Large Water Level Fluctuations Research Articles

Hyperexpansion of genetic diversity and metabolic capacity of extremophilic bacteria and archaea in ancient Andean lake sediments

BackgroundThe Andean Altiplano hosts a repertoire of high-altitude lakes with harsh conditions for life. These lakes are undergoing a process of desiccation caused by the current climate, leaving terraces exposed to extreme atmospheric conditions and serving as analogs to Martian paleolake basins. Microbiomes in Altiplano lake terraces have been poorly studied, enclosing uncultured lineages and a great opportunity to understand environmental adaptation and the limits of life on Earth. Here we examine the microbial diversity and function in ancient sediments (10.3–11 kyr BP (before present)) from a terrace profile of Laguna Lejía, a sulfur- and metal/metalloid-rich saline lake in the Chilean Altiplano. We also evaluate the physical and chemical changes of the lake over time by studying the mineralogy and geochemistry of the terrace profile.ResultsThe mineralogy and geochemistry of the terrace profile revealed large water level fluctuations in the lake, scarcity of organic carbon, and high concentration of SO42--S, Na, Cl and Mg. Lipid biomarker analysis indicated the presence of aquatic/terrestrial plant remnants preserved in the ancient sediments, and genome-resolved metagenomics unveiled a diverse prokaryotic community with still active microorganisms based on in silico growth predictions. We reconstructed 591 bacterial and archaeal metagenome-assembled genomes (MAGs), of which 98.8% belonged to previously unreported species. The most abundant and widespread metabolisms among MAGs were the reduction and oxidation of S, N, As, and halogenated compounds, as well as aerobic CO oxidation, possibly as a key metabolic trait in the organic carbon-depleted sediments. The broad redox and CO2 fixation pathways among phylogenetically distant bacteria and archaea extended the knowledge of metabolic capacities to previously unknown taxa. For instance, we identified genomic potential for dissimilatory sulfate reduction in Bacteroidota and α- and γ-Proteobacteria, predicted an enzyme for ammonia oxidation in a novel Actinobacteriota, and predicted enzymes of the Calvin–Benson–Bassham cycle in Planctomycetota, Gemmatimonadota, and Nanoarchaeota.ConclusionsThe high number of novel bacterial and archaeal MAGs in the Laguna Lejía indicates the wide prokaryotic diversity discovered. In addition, the detection of genes in unexpected taxonomic groups has significant implications for the expansion of microorganisms involved in the biogeochemical cycles of carbon, nitrogen, and sulfur.EPcqnK6xUD66cr6MUL2q3UVideo

Control of small pressurized water reactors under single-loop operation based on MFAPC theory

Small pressurized water reactors can supply power to ships, and single-loop operation is adopted to improve maneuverability under some abnormal conditions. Large key parameter fluctuations and the potential risk of human errors occur in conventional single-loop operation. Therefore, an automatic rapid power reduction method is proposed to improve the control performance of single-loop operation. An automatic rapid power-reduction method based on conventional control systems was tested. Poor power control performance and large fluctuations in steam generator water level were observed. Reactor power and steam generator water level control systems improved by the model-free adaptive predictive control (MFAPC) theory were developed, and the parameters of the MFAPC controller were optimized by the differential evolution method. The simulation results under single-loop operation show that the improved control systems reduce the overshoot of the reactor power and effectively suppress the water level fluctuation of the steam generator.

A reduced-complexity shoreline model for coastal areas with large water level fluctuations

A new reduced-complexity, 1-D shoreline model has been developed, calibrated, and tested with a set of shoreline positions detected from high-resolution satellite images. Motivated by recent large interannual water level fluctuations and associated shoreline changes in the Great Lakes, the model is built on previous models that are based on the disequilibrium concept, with extensions for water level effects. Unlike other shoreline models, the model includes two different sources of disequilibrium, wave disequilibrium and water level disequilibrium. The model also includes a passive flooding term to account for the instantaneous effect of the water level changes on the shoreline position. Case studies forced by seasonally-varying waves and water levels varying on seasonal and interannual timescales highlight the model's ability to enhance wave-driven shoreline change when water level variations are additionally present. The model was applied to two sites along the Lake Michigan shoreline, Jeorse Park and West Beaches, with shoreline time series extracted from multispectral satellite imagery. When calibrated and applied to an eleven year period of decreasing water levels, the new model shows significant skill in simulating and forecasting the shoreline position in the two study areas, with modest improvement over existing models. The simulation results additionally highlight the dominance of water level disequilibrium over wave disequilibrium for the study sites. When applied to a nearly forty year simulation of West Beach, the new model shows excellent ability to model the shoreline response to water level and wave fluctuations over a range of timescales. Comparison models are seen to be incapable of capturing the water level effects, particularly when water level trends differ from the calibration period. Overall, the model results and parameters show the importance of the newly introduced water level disequilibrium in modulating wave-driven shoreline change. Finally, while the shoreline model was motivated by Great Lakes coastal processes, it may provide new predication abilities for coastlines where water level fluctuations and trends play a role in shoreline changes. • A new shoreline model is developed, tested, and compared to existing models. • The model is based on the concept of combined wave and water level disequilibrium. • The model is applied to two case studies along the Lake Michigan shoreline. • The model successfully simulates shoreline changes enhanced by water level changes.

Effects of drawdown on growth and reproduction of submerged macrophyte Vallisneria spinulosa

Water regime plays a determinant role in plant community development and patterns of plant zonation in wetlands. The waters located in the middle reach of the Yangtze River (China) have experienced a large decrease in wetland area from human activities for a long time, especially after the hydrological drought events in recent years. This outdoor study was conducted to clarify the morphological responses and reproductive strategy of Vallisneria spinulosa to water depth gradients (0.6 m, 1.0 m, 1.5 m) and to drawdown (down to 0.3 m). In static water, water depth of 1.0 m was the best condition for V. spinulosa to grow, manifested as high biomass of vegetative parts, tubers and sexual structures. However, V. spinulosa growing in water depth of 1.5 m was able to adapt to the decline in water depth in autumn, expressed as increased ramet number, stolon weight and belowground biomass. The low water depth of 0.6 m produced small plants with slight vegetative biomass and drawdown produced more tuber biomass. The drawdown caused a decline in vegetative ratio of V. spinulosa. Moreover, it caused an increase in clonal ratio at water levels of 1.5 m and 0.6 m, and a decline in sexual ratio at water levels of 1.5 m and 1.0 m. The results show that under the condition of relatively large fluctuations in water level, V. spinulosa will reduce the allocation of sexual biomass and increase the allocation of clonal biomass in order to cope with environmental changes so that it can proliferate better. Thus, water level changes have a great influence on the growth and reproduction of V. spinulosa.

Multi-proxy indications of depositional evolution and paleo-natural disasters (flooding and fire) in the southern part of the Korean Peninsula during the Holocene

Understanding paleoenvironmental changes and corresponding driving forces can provide valuable information for predicting and preparing for future climate change. However, under the complex climate system, the driving mechanisms behind hydroclimatic variability in terms of timescales and magnitude are still unclear, and the various ecological responses are not clear. Here, we reconstruct the history of swamp evolution and climate changes in the southern part of the Korean Peninsula during the Holocene based on multi-proxy data (palynomorphs, microscopic charcoal, diatoms, grain size, total organic carbon, C/N ratio, and δ13CTOC data). The climatic conditions in the study area gradually became cold and dry due to the weakening East Asian summer monsoon (EASM) after ca. 5400 cal yr BP, as evidenced by the shift in vegetation communities from temperate broad-leaved forests dominated by Quercus to mixed conifer and deciduous broad-leaved forests with increased cold/dry-tolerant taxa. After ca. 4700 cal yr BP, microscopic charcoal concentration to terrestrial pollen concentration values are relatively high together with a sharp decrease in palynomorph concentrations and the proportions of arboreal pollen, representing open forest with fewer plants due to frequent wildfires. In addition, the quasi-millennial frequencies of seasonal fires (dry spring) and flooding (summer rainfall) were identified in our study area during the Late Holocene, which correspond to lower sea surface temperatures of the western tropical Pacific and stronger El Niño Southern Oscillation (ENSO) activity periods. After ca. 8200 cal yr BP, the depositional environment underwent gradual backswamp expansion due to high precipitation, strengthened EASM, and relative sea-level rise during the Early to Middle Holocene. During the Late Holocene, ENSO-driven extreme hydroclimatic variability, such as frequent flooding and fire, had significant impacts on not only swamp development with large fluctuations in water level but also long-term vegetation and aquatic ecosystem dynamics.

National framework for ranking lakes by potential for anthropogenic hydro-alteration

Lakes face multiple anthropogenic pressures that can substantially alter their hydrology. Dams and land use in the watershed (e.g., irrigated agriculture) can modify lake water regimes beyond natural ranges, and changing climate may exacerbate anthropogenic stresses on lake hydrology. However, we lack cost-effective indicators to quantify anthropogenic hydrologic alteration potential in lakes at regional and national extents. We developed a framework to rank lakes by the potential for dams and land use to alter lake hydrology (HydrAP) that can be applied at a national scale. The HydrAP framework principles are that 1) dams are primary drivers of lake hydro-alteration, 2) land use activities are secondary drivers that alter watershed hydrology, and 3) topographic relief limits where land use and dams are located on the landscape. We ranked lakes in the United States Environmental Protection Agency National Lakes Assessment (NLA) on a HydrAP scale from zero to seven, where a zero indicates lakes with no potential for anthropogenic hydro-alteration, and a seven indicates large dams and/or intensive land use with high potential to alter lake hydrology. We inferred HydrAP population distributions in the conterminous US (CONUS) using the NLA probabilistic weights. Half of CONUS lakes had moderate to high hydro-alteration potential (HydrAP ranks 3–7), the other half had minimal to no hydro-alteration potential (HydrAP ranks 0–2). HydrAP ranks generally corresponded with natural and man-made lake classes, but >15% of natural lakes had moderate to high HydrAP ranks and ~10% of man-made lakes had low HydrAP ranks. The Great Plains, Appalachians, and Coastal Plains had the largest percentages (>50%) of high HydrAP lakes, and the West and Midwest had the lowest percentages (~30%). Water residence time (τ) and water-level change were associated with HydrAP ranks, demonstrating the framework’s intended ability to differentiate anthropogenic stressors that can alter lake hydrology. High HydrAP lakes had shorter τ in all ecoregions, but HydrAP relationships with water-level change varied by ecoregion. In the West and Appalachians, high HydrAP lakes experienced excessive water-level declines compared to low-ranked lakes. In contrast, high HydrAP lakes in the Great Plains and Midwest showed stable water levels compared to low-ranked lakes. These differences imply that water management in western and eastern mountainous regions may result in large water-level fluctuations, but water management in central CONUS may promote water-level stabilization. The HydrAP framework, using accessible national datasets can support large-scale lake assessments and be adapted to specific locations where data are available.

Paleolimnological assessment of six lakes on the Kissimmee Chain, with implications for restoration of the Kissimmee–Okeechobee–Everglades system, Florida, USA

Whitmore TJ, Riedinger-Whitmore MA, Reed ZE, Curtis JH, Yang H, Evans DE, Cropper NR, Alvarado KS, Lauterman FM, Scott A, Leonard CR, Franklin DL. 2020. Paleolimnological assessment of six lakes on the Kissimmee Chain, with implications for restoration of the Kissimmee–Okeechobee–Everglades system, Florida, USA. Lake Reserv Manage. 36:218–242. The Kissimmee Basin in south central Florida contains a large, freshwater network that includes the Kissimmee River and nearly 2 dozen lakes that are headwaters of the Florida Everglades. Management of these lakes is an important part of Everglades restoration. We report a paleolimnological investigation of 6 lakes in the Upper Kissimmee Basin. Engineering activities connected the lakes and permanently altered hydrology in the 19th and 20th centuries. The lakes were naturally meso-eutrophic, but changes in lake levels and nutrient loading contributed to different degrees of eutrophication. Cyanobacteria were present historically at low levels in Lakes East Tohopekaliga, Cypress, and Tohopekaliga, but increased during the 20th century. Lake Jackson lacked cyanobacteria until recently, but Lakes Kissimmee and Marian have had high levels of cyanobacteria since predisturbance times. Profound changes in the lakes occurred after engineering activities eliminated natural large fluctuations in water levels that periodically dried large portions of the basins. Salt-tolerant biological indicators previously alternated with freshwater organisms. Large water-level fluctuations moderated aquatic-plant standing crops and reduced organic matter accumulation. Lakes Kissimmee and Marian showed greatest evidence of former associated wetlands, but lacked large variations in water levels. We recommend disconnecting these lakes from each other and from the Kissimmee River to reestablish large, natural fluctuations in water levels that were part of healthy ecosystem function. Former wetlands should be restored to slow the downstream cascade of nutrients to Lake Okeechobee and the Everglades. This study demonstrates that paleolimnology is useful for assessing hydrological changes that potentially affect lake restoration efforts.

Characterizing marsh wetlands in the Great Lakes Basin with C-band InSAR observations

There is limited research focusing on Interferometric Synthetic Aperture Radar (InSAR) applications in the Great Lakes coastal wetlands with large water level fluctuations. In this study, we investigated the potential of using C-band SAR data to characterize marsh wetland and monitor water level changes along the coast of the Great Lakes. InSAR analysis was conducted using Radarsat-2 and Sentinel-1 data collected at Long Point, Ontario, Canada over the period of 2016–2018. Observations indicated that both backscattering coefficients and coherence from tall plants (e.g. cattail/Phragmites), short plants (e.g. grass), and water varied with different sensor modes (incidence angles and polarizations) in response to changes in phenology, disturbance, and water level. InSAR phase changes were closely related to fluctuations in water level and flow direction. We evaluated InSAR time series observations using measurements from water level loggers based on correlation and root mean square error (RMSE). It was found that correlation between InSAR measurements and water level changes in the field varied depending on the site, type of wetland vegetation, incidence angle and polarization. Although results from some sensor modes provided good correlation at a few locations, the low fringe rate and RMSE between 9 and 28 cm indicated that InSAR observations of water level changes were generally underestimated.

Thermal and Hydrodynamic Changes under a Warmer Climate in a Variably Stratified Hypereutrophic Reservoir

We quantified effects of future climate warming on temperature and stability in a variably stratified, hypereutrophic reservoir with large fluctuations in water level by calibrating a 2-D model (CE-QUAL-W2, version 3.7.1, Portland State University, Portland, USA) of reservoir hydrodynamics using a time series (1992 to 2011) of inflow and air and water temperature. The model was then forced with increased air temperature projected by an ensemble of climate models that accounted for complex local topography and seasonality, with greater warming in summer. Warming increased annual evaporation rates by 2.6 to 7.9%. Water temperature increased by 0.44 (whole-reservoir; p < 0.05), 0.47 (epilimnion; p < 0.01), and 0.30 °C (hypolimnion; p < 0.05) per 1 °C increase in air temperature. Thickness of the epilimnion and hypolimnion diminished, with expansion of the metalimnion. Schmidt stability correlated with mean water depth over a wide range of depths (3.9 to 8.1 m; Adj. R2 = 0.91 to 0.93; p < 0.001). Increased air temperature increased mean annual stability by 6.1 to 23.6 J m−2 when depth was large and the reservoir stratified, but when depth was low (due to combined low inflow and, in preceding years, high withdrawals), inhibiting stratification, then water temperatures increased evenly (and more) throughout the vertical profile so change in mean annual stability was near zero (−0.1 to 1.1 J m−2). Combined effects of reservoir management (volume, timing, and elevation of water withdrawal) and climate warming (temperature of air and benthic sediment) can impact the hydrodynamic regime differently under variably stratified conditions with implications for release of phosphorus from sediment and vertical transport of phosphorus to the euphotic zone.

Monitoring and Water Table Control For Plantation on Peatland in Indonesia

Drainage construction for plantations development on peatlands often caused controversy. Dranage construction will be followed by subsidence of peatland . To be able to extend the chance to get profit in the plantation business subsidence prevention efforts are needed. Setting water level and the prevention of excessive drainage is one of the efforts to reduce the rate of subsidence of the peat.This study is based on literature review by collecting information from various sources and then comparing and analyzing it so that information is obtained on a comprehensive subject matter. Literature review include: monitoring parameters, types of equipment for monitoring, pattern placement monitoring equipment, the range and the frequency of monitoring. From the study concluded that the water level necessary to measure on land and channels using dipwell and staff gauges. Observations were made with a combination of automated recording device and manual recording. Both are quite accurate, but the use of automatic registers in remote locations saves time, and if an automatic device is installed in an area that has the potential to have large water level fluctuations and runs quickly, it will provide more accurate data. Observations on dams for water level control are installed at every 20 cm drop in hidraulic head.

Effects of Extreme Events on Arsenic Cycling in Salt Marshes

AbstractExtreme events such as storm surges, intense precipitation, and supermoons cause anomalous and large fluctuations in water level in tidal salt marshes, which impacts the sediment biogeochemistry that dictates arsenic (As) cycling. In addition to changes in water level, which impacts soil redox potential, these extreme events may also change salinity due to freshwater inputs from precipitation or saltwater inputs due to surge. It is currently unknown how As mobility in tidal salt marshes will be impacted by extreme events, as fluctuations in salinity and redox potential may act synergistically to mobilize As. To investigate impacts of extreme events on As cycling in tidal salt marshes, we conducted a combined laboratory and field investigation. We monitored pore water and soil samples before, during, and after two extreme events: a supermoon lunar eclipse followed by a storm surge and precipitation induced by Hurricane Joaquin in fall 2015 at the St. Jones Reserve in Dover, Delaware, a representative tidal salt marsh in the Mid‐Atlantic United States. We also conducted soil incubations of marsh sediments in batch and in flow‐through experiments in which redox potential and/or salinity were manipulated. Field investigations showed that pore water As was inversely proportional to redox potential. During the extreme events, a distinct pulse of As was observed in the pore water with maximum salinity. Combined field and laboratory investigations revealed that this As pulse is likely due to rapid changes in salinity. These results have implications for As mobility in the face of extreme weather variability.

Response of three arid zone floodplain plant species to inundation

For species to persist on floodplains and in temporary wetlands in arid climates, where large and unpredictable water level fluctuations are common, at least one life history stage must be able to survive inundation. We investigated the survival and performance (RGR, total biomass and above-to-belowground biomass (A:B)) of three common and often coexisting arid zone floodplain species: Xanthium strumarium, Cyperus gymnocaulos and Ludwigia peploides. Observations suggested the species had different responses to inundation, which was tested in a controlled pond experiment. Plants were held at three elevations (+ 10 cm, − 20 and − 70 cm) and subjected to three hydrological regimes (static 90 cm, 1 and 5 cm day−1 inundation) for 16 weeks. Xanthium strumarium died when completely inundated for longer than 4 weeks but when partially flooded survived, showed lower growth rates, increased A:B and produced adventitious roots. C. gymnocaulos showed reduced growth rates when partially flooded and senesced to rhizomes when completely inundated for longer than 4 weeks, which re-sprouted after inundation pressure was removed. L. peploides responded positively to flooding with increased A:B and the production of adventitious roots. The species exhibited three contrasting responses to inundation, which do not necessarily fit neatly within existing water regime functional classification frameworks.

Fish communities in small subtropical reservoirs subject to extensive drawdowns, with focus on the biology of Enteromius paludinosus (Peters, 1852) and Clarias gariepinus (Burchell, 1822)

AbstractSmall reservoirs are characterised by extreme fluctuations in water levels, but how this affects fish communities is not well understood. The aim of the study was to investigate fish communities in two small reservoirs which experience large water level fluctuations over two study years, wet and dry. Six fish species were caught in both reservoirs during the sampling period. The numerically dominant fish species was Enteromius paludinosus in both reservoirs, with Clarias gariepinus contributing the high overall fish biomass. The cyprinids Enteromius lineomaculatus and Enteromius trimaculatus occurred in small numbers, as well as the cichlids Oreochromis mossambicus and Tilapia sparrmanii. Using GLMM, the abundance of both C. gariepinus and E. paludinosus across the two reservoirs was found to be significantly associated with total nitrogen and inorganic nitrogen. C. gariepinus abundances were also associated with water transparency and reactive phosphorus whilst E. paludinosus abundances were associated with ammonia, alkalinity, total dissolved solutes and water depth. E. paludinosus bred mostly during the rainy year. Fish migrations and spawning events were largely triggered by rainfall. Differences between the fish populations in the two reservoirs were small based on fisheries metrics due to the biological attributes of the dominant species, E. paludinosus and C. gariepinus. The shallowness and frequent water level fluctuations in small reservoirs possibly do not allow for specialised habitats to develop, which could lead to high fish species diversity. Their suitability for small‐scale fisheries has to be reconsidered as the demand for water for irrigation far outweighs that of the fishery.

Methane emission through ebullition from an estuarine mudflat: 2. Field observations and modeling of occurrence probability

AbstractEbullition can transport methane (CH4) at a much faster rate than other pathways, albeit over limited time and area, in wetland soils and sediments. However, field observations present large uncertainties in ebullition occurrences and statistic models are needed to describe the function relationship between probability of ebullition occurrence and water level changes. A flow‐through chamber was designed and installed in a mudflat of an estuarine temperate marsh. Episodic increases in CH4 concentration signaling ebullition events were observed during ebbing tides (15 events over 456 ebbing tides) and occasionally during flooding tides (4 events over 455 flooding tides). Ebullition occurrence functions were defined using logistic regression as the relative initial and end water levels, as well as tidal amplitudes were found to be the key functional variables related to ebullition events. Ebullition of methane was restricted by a surface frozen layer during winter; melting of this layer during spring thaw caused increases in CH4 concentration, with ebullition fluxes similar to those associated with large fluctuations in water level around spring tides. Our findings suggest that initial and end relative water levels, in addition to tidal amplitude, partly regulate ebullition events in tidal wetlands, modulated by the lunar cycle, storage of gas bubbles at different depths and seasonal changes in the surface frozen layer. Maximum tidal strength over a few days, rather than hourly water level, may be more closely associated with the possibility of ebullition occurrence as it represents a trade‐off time scale in between hourly and lunar periods.

The response of Phragmites to fluctuating subsurface water levels in constructed stormwater management systems

Area-efficient constructed systems for stormwater management and bioretention may involve large fluctuations in subsurface water levels. Such fluctuations challenge vegetation by forcing roots to explore deeper layers to access water during dry periods. In a controlled experiment, we studied growth patterns and the ability of Phragmites australis roots to track subsurface water level fluctuations of differing amplitude and frequency in substrates with contrasting water-holding capacity. We found that P. australis was able to adjust its rooting pattern to considerable subsurface water level fluctuations (to well below 120cm), but that substrate characteristics can restrict its ability to adjust to larger fluctuations. Fluctuation amplitude was the driving factor for plant growth and biomass allocation responses, while substrate characteristics and fluctuation frequency were less important. When not exposed to large water level fluctuations, P. australis grew larger shoots and only explored intermediate rooting depths. There was a negative relationship between root and rhizome biomass, showing a resource-based trade-off and short-term costs of adjusting rooting patterns to large water level fluctuations. These results indicate that P. australis is suited for systems with considerable subsurface water fluctuations, but constraints on its flexibility need to be investigated.

Water quality characteristics of Poyang Lake, China, in response to changes in the water level

As one of the few remaining lakes that are freely connected with the Yangtze River, Poyang Lake exhibits large annual water level (WL) fluctuations. In this study, weekly samples were collected at the north end of Poyang Lake from September 2011 to December 2012, and we investigated the mechanism of limnological responses to fluctuations in the WL. The study covers three seasons that were associated with WL fluctuations ranging from 8 to 19 m. Spearman's rank correlations and multivariate non-metric multidimensional scaling analyses indicated that low and high WL periods differed in a number of water quality characteristics. The low WL period coincided with the non-growing season and was associated with the peak concentrations of nitrogen, the highest turbidity (Turb), and the lowest water temperature. The high WL period was mainly characterized by enhanced chlorophyll a concentration. Spearman's rank correlations revealed positive relationships between the WL and the concentrations of NO3-N and PO4-P and negative relationships between the WL and the Turb, total nitrogen, total phosphorus, NO2-N, and NH4-N concentrations. All results support the conclusion that the large WL fluctuations are the principal drivers for physicochemical variables in this floodplain lake ecosystem.

Impact of large water level fluctuations on geomorphological processes and their interactions in the shore zone of a dam reservoir

Abstract Bratsk Reservoir is the second largest reservoir in the world in terms of volume (170 km 3 ) and one of the largest in terms of area (about 5500 km 2 ). It was created in 1967 and is characterized by a long-term exploitation regime, with water level fluctuations of 1.1 to 6.6 m per year and up to 10 m per decade. We summarize a series of detailed field investigations and monitoring conducted in 2001–2013, concerning various geomorphological processes in the shore zone of Bratsk Reservoir. The processes were initiated (bluff recession, accumulation processes, aeolian processes, linear erosion) or intensified (karst processes and landslides) as a result of creation of the reservoir. The course of geomorphological processes is conditioned by water level fluctuations in the reservoir. In periods of high water level, coastal slope erosion with bluff recession and activation of landslides are observed, whereas during low water level, aeolian processes are activated, while karst processes and linear erosion are intensified. Geomorphological processes occurring near the shore of Bratsk Reservoir often interact. Although the reservoir has been exploited for nearly 50 years, the rate of geomorphological processes taking place in its shore zone is not declining, and the area where these processes take place is increasing.

Performance of the Phytoplankton Index for Lakes (IPLAC): A multimetric phytoplankton index to assess the ecological status of water bodies in France

A new phytoplankton-based index was designed to respond to the Water Framework Directive (WFD) requirements concerning the assessment of lake ecological status. The “Indice Phytoplancton Lacustre” (IPLAC) is a multimetric index, taking into account biomass, abundance and species composition of communities. The first metric is based on the total phytoplankton biomass (MBA), the second on the abundance and taxonomic composition (MCS) of 165 indicator taxa. The IPLAC was developed on 2 independent databases, one for the calibration and the second for the validation of the metrics. The calibration dataset was composed of 255 “lake-years” from 214 distinct lakes sampled between 2005 and 2012. The validation dataset included 173 lake-years in order to confirm the response of the index to the trophic gradient and anthropogenic pressure.The results show that the IPLAC correctly highlights chemical pressure (eutrophication). Especially high Pearson correlations are shown with total phosphorus (r=−0.71, p-value<0.001), chlorophyll-a (r=−0.83, p-value<0.001) and water transparency (r=0.73, p-value<0.001) which are the main proxies for the trophic level. Corine land cover was used as an indication of the anthropogenic pressure and good correlations are also found with the watershed land use, negatively correlated with agricultural area (r=−0.60, p-value <0.001), population density (r=−0.36, p-value <0.001) and positively with forest area (r=0.57, p-value <0.001).The index is WFD-compliant and is dedicated to natural lakes and artificial water bodies in metropolitan France, and will be routinely used by the French Ministry of the Environment to assess lake ecological status through the phytoplankton community. However, the results must be carefully interpreted in two cases: reservoirs with large water level fluctuations, and samples that include less than 5 indicator species.

Use of MODIS satellite images for detailed lake morphometry: Application to basins with large water level fluctuations

Lake morphometry is essential for managing water resources and limnetic ecosystems. For reservoirs that receive high sediment loads, frequent morphometric mapping is necessary to define both the effective life of the reservoir and its water storage capacity for irrigation, power generation, flood control and domestic water supply. The current study presents a methodology for updating the digital depth model (DDM) of lakes and reservoirs with wide intra and interannual fluctuations of water levels using satellite remote sensing. A time series of Terra MODIS satellite images was used to map shorelines formed during the annual water level change cycle, and were validated with concurrent Landsat ETM+ satellite images. The shorelines were connected with in-situ observation of water levels and were treated as elevation contours to produce the DDM using spatial interpolation. The accuracy of the digitized shorelines is within the mapping accuracy of the satellite images, while the resulting DDM is validated using in-situ elevation measurements. Two versions of the DDM were produced to assess the influence of seasonal water fluctuation. Finally, the methodology was applied to Lake Kerkini (Greece) to produce an updated DDM, which was compared with the last available bathymetric survey (1991) and revealed changes in sediment distribution within the lake.

Impact of alternating wet and dry periods on long-term seasonal phosphorus and nitrogen budgets of two shallow Mediterranean lakes

The water balance, with large seasonal and annual water level fluctuations, has a critical influence on the nitrogen and phosphorus dynamics of shallow lakes in the semi-arid climate zone. We constructed seasonal water and nutrient budgets for two connected shallow lakes, Lakes Mogan and Eymir, located in Central Anatolia, Turkey. The study period covered 20years with alternations between dry and wet years as well as restoration efforts including sewage effluent diversion and biomanipulations in Lake Eymir. Both lakes experienced a 1–2m water level drop during a drought period and a subsequent increase during the wet period, with seasonal water level fluctuations of 0.60 to 0.70m. During wet years with high water levels, small seasonal differences were observed with a nutrient peak in spring caused by external loading and nutrient loss via retention during summer. During years with low water levels, nutrient concentrations increased due to internal and external loading, exacerbated by evaporative water loss. In Lake Eymir, a shift to eutrophic conditions with turbid water occurred under low water level conditions and consequent internal loading of P from the sediment, causing high nutrient concentrations in summer. Our results indicate a threat of lakes drying out in the semi-arid climate zone if evaporation increases and precipitation decreases as anticipated from the global climate change predictions. In addition, our results show the influence of the water balance on the eutrophication of shallow lakes in the Mediterranean climate zone and highlight the ultimate consequences for lake management.