biological sources and humification environment. Statistical analysis of the properties of these humic substances allowed us to separate the rivers into three groups. These groups were directly related to the geological features and vegetation of the terrestrial ecosystems into which they drain: - The Autana, Atabapo, Chola, Negro which belong to the Amazon basin on the Guayana Shield, each with typical blackwater riverine forest. - The Caroni, belonging to the Orinoco basin on the Guayana Shield and with tropical humid forest and rainforest. - The Morichal Largo which draines the Mesa Formation from the eastern Llanos and has gallery forest of Mauritia flexuosa.
T Vegas-Vilarrúbia, J Paolini, R Herrera (1988)  A physic-chemical survey of blackwater rivers from the Orinoco and Amazon basins in Venezuela.   Archiv fuer Hydrobiologie 111: 491 – 506.  
Abstract: Numerous blackwater rivers from different localities, including the basins of the Orinoco and the Amazon in Venezuela, were sampled to measure their main physico-chemical variables. Although most rivers showed low N and P concentrations, high DOC and relatively high dissolved silicates, there was a wide range of variation in pH,conductivity and cations concentrations compared with values reported in the literature from the Brazilian Amazon for such rivers. Using multivariate statistical methods we separated them in distinct groups. When we only considered the variables Fe, Na+K and Ca+Mg, we obtained a similar grouping, which is clearly the basin's geology. In the light of these results, Sioli's typology for tropical rivers does not seem applicable to Venezuelan rivers. More detailed studies of organic matter in all its forms is necessary to understand the basic differences and similarities amog backwater rivers.
F C Hartman, G M LaMuraglia, Y Tomozawa, R Wolfenden (1975)  The influence of pH on the interaction of inhibitors with triosephosphate isomerase and determination of the pKa of the active-site carboxyl group.   Biochemistry 14: 24. 5274-5279 Dec  
Abstract: Ionization effects on the binding of the potential transition state analogues 2-phosphoglycolate and 2-phosphoglycolohydroxamate appear to be attributable to the changing state of ionization of the ligands themselves, therefore it is unnecessary to postulate the additional involvement of an ionizing residue at the active site of triosephosphate isomerase to explain the influence of changing pH on Ki in the neutral range. The binding of the competitive inhibitor inorganic sulfate is insensitive to changing pH in the neutral range. 3-Chloroacetol sulfate, synthesized as an active-site-specific reagent for triosephosphate isomerase, is used to provide an indication of the pKa of the essential carboxyl group of this enzyme. Previously described active-site-specific reagents for the isomerase were phosphate esters, and their changing state of ionization (accompanied by possible changes in their affinity for the active site) may have complicated earlier attempts to determine the pKa of the essential carboxyl group from the pH dependence of the rate of inactivation. Being a strong monoprotic acid, chloroacetol sulfate is better suited to the determination of the pKa of the carboxyl group. Chloroacetol sulfate inactivates triosephosphate isomerase by the selective esterification of the same carboxyl group as that which is esterified by the phosphate esters described earlier. From the pH dependence of the rate of inactivation of yeast triosephosphate isomerase, the apparent pKa of the active-site carboxyl group is estimated as 3.9 +/- 0.1.
D L Peterson, J M Gleisner, R L Blakley (1975)  Bovine liver dihydrofolate reductase: purification and properties of the enzyme.   Biochemistry 14: 24. 5261-5267 Dec  
Abstract: A purification procedure is reported for obtaining bovine liver dihydrofolate reductase in high yield and amounts of 100-200 mg. A key step in the procedure is the use of an affinity gel prepared by coupling pteroyl-L-lysine to Sepharose. The purified reductase has a specific activity of about 100 units/mg and is homogeneous as judged by analytical ultracentrifugation, polyacrylamide gel electrophoresis, and titration with methotrexate. The products of the first step of Edman degradation indicated a minimum purity of 79%. The reductase has a molecular weight of about 21500 on the basis of amino acid composition and 22100 +/- 300 from equilibrium sedimentation. It is not inhibited by antiserum to the Streptococcus faecium reductase (isoenzyme 2). Unlike the reductase of many other vertebrate tissues, the bovine enzyme is inhibited by mercurials rather than activated and it has a single pH optimum at both low and high ionic strength. However, the position of the pH optimum is shifted and the activity increased by increasing ionic strength. Automatic Edman degradation has been used to determine 34 of the amino-terminal 37 amino acid residues. Considerable homology exists between this region and the corresponding regions of the reductase from S. faecium and from Escherichia coli. This strengthens the idea that this region contributes to the structure of the binding site for dihydrofolate.
E Montoya, V Rull, T Vegas-Vilarrúbia  Non-pollen palynomorph studies in the Neotropics: the case of Venezuela.   Review of Palaeobotany and Palynology. 186: 102. 130  
Abstract: This paper summarises the NPP studies developed so far in a wide range of environments from Venezuelan lowlands, midlands and highlands, as an example of a growing discipline in a Neotropical area. The studies discussed include both modern analogues from surface sediments and Late Quaternary sequences combining pollen and spores with NPP analyses. Emphasis is placed on the utility of NPP as palaeoecological indicators both individually and collectively (NPP assemblages), as well as in combination with other proxies. The main advantages of using NPP instead of only pollen and spores are highlighted using case studies as examples. Among them, the occurrence of NPP in samples barren for pollen and spores, the independent indicator nature of NPP, and their capacity to reveal previously unnoticed environmental shifts (notably those related to local conditions), are emphasised. The main results obtained in all these analyses are discussed in the frame of several areas of the NPP study that are considered crucial (methods, taxonomy, indicator value and statistical treatment). Some ideas for future developments are proposed in each of these areas, and the need for closer collaboration among NPP specialists is strengthened, in a way towards unification and standardisation.

Book chapters

T Vegas-Vilarrúbia, P López, F Baritto, G Meleán, M E Ponce, O Gómez (2006)  Vegetation –soils relationships in a wetland area of the Orinoco delta plain (Venezuela)   In: Environmental Problems in Coastal Regions VI: Including Oil and Chemical Spills Studies. Ecology and Environment 88 Edited by:C.A. Brebbia (ed.). 315 – 324. Wessex Institute of Technology  
Abstract: The Orinoco Delta is one of the last world's great river deltas with pristine ecosystems. But it is also an important oil and gas reservoir area. Currently, little scientific and factual knowledge is available to assess the effect of oil exploitation activities. Understanding vegetation and soils relationships is fundamental to delineate conservation strategies to maintain species richness, essential ecological processes and life support systems. To meet these needs, our research objectives were to characterize soil conditions supporting different vegetation units of the Lower Orinoco Plain and to relate soil characteristics with vegetation assemblages. For these purposes, surface and bottom soil samples were taken in 227 sites, which were distributed proportionally to each vegetation unit coverage. Samples were analysed for salinity, chlorides, carbonates, pH, organic carbon, exchangeable acidity, aluminium, hydrogen, calcium, potassium and sodium. Average thickness of the surface organic layer was 2.32 m, reaching 6 m in some places. Organic carbon content did not differ significantly among soils from different vegetation units. Lowest surface pH values were found in forests and meadows (< 4.5). Bottom pH was less variable and almost neutral. The highest salinity values were found in mangrove soils (1.80Ⱐ± 0.12), the lowest in palm forests (0.06Ⱐ± 0.02). Main differences among soil samples were related with cation exchange capacity (68.3 meq/100g ± 81.5), percent base saturation (91.9% ± 11.0), and acidity (2.30 meq/100g ± 3.46). Our results indicated that content of salts and cations and soil acidification were the main factors in determining vegetation arrangements.
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