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Most information on rotifers living in lake sands comes from the 1930s, when the first reports on this subject by Jerzy Wiszniewski appeared. After some decline in the interest in lake psammon in the following years, research on lake psammon returned in the last decade of the twentieth century. The last comprehensive review of ecology of psammon Rotifera was included in the excellent 1998 publication by Schmid-Araya on Rotifera in interstitial sediments. More than 20 papers have been published since that time. So far, research conducted almost exclusively in the northern hemisphere have dealt with issues related to distribution of rotifers, their species structure and diversity as well as to their relation to abiotic and biotic factors. The aim of the present study was to collect all available information on psammon rotifers, assess the shortcomings in our knowledge and fill these gaps with the results of some of my recent research. The results of the study show that the species richness of this group in geographical terms is still unknown. It means we also do not know the level of endemism among the psammon rotifers. The role of psammon rotifers in benthic food webs is another issue requiring research. [ABSTRACT FROM AUTHOR]

Invasion of non-native fishes threatens freshwater biodiversity worldwide. Yet, detailed estimates of population demography for invasive species, such as population size and body size, are rarely integrated in evaluating aquatic community responses. Our study capitalised on detailed brook trout population demographic data collected for a replicated whole lake ecosystem experiment involving experimental harvesting of exotic brook trout in nine mountain lakes. We applied environmental DNA (eDNA) metabarcoding and morphological taxonomy to examine the response of crustacean zooplankton and macroinvertebrate communities to gradients in brook trout effective density and lake elevation. Density-dependent effects of brook trout on crustacean zooplankton and macroinvertebrate communities were detected even decades after their first introductions (between 1926 & 1980). However, they were moderated by environmental factors such as elevation, lake maximum depth and dissolved organic carbon. Elevation was important in structuring crustacean zooplankton and macroinvertebrate community composition. While there were differences in explanatory variables when describing communities characterized by eDNA metabarcoding and morphological taxonomy, the principal environmental factors that structured the communities were similar. Our paper highlights persisting density-dependent impacts of exotic trout on invertebrate communities even decades after first introduction, and it considers the conservation implications for lake restoration. [ABSTRACT FROM AUTHOR]

Water-level fluctuations (WLF) in lakes and rivers, especially their extent, frequency and duration, are dominant forces controlling the functioning of these ecosystems. In particular, WLF play an important role in the lake’s littoral and aquatic–terrestrial interface processes. WLF may take place on different spatial and temporal scales under natural conditions but water levels have been artificially modified in regulated lakes, and their impacts are expected to be enhanced within the actual global change scenarios with forthcoming management problems. This article presents an overview on the literature published on this important topic since 1991 by using journals indexed in the ISI Web of Knowledge. The overall objective was to examine temporal and spatial trends in publications on WLF, the specific aspect of WLF concerned and their main effects. Throughout the article we have used case studies to illustrate different effects of WLF on the variety of lake habitats and indicators that have been studied. Overall, the number of papers published on the subject since the 1990s has risen steadily, when less than ten papers were published each year; until 2006 and peaking in 2005. The greatest number of papers on WLF has been carried out in Europe and North America (c. 73%). These data also showed that the effects of WLF have not been studied equally for different groups of organisms. There is a greater interest on macrophytes, which are the most studied group of organisms (18.4% of the papers). Nearly 7% of the papers deal with algae, and zooplankton and invertebrates account for a 7% followed by fish. WLF effects on ecosystems are very complex, and the biological effects in lakes are greatest in shallow water and littoral areas, where even small changes in water levels can result in the conversion of large areas of a standing-water environment in air exposed habitats. Finally, these data might serve to highlight knowledge gaps still existing on this topic and, in particular, some of the approaches that can potentially contribute to solve several of these lacunae are explored. [ABSTRACT FROM AUTHOR]

Ichthyofauna in the littoral zone the southern extremity of Lake Baikal was investigated. Modern data were obtained on fish composition in waters most affected by anthropogenic factors, where the probability of resultant changes in the fish community is highest. Long-term fish sampling was carried out in the zone of discharge and spread of wastes from Baikal Pulp and Paper Mill (BPPM); in regions near urban settlements; and near shore-protection construction operations. The data were compared with material previously collected, and with fish communities sampled in distant (control) areas. Variations in the composition of community are shown: some species that used to be absent were recorded in these areas, and possible reasons for their appearance are discussed. No distinct changes in the littoral fish were found attributable to anthropogenic influences. Recommendations on ichthyologic monitoring are proposed. [ABSTRACT FROM AUTHOR]

