Seasonal Water Level Fluctuations Research Articles

Wetland habitat stability assessment in hydro-geomorphological (HGM) and surface water availability (SWA) conditions in a lower Gangetic floodplain region of Eastern India

Floodplain wetlands in their optimum habitat condition act as the preventive mechanism from environmental degradation like pollution, lowering of groundwater table, flood, temperature control and others. Therefore, the protection and stability condition assessment of these wetlands are very much indispensable for the sake of the environment. In the present work, the habitat stability assessment of the wetlands of a floodplain region produced by River Ganga has been done considering the hydro-geomorphological (HGM) and surface water availability (SWA) parameters. The fuzzy classification (FC) and composite indexing (CI) method have been applied to perform the analysis. The result suggests that 16%–24% of wetland area is very highly prone to loss and 33%–36% area needs proper management whereas only 9%–11% wetlands are very highly stable. The wetlands have shown a rise in the average seasonal water level fluctuation from 2.18 m in 2014 to 3.38 m in 2018 which indicates more drying out condition during lean months. From morphogenetic perspective, nearly 43% of wetlands are riverine and in terms of HGM classification 77% of the wetlands are groundwater depressions (GWD). So, lack of water supply all throughout the year, seasonal water level fluctuation and absence of active river-wetland links are mainly responsible for the degradation of habitat stability condition of the wetlands. The results have been validated over different ground locations using kappa index and ROC curve method. It suggests that both these methods are very much accurate and between these two, FC method has given better result.

Water-level fluctuation (WLF) of Panchet dam in India and assessment of its human risk using AHP method

This paper is an endeavor to probe into the temporal and seasonal water-level fluctuation (WLF) of Panchet dam in India since 2005–2016 and analysis of its risk to the dam-surrounding people, using analytical hierarchy process (AHP). The present study specifies that 30% storage capacity of the reservoir has been reduced within 60 years because of rapid sedimentation, while the trend analysis indicates that 50% and 100% storage capacity will be blocked within 130 years and 250 years respectively, if the present state continues. Thus it reveals a 250 years’ active life span of the dam. Average temporal WLF of the dam is 12 mts and significant at the 5% level of significance (p < 0.05) whereas, seasonal WLF is 8 mts and also significant at the 1% level of significance (p < 0.01). This temporal and seasonal WLF leads to significant rise and fall of water level that poses threat to the people of 92 villages situated within 1 km buffer area of the dam. Nine human risk alternatives (A1–A9) resulted from the WLF of the dam are identified using Delphi Questionnaire then rated and prioritized them using AHP method. Risk prioritization result varies from 9.90 to 10.29 calculated on the basis of consistency measure (CM) value. It indicates that ‘Population displacement’ (A3) and ‘Inundation of settlement’ (A2) are the highest (CM 10.29) and lowest (CM 9.90) vulnerable among the risk alternatives obtaining maximum and minimum CM values respectively.

How suitable are man-made water bodies as habitats for Odonata?

Many studies have reported a negative impact of freshwater habitat modification on biota. Nevertheless, some man-made water bodies have proven to be valuable for biodiversity conservation as they can harbour many species. We investigated 36 man-made water bodies to determine their suitability as habitats for Odonata. Larvae were sampled in littoral, during the summer months of 2016 and 2017. At each sampling site, ten samples were collected using a benthos hand net. A total of 21 Odonata species was recorded. Odonata assemblages mainly consisted of common widespread species. Yet, at Vlačine Reservoir, located in the Dinaric Western Balkan ecoregion, we also recorded a rare and endangered Mediterranean species,Lindenia tetraphylla(Vander Linden, 1825). Aquatic and riparian vegetation, water level fluctuations and dissolved oxygen concentration had the highest influence on Odonata, showing that man-made water bodies with a well-developed riparian zone and aquatic vegetation, and with low daily and seasonal water level fluctuations, can provide suitable habitats for diverse Odonata species. Odonata are among the sensitive freshwater insects widely used as ecological indicators and umbrella species, therefore these results about their assemblages in heavily modified and man-made habitats could contribute to future conservation activities of freshwater biota and habitats.

