Natural Water Level Fluctuations Research Articles

Effects of constant high water levels in winter on waterbird diversity in Caizi Lakes: A functional perspective

The middle and lower Yangtze River floodplain lakes are important stopover and wintering sites for migratory birds on the East Asian–Australasian Flyway. The periodic water level fluctuation of the lakes plays a critical role in the aggregation of waterbirds. However, the construction of a series of gates and dams has impeded the hydrological connectivity between rivers and lakes and disrupted the natural water level fluctuation patterns of lakes. The water level status of lakes influences habitat utilization by waterbirds. In recent years, Caizi Lakes, the gate-controlled lakes connected to the Yangtze River due to the need for water level regulation requirements, has experienced sustained high water levels in winter, which can reduce habitat quality and in turn influence waterbirds activity. In the present study, wintering waterbirds in Caizi Lakes were surveyed during the 2021–2022 (W1) and 2022–2023 (W2) wintering periods. Moreover, we explored the effects of constant high water levels in winter on waterbird assemblages by comparing species richness, abundance, and functional alpha and beta diversity. Correlation analyses were then performed to elucidate the relationship between habitat factors and water level changes during the wintering period of migratory waterbirds and between changes in various habitat factors and wintering waterbird assemblages under different hydrological conditions. The results showed that functional beta diversity was more sensitive to changes in waterbird assemblages in Caizi Lakes than functional alpha diversity. Moreover, constant high water levels in the mid-wintering period decreased suitable habitats for wintering waterbirds, increased functional turnover among waterbird assemblages, increased total dissimilarity among assemblages significantly, and decreased the level of functional nestedness significantly. Additionally, the areas of the three wetland habitats in Caizi Lakes were significantly correlated with water level changes during W1 and relatively less affected by water level changes under constant high water level conditions during W2. The changes in habitat area were influenced primarily by anthropogenic activities, with an increase in meadow area favorable for species richness and abundance, as well as functionally nested components. Water level regulation should take into consideration the natural hydrological rhythms of the declining water level to ensure that adequate and suitable habitats are provided for wintering waterbirds.

Comparative flooding tolerance of Typha latifolia and Phalaris arundinacea in wetland restoration: Insights from photosynthetic CO2 response curves, photobiology and biomass allocation

Tall helophytes such as Typha latifolia and Phalaris arundinacea often rapidly colonise after rewetting of former agricultural soil and are therefore often the first plants to contribute to the soil carbon pool. In this study we carried out a mesocosm experiment where these two species grew at three different water levels relative to the soil surface (−15 cm, 0 cm, +15 cm). After eight weeks' growth, measurements of photosynthetic CO2-response curves, stomatal conductance and chlorophyll fluorescence of photosystem II were carried out to detect flooding stress. After 10 weeks’ growth, the plants were harvested and biomass production, biomass allocation and specific leaf area were determined. T. latifolia had a higher and more stable photosynthetic performance across all water level treatments, which resulted in an overall higher aboveground and belowground production than P. arundinacea. In contrast, Vcmax and Jmax decreased by 41 % and 42 %, respectively from drained to flooded conditions with signs of flooding stress as impairment of the photosynthetic apparatus. Moreover, increasing water level resulted in maintenance of aboveground organs for P. arundinacea but a decrease in allocation to belowground organs. P. arundinacea did not invest in a higher specific leaf area to counter the decreased photosynthesis under flooding. From −15 cm to 0 cm water levels, P. arundinacea showed a 68 % reduction in belowground biomass, which has negative implication for carbon retention immediately after rewetting. In contrast, recolonization of T. latifolia is likely to be a suitable contributor to the soil carbon pool due to its stable physiology and high above- and belowground biomass production at all water depths, and also likely under natural water level fluctuations. We showed that even though both species are generally considered wetland plants, they are likely to support considerably different photosynthetic carbon assimilation and soil carbon sequestration rates.