Autotrophic lakes are regarded to function as net autotrophic systems in which mobilization of solar energy by phytoplankton, benthic algae, and macrophytes forms the base of primary production. However, they are also subsided by allochthonous inputs. In this paper, we tested three hypotheses explaining the role of allochthonous subsidies as a driving force of autotrophic, bacterial, and heterotrophic production. The studies for this paper were conducted every fortnight from November 2015 to October 2017 in a small, shallow, temperate, eutrophic lake supplied with waters from four streams and drained by a single outlet. Changes in plankton biomass as well as variations in environmental conditions were estimated on the basis of the samples and measurements collected vertically in the water column (every 0.5 m depth) in the central part of the lake. Loads of nutrients and organic and inorganic matter were measured in both the inlets and the outlet of the lake, and on the basis of the differences between input and output loading, the amount of allochthonous subsidies in the lake was computed. Allochthonous subsidies affected the autotrophic production directly by supplying assimilable nutrients, and indirectly by providing allochthonous organic matter that supplemented the diet of omnivores and thus hampered their grazing pressure on phytoplankton. Bacterioplankton utilized allochthonous organic matter as well as effectively competed with phytoplankton for allochthonous nutrients. Dominant species of heterotrophic plankton were feeding opportunists, and thus inputs of allochthonous subsidies indubitably fostered high biomass of these species in the periods of low availability of autochthonous sources of food. Our finding suggests that allochthonous subsidies significantly affect trophic structure and impact both autotrophic and heterotrophic mobilization of energy through food chains in freshwater ecosystems. [ABSTRACT FROM AUTHOR]

In many temperate oligotrophic lakes, algal accumulations can form below the mixing zone. However, Deep Chlorophyll Maxima (DCM) have also been found in some eutrophic, tropical lakes and in this paper we aim to identify if they are recurrent features in these kinds of lakes and to recognize the factors that favor their formation. We analyzed 5 years of thermal stratification, water quality, and chlorophyll a concentrations in a tropical eutrophic lake in Central Mexico. Thermal stratification patterns were characteristic of warm monomictic lakes. Full water column deoxygenation during winter mixing was recorded in 3 of the analyzed years, and an increase of ~ 1 °C in the hypolimnion was detected between 2011 and 2015. DCM were detected in 4 out of the 5 studied years, at the top of the hypolimnion when the water column was stratified (spring–summer). This study is the first report of recurrent DCM formation in the northern limit of the Neotropics. It confirms that high light penetration is a necessary condition for DCM. Stratified nutrients with epilimnetic P depletion are also factors favoring DCM formation. [ABSTRACT FROM AUTHOR]

Lake Balaton, the largest lake in Central Europe, underwent severe eutrophication from the 1960s to the 1990s, due to phosphorus loadings from external anthropogenic sources. The subsequent and complex eutrophication control and lake restoration program resulted in a significant decrease in the external phosphorus loading to the lake. Consequently, Lake Balaton has been returning to its former meso-eutrophic character. In this paper, we explore the long-term dynamics of chlorophyll a (Chl a) concentration, a proxy for phytoplankton biomass, and zooplankton biomass in Lake Balaton during its re-oligotrophication period from 2001 to 2017, and attempt to draw some conclusions on the subsequent changes in the fish stock. We found a proportional decrease in zooplankton and phytoplankton biomasses at moderate phytoplankton levels. However, below a certain phytoplankton concentration (< 10 μg l−1 Chl a), the decrease in phytoplankton biomass was not coupled with a further decline in zooplankton biomass because the fraction of small phytoplankton, edible for zooplankton, showed a much smaller decrease in biomass compared with large non-edible phytoplankton. Thus, improvements in water quality (i.e., reduced nutrient loading), partly via concomitant changes in the phytoplankton size distribution, did not cause a large difference in the fish stock in this shallow lake. [ABSTRACT FROM AUTHOR]

This paper reports a study of oxygen and redox conditions, trophic status, and phytoplankton community in the meromictic Lake Idro (Italy) from 2010 to 2014. The sequence of causes and effects of meromixis are also evaluated by comparing recent research with studies conducted from the late 1960s to the mid-1990s. In the last half century, Lake Idro was steadily meromictic due to solutes which accumulated in its deep waters, along with both dissolved nutrients and chemically reduced substances produced by the anaerobic microbial metabolism. These substances were retained in bottom waters and made unavailable to upper layers until stratification broke. Mixing episodes occurred in 2005-2006 altering stratification, and oxygen and nutrient distribution within the lake. The potential full overturn effects were also evaluated as potential oxygen consumption due to the oxidation of reduced substances to forecast possible oxygen exhaustion and collapse of biological communities. Finally, meromixis is discussed as a potential threat for deep perialpine lakes using Lake Idro as a reference to comparatively evaluate the present status and possible future trends. [ABSTRACT FROM AUTHOR]