Coastal geomorphic response to seasonal water-level rise in the Laurentian Great Lakes: An example from Illinois Beach State Park, USA

Hydrodynamic processes, such as fluctuating water levels, waves, and currents, shape coastlines across timescales ranging from minutes to millennia. In large lacustrine systems, such as the Laurentian Great Lakes, the role of water level in driving long-term (centuries to millennia) coastal evolution is well understood. However, additional research is needed to explore short-term (weeks to months) beach geomorphic response to fluctuating water level. Developing a process-focused understanding of how water level fluctuations shape coastal response across these shorter time scales is imperative for coastal management. Here, we present measurements of geomorphic response along a lacustrine beach ridge plain to seasonal water level fluctuations during a decadal high-stand in Lake Michigan water level. Frequent topographic change measurements revealed high spatial and temporal variability in geomorphic response to rising lake level. Sites immediately downdrift of shore protection began to erode immediately as lake level increased. The co-occurrence of peak seasonal lake levels and a modest increase in wave energy resulted in erosion and overwash at sites that resisted erosion during the initial seasonal rise in lake level. None of the sites in this study returned to their initial morphology following seasonal lake level rise. Given that peak water levels were nearly identical in 2017 and 2018, yet the majority of erosion at our sites occurred in 2017, we postulate that erosion associated with seasonal lake level rise is primarily a function of the change in annual maximum water level from year to year, rather than solely the elevation of the water level.

Predicting hydrological impacts of the Yangtze-to-Huaihe Water Diversion Project on habitat availability for wintering waterbirds at Caizi Lake

Quantifying the relationship between hydrological regime and habitat availability is the first step to predict potential impacts of water engineering projects on waterbirds, particularly in periodically flooded wetlands. The proposed Yangtze-to-Huaihe Water Diversion Project (YHWD) cuts through Caizi Lake, which is of international importance for wintering waterbirds. In order to explore the potential impacts of the project on habitat availability for the wintering waterbirds, we first built linear models to fit relationships between land cover patterns and water level dynamics in the lake, and then used generalized linear mixed models to test effects of habitat variables (water area, grassland area and mudflat area) on bird abundances of different functional groups. The avian habitat use differed among guilds, and was correlated with the land cover pattern, which was strongly dependent on seasonal water level fluctuations. Following water recession in autumn, the exposure of riparian habitats was more prominent in the eastern part of the lake, where the channel of the proposed YHWD project is located. This part of the lake is also where we located most of the important bird areas. Compared to the current situation, 54.3% of the grassland and 60.5% of the mudflats are predicted to be lost during winter due to the projected water level rise, resulting in reduced habitat availability for grass foragers, invertebrate eaters and tuber feeders. In order to mitigate potential impacts of the YHWD project, we suggest habitat compensations by construction of artificial habitats, and maintenance of water level regime at the whole lake by restoring similarity in water level fluctuations between Xizi Lake and Caizi Lake.

Magnitudes and Drivers of Greenhouse Gas Fluxes in Floodplain Ponds During Drawdown and Inundation by the Three Gorges Reservoir

AbstractHydropower reservoirs are well‐known emitters of greenhouse gases to the atmosphere. This is due in part to seasonal water level fluctuations that transfer terrestrial C and N from floodplains to reservoirs. Partial pressures and fluxes of the greenhouse gases CH4, CO2, and N2O are also a function of in situ biological C and N cycling and overall ecosystem metabolism, which varies on a diel basis within inland waters. Thus, greenhouse gas emissions in hydropower reservoirs likely vary over seasonal and diel time scales with local hydrology and ecosystem metabolism. China's Three Gorges Reservoir is among the largest and newest in the world, with a floodplain that encompasses approximately one third of the reservoir area. We measured diel partial pressures and fluxes of greenhouse gases in ponds on the Three Gorges Floodplain. We repeated these measurements on the submerged floodplain following inundation by the Three Gorges Reservoir. During reservoir drawdown, CH4 ebullition comprised 60–68% of emissions from floodplain ponds to the atmosphere. Using linear mixed effects modeling, we show that partial pressures of CH4 and CO2 and diffusive CO2 fluxes in floodplain ponds varied on a diel basis with in situ respiration. Floodplain inundation by the Three Gorges Reservoir significantly moderated areal CH4 diffusion and ebullition. Diel pCO2, pCH4, pN2O, and diffusive fluxes of CO2 on the submerged floodplain were also driven by in situ respiration. The drawdown/inundation cycle of the Three Gorges Reservoir therefore changes the magnitudes of aquatic greenhouse gas fluxes on its floodplain.

Monitoring of vertical deformation response to water draining–recharging conditions using BOFDA-based distributed optical fiber sensors

Land subsidence is a geological disaster, which has a variety of inducements. This paper presents the results on the investigation of the soil deformation in land subsidence with a combination of laboratory and field experiments using the distributed fiber optics sensing (DFOS) technology. The laboratory experiment was mainly carried out to study the soil deformation in draining–recharging cycles based on Brillouin optical frequency domain analysis (BOFDA). In the field experiment, the BOFDA technology and some grating sensors were applied in a borehole in the Yangtze River Delta region, to monitor the pore pressure in certain specific strata and the change in strata parameter of the full borehole with the data that monitored 2 years. The result of the laboratory experiment demonstrated that the soil structures changed in the draining–recharging cycles. The soil gradually tends toward elastic deformation. The field experiment results show that the main deformation occurs at the aquitards adjacent to the pumping aquifer. The compression amount in the vertical distribution is not uniform which is related to the distance from the pumping aquifer and the soil properties. The compressive deformation of each layer is closely related to the change in groundwater level. The result proposes that the BOFDA technology is suitable for monitoring land subsidence caused by seasonal water-level fluctuations and dewatering projects. It is also of great significance to investigate land subsidence mechanisms.

Drivers and Changes of the Poyang Lake Wetland Ecosystem

This paper serves as both a review of the latest science on the Poyang Lake wetland ecosystem and as an introduction to this Special Issue guest-edited by Jun Xu. Poyang Lake is the largest freshwater lake in China and one of the largest freshwater lake/wetland complexes in Asia. Poyang Lake’s associated floodplain wetlands play a critical role for regional and global biodiversity conservation, particularly wintering migratory birds. Since the Three Gorges Dam became operative in 2003, the magnitude and frequency of extreme seasonal water-level fluctuations in Poyang Lake have increased significantly. We review the existing literature and contributions to this Special Issue on the Poyang Lake wetland ecosystem and their biota in relation to impacts from the Three Gorges Dam. Resulting impacts on, and adaptations of, Poyang Lake biota to the hydrological changes caused by operation of the dam are poorly understood. Adaptive management of this lake and its associated wetlands needs to be further assessed through comprehensive, long-term monitoring covering a wide range of parameters related to the system’s hydrological characteristics, water quality, geomorphology, aquatic biota, wetland vegetation, and associated wetland fauna.

Distinct Bacterial Communities in Wet and Dry Seasons During a Seasonal Water Level Fluctuation in the Largest Freshwater Lake (Poyang Lake) in China.

Water level fluctuations (WLFs) are an inherent feature of lake ecosystems and have been regarded as a pervasive pressure on lacustrine ecosystems globally due to anthropogenic activities and climate change. However, the impacts of WLFs on lake microbial communities is one of our knowledge gaps. Here, we used the high-throughput 16S rRNA gene sequencing approach to investigate the taxonomic and functional dynamics of bacterial communities in wet-season and dry-season of Poyang Lake (PYL) in China. The results showed that dry-season was enriched in total nitrogen (TN), nitrate (NO3-), ammonia (NH4+), and soluble reactive phosphorus (SRP), while wet-season was enriched in dissolved organic carbon (DOC) and total phosphorus (TP). Bacterial communities were distinct taxonomically and functionally in dry-season and wet-season and the nutrients especially P variation had a significant contribution to the seasonal variation of bacterial communities. Moreover, bacterial communities responded differently to nutrient dynamics in different seasons. DOC, NO3-, and SRP had strong influences on bacterial communities in dry-season while only TP in wet-season. Alpha-diversity, functional redundancy, taxonomic dissimilarities, and taxa niche width were higher in dry-season, while functional dissimilarities were higher in wet-season, suggesting that the bacterial communities were more taxonomically sensitive in dry-season while more functionally sensitive in wet-season. Bacterial communities were more efficient in nutrients utilization in wet-season and might have different nitrogen removal mechanisms in different seasons. Bacterial communities in wet-season had significantly higher relative abundance of denitrification genes but lower anammox genes than in dry-season. This study enriched our knowledge of the impacts of WLFs and seasonal dynamics of lake ecosystems. Given the increasingly pervasive pressure of WLFs on lake ecosystems worldwide, our findings have important implications for conservation and management of lake ecosystems.

Impact of seasonal water-level fluctuations on autumn vegetation in Poyang Lake wetland, China

Water level fluctuations (WLF) are natural patterns that are necessary for the survival of various plants, and WLF guarantee both the productivity and the biodiversity of wetlands. However, the underlying mechanisms of how changes in vegetation are linked to seasonal WLF remain unclear. Using vegetation and hydrological data from 1989 to 2009, we identified the key seasonal fluctuations and their impacts on vegetation in the Poyang Lake wetland by utilizing a tree-based hierarchical model. According to our results: 1) WLF in summer had significant impacts on both sedges and reeds. The severe summer floods promoted the expansion of sedges, while they inhibited the expansion of reeds; 2) WLF in autumn also greatly impacted sedges, while reeds were severely affected in spring. Specifically, we found that low water levels in autumn led to the expansion of sedges, and low water levels in spring led to the expansion of reeds. The results were well corroborated through comparisons of the vegetation distribution patterns over the last two decades (i.e., the 1990s and 2000s), which may shed light on corresponding water resource and wetland management.

A novel interpolation method for InSAR atmospheric wet delay correction

The accuracy and capability of Differential interferometric Synthetic Aperture Radar (DInSAR) depends on the phase errors. In particular, errors associated with Atmospheric Wet Delay (AWD) should be reduced to ensure reliable results from the interferometric process. This paper addresses a new method for AWD estimation based on MEdium Resolution Imaging Spectrometer (MERIS) water vapor image which is used as an auxiliary data to correct AWD effects on ENVIronment SATellite (ENVISAT) Advanced Synthetic Aperture Radar (ASAR) interferogram. We also explore the possibility of using MERIS data under cloudy conditions and we propose a novel method for the interpolation of water vapor in the presence of clouds using a hybrid technique we name Three Dimensional Inverse Distance Weighted (3D-IDW). It is shown that the proposed method succeeds to provide a quite realistic prediction of MERIS water vapor distribution on cloudy area. Obtained results show that 3D-IDW method succeeds to estimate IWV for each cloudy pixel with RMSE not exceeding 0.094 g/cm2 over area masked by 90% of cloud. The proposed method was tested on Mitidja region (north central Algeria), using a couple of Advanced Synthetic Aperture Radar (ASAR) and MERIS images on the 65 descending track. The results demonstrates an improvement of 15% in the standard deviation of interferogram after ADW correction. Finally, the obtained surface deformation reveals the presence of subsiding districts which may be linked to seasonal water level fluctuation and overdrafting groundwater confirming the results of previous study. Index termsDifferential Interferometry Synthetic Aperture Radar (DInSAR), Atmospheric Wet Delay (AWD), water vapor, interpolation, Inverse Distance Weighted (IDW), MERIS, subsidence.

Secondary seed dispersal in hydro‐fluctuation belts and its influence on the soil seed bank

AbstractThe completion of the Three Gorges project altered the water level fluctuations from “summer submersion and winter exposure” to “summer exposure and winter submersion.” The reverse seasonal flooding has dramatically changed both the time and duration of exposure and submergence of reservoir banks. Secondary seed dispersal by water is the primary method of dispersal in hydro‐fluctuation belts. This study conducted field sampling and germination experiments to evaluate the effects of reverse seasonal flooding on species composition, diversity, and density of the secondary seed dispersal system and the soil seed bank, and their changes with elevation, in the Xiangzi River. The results indicate that that the secondary seed dispersal system and soil seed bank were associated with 42 and 50 plant species, respectively, and their average seed densities were 1,876.27 and 7,322.18 seeds/m2, respectively. The quantity of seeds from secondary seed dispersal accounted for 20.40% of the soil seed bank. The species life‐form composition of both consisted mainly of annual and perennial grasses. Among these grasses, the dominant species in the secondary seed dispersal system were Cynodon dactylon and Paspalum distichum, whereas the dominant species in the soil seed bank were Solanum nigrum and Rumex dentatus. Due to the effects of reverse seasonal water level fluctuations, the species composition and quantity of the soil seed bank and secondary seed dispersal system largely exhibited similar spatial distribution characteristics, but some differences were observed. The species quantity, species diversity index, and seed density in the soil seed bank were the highest in the middle section of the hydro‐fluctuation belt, followed by the top section and then the bottom section. Conversely, the species quantity, species diversity index, and seed density in the secondary seed dispersal system were highest at the top section, followed by the middle section and then the bottom section.

The Spatial Heterogeneity of Vegetation, Hydrology and Water Chemistry in a Peatland with Open-Water Pools

Ombrotrophic bogs can comprise a mosaic of vegetation patches and open-water pools, with hydrological and biogeochemical connections between pools and the surrounding peat and vegetation. To establish these connections, we studied the spatial heterogeneity of hydrology and water chemistry in two zones of distinct vegetation assemblages in the subboreal Grande plee Bleue peatland, southern Quebec, Canada. We show that seasonal water-level fluctuations are greater and organic C, N and P concentrations are higher in the peat pore water of a forested zone than in a neighboring open-bog zone; that vegetation is responsible for 69% of the spatial variations in hydrology and water chemistry. Vegetation also explains 31% of the temporal variation in water chemistry, with higher increases in C, N and P concentrations over the growing season in the forested peat and pools than in the open-bog zone. We also show that C, N and P concentrations and water-level fluctuations in pools, especially during precipitation events, were lower than in the surrounding peat. Our results suggest the existence of small “watersheds” to the pools with water flowing in during wet and out during dry periods. Localized patterns emerge from the vegetation–hydrology–water chemistry interactions, with pools influencing the persistence of trees in the central part of an ombrotrophic bog.

Fish assemblage structure in relation to seasonal environmental variation in sub‐lakes of the Poyang Lake floodplain, China

AbstractThe Yangtze River and its watershed have undergone vast changes resulting from centuries of human impacts, yet ecological knowledge of the system is limited. The seasonal variation and spatial variation of three sub‐lakes of Poyang Lake, a huge wetland in the middle Yangtze Basin, were investigated to examine how fish assemblages respond to seasonal hydrology and associated environmental conditions. In all three sub‐lakes, fish assemblage structure revealed strong variations associated with seasonal water level fluctuation. Fish species richness in all sub‐lakes was highest during the middle of the monsoon season and lowest during the dry season. Fish numerical abundance and biomass varied significantly, with several of the most common species having inconsistent patterns of seasonal variation among sub‐lakes. Fish assemblage structure was significantly associated with environmental gradients defined by water level, aquatic macrophyte coverage, conductivity and dissolved oxygen concentration. Assemblage composition in all three sub‐lakes underwent strongest shifts between December and April, the period when water levels were lowest and fishing has the greatest impact on fish stocks. Future impacts that change the hydrology of the middle Yangtze would alter the dynamics of habitat connectivity and affect environmental conditions and fish assemblages of the Poyang Lake wetland system.

Geobotany in a fault in the world’s largest continuous wetland in central South America

The Pantanal is located in the center of South America in a tectonically active sedimentary basin of Quaternary age. Even though the relief is flat and the diversity of the sediments is low, its vegetation cover has high variability resulting from seasonal fluctuations in water levels and the presence of four surrounding biomes. Changes in elevation of less than 1 m influence the length and intensity of floods, powerfully affecting the vegetation. Faults with small vertical displacement can generate abrupt vegetation changes and, consequently, expressive vegetation lineaments. This study characterizes a lineament in the northern Pantanal, considering Land Surface Phenology, estimates of precipitation, and floristic survey. The phenological metrics, obtained from a 15-year time series from the Moderate Resolution Imaging Spectroradiometer processed by TIMESAT software, discriminate evergreen forests in the NW of this lineament from savanna-like physiognomies in the SE region. Plant taxonomic identification shows two distinct regional strata with a clear separation between species adapted to prolonged floods in the NW and typical species of the Cerrado biome, mostly xeromorphic, in the SE. Data from the Tropical Rainfall Measuring Mission complemented the analysis, showing different dependence on local rains on different sides of the lineament. The entire dataset defines this geological structure as a driver of the Pantanal’s plant communities, being a boundary for the extensive establishment of propagules of the Amazon biome. This research, in addition to advancing knowledge of this singular region, which is essential for management studies, can be a stimulus to biological and forest investigations.

Effects of seasonal water-level fluctuation on soil pore structure in the Three Gorges Reservoir, China

Inundation of the Three Gorges Reservoir has created a 30-m water-level fluctuation zone with seasonal hydrological alternations of submergence and exposure, which may greatly affect soil properties and bank stability. The aim of this study was to investigate the response of soil pore structure to seasonal water-level fluctuation in the reservoir, and particularly, the hydrological change of wetting and drying cycles. Soil pore structure was visualized with industrial X-ray computed tomography and digital image analysis techniques. The results showed that soil total porosity (> 100 μm), total pore number, total throat number, and mean throat surface area increased significantly under wetting and drying cycles. Soil porosity, pore number and throat number within each size class increased in the course of wetting and drying cycles. The coordination number, degree of anisotropy and fractal dimension were indicating an increase. In contrast, the mean shape factor, pore-throat ratio, and Euler-Poincare number decreased due to wetting and drying cycles. These illustrated that the wetting and drying cycles made soil pore structure become more porous, continuous, heterogeneous and complex. It can thus be deduced that the water-level fluctuation would modify soil porosity, pore size distribution, and pore morphology in the Three Gorges Reservoir, which may have profound implications for soil processes, soil functions, and bank stability.

Trapeamento de LNAPL observado por meio da técnica de fluorescência induzida por laser (LIF)

Modelos conceituais de áreas contaminadas são, em geral, os primeiros resultados significativos do gerenciamento ambiental. Contudo, é necessário entender a complexidade dos meios contaminados para que seja adotada a melhor alternativa de remediação. A distribuição espacial em subsuperfície da fase liquida não aquosa menos densa que a água (LNAPL – Light Non-Aqueous Phase Liquid), geralmente de elevada variabilidade espacial e, consequentemente, complexa, deve ser mais bem conhecida. Além disso, a flutuação sazonal do nível d’água promove os fenômenos de trapeamento e destrapeamento de LNAPL e define uma zona de redistribuição vertical (smear zone) da contaminação, aumentando a complexidade do cenário. Com o objetivo de preencher lacunas deixadas pelas técnicas convencionais de investigação, foi empregada a técnica de fluorescência induzida por laser (LIF) para avaliação do fenômeno de trapeamento em uma área contaminada por querosene de aviação, situada no interior do estado de São Paulo. Os resultados dos ensaios de fluorescência e medição do nível d’água do aquífero local indicam LNAPL trapeado na porção saturada com limites bem marcados que definem a smear zone. Análises qualitativas revelam similaridade da contaminação na maioria dos pontos investigados, com baixa intensidade de sinal de fluorescência nos menores comprimentos de onda de resposta, compatível com depleção de hidrocarbonetos mais leves pela atenuação natural.

Water level fluctuations and the ecosystem functioning of lakes

Abstract Hydrological regimes are key drivers of productivity and structure in freshwater ecosystems but are increasingly impacted by human activity. Using 17 published food web models of 13 African lakes as a case study, we explored relationships between seasonal and interannual water level fluctuations and 15 attributes related to ecosystem function. We interpreted our results in the context of Odum's ecosystem maturity hypothesis, as systems with higher magnitude fluctuations may be kept at an earlier maturity stage than those that are relatively stable. The data we compiled indicate that long-term changes in the hydrological regimes of African lakes have already taken place. We used Least Absolute Shrinkage and Selection Operator (LASSO) regression to examine relationships between ecosystem attributes and seven physical characteristics. Of these characteristics, interannual water level fluctuation magnitude was the most frequently retained predictor in the regression models. Our results indicate that interannual water level fluctuations are positively correlated with primary and overall production, but negatively correlated with fish diversity, transfer efficiency, and food chain length. These trends are opposite those expected with increasing ecosystem maturity. Interestingly, we found seasonal water level fluctuations to be positively correlated with biomass. An increase in standing biomass is generally associated with more mature ecosystems. However, we found that less production and biomass occurred at high trophic levels in highly fluctuating compared to relatively stable systems. This synthesis provides evidence that water level fluctuations are a key process influencing ecosystem structure and function in lakes.

Lake Peipsi as a biggest transboundary lake in Europe

Lake Peipsi sensu lato (s.l.) (Chudskoe or Chudsko-Pskovskoe in Russian) (3555 km2) is the biggest international lake in Europe and the fourth largest lake in Europe after the Ladoga, the Onega, and the Vänern with respect to surface area and is located in the Baltic Sea water basin. Three states share its water basin – the Russian Federation 59%, Estonia 34% and Latvia 7% of the basin area. The formation and distribution of the structural types of bottom deposits of Lake Peipsi is determined by hydro-meteorological (waves, currents, seasonal water-level fluctuations, lake ice impacts) as well as by the local geologic and geomorphologic factors like the topography and coastal morphology. The central part of the Lake Peipsi s.s. is 9–11 m deep; the coastal zone is shallow and the rather monotonous floor descends for some kilometres in the eastern and western coasts. The main land cover of the Lake Peipsi catchment is forest (50–70%) and agricultural lands (~30%). The water quality of the Lake Peipsi basin depends on natural processes and human activities. The trophic level of Lake Peipsi has increased step by step from mesotrophic-eutrophic to eutrophic-hypertrophic during the past decades. The main commercial fishes of Lake Peipsi are lake smelt, perch, ruff, roach, bream, pike, vendace and pikeperch. Being officially approved by the Estonian-Russian Transboundary Water Commission, the Lake Peipsi basin Management Programme forms a base for the future joint actions in the basin. River Basin Management Plan (RBMP) has been established for the shared river basin district, but separately in Estonia and Russia. Both sides notify each other regularly on the planned and implemented measures, however, the implementation of such measures is decided and done independently from each other. The management measures in Estonia should prioritize land use issues, such as a reduction of diffuse emissions from agriculture; in contrast, the Russian policy should focus on improved municipal and industrial waste-water treatment and the drinking water quality.

Driving factors of temporary and permanent shallow lakes in and around Hwange National Park, Zimbabwe

Small aquatic ecosystems in semi-arid environments are characterised by strong seasonal water level fluctuations. In addition, land use as well as artificial pumping of groundwater to maintain water resources throughout the dry season may affect the functioning of aquatic ecosystems. In this study, we investigated pans situated in and around Hwange National Park, Zimbabwe, where certain waterholes are artificially maintained during the dry season for conservation purposes. We monitored 30 temporary and permanent waterholes for 7 months across the wet and dry seasons in 2013, and analysed them for standard parameters to investigate seasonal variations, assess the effects of land use and pumping on lake functioning, and determine the driving factors of these aquatic systems. Results show an increase in conductivity, hardness, and turbidity when temporary pans dry up and permanent ones are filled with groundwater. Prominent parameters explaining the diversity of aquatic ecosystems are water hardness, conductivity, turbidity, and the presence of vegetation. Seasonality differences in certain parameters suggest the influence of water level fluctuations associated with rainfall, evaporation, and pumping activities. Further, the distinction between turbid pans and those with clear water and vegetation suggests the alternative functioning of pans. Land use had no significant effects, while the effects of pumping are discussed. In times of water scarcity, animals gather around artificially maintained waterholes and foul water with faeces and urine, thus inducing water eutrophication.