Response of yellow perch to water level fluctuations in oligotrophic, north‐temperate inland lakes

AbstractInformation on yellow perch Perca flavescens population dynamics and responses to various abiotic and biotic factors in oligotrophic, north‐temperate inland lakes is limited. Water level fluctuations are known to influence available habitat and biological communities within the littoral zones of lakes, yet research is lacking for yellow perch in Wisconsin. The goal of our study was to characterize yellow perch population‐level responses to natural water level fluctuations in four northern Wisconsin lakes using a 39‐year time series. On average, increasing water level periods correlated with lower mean fyke net and gill net relative abundances (catch‐per‐unit‐effort), though generally not statistically significant. Yellow perch mean relative weight varied among lakes and was significantly greater during increasing water level periods for all lakes except one. The lack of statistically significant findings potentially suggests a buffering mechanism of north‐temperate oligotrophic lakes due to their small surface area to volume ratios, relative lack of nutrients, and(or) littoral structural habitat compared to other systems (e.g., shallow eutrophic lakes). Our results suggest that natural water level fluctuations may not be an environmental concern for yellow perch populations in some north‐temperate oligotrophic inland lakes.

Wrack line formation and composition on shores of a large Alpine lake: The role of littoral topography and wave exposure.

Wrack lines are a key formation along shorelines that provide organic matter and bring ecological diversity to the local environment. Although wrack line formation has been extensively studied along marine beaches and estuaries, in contrast, knowledge about the environmental variables that promote wrack line formation within inland lakes is widely lacking. In one of the first studies to focus on wrack line formation on lakesides, we analysed the dimensions, volume, elevation and particulate composition of 36 wrack lines across 20 shore sections of a large, oligotrophic Alpine lake with natural water level fluctuations (Lake Constance-Obersee). Using multivariate partial least squares (PLS) regression, we identified the key environmental variables that drive wrack accumulation in lakeside areas. Our results demonstrate that wrack line volume increased with (1) the width of the eulittoral zone as an indicator of the swash conditions (up-rush vs. down-wash), (2) high exposure to wind waves as indicated by the total effective fetch, (3) high exposure to ship waves (catamaran ferry), and (4) the width of the sublittoral zone as an indicator of the availability of source material (Chara spp.) and of the wave energy dissipation rate of the incoming deep water waves. Sediment texture played only a minor role. Wide eulittoral zones and high ship wave exposure favoured high proportions of lake-borne components (Chara remains, mollusc shells), while the reverse was true for land-based components. Anthropogenic wastes were only present in small proportions. We discuss four main factor groups influencing the amount of wrack in marine beaches and on lakeshores considering similarities (waves, breakers, swash, dissipation, relief) and differences (tides vs. annual water level fluctuations) of the two systems, and point out research gaps. We demonstrate that wrack line formation is also important in large inland lakes and can be analysed using basic ideas from relevant marine studies.

Water level fluctuations associated with hydrological connectivity consolidate the food web stability of the largest Chinese freshwater lake via mediating trophodynamics and trophic structure

Variation in hydrological connectivity (HC) between rivers and lakes gives rise to periodic large water level fluctuation (WLF) in river-connected lakes (RCL). However, how WLF shapes the material cycling and concomitant trophodynamics of RCL remain unclear. Here we evaluated the resource availability, relative contributions of autochthonous and allochthonous carbon sources (by Bayesian mixing models) and trophic structure (using δ13C and δ15N) of Lake Poyang, the largest freshwater lake in China, during different hydrological periods. Terrestrial C3 plants in the aquatic/terrestrial transition zones (ATTZ) were the main supporter of aquatic consumers all year round. Compared with historical data, the contributions of autochthonous production to aquatic food webs were low. This is primarily ascribed to the influences of hydrological regimes in that the operation of Three Gorges Dam and HC changed the rhythm of WLF in Lake Poyang, restricting the production of aquatic vegetation and epiphytic algae. Most common fish species indicated higher trophic positions (TPs) during the dry than wet season, but only eleven of thirty-six common species showed a statistically significant increase (p < 0.05). Our study reveals a relatively consistent trophic diversity of consumer communities (fish and aquatic invertebrates) during dry and wet seasons, but each trophic guild showed specific trophic response to WLF, as they flexibly adjusted feeding strategies and the degree of trophic niche differentiation. Although WLF triggered fluctuations in the resource availability and species composition of lake food webs, and the TPs and trophic niches of aquatic consumers during different hydrological periods, the resource diversity and habitat complexity driven by HC and WLF reduced the strength of trophic interactions, and thus resulted in overall stability of food web trophodynamics and trophic structure of Lake Poyang. Our findings highlighted the importance of HC and natural WLFs in maintaining the ecosystem stability of large floodplain lakes, and that seasonal WLF patterns should be maintained in future floodplain lake management to conserve biodiversity and the resilience of ecological functions.