Guest editors: Alonso Ramírez, Checo Colon-Gaud, Margarita Caballero & Gabriela Vázquez / Recent Advances in Tropical Lake Research Studies on tropical lakes have provided valuable information for advancing our understanding of limnology and lake ecology in general. The lack of a solid understanding of tropical lake processes (biology, seasonality, water quality) hinders our ability to manage and conserve lake ecosystems. We hope this group of papers aid in advancing our understanding of lake ecosystems in tropical latitudes and lakes in general. [Extracted from the article]

The results of a study of littoral chironomid communities from 89 lakes in the Alps are presented. The lakes are located on the northern and southern sides of the Alps from the western Bernese to the eastern Julian Alps. Due to the different origins of the data set here considered, different sampling years and sampling methodologies were adopted. All of the lakes were sampled during the ice-free season, but 79/89 lakes were sampled mainly in autumn 2000, while for a few of them the sample dated back to 1996 or the early 90s. Samples were taken by kicking the different substrata or a stretch of lakeshore (10–30 m) for at least 2–5 min with a standard net and were then preserved in alcohol. Larvae and pupal exuviae were sampled by skimming the lake surface with the same net, to extend identification to species level. Notwithstanding the large altitudinal gradient, almost all of the lakes are situated above the timberline, and show a wide range of morphological (depth, watershed and lake area) and chemical characteristics. Chironomids were the most abundant insects represented in these lakes, with highest abundances at pH between 6.0 and 7.5. In particular, Orthocladiinae and Chironominae were the two subfamilies with the widest distribution. Altitude and temperature played an important role in determining their distribution, the higher altitudes were dominated by the former, whereas the latter were more numerous in lower lakes. The prevalence of Orthocladiinae and Tanytarsini at high altitudes was regarded as a general pattern of taxonomic composition in harsh climatic areas. A reverse condition occurred only in the Julian Alps, where Tanytarsini dominate, followed by Tanypodinae and rare Orthocladiinae. Although our results demonstrated that the composition of chironomid assemblages was also determined by pH, the pattern was unbalanced. Due to the fact that no cases of strong water acidification were present, taxa restricted to very low pH were poorly represented (only three taxa— Limnophyes, Endochironomus and Orthocladius (O.) spp.) compared with circumneutral (8) and alkaline (14) taxa, which occurred in slightly acid and non-acidified soft water lakes. As regard conductivity and altitude, we found that almost all the taxa present at higher pH were contemporary present at conductivity higher than 100 μeq l−1 and altitude lower than 2100 m a.s.l. At species level, Pseudodiamesa branickii, Corynoneura arctica, Heterotrissocladius marcidus and Paratanytarsus austriacus resulted to be the most ubiquitous and abundant species in the Alps. When the west to east distribution of taxa was taken into account, Chironomini (particularly the genera Chironomus and Dicrotendipes) and Tanypodinae ( Larsia and Paramerina) were more typical of the eastern lakes (JA). They may be better indicators of more alkaline waters. Assembling all the existing data and presenting a comprehensive panorama of lake-littoral chironomid taxa of the Alps was one of the aims of this paper. Further monitoring, but also harmonization of the sampling methodologies and taxonomical identification including inter-calibration exercises among laboratories are recommended, to provide reliable basis and more knowledge for future studies of comparative biogeography, and to preserve these environments where global climatic changes may cause abrupt shifts in the faunal assemblages with a loss of taxa typical of these mountainous areas. [ABSTRACT FROM AUTHOR]

The Saimaa lake complex (4460 km2) is a mosaic of interconnected basins draining into the Gulf of Finland via Lake Ladoga. Limnologically, most of the basins are dysmesotrophic or oligotrophic, while some areas are markedly affected by nutrient loading. Aquatic research has been conducted in the Lake Saimaa area with the 27-metre research vessel R/V Muikku since 1989, and the laboratory and research facilities on the vessel have been built up and enhanced over this time to include temporally and spatially reliable automatic measuring systems such as CTD (ConductivityTemperatureDepth) probes and a continuous-flow in vivo fluorometer. This paper uses linear regression to compare vertical CTD measurements with standardised laboratory analyses of water temperature, O2 concentration, conductivity and pH in different basins of the Lake Saimaa complex from data sets collected on board R/V Muikku in 2000–2001, and tests in vivo automatic fluorometer measurements of filtered and unfiltered discrete water samples from the Haukivesi basin of Lake Saimaa against in vitro chlorophyll-a concentrations. All the linear regressions showed a significant overall consistency between the CTD and fluorometer results and the laboratory analyses, but the pH comparisons showed some instability between methods. Clear spatial and vertical variations in conductivity and oxygen concentrations were apparent in the CTD results for three basins (Lakes Pyhäselkä, Haukivesi and Etelä-Saimaa), and there was also a significant linear relationship of unfiltered and filtered in vivo fluorescence to in vitro chlorophyll-a concentrations. The unfiltered fluorometer measurements were nevertheless markedly higher than those obtained from filtered water samples. Thus humic and other dissolved substances in lake water may be said to yield enhanced fluorometer readings independent of the chlorophyll-a concentrations, as has been noted earlier in similar studies. [ABSTRACT FROM AUTHOR]

Phytoplankton in karst lakes is characterized by co-occurrence of chrysophytes (Chrysophyceae), dinoflagellates (Dinophyceae), and diatoms (Bacillariophyta) as the most diverse and abundant group. Using Reynolds functional approach in ecological phytoplankton investigations makes karstic lakes comparable and facilitates interpretation of their responses to changing environmental conditions. Accurate taxonomic identification to species level, based on precise resolution of specific characteristics by electron microscopy, is essential in order to correctly associate species into coda. This paper defines the most abundant centric diatoms and coexisting species in the phytoplankton of karst lakes in Croatia as a contribution to better description of phytoplankton functional groups dominated by centric diatoms. Several representatives for diatom-based Reynolds functional groups of four lakes in Croatia were described in this paper: Pantocsekiella costei and Stephanocostis chantaica for group A, Pantocsekiella ocellata and Cyclotella distinguenda for group B, and Stephanodiscus neoastraea for group C, together with their ecological preferences which clearly correspond to pertaining functional classification. Selected and coexisting functional groups define natural, oligo- to mesotrophic karst deep lake systems. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms have a strong impact on the food web structure, interactions and ecosystem functioning. The aim of this study was to describe the seasonal changes in composition and abundance of heterotrophic nanoflagellates, ciliates, rotifers, and crustaceans in relation to algae and nutrients in a shallow eutrophic lake (north-eastern Poland) dominated by cyanobacteria and exposed to the strong impact of cormorants. Our results showed that algae accounted for a small part of the total phytoplankton abundance (9–40%) and biomass (10–21%) and were dominated by diatoms and cryptophytes. All of the studied groups of planktonic organisms were quite rich in species (95 algal, 79 ciliate, 44 rotifer and 25 crustacean species) and relatively abundant. Copepods formed a substantial part (45–83%) of the total zooplankton biomass during all seasons. Relatively low algal to zooplankton biomass ratio (0.8–1.1) suggests that during spring, summer, and winter algae were not sufficient food resources for metazooplankton, which supplemented its diet with protists (heterotrophic nanoflagellates and ciliates). In a shallow lake dominated by cyanobacteria, winter (ice-covered period) may be a more favourable period for the growth of some groups of algae, ciliates and rotifers than other seasons due to decreasing abundance of cyanobacteria. [ABSTRACT FROM AUTHOR]

The bioturbation potential of three freshwater operculate snails, Filopaludina bengalensis, Gabbia orcula and Melanoides tuberculata, was compared, using water column depth and sediment surface area as the explanatory variables. Assessment of nutrient fluxes from sediment to overlying water was estimated in glass microcosms, that varied in height (tall, medium, short) and base (narrow, wide), resulting in six habitat conditions. In course of movement and grazing, all the three snail species modified surface architecture of the sediment. Besides, the snails modulated NOXˉ (NO2ˉ-N + NO3ˉ-N), NH4+-N and PO43−-P concentrations and other parameters (TDS, conductivity) of the water column in significantly varying proportions. Snail-induced changes in the rate of nutrient flux were highest for F. bengalensis. Periphytic chlorophyll-a concentration was reduced in all snail-treated microcosms compared to the control. Grazing, scraping and movement of snails on sediment facilitated the release of the nutrients in a species-specific manner depending on sediment surface area and water column depth of the microcosm. Apparently, snails may be useful in mobilizing the sediment content in freshwater lakes and ponds, facilitating ecosystem processes. [ABSTRACT FROM AUTHOR]

We used macrozoobenthos data (abundance, biomass, and community structure) spanning 69 years including annual surveys from 1997 to 2016 in three connected lakes with different trophic states located in the north-west of Belarus (lakes Naroch, Myastro, and Batorino) to investigate the relationships between Carlson's trophic state indices (TSI) and macrozoobenthos. We studied the response of the macrozoobenthos both over time and by depth zone. We found that there is an inverse relationship between lake productivity as measured by chlorophyll-based TSI and macrozoobenthos abundance and biomass both when comparing the three Narochianskie lakes and in the long-term dynamics within each lake. Lake-wide and littoral zone benthic biomass decreased significantly with increasing trophic state. Macrozoobenthos community structure also differed among lakes, with Chironomidae dominating in the most productive lake (Batorino), Chironomidae and Mollusca dominating in Lake Myastro, which had an intermediate trophic state, and Mollusca dominating in the lake with the lowest TSI (Naroch). We found significant differences both in the average benthos biomass and in the composition of macrozoobenthos between the profundal (silt and lack of macrophytes) and littoral zones (presence of macrophytes) within each lake. We argue that bottom substrates, macrophytes, and dreissenid mussels were more important for macrozoobenthos than trophic state in these lakes. Several benthic invertebrate taxa differed among lakes and are potential indicators of trophic state. [ABSTRACT FROM AUTHOR]

In this work, we characterised the cyanobacterial communities in the plankton and littoral biofilm of 38 lakes and in the biofilm of 21 rivers in the Alps and surrounding subalpine regions by 16S rRNA gene metabarcoding. We found little overlap in the distribution of amplicon sequence variants (ASVs) between the three habitats and between water bodies. The differences were caused by environmental filtering acting on the selection of the most abundant ASVs and a high contribution of rare oligotypes. The differentiation of community and genotype composition from specific water bodies was explained to a significant extent by environmental variables and morphometry. The taxonomic consistency of ASVs classified under the same genus name was assessed by phylogenetic analyses performed on three representative dominant genera, namely Cyanobium, Tychonema and Planktothrix. The analyses revealed eco-evolutionary adaptations in lakes and rivers, including some evidence for a polyphyletic nature. Monitoring individual genotypes in relation to environmental conditions will be useful to define the ecological amplitude of these taxa. However, the persistence or ephemeral nature of some of the rarest and most unusual ASVs has remained unknown. [ABSTRACT FROM AUTHOR]

Pikeperch (Sander lucioperca Linnaeus, 1758) is a wide-ranged percid predator fish characterised by a great ecological value in the Eurasian freshwater and brackish ecosystems. It is also one of the most famous fish species of Lake Balaton (Hungary), where a unique (genetically separated) pikeperch stock lives. However, until now, no detailed information was available about the pikeperch population genetic structure in Lake Balaton. In the present study, the population genetic structure of the pikeperch assemblages in the lake was revealed by using microsatellite markers. Commercial fishery and angler catch data going back more than 100 years verified that the pikeperch has always been a key element of Lake Balaton's fish stock utilization. Results of genetic data analyses showed that the pikeperch in the Lake Balaton forms a metapopulation system, in which only the westward stocks show certain separation. Moreover, it seems that the exploitation and mass fish kills that happened in the 1960s and 1970s may have had only a slight impact on the population genetic structure of Balaton pikeperch stocks. The information about genetic features and utilization changes of pikeperch stocks can help to develop area-specific management plans and ensure the long-term survival of this carnivore fish species characteristic of Lake Balaton. [ABSTRACT FROM AUTHOR]

We re-examined the effects of acidification on Scandinavian freshwater lakes using paleolimnological reconstructions focused on subfossil chironomids. Our study showed a widespread shift in chironomid community composition occurring at around 1960 and corresponding with the maximum fallout of anthropogenic SO42− deposition. Results also showed that taxonomic turn-over was higher in chironomid records from nitrogen-limited lakes, likely due to the cumulative effects of acidification and eutrophication driven by atmospheric nitrogen deposition. Despite strong evidence of chemical recovery from acidification, all lake records failed to show a return to pre-acidified community compositions and most chironomid communities instead continue to follow the trajectories triggered by acidification. We hypothesized that when SO42− deposition started to decrease after 1980, a period also marked by rapid environmental and climatic changes, the influence of pH and/or other acidification-related variables in structuring chironomid community became less important, thus, giving more relative importance to other drivers, such as brownification and climatic processes. Results, therefore, suggest the key role of acidification in shaping the response of chironomid communities to future environmental changes. Future paleolimnological studies will contribute to better manage aquatic ecosystems recovering from acidification worldwide by allowing managers to quantify the efficacy of different management actions taken to mitigate acidification as well as to redefine appropriate restoration targets. [ABSTRACT FROM AUTHOR]

To prevent lake degradation, water level management has been a major focus of research in the past several decades. There are, however, some shortcomings in the traditional studies, and the protection of entire ecosystems is difficult to achieve in practice. In this paper, the framework of a new method for determining ecosystem-based water level regimes (WLRs) for lake protection is proposed. First, historical WLRs are divided into several sub-stages. Then, ecosystem statuses corresponding to different WLRs are quantified and compared. Finally, parameters of optimal and acceptable WLRs are used to determine water level management goals. The proposed method was applied to Baiyangdian Lake, the largest shallow lake in the North China Plain, to test its effectiveness. Results showed that to protect the ecosystem at the optimal status, 50% of the parameter values should fall within the range of the 25th and 75th percentiles of Stage I; and to protect the ecosystem from reverse succession, 50% of the water level parameter values should fall within the range of the 25th and 75th percentiles of Stage II. This method takes ecosystem status into account, and has high practicability in water resources management. [ABSTRACT FROM AUTHOR]

Hydrilla has been in New Zealand since the 1960s and formed major infestations in four lakes in the Hawkes Bay region. Challenges to controlling hydrilla in New Zealand have included a lack of tools and the changing responsibilities of local management agencies. A grass carp field trial was initiated in 1988 in the smallest of the hydrilla infested lakes to assess the feasibility of eradicating hydrilla. After the main hydrilla beds were consumed, regrowth from tubers still occurred for a further 12 years. In 2008, grass carp were released into the remaining three hydrilla-infested lakes in a central government led response to eradicate hydrilla. This paper describes the changes in the flora and fauna in the largest of these lakes, Lake Tutira, following the introduction of grass carp and the removal of the hydrilla weed beds. Annual surveys of aquatic vegetation and macroinvertebrates in the lake from 2008 to 2012 have shown that, following the removal of the hydrilla weed beds by 2010, there was a shift in grass carp grazing to marginal emergent plants, and a general increase in the distribution of the native plant vegetation, although there was some evidence of a decline in charophyte abundance. Macroinvertebrate diversity was maintained although there were changes in the relative abundance of taxa linked to changes in the littoral vegetation. [ABSTRACT FROM AUTHOR]

The implementation of the Water Framework Directive has required intense research in applied aquatic ecology in Europe, and thus created challenges for data management in international research projects. In the project Waterbodies in Europe: Integrative Systems to assess Ecological status and Recovery (WISER), biological and environmental data from rivers, lakes, transitional and coastal waters in 26 European countries were collated. More than one million records of biological observations were stored in the project's central database, representing phytoplankton, macrophytes, macroalgae, angiosperms, phytobenthos, invertebrates and fish. The central database includes new data from the WISER field campaign in lakes and transitional/coastal waters during 2009-2010 (more than 6,000 biological samples from 58 waterbodies in 14 countries). The purpose of this paper is to provide an overview of the data collated within WISER, in order to facilitate future re-use of these data by other scientists. More specifically, the objectives are to (1) describe the data management in WISER, (2) describe the structure and content of the WISER central database and (3) share experiences and give recommendations for data management in large ecological research projects. [ABSTRACT FROM AUTHOR]

Despite improvements in wastewater treatment systems, the impact of anthropogenic nutrient sources remains a key issue for the management of European lakes. The Water Framework Directive (WFD) provides a mechanism through which progress can be made on this issue. The Directive requires a classification of the ecological status of phytoplankton, which includes an assessment of taxonomic composition. In this paper, we present a composition metric, the plankton trophic index, that was developed in the WISER EU FP7 project and demonstrate how it has been used to compare national phytoplankton classification systems in Northern and Central Europe. The metric was derived from summer phytoplankton data summarised by genus from 1,795 lakes, covering 20 European countries. We show that it is significantly related to total phosphorus concentrations, but that it is also sensitive to alkalinity, lake size and climatic variables. Through the use of country-specific reference values for the index, we demonstrate that it is significantly related to other national phytoplankton assessment systems and illustrate for a single European (intercalibration) lake type how it was used to intercalibrate WFD boundaries from different countries. [ABSTRACT FROM AUTHOR]

Phytoplankton constitutes a diverse array of short-lived organisms which derive their nutrients from the water column of lakes. These features make this community the most direct and earliest indicator of the impacts of changing nutrient conditions on lake ecosystems. It also makes them particularly suitable for measuring the success of restoration measures following reductions in nutrient loads. This paper integrates a large volume of work on a number of measures, or metrics, developed for using phytoplankton to assess the ecological status of European lakes, as required for the Water Framework Directive. It assesses the indicator strength of these metrics, specifically in relation to representing the impacts of eutrophication. It also examines how these measures vary naturally at different locations within a lake, as well as between lakes, and how much variability is associated with different replicate samples, different months within a year and between years. On the basis of this analysis, three of the strongest metrics (chlorophyll- a, phytoplankton trophic index (PTI), and cyanobacterial biovolume) are recommended for use as robust measures for assessing the ecological quality of lakes in relation to nutrient-enrichment pressures and a minimum recommended sampling frequency is provided for these three metrics. [ABSTRACT FROM AUTHOR]

The EU-funded research project WISER ('Water bodies in Europe: Integrative Systems to assess Ecological status and Recovery') developed new assessment methods required by the EU Water Framework Directive (WFD) for lakes, coastal and transitional waters. WISER also addressed the recovery of biotic assemblages from degradation. The results are summarised in five key messages, supported by papers in this special issue and by WISER results published elsewhere: (1) Response to stress differs between organism groups, water types and stressors; a conceptual model is proposed summarising how the individual organism groups respond to different types of degradation in rivers, lakes, transitional and coastal waters. (2) The sources of uncertainty differ between BQEs and water types, leading to methodological suggestions on how to design WFD sampling programmes. (3) Results from about 300 current assessment methods indicate geographical variations in metrics but assessments are comparable at an aggregated level ('ecological status'). (4) Scale and time matter; restoration requires action at (sub)-basin levels and recovery may require decades. (5) Long-term trends require consideration; the effects of both degradation and restoration at the water body or river basin scales is increasingly superimposed by multiple stressors acting at large scales, in particular by climate change. [ABSTRACT FROM AUTHOR]

Loch Leven is a large, shallow lake in lowland Scotland, UK. Scientific research began here almost 200 years ago. Early research characterised the biodiversity and physical characteristics of the loch, providing an important historical background for future research. In the mid-1960s, this ad hoc approach was superseded by a more structured research programme under the umbrella of the International Biological Programme. This was the beginning of the Loch Leven long-term monitoring programme. Today, the results of these studies form one of the longest and most comprehensive limnological datasets for shallow freshwater lakes in the world, comprising more than 500 physical, chemical and biological variables collected at two-weekly intervals. To celebrate the 40th anniversary of the start of the long term monitoring programme, and to highlight the scientific investigations still being conducted at Loch Leven, the NERC Centre for Ecology & Hydrology (CEH) organised a symposium entitled "Loch Leven: 40 years of scientific research" in Kinross, Scotland, UK, on 11 December 2008. This examined the role of long-term monitoring in developing our understanding of the links between pollution, climate change and ecological responses in shallow lakes. This article introduces a series of papers summarising the scientific results presented at this meeting. [ABSTRACT FROM AUTHOR]

iming at building the carbon budget for further climate change impact research in the large and shallow northern temperate Lake Võrtsjärv, the present paper focuses on reconstructing the full phytoplankton primary production (PP) data series for the lake for the period of 1982-2009 covered by disconnected measurements, and testing the uncertainties involved both in the PP measurements and bio-optical modelling. During this 28-year period, in situ PP was measured in Võrtsjärv in 18 years with C-assimilation technique. We reconstructed the full time series using a semi-empirical PP simulation model based on continuously measured PAR irradiance and interpolated values of monthly measured chlorophyll a ( C). The modelling results, which proved highly reliable during the calibration phase, correlated rather weakly with the annual PP estimates for the 18 years, which were based on 2-h incubations at midday, 1-2 times per month. Being based on continuous irradiance data, the modelled PP can be considered more reliable than the sparse measurements, especially for short to medium term studies. We demonstrate that in the long-term, the bio-optical method can be biased if changes in water colour or water level alter the light climate causing adaptive responses in the cellular chlorophyll content of light-limited phytoplankton. [ABSTRACT FROM AUTHOR]

Ancient sister lakes are considered to be ancient lakes lying in close geographic proximity, sharing a related origin and significant time of co-existence, usually having hydrological connection as well as a balanced degree of faunal overlap and distinctness. A paradigm for studying sister lake relationships are the ancient lakes Ohrid and Prespa in the Balkans, which are characterized by high degrees of endemicity. Three general patterns of endemic species can be distinguished for these lakes: (1) taxa that are endemic to either lake, with no close relatives in the respective sister lake, (2) closely related but distinct endemic taxa in both lakes (sister species) and (3) shared endemic taxa occurring in both lakes. In the present paper, two endemic freshwater pulmonate gastropod species, Radix relicta (Lake Ohrid) and R. pinteri (Lake Prespa), are used to study the evolution of presumed sister species based on biogeographical and comparative DNA data from world-wide Radix taxa. Phylogenetic, phylogeographical and parametric bootstrap analyses all suggest a sister group relationship of R. relicta and R. pinteri (pattern 2 of endemic diversity). Sister to these two taxa is the widespread R. ampla, which does not occur in the vicinity of lakes Ohrid and Prespa. The southern feeder spring complexes of Lake Ohrid are inhabited by another lineage ( Radix sp. 1), which resembles Radix relicta in morphology/anatomy. For Lake Prespa, the widespread R. auricularia was reported in addition to the endemic R. pinteri. Comparative phylogenetic data favour a western Adriatic zoogeographical affinity of lakes Ohrid and Prespa over an Aegean-Anatolian faunal connection. The status of lakes Ohrid and Prespa as sister lakes is evaluated in the light of current knowledge on gastropod speciation and endemism in these hotspots of biodiversity. [ABSTRACT FROM AUTHOR]

This paper delivers a conceptual framework for the ecological functioning and biodiversity patterns of lakes that is based on the floodpulse concept (FPC). The specific characteristics of rivers and lakes considering water-level fluctuations are compared, with respect to catchment linkages, temporal patterns, and hydraulic forces of flooding and drawdown. The influences of floodpulses on element cycles, biodiversity, and adaptations of lake biota are analyzed, and the importance of multi-annual flooding cycles is highlighted. The degree by which these water-level fluctuations influence lake ecosystems strongly depends on lake morphology, where shallow lakes or those with large shallow margins are the most sensitive. Although floodpulses play a major role for ecosystem services such as lake management and climate change mitigation schemes, this issue is only scarcely dealt with. Tenets of the extended FPC for lakes are formulated in order to overcome this problem. [ABSTRACT FROM AUTHOR]

Research to develop tools to assess the ecological status of phytobenthos, as required in Annex V of the European Union Water Framework Directive, has focussed largely on diatoms. Diatoms are often the most abundant and diverse group of algae within the phytobenthos and have been used widely for other monitoring purposes. However, there is little empirical justification for the use of diatoms as proxies for the wider phytobenthos. In this paper, we re-examine an existing dataset compiled largely from littoral samples from standing waters in the English Lake District and compared transfer functions for total phosphorus, dissolved inorganic carbon, conductivity and calcium concentration generated from diatoms and non-diatoms separately and together. The results show that transfer functions generated from diatoms alone are as powerful as transfer functions generated from diatoms and non-diatoms combined, while transfer functions generated from non-diatoms alone are less effective. These results provide support for the use of diatoms as proxies for phytobenthos when ecological status is being assessed. [ABSTRACT FROM AUTHOR]

Diatom analyses of sediment cores extracted from three lakes in coastal southeastern South Australia reveal that, for most of the mid-late Holocene, they were shallow, brackish to saline systems with limited flow of water from continental sources. The construction of a substantial network of drains in the early years of settlement, to maximise transportation and agricultural production through wet winters, lead to abrupt freshening of the lakes. Interestingly, despite substantial nutrient loads to Lake Bonney SE (there are two Lakes Bonney and Frome in South Australia, which is why the lakes in the southeast of the state are differentiated with ‘SE’) associated with the commissioning and expansion of pulp and paper mills, a wastewater treatment plant discharge and agricultural runoff, there is only moderate evidence of nutrient enrichment in the lake, possibly because the post-impact assemblages are dominated by taxa with broad ecological preferences. Despite being preserved within a conservation park, eutrophication associated with agriculture is evident in the diatom assemblages of Lake Frome SE, which has a catchment more than twice that of Lake Bonney SE. Mullins Swamp, on the other hand, supports few indicators of eutrophic conditions. The freshening of these lakes is against the tide of salinisation from rising saline groundwaters in most wetlands across southeastern Australia. [ABSTRACT FROM AUTHOR]

The progressive decrease in water quality experienced by the Mediterranean, nutrient rich reservoir, Lake Arancio (Southwestern Sicily, Italy), has been accompanied by modifications in both phytoplankton shape and size. Since nutrient concentrations are always far from being limiting, in the present paper attention was focussed on the effects exerted by physical constraints (e.g., mixing, light availability) on the morphological variation observed in phytoplankton. The surface–volume ratio and its product with the maximal linear dimension were chosen as morphological descriptors to trace the trajectories followed by the dominant morphotypes in Lake Arancio. One of these descriptors was compared to the mixing depth—euphotic depth ratio, considered as a good descriptor of the underwater light climate. The strong influence exerted by light transmission and mixing regime on phytoplankton morphological traits and thus on its composition in this environment confirms the paramount importance of both light transmission and the peculiar hydrological regime to which reservoirs are subjected, especially in Mediterranean climate, and points out the need to integrate hydrology into ecological studies and management procedures. [ABSTRACT FROM AUTHOR]

Lakes are common features of alpine landscapes, and the attention given to alpine lakes has increased recently in response to increased recognition of the important role that these freshwaters play as sensible indicators of climate change. Despite this general research interest, there is nevertheless a general lack of information about zoobenthos especially of lakes in the Alps, and only few published data are available, which has made it nearly impossible to draw general conclusions in respect to benthic community structure, profundal and/or littoral food webs. This paper aims to explore the relationships between main environmental/catchment properties of 55 lakes and their littoral benthic fauna across three regions of the Alps. We provide updated information on relative abundance, species richness, distribution and ecology of macroinvertebrates which occur and are typical in the littoral of high-mountain lakes of the Alps. These lakes were located in the Lago-Maggiore Watershed (Italy and Switzerland), in South Tyrol (Italy) and in North/East Tyrol (Austria), between 1840 and 2796 m a.s.l., in catchments undisturbed by human activities. As the studied lakes are situated above the tree line, they were characterised by low nutrient levels indicating an oligotrophic status. Lake water chemistry corresponded closely to the geo-lithology of the catchment and some parameters (especially nutrient concentrations) differed between the regions. The macroinvertebrates were dominated by insects which to a high degree were chironomid larvae and pupae. Other insect orders were typical cold stenotherm species of Ephemeroptera, Plecoptera and Trichoptera. Non-insect macroinvertebrates contributed to the 144 taxa found. Other than lