Role Of Lakes Research Articles

Prediction of long-term changes of weak diurnal stratification in shallow lakes using artificial neural networks

ABSTRACT Thermal stratification plays a key role in lakes' ecosystems. In contrast to deep lakes, the thermal structure of shallow polymictic lakes is characterized by a weak stratification with an apparent diurnal cycle. Long-term changes in stratification are governed by climate change and anthropogenic effects such as water level regulation. We developed a simple and robust model system consisting of an energy balance model to estimate depth-averaged water temperatures and an artificial neural network (ANN) model to predict stratification with high temporal resolution. One novelty of our approach is that instead of directly estimating water temperatures at different depths, we simulated the potential energy anomaly index, the indicator of stratification's strength. The ANN-based model's performance was assessed against a physical-based one-dimensional model (General Ocean Turbulence Model) by modeling a 40-year-long period from 1981 to 2020. The new model accurately predicts a shallow lake's weak stratification and its diurnal cycle. Besides, the model proved reliable on longer time scales, capturing the effect of climate change, anthropogenic water level regulation, and their synergistic interaction on the change of stratification's intensity and duration.

Co-influence of biochar-supported effective microorganisms and seasonal changes on dissolved organic matter and microbial activity in eutrophic lake

DOM (dissolved organic matter) play a crucial role in lakes' geochemical and carbon cycles. Eutrophication evolution would influence nutrient status of waters and investigating the DOM variation helps a better understanding of bioremediation on environmental behavior of DOM in eutrophic lakes. In our study, the contents, compositions and characteristics of systematic DOM&SOM (sediment organic matter) were greatly influenced by seasonal changes. But the effective bioremediations obviously reduced the DOM concentration and thus mitigated the eutrophication outbreak risks in water bodies due to the increased MBC (microbial biomass carbon), microbial activity and metabolism. In early summer, the overall DOM in each treatment were readily low levels and derived from both autochthonous and exogenous origins, dominated by fulvic acid-like. In midsummer, the DOM contents and characteristics in each treatment increased significantly as phytoplankton activity improved, and the majority of DOM were humic acid-like and mainly of biological origin. The greatest differences of enzymes, MBC, microbial metabolism and DOM&SOM removal among different treatments were observed in summer months. In autumn, the systematic DOM&SOM slightly reduced due to the deceased microbial activity, in which the microbial humic acids were main component and derived from endogenous sources. Additionally, the gradually decreased SOM with cultivated time in each treatment was a result of microbiological conversion of SOM into DOM. For various treatments, BE, BE.A, BE.C and BE.E increased the MBC, enzymatic and microbial activities due to the application of biochar-supported EMs. Among these, BE and BE.A, especially BE.A with oxygen supplement, achieved the most desirable effect on reducing systematic DOM&SOM levels and increasing enzymatic and microbial activities. The group of EM also reduced the levels of DOM&SOM as improved degradation of EMs for DOM. However, BC, BE.C and BE.E finally did not achieved the desirable effect on reducing DOM&SOM due to the suppression of microbial activities, respectively, from high dose of biochar, weakening of dominant species and additional introduction of EMs in low liveness.

Role of Lakes, Flood, and Low Flow Events in Modifying Catchment‐Scale DOC:TN:TP Stoichiometry and Export

AbstractThe balance of organic carbon (OC), nitrogen (N) and phosphorus (P) plays a crucial role in determining the processing, retention, and movement of these solutes across the aquatic continuum. Floods and droughts can significantly alter the quantity and ratios of OC:N:P export within inland waters, but how these ratios change, and are coupled within watersheds that integrate rivers and lakes, is not well known. We investigated the stoichiometry and export of dissolved organic carbon (DOC), total N (TN) and total P (TP) in two lake watersheds (10 inflows, 2 outflows) in the southern Boreal Shield over a 37‐year period. Although DOC, TN, and TP concentration behaved similarly, DOC:TN:TP ratios varied seasonally, strongly modulated by stream discharge. DOC:TN, DOC:TP and TN:TP export initially increased rapidly with increasing discharge, peaking at 10%–20% exceedance of the annual discharge for DOC:TP and TN:TP ratios, indicating a rapid depletion of catchment OC sources. Both flood and low flow events resulted in lower DOC:TN and lower DOC:TP export—thereby increasing the relative contributions of stream TN and TP. Consequently, elevated annual discharge coupled with infrequent but high floods and periods of low flow events increased the contributions of TN and TP relative to DOC. Overall, the lakes retained DOC, while increasing TN relative to TP. Nonetheless, the flow regime played a role in modulating nutrient retention in the lakes, likely due to changes in residence time, and the interplay of physical, photochemical, and biological degradation processes.

A diverse influence of dissolved natural organic matter on light irradiance measurements in lakes

Abstract Light penetration plays a vital role in lakes and drinking water reservoirs, influencing fundamental processes such as primary production and thermal budgets. The Secchi depth (ZSD) and the compensation depth (ZCD) are commonly used measurements in this context. ZSD is determined through visual inspection using a Secchi disc, while ZCD represents the depth at which photosynthetic activity balances respiration and can be measured using a quantum irradiance sensor. Through in situ water-core samples from 23 lakes within a lake district in Southeastern Norway, we observed that DNOM exerts a diverse influence on these light irradiance measurements. If DNOM concentrations are reduced to half or a quarter of the current concentration, similar to what was measured during the 1980s, the median ZCD:ZSD ratios are estimated to have decreased by approximately 30 and 60% since then, respectively. Conversely, a plausible future climate-driven doubling or quadrupling of the present DNOM concentrations are estimated to further decrease the median ZCD:ZSD ratios in the lake district with approximately 10 and 25%, respectively. From this, the ZCD:ZSD ratios seem to have experienced a considerable long-term decline attributed to both climate change and the recovery from acid rain, and a further climate-driven decrease is expected.

Environmental predictors of lake fish diversity across gradients in lake age and spatial scale

Abstract Freshwater ecosystems have experienced a great loss of biodiversity in the recent century due to eutrophication and loss of habitats, particularly in agricultural lowlands. Some of these ecosystems have recently been re‐established, or entirely new lakes have been created to improve nutrient removal, biodiversity, and recreation. Fish have an important structuring role in lake ecosystems, but little is known about the temporal development of fish species richness or composition in new or re‐established lakes, especially in comparison with natural lakes. We investigated the influence of environmental variables and landscape features on fish species richness and fish assemblage in drainage basins and in 34 new (between 0 and 99 years) and 193 natural lakes in Denmark, using structural equation modelling. Fish species richness in drainage basins is influenced primarily by basin elevation, lake area, and salinity at the basin outlet; low‐salinity coastal regions are important migration pathways for many freshwater fish species, not just for anadromous or catadromous species. Land use does not appear to influence richness at the drainage basin scale, indicating that the influence of anthropogenic activities is minor or that significant effects thereof occurred a long time ago (decades to centuries). The drainage basin richness defines the apparent pool of species that may colonise lakes within the basin, but the actual number of species is particularly influenced by stream network connectivity. Disconnected lakes have fewer species, a deficit that is sustained over long time scales. In addition to the influence of stream connectivity, lake characteristics such as elevation, surface area, and water chemistry (alkalinity and pH) are also important predictors of fish species richness, whereas we did not find any effect of lake nutrient concentrations. The direct effect of land use was not evaluated. Ordination analysis shows that fish assemblage depends on both lake type (new/natural) and stream connectivity (connected/disconnected). Furthermore, species‐specific occurrences reveal some differences between new and natural lakes and indicate that stocking plays a role in new lakes. While new and natural lakes may initially differ in terms of both how many and which species they contain, they converge over time in a process that can be enhanced by improving stream connectivity.

Lakes protect downstream riverine habitats from chloride toxicity

AbstractFreshwater salinization from anthropogenic activities threatens water quality and habitat suitability for many lakes and rivers in North America. Recognizing that salinization is a stress on freshwater environments globally, research on watershed salt transport is necessary for informed management strategies. Prior to this research, there were few studies that examined salt export regimes along a river–lake continuum to investigate the drivers, temporal dynamics, and modulators of freshwater salinization. Here, we use high‐frequency in situ monitoring to assess specific conductance–discharge (cQ) relationships, chloride concentrations and fluxes, and the role of lakes in downstream salt transport. The Upper Yahara River Watershed in southern Wisconsin, USA, is a mixed urban and agricultural watershed where the lakes' chloride concentrations have risen from < 5 mg L−1 in the 1940s to > 50–80 mg L−1 in 2021. Our results suggest cQ behavior depends on land use, with urban areas exhibiting more frequent mobilization events during stormflow and agricultural areas exhibiting predominantly dilution dynamics. In addition, chloride loading is driven by hydrology and watershed size whereas concentrations and yields are a function of anthropogenic drivers like urbanization. We demonstrate how an in‐network lake attenuates downstream salinity, dampening the hydrologic, anthropogenic, and seasonal patterns observed in rivers upstream of the lake. Importantly, biogeochemical processes in lakes overlay a seasonal signal on salinity that must be considered when investigating temporal dynamics of anthropogenic salinization. This research contributes to understanding of temporal dynamics of salt export through watersheds and can be used to inform management strategies for habitat protection.

Metagenomics reveals the diversity and role of surface-water microbes in biogeochemical cycles in lakes at different terrain ladders

As the most important component of ecosystems, microbial communities play a significant role in global biogeochemical cycles. Geographical barriers created by topographic differences are proposed as one of the main factors to shape microbial diversity, functional composition and their evolution across aquatic ecosystem. There are few studies that compare the microbial community structure and functional potential of lakes with different terrain ladders (terrains of contrasting elevation levels), especially those involving Qinghai-Tibet Plateau. This study compared microbial 16S rRNA data from 51 lakes with different terrain ladders, showing that the composition of the dominant microbial community was similar, but the microbial abundance was quite different in different terrain ladders. Actinobacteria, Proteobacteria, Cyanobacteria, Planctomycete, Verrucomicrobia and Bacteroidetes were the dominant taxa. Through the correlation analysis between environmental factors and the microbial community structure, it was found that two environmental factors (elevation and salinity) had significant contributions to the microbial composition. Metagenomics of six representative lakes revealed the relationship between microbial composition and metabolic processes related to carbon, nitrogen and sulfur cycles. The comparative analysis of genes related to metabolism cycles showed that functional processes such as aerobic respiration, nitrogen assimilation, the mineralization of nitrogen and sulfur had highest metabolic potential in the ecosystems. The analysis of indicator species based on the metabolic process in the carbon, nitrogen and sulfur cycles showed that the microbial community structure is related to the dominant metabolic functions within biogeochemical cycles. Different dominant species play an important and distinct role in lakes with different gradients. Actinobacteria, Cyanobacteria and Proteobacteria were the most important indicator species on the Qinghai-Tibet Plateau, Yunnan-Guizhou Plateau and the middle and lower reaches of the Yangtze River Plain, respectively. In general, this study explored the functional distribution patterns of the dominant microbial communities in the lakes in biogeocycles.

Controls on Terrestrial Carbon Fluxes in Simulated Networks of Connected Streams and Lakes

AbstractInland waters play a critical role in the carbon cycle by emitting significant amounts of land‐exported carbon to the atmosphere. While carbon gas emissions from individual aquatic systems have been extensively studied, how networks of connected streams and lakes regulate integrated fluxes of organic and inorganic forms remain poorly understood. Here, we develop a process‐based model to simulate the fate of terrestrial dissolved organic carbon (DOC) and carbon dioxide (CO2) in artificial inland water networks with variable topology, hydrology, and DOC reactivity. While the role of lakes is highly dependent on DOC reactivity, we find that the mineralization of terrestrial DOC is more efficient in lake‐rich networks. Regardless of typology and hydrology, terrestrial CO2 is emitted almost entirely within the network boundary. Consequently, the proportion of exported terrestrial carbon emitted from inland water networks increases with the CO2 versus DOC export ratio. Overall, our results suggest that CO2 emissions from inland waters are governed by interactions between the relative amount and reactivity of terrestrial DOC and CO2 inputs and the network configuration of recipient lakes and streams.

Primary production modeling identifies restoration targets for shifting shallow, eutrophic lakes to clear-water regimes

Benthic primary production (BPP) plays an important functional role in lakes, improving water quality by stabilizing clear-water regimes. Shallow, eutrophic lakes lacking BPP communities can be difficult to restore because self-stabilizing feedbacks of phytoplankton dominance can impede the establishment of BPP. BPP in lakes is light limited, and ecosystem models can provide guidance for determining the water clarity necessary to re-establish BPP dominance. We developed a multi-tiered framework for the restoration of shallow, eutrophic lakes that incorporates multiple turbidity sources, lake morphometry, and water-level fluctuations to determine water-clarity thresholds above which BPP dominance may be established. We present a case study applying this restoration target framework to a large, shallow lake (Utah Lake, Utah, USA), where water clarity was greatly impeded by sediment resuspension and high algal biomass. Our analysis, which used commonly available lake-monitoring data, indicated that a return to BPP dominance is possible in Utah Lake, particularly if external nutrient loading to its shallow, wind-protected bays is reduced. Our novel framework incorporates regime shift theory to improve shallow, eutrophic lake restoration efforts. By incorporating ecological feedbacks when identifying the restoration targets necessary for returning a lake to a self-stabilizing, clear-water regime, this restoration target framework offers economical and logistical advantages over strategies that focus solely on phytoplankton management or fish biomanipulation.

A novel approach for accurate quantification of lake residence time — Lake Kinneret as a case study

Water residence time, which is affected by increasing water demands and climate change, plays a crucial role in lakes and reservoirs since it influences many natural physical and ecological processes that eventually impact the water quality of the waterbody. Thus, accurate quantification of the water residence time and its distribution is an important tool in lake management. In this study we present a novel approach for assessing the residence time in lakes and reservoirs. The approach is based on the Leslie matrix model that was originally developed for the analysis of age-structured biological population dynamics. In this approach the water in the lake is divided into different age classes each representing the time since the “parcel” of water entered the lake and provides an overall picture of the water age structure. The traditional approach for calculating residence times, which relies only on the lake volume and annual inflow or outflow volumes thereby disregarding any previous information, is very sensitive to large interannual variation. While the proposed approach produces the fraction and volume distribution curves of all age classes within the lake for each simulated timestep. Thus, in addition to mean residence time, the fraction of young water (FYW), quantifying the “young” fraction of water in the lake can be analyzed. The same is true for any other age class of water.The approach was applied to Lake Kinneret (Sea of Galilee) historical data collected over 32 years (1987-2018) and for prediction of long-term time series based on several future scenarios (inflows and outflows). It offers a more accurate quantification of the mean residence time of water in a lake and can easily be adapted to other waterbodies. Comparison of simulation results may serve as basis for determining the lake's management policy, by controlling the inflows and outflows, that will affect both the mean residence time and the fraction of “young/old” age classes of water.

Shoring up the foundations of production to respiration ratios in lakes

AbstractThe ratio of primary production to ecosystem respiration rates (P:R ratio) is an ostensibly simple calculation that is used to characterize lake function, including trophic status, the incorporation of terrestrial organic carbon into lacustrian food webs, and the direction of carbon dioxide (CO2) flux between a lake and the atmosphere. However, many predictive links between P:R ratios and lake ecosystem function stem from a historically plankton‐centric perspective and the common use of the diel oxygen curve approach. We review the evolution of the use of P:R ratios and examine common assumptions underlying their application to (1) eutrophication, (2) carbon flux through lake food webs, and (3) the role of lakes in the global carbon budget. Foundational P:R studies have been complicated principally by the following: most P:R ratios were calculated from mid‐lake measurements and failed to incorporate nonplanktonic dynamics; there has been confusion regarding the food web implications when P:R ≠ 1; and CO2 fluxes between lakes and the atmosphere are influenced by nonmetabolic processes. We argue for a re‐assessment, or shoring up, of several fundamental assumptions that continue to guide metabolism research in lakes by accounting for mixing, benthic‐littoral processes, groundwater fluxes, and abiotic controls on gas dynamics to better understand lake food webs and accurately integrate lake ecosystems into landscape‐scale carbon cycling models.

Beavers in lakes: a review of their ecosystem impact

The aim of this review is to analyze the literature on the impact of beavers on lakes, summarize their effects, describe consequences for biotic and abiotic components, and highlight unresolved issues and perspectives. Beaver activity changes vegetation structure to the greatest extent, indirectly affecting other ecosystem components. Damming of flowing lakes increases the littoral area, which affects diversity and abundance of invertebrates, amphibians, birds, and mammals. Beavers’ alteration of the water regime and heterogeneity and connectivity of habitats has significant effects on zoobenthos, fish, and amphibians. Changes in hydrochemical properties directly affect phytoplankton and benthos. Unlike river ecosystems, where habitats are altered from flowing to still water, in lake ecosystems, habitat type is not usually changed (from lotic to lentic) but their quality (e.g., heterogeneity, connectivity) is. Beaver activity in rivers leads to increased limnophilic biodiversity, but in lakes, it leads to conservation of pre-existing lentic ecosystems. Therefore, impacts of beavers could be of greater importance to limnophilic complexes in lakes than to streams, especially after long time of beaver absence. Digging activity has a more significant role in lakes (especially floodplain) than in rivers. Beaver alteration of heterogeneity and connectivity of habitats is well studied, but not enough is known about impacts on the water regime of seasonally flowing waters, hydrochemical changes (especially eutrophication), amphibian life cycles, phytoplankton and zooplankton communities, parasitocenoses, and coarse woody debris. Methodological difficulties are noted, which are associated with the correct choice of control lakes. Further studies on riverine lakes are crucial. In considerations of climatic changes and anthropogenic impact, beavers may be an additional aid to conserving small lake ecosystems.

Seasonal changes in primary production and respiration in a subtropical lake undergoing eutrophication.

The balance between gross primary production (GPP) and respiration (R) is frequently used to estimate the role of lakes in the carbon cycle. Seasonal changes in the carbon cycle of subtropical lakes are often underestimated, but changes in meteorological and limnological characteristics often follow the well-defined climatic seasons. Based on 1year's free-water dissolved oxygen and temperature measurements, we investigated the seasonal changes in primary production and respiration in subtropical Peri Lake in Southern Brazil, which is currently undergoing eutrophication. We expected that periods of high light availability and temperature would lead to a net autotrophic condition. Furthermore, we explored the seasonal coupling between GPP and R, expecting that different sources of organic matter would have different effects on the metabolic rates. We found that Peri Lake was predominately net heterotrophic (GPP <R). GPP was high during summer and autumn and low in winter, as was R, coinciding with the seasonal changes occurring in light and temperature. Light conditions were of essential importance for the variations in GPP, while respiration was fueled by both autochthonous and allochthonous organic matter. Constant external input of organic matter resulted in a generally low coupling between GPP and R. A tighter coupling between GPP and R was observed in spring as a result of higher productivity, while a decoupling in autumn was due to intensified allochthonous organic matter runoff caused by rainfall and wind. We found that higher productivity rates in summer did not shift the system to an autotrophic condition and that Peri Lake functioned as a carbon source, light and organic matter being the prime drivers for the metabolic rates.

Denitrification and dissimilatory nitrate reduction to ammonium in freshwater lakes of the Eastern Plain, China: Influences of organic carbon and algal bloom

Denitrification (DNF) and dissimilatory nitrate reduction to ammonium (DNRA) are critical dissimilatory nitrate reduction pathways that determine nitrogen (N) removal and internal recycling in aquatic environments. However, the relative important of DNRA, and the influences of environmental factors on DNF and DNRA, have not been widely studied in freshwater lakes. In our study, we used N isotope-tracing to investigate the potential rates of DNF and DNRA in 27 lakes from the Eastern Plain Lake Zone (EPL), China. In the EPL lakes, DNF was the dominant nitrate reduction process, however DNRA was still important, accounting for around 4.3%–21.9% of total nitrate reduction. The sediment organic carbon was the primary factor controlling the rates of dissimilatory nitrate reduction, accounting for 28.3% and 37.9% of the variance in DNF and DNRA rates, respectively. High algal biomass accelerated DNF rates, while indirectly affected DNRA via changing the quality of organic carbon. The greater contributions of DNRA to dissimilatory nitrate reduction were found in lakes with higher sulfate concentrations. DNRA coupled to sulfur cycling may play an important role in lakes with high sulfate concentrations and high sediment organic carbon. This study highlights the important role played by DNRA in total nitrate reduction pathways of freshwater lakes. Mitigation strategies for N pollution and algal blooms should not only target decrease of nutrient input, strategies should also create a suitable environment for improving N removal and inhibit N recycling.

Role of flow-through lakes in reducing pollutants outgoing from rural areas

This study assessed the water quality in Lake Wydmińskie (Warmińsko-Mazurskie Voivodeship) based on the content of both organic and inorganic pollutants flowing into the lake with water from drainage systems. The study demonstrated that the water flowing into the lake through drainage ditches that drain the improved part of the catchment area of the lake, was a potential source of diffuse pollutants and excess chemical components were deposited in the lake which could lead to its degradation. The most polluted water was found in the main tributary and the lake bay fed by its water. For this reason, it was concluded that the greatest problem was the area-wide sources of pollutants outgoing from agricultural areas. It was also found that water flowing out of the lake was of a considerably better quality than water flowing into the lake through the ditches. This clearly indicates the accumulative role of the lake on the route of pollutant migration from agricultural sources.

Simulations of the Impact of Lakes on Local and Regional Climate Over the Tibetan Plateau

ABSTRACTBecause of the high elevation and complex topography of the Tibetan Plateau (TP), the role of lakes in the climate system over the Tibetan Plateau is not well understood. For this study, we investigated the impact of lake processes on local and regional climate using the Weather Research and Forecasting (WRF) model, which includes a one-dimensional physically based lake model. The first simulation with the WRF model was performed for the TP over the 2000–2010 period, and the second was carried out during the same period but with the lakes filled with nearby land-use types. Results with the lake simulation show that the model captures the spatial and temporal patterns of annual mean precipitation and temperature well over the TP. Through comparison of the two simulations, we found that the TP lakes mainly cool the near-surface air, inducing a decreasing sensible heat flux for the entire year. Meanwhile, stronger evaporation produced by the lakes is found in the fall. During the summer, the cooling effect of the lakes decreases precipitation in the surrounding area and generates anomalous circulation patterns. In conclusion, the TP lakes cool the near-surface atmosphere most of the time, weaken the sensible heat flux, and strengthen the latent heat flux, resulting in changes in mesoscale precipitation and regional-scale circulation.

Trophic status may influence top–down effects of anadromous alewife Alosa pseudoharengus (Actinopterygii, Clupeidae) in lakes

We investigated the seasonal influence of an effective size-selective planktivore, the anadromous alewife (Alosa pseudoharengus Wilson), on summer zooplankton and phytoplankton communities in a series of lakes in Maine, USA (4 with and 4 without alewife) that ranged from oligotrophic to eutrophic to determine the role of lake trophic state in influencing the relative strength of top–down forces on phytoplankton biomass. Predation by young of the year alewife reduced the mean body length of cladoceran and copepod biomass from spring to summer in alewife lakes, while mean body length remained unchanged in nonalewife lakes. Cladoceran biomass decreased substantially from spring to summer in 3 of 4 alewife lakes, increasing only in the most eutrophic lake. Conversely, cladoceran biomass increased from spring to summer in 3 of 4 nonalewife lakes. Predation by alewife on zooplankton did not have consistent cascading effects on phytoplankton biomass. Analysis of planktonic biomass ratios (phytoplankton biomass: zooplankton biomass) suggests that cascading effects were stronger in oligotrophic systems and weakened with increasing trophic status, as ratios in alewife and nonalewife lakes converged at higher total phosphorous levels. Our results suggest that lake trophic status may influence the relative importance of top–down control of both zooplankton and phytoplankton biomass. The mechanisms that explain this pattern remain elusive and likely require additional efforts to estimate alewife densities, rates of zooplankton and phytoplankton production relative to consumption, and the influence of other physical lake features.

The rotifer community and its functional role in lakes of a neotropical floodplain

Aquatic communities vary depending on local factors, such as environmental conditions and biological interactions and regional factors, such as the hydrological regime in floodplains. This study analyzed the community structure of rotifers and their secondary production in two lakes of an Upper Paraná River floodplain (Brazil) differing in their hydrology: one connected to the river and the other isolated. Integrated samples of the water column were collected daily during 15 days in the low and high water periods. Three statistical methods, ANOVA, MRT, and IndVal were applied to distinguish the structure, biomass, and secondary production of their rotifer communities. The rotifer fauna was rich (91 species). Temperature, an indicator of seasonal change, and hydrological connection to river were major factors structuring rotifer communities. The community presented differences between periods in the isolated lake, but had a higher stability in the connected lake. We identified 34 indicator species of the groups formed by the MRT analysis. Production was low and consistent in the connected lake (∼1.5 µg DW m−3 day−1), being higher and more variable in the isolated lake (peaking at ca. 60–90 µg DW m−3 day−1). Results also showed that changing environmental conditions verified in the low water period and in the isolated lake were determinant for both the community structure and the secondary production of rotifers. We demonstrate that not only flooding but also the levels of isolation from the river during low water period are the driving forces for the structure and dynamics of organisms in floodplains. Thus, the isolated lakes represent important areas for rotifer biodiversity.

Interactive lakes in the Canadian Regional Climate Model, version 5: the role of lakes in the regional climate of North America

ABSTRACTTwo one-dimensional (1-D) column lake models have been coupled interactively with a developmental version of the Canadian Regional Climate Model. Multidecadal reanalyses-driven simulations with and without lakes revealed the systematic biases of the model and the impact of lakes on the simulated North American climate.The presence of lakes strongly influences the climate of the lake-rich region of the Canadian Shield. Due to their large thermal inertia, lakes act to dampen the diurnal and seasonal cycle of low-level air temperature. In late autumn and winter, ice-free lakes induce large sensible and latent heat fluxes, resulting in a strong enhancement of precipitation downstream of the Laurentian Great Lakes, which is referred to as the snow belt.The FLake (FL) and Hostetler (HL) lake models perform adequately for small subgrid-scale lakes and for large resolved lakes with shallow depth, located in temperate or warm climatic regions. Both lake models exhibit specific strengths and weaknesses. For example, HL simulates too rapid spring warming and too warm surface temperature, especially in large and deep lakes; FL tends to damp the diurnal cycle of surface temperature. An adaptation of 1-D lake models might be required for an adequate simulation of large and deep lakes.

Multi-temporal assessment of bio-physical parameters in lakes Garda and Trasimeno from MODIS and MERIS

Lake surface temperature (LST) reflects meteorological and climatological forcing more than any other physical lake parameter. LST is also strongly related to the mean temperature of the upper stratum which plays an important role in lake’s biology depending, among other factors, on the dynamics of phytoplankton and thence of chlorophyll-a concentrations (chl-a). Satellite remote sensing is a valuable tool to study these two bio-physical parameters by providing synoptically data at spatial/temporal resolutions not achievable with traditional techniques. In this study MODIS and MERIS data are used to assess LST and chl-a concentration in two important Italian lakes. Images data of Lake Garda in the time range from 2�� 4 to 2�� 9 and Images data of Lake Garda in the time range from 2�� 4 to 2�� 9 and mages data of Lake Garda in the time range from 2�� 4 to 2�� 9 and of Lake Trasimeno from 2�� 5 to 2�� 8 were used. The complexities of processes dealing with lacustrine ecosystems is reflected by the weak of correlation found between chl-a and LST in both lakes by using the entire dataset. However, by considering the time of the year with highest biological activity (i.e. from the end of spring to mid of summer) a positive correlation ( the end of spring to mid of summer) a positive correlation ( ) a positive correlation (r>� .5) was found between the two parameters in Lake Trasimeno. This behaviour was also observed in Lake Garda by considering LST and chl-a data from different areas. In particular the shallower south-east basin of Lake Garda was characterised by higher LST and chl-a concentrations.