Responses of lakeshore herbaceous plant guilds to altered water level fluctuations in Yangtze floodplain lakes, China

River–lake disconnection has led to alterations in natural water level fluctuations (WLFs) in lakes along the middle and lower reaches of the Yangtze River to various extents. To predict the effects of altered WLFs on lakeshore vegetation, lakeshore herbaceous plant guilds (LPGs) in six Yangtze floodplain lakes were classified in this study. The lakeshore herbaceous plant distribution pattern, main influencing factors, and responses of different LPGs to altered WLFs were analyzed. A total of 130 plant species were identified from the six lakes. With the increase in the amplitude of WLFs, the total species number in the six lakes showed a hump–shaped trend, whereas the lakeshore herbaceous plant coverage showed a positive correlation. The Qili Lake with the largest WLFs had the lowest species number and highest plant coverage. The species numbers, average biomass, and coverage of lakeshore herbaceous plants in all the six lakes were obviously higher in spring than in autumn. The lakeshore herbaceous plants in the six lakes were classified into eight guilds. Small differences in pH, organic matter, total nitrogen, and total phosphorus were detected in the substrate among the eight LPGs, but obvious differences in soil moisture content and duration and depth of submergence were observed. The canonical correspondence analysis showed that the main environmental factors affecting the distribution of different LPGs in the six lakes in spring and autumn were the amplitude of WLFs and duration of submergence. The regression analyses showed that the biomass of perennial mesophyte with erect stem guild and perennial hygrophyte with well–developed rhizome guild responded sensitively to alterations in the amplitude of WLFs and duration of submergence, and the guilds could be considered as indicator groups at a regional scale. Morphological parameters such as plant height, stem diameter, leaf thickness, and specific leaf area of the eight LPGs showed no significant linear relationships with the increase in WLFs. The use of these parameters in the evaluations of alterations in WLFs needs to be further analyzed.

The level of water in the river flowing through the breeding site shapes the body condition of a lekking bird\u2014the Great Snipe Gallinago media

The display of lekking Great Snipe males is an energetically demanding activity and therefore, access to the rich feeding sites in the proximity of their leks is essential. During the breeding season, Great Snipes mostly prey on earthworms, whose availability is affected by moisture and penetrability of the soil. In this study, we investigated the relation between the body condition of displaying Great Snipe males and the water level of the river flowing through their breeding grounds, which can affect soil characteristics. We found that the body condition of males decreased over the course of the lekking period in May, showing the great energetic expenditure of their advertising display in courtship. The high water level in the river resulted in the increase in body condition of birds, probably due to improved prey availability, as earthworms moved closer to the ground surface in search of optimal conditions. Further rise in the water level caused flooding of the meadow and a decrease in the body condition of lekking Great Snipes, possibly because of the deterioration of feeding condition, as earthworms tend to leave flooded areas. Moreover, as the flooded area enlarged, the floodplain became inaccessible for foraging Great Snipes, due to their relatively short legs restricting them from wading in deep water. Our results show that for the lowland leks of the Great Snipe to be preserved it is advisable to allow for the natural water level fluctuations in the river shaping the hydrological conditions of the floodplains.

Biogeochemistry of Mediterranean Wetlands: A Review about the Effects of Water-Level Fluctuations on Phosphorus Cycling and Greenhouse Gas Emissions

Although Mediterranean wetlands are characterized by extreme natural water level fluctuations in response to irregular precipitation patterns, global climate change is expected to amplify this pattern by shortening precipitation seasons and increasing the incidence of summer droughts in this area. As a consequence, a part of the lake sediment will be exposed to air-drying in dry years when the water table becomes low. This periodic sediment exposure to dry/wet cycles will likely affect biogeochemical processes. Unexpectedly, to date, few studies are focused on assessing the effects of water level fluctuations on the biogeochemistry of these ecosystems. In this review, we investigate the potential impacts of water level fluctuations on phosphorus dynamics and on greenhouse gases emissions in Mediterranean wetlands. Major drivers of global change, and specially water level fluctuations, will lead to the degradation of water quality in Mediterranean wetlands by increasing the availability of phosphorus concentration in the water column upon rewetting of dry sediment. CO2 fluxes are likely to be enhanced during desiccation, while inundation is likely to decrease cumulative CO2 emissions, as well as N2O emissions, although increasing CH4 emissions. However, there exists a complete gap of knowledge about the net effect of water level fluctuations induced by global change on greenhouse gases emission. Accordingly, further research is needed to assess whether the periodic exposure to dry–wet cycles, considering the extent and frequency of the cycles, will amplify the role of these especial ecosystems as a source of these gases and thereby act as a feedback mechanism for global warming. To conclude, it is pertinent to consider that a better understanding about the effect of water level fluctuations on the biogeochemistry of Mediterranean wetlands will help to predict how other freshwater ecosystems will respond.

Synergy between Satellite Altimetry and Optical Water Quality Data towards Improved Estimation of Lakes Ecological Status

European countries are obligated to monitor and estimate ecological status of lakes under European Union Water Framework Directive (2000/60/EC) for sustainable lakes’ ecosystems in the future. In large and shallow lakes, physical, chemical, and biological water quality parameters are influenced by the high natural variability of water level, exceeding anthropogenic variability, and causing large uncertainty to the assessment of ecological status. Correction of metric values used for the assessment of ecological status for the effect of natural water level fluctuation reduces the signal-to-noise ratio in data and decreases the uncertainty of the status estimate. Here we have explored the potential to create synergy between optical and altimetry data for more accurate estimation of ecological status class of lakes. We have combined data from Sentinel-3 Synthetic Aperture Radar Altimeter and Cryosat-2 SAR Interferometric Radar Altimeter to derive water level estimations in order to apply corrections for chlorophyll a, phytoplankton biomass, and Secchi disc depth estimations from Sentinel-3 Ocean and Land Color Instrument data. Long-term in situ data was used to develop the methodology for the correction of water quality data for the effects of water level applicable on the satellite data. The study shows suitability and potential to combine optical and altimetry data to support in situ measurements and thereby support lake monitoring and management. Combination of two different types of satellite data from the continuous Copernicus program will advance the monitoring of lakes and improves the estimation of ecological status under European Union Water Framework Directive.

Modeling on naturalization of inflow and outflow nutrients sources of Blue Nile River at the Lake Tana in Basaltic Plateau of Ethiopia

Lake Tana is the largest natural reservoir in Ethiopia and the head water of Abbay basin. However, after building of an irrigation weir and further lying Tunnel to Tana Belles, Lake Tana maximum amplitude of water level canges from 2.18 to 3.56 m that differ substantially in 1.38 m from amplitude of natural water level fluctuation. Understanding the natural characteristics of the Lake is important to know its water balance and for sustainable development. But it is difficult to study the natural characteristics of the Lake and its water balance using the regulated water level and outflow data sets. Thus it is evident that the regulated water level and outflow data sets have to be first naturalized before they are used for any analysis and modeling. Lake level and outflow data that have been collected since 1976 were considered to assess the regulation effect and then for naturalization. Inflows to the Lake from the main tributaries have also been collected to find if there are any correlations with either the Lake Level and/or the outflow. Regression analyses were used to develop the naturalization models. The regression analyses of flows from Gilgel Abay and Gummar with Lake Level shows that there is a very good correlation between them in different seasons. Besides, same has also been observed between Lake Level and out flow. These relationships can be used to naturalize the regulated outflow and water level.

Differences of Regulative Flexibility between Hydrological Isolated and Connected Lakes in a Large Floodplain: Insight from Inundation Dynamics and Landscape Heterogeneity

The inundation areas of floodplains are crucial to wetland ecosystems, especially in supporting biodiversity. Accurately identifying the spatial and temporal patterns of inundation areas is important for understanding floodplain ecosystem processes. Here, lakes in the Yangtze River Floodplain were divided into two types according to hydrological conditions: the natural connected lakes (Dongting Lake and Poyang Lake) with natural water level fluctuations and the isolated lakes (lakes in Jianghan Plain) with stable water levels. We established a method to identify inundation areas using multi-sources remote sensing data based on the Google Earth Engine. The dynamics of inundation areas were determined, and the relative indices were calculated in common year (2017) and a drought year (2018). The differences between the connected lakes and the isolated lakes were analyzed, and impacts of hydrological fluctuations on inundation area and habitat quality were evaluated. The results show that lakes with natural hydrological fluctuations have a greater regulative flexibility, with both patch density (PD) and submerged elasticity index (SEI) values higher than that of isolated lakes. The trend of the vegetation index in the connected lakes and in the isolated lakes is also different. The mean EVI in Dongting Lake and Poyang Lake showed a U-shaped trend which is similar to the shape of the trend of PD. The trend of mean enhanced vegetation index (EVI) in the isolated lakes is the opposite and has a lower range of variation over a year. This study provides new indicators and rapid methods for habitat quality assessment in floodplains, as well as presenting scientific information useful for improving wetland management in the middle and lower Yangtze River.

Do anthropogenic hydrological alterations in shallow lakes affect the dynamics of plankton?

• Plankton was affected differently by natural and anthropogenic water level changes. • Higher total plankton biomass with anthropogenic WL regulation. • Higher zooplankton species richness with anthropogenic WL regulation. • Higher phytoplankton species richness with natural WL changes. • Higher cyanobacterial microcystins concentration with anthropogenic WL regulation. Anthropogenic and natural climate-impacted water level (WL) fluctuations are one of many environmental problems affecting natural ecosystems. The aim of this study was to explain differences in the development of autotrophic and heterotrophic plankton in two shallow, temperate, embanked lakes with different modes of WL regulation. Lake Mytycze has natural WL changes supplied exclusively by precipitation; a decrease in water level was predominantly due to more evaporation than precipitation. In this lake, nutrient concentration, particulate matter, growth of toxigenic cyanobacteria and contamination with microcystins correlated positively with decreases in WL. Lake Tomaszne has anthropogenic WL regulation, elevated values of nutrients and particulate matter, but they were caused by the periodic, abrupt entrance of river waters rich in allochthonous nutrients, organic and inorganic particles. In this lake, a higher biomass of cyanobacteria was observed than in the lake with natural WL changes; the concentrations of intracellular microcystins in water correlated positively with the biomass of toxigenic species. In both lakes, decreases in the biomass of algivorous crustaceans correlated with the occurrence of cyanobacterial biomass. Biomasses of algivorous crustaceans increased abruptly when concentration of microcystins diminished below 2 μg∙dm −3 . These biomass peaks occurred due to rapid development of the cladocerans; Bosmina longirostris was found in the lake with natural WL changes and Daphnia cucullata was found in the lake with anthropogenic WL regulation. The development of predacious crustaceans was not related to the blooms of filamentous cyanobacteria or the biomass of algivorous crustaceans (as potential prey). In both lakes, Thermocyclops crassus and Mesocyclops leuckartii (Copepoda) contributed significantly to the biomass of predacious crustaceans; their abundance correlated positively with the amount of particulate matter, which was probably utilised as an alternative food source. These findings illustrate indirect influence of WL on plankton composition and biomass through alteration of environmental variables. The results indicate that the mode of WL regulation (natural vs anthropogenic) must be taken into consideration when estimating the influence of WL changes on plankton dynamics.

Assessing biological diversity and thermodynamic indicators in the dam decommissioning process

Abstract Water level regulation is one of the most common anthropogenic disturbances of lentic ecosystems, which is especially evident in shallow lakes. The objective of this study was to assess the ecological effects of water level regulation in a shallow lake using thermodynamic indicators to support decision makers in a dam decommissioning process. For that we tested three hypotheses: 1) the regulated lake supports lower taxonomic diversity than the naturally fluctuating lake; 2) the structure of the benthic macroinvertebrate assemblage is different in the regulated lake than in the naturally fluctuating lake; 3) the regulated lake supports less complex benthic macroinvertebrate assemblages than the naturally fluctuating lake. Our results show that the first hypothesis, tested using taxa richness, Shannon-Wiener and Simpson diversity indices, was not validated. The second hypothesis was tested using taxonomic composition and was validated, with the two types of lakes exhibiting dissimilar macroinvertebrate assemblages. The third hypothesis, tested using two thermodynamic based indicators, eco-exergy and specific eco-exergy, was partially supported, which was illustrated, overall, by higher eco-exergy (degree of complexity) of the benthic assemblages in the naturally fluctuating lake, although the specific eco-exergies (capacities to use external energy resources) were similar. As a whole, our results endorse the importance of natural water level fluctuations as a driving force in shallow lake ecosystems and reinforced the idea that dam decommissioning is a good option for restoring natural conditions in this type of ecosystem.

Ecological impacts of winter water level drawdowns on lake littoral zones: a review

Freshwater littoral zones harbor diverse ecological communities and serve numerous ecosystem functions that are controlled, in part, by natural water level fluctuations. However, human alteration of lake hydrologic regimes beyond natural fluctuations threaten littoral zone ecological integrity. One type of hydrologic alteration in lakes is winter water level drawdowns, which are frequently employed for hydropower, flood control, and macrophyte control, among other purposes. Here, we synthesize the abiotic and biotic responses to annual and novel winter water level drawdowns in littoral zones of lakes and reservoirs. The dewatering, freezing, and increased erosion of exposed lakebeds drive changes in the littoral zone. Shoreline-specific physicochemical conditions such as littoral slope and shoreline exposure further induce modifications. Loss of fine sediment decreases nutrient availability over time, but desiccation may promote a temporary nutrient pulse upon re-inundation. Annual winter drawdowns can decrease taxonomic richness of macrophytes and benthic invertebrates and shift assemblage composition to favor taxa with r-selected life history strategies and with functional traits resistant to direct and indirect drawdown effects. Fish assemblages, though less directly affected by winter drawdowns (except where there is critically low dissolved oxygen), experience negative effects via indirect pathways like decreased food resources and spawning habitat. We identify eight general research gaps to guide future research that could improve our understanding about the complex effects of winter drawdowns on littoral zone ecology.

Lake level fluctuations boost toxic cyanobacterial "oligotrophic blooms".

Global warming has been shown to strongly influence inland water systems, producing noticeable increases in water temperatures. Rising temperatures, especially when combined with widespread nutrient pollution, directly favour the growth of toxic cyanobacteria. Climate changes have also altered natural water level fluctuations increasing the probability of extreme events as dry periods followed by heavy rains. The massive appearance of Dolichospermum lemmermannii ( = planktonic Anabaena), a toxic species absent from the pelagic zone of the subalpine oligotrophic Lake Maggiore before 2005, could be a consequence of the unusual fluctuations of lake level in recent years. We hypothesized that these fluctuations may favour the cyanobacterium as result of nutrient pulses from the biofilms formed in the littoral zone when the lake level is high. To help verify this, we exposed artificial substrates in the lake, and evaluated their nutrient enrichment and release after desiccation, together with measurements of fluctuations in lake level, precipitation and D.lemmermannii population. The highest percentage of P release and the lowest C∶P molar ratio of released nutrients coincided with the summer appearance of the D.lemmermannii bloom. The P pulse indicates that fluctuations in level counteract nutrient limitation in this lake and it is suggested that this may apply more widely to other oligotrophic lakes. In view of the predicted increase in water level fluctuations due to climate change, it is important to try to minimize such fluctuations in order to mitigate the occurrence of cyanobacterial blooms.

The contribution of lake benthic algae to the sediment record in a carbonate mountain lake influenced by marked natural water-level fluctuations

Lake Tovel is an oligotrophic, meromictic, mountain lake of the Dolomites that undergoes marked seasonal water-level fluctuations (WLFs). We used neo- and paleolimnological data collected since 1999 to test the utility of algal and cyanobacterial pigments and diatom and chironomid biodiversity as proxies for WLF and to highlight the contribution of benthic algae to the sediment record. We found that detailed knowledge of present-day spatiotemporal patterns of WLF is essential for a complete and correct interpretation of paleolimnological data. Scytonemin, a cyanobacteria-specific photoprotective pigment, was produced by epilithic cyanobacteria in the depth zone affected by WLF and should be considered a proxy for the extent of WLF. The phytobenthos was as important as phytoplankton as a source of sedimentary pigments. We used information gained on the detailed distribution of diatoms at different depths and on different substrata in the 2 basins to show the probable location in the lake from which taxa in sediment cores originated to aid in interpretation of the sediment archive (including identification of periods of active hydrology). We sampled present-day chironomids in springs and streams feeding the lake and along a depth transect in the main basin. The taxa found were all rheophilic, crenophilous, or typical of the littoral zone of oligotrophic lakes. We interpreted sections of the cores containing large numbers of Orthocladiinae and Diamesinae head capsules as indicative of periods of active hydrology (including sudden and marked WLF) because the littoral taxa found in the cores must have been derived from the littoral zone by sediment focusing or slumps. Thus, we identified useful proxies of WLF in mountain, carbonate lakes.

Developing water level regulation strategies for macrophytes restoration of a large river-disconnected lake, China

Natural water regime is important for the germination, growth and distribution of aquatic plants. In order to restore the macrophytes of the Chaohu Lake, field investigations were conducted in 2010–2012, hydrological data were also collected for analysis. The results showed that macrophytes of the Chaohu Lake have changed greatly after disconnection from the Yangtze mainstem, and the alteration of natural water level fluctuation (WLF) was the primary factor. After disconnection, the water level of January–March was controlled and maintained at a higher level; while that of April–June was gradually decreased due to irrigation and flood control. Such a water level regime is completely opposed to the natural condition, and is unfavorable to the germination and growth of macrophytes. Combined the life history with hydrological data, we then analyzed the water level requirements of macrophytes in different life history stages. Based on the water demands of agriculture, industry, shipping and others, we developed specific measures for water level regulation, and tested using water budget equation. The results of this study should be useful for the recovery of aquatic vegetation in other similar regulated lakes.

Does distance between aquatic plant assemblages matter in defining similarity between them during high water‐level periods?

Aquatic environments are subject to natural water-level fluctuations. These fluctuations, in turn, are responsible for causing changes in biota in the aquatic environment, particularly those that colonize floodplains. The flood pulse concept predicts that water-level fluctuations are responsible for the formation of mosaics in biota at a small scale. During high water-level periods, however, there is evidence that the similarity among biological assemblages increases. Within this theoretical context, the present study focuses on determining whether or not the spatial distance between assemblages is a relevant factor for the similarity among them during high water-level periods and, if not, what environmental variables are associated with them? Accordingly, the present study evaluated the association between aquatic plant assemblages and some environmental variables, with emphasis on the spatial distance among assemblages. The study results indicated no association between the similarity of the assemblages and the spatial distances between them. The environmental variables most associated with the assemblages were the total phosphorus and nitrate concentrations. It was concluded that, during high water-level periods, the spatial distance between aquatic plant assemblages was not a relevant factor for greater similarity among them. Rather, the total phosphorus and nitrate concentrations were the environmental factors most associated with the assemblages.

Alteration of wetland hydrology in coastal lagoons: Implications for shorebird conservation and wetland restoration at a Ramsar site in Sri Lanka

Many of the world’s lagoons and estuaries, representing the most important habitat for shorebirds, are increasingly degraded, often associated with dramatic declines in shorebirds, particularly in Asia. We investigated effects of hydrology on shorebird communities of two coastal lagoons of a Ramsar site in south-east Sri Lanka. One of the lagoons (Bundala) experienced natural water level fluctuations, while the other (Embilikala) had high stable water levels (>10cm), maintained by inflows from irrigated agriculture. These inflows dramatically affected composition and abundance of shorebird communities and their prey. Tactile and visual foraging shorebirds were consistently more abundant on Bundala than Embilikala lagoon. Their feeding efficiency was significantly (50%) higher on Bundala, where large (500μm) benthic prey were more abundant than on Embilikala. Contrastingly, small (60μm) planktonic prey dominated the hydrologically stable Embilikala lagoon where pelagic foraging shorebird species dominated the shorebird community. On both lagoons, visual and tactile species foraged predominantly in shallow water (1–10cm). Pelagic shorebirds also foraged in water depths >10cm but 20% less efficiently than in shallower water. Effective shorebird conservation depends on reducing anthropogenic impacts that detrimentally affect functional processes and habitat value. The detrimental effect of altered hydrology on Embilikala lagoon could be reversed by diverting drainage water. Re-establishing a natural hydroperiod, would increase the productivity of the lagoon for foraging shorebirds. Restoration of shorebird habitat on this Ramsar site could also improve other ecosystem services such as fisheries and tourism. Changes to the hydrology of coastal lagoons elsewhere may be similarly affected.

Development and Evaluation of a Regulatory Model for Pesticides in Flooded Applications

The pesticides in flooded applications model (PFAM) is a regulatory model for government agencies and others interested in estimating water concentrations of pesticides used in flooded agriculture applications such as rice paddies and cranberries bogs. PFAM was designed around the specific parameters that are typically available for a pesticide risk assessment, thereby simplifying the model and allowing the user to concentrate on only the most relevant model inputs. The model considers the fate properties of pesticides and allows for the specifications of typical flooded agriculture management practices such as scheduled water releases and refills. It also allows for natural water-level fluctuations resulting from precipitation and evapotranspiration. Model quality assurance requirements for regulatory models aimed at protecting the public are that the models err on the high side of measured data and at the same time should not cause undue burden to stakeholders by being overly conservative. For the studies herein, PFAM did tend to err on the high side of the data yet provided more realistic estimates than the currently used methods, which thereby reduced stakeholder burden. As is also important for a regulatory model, PFAM is nonproprietary and freely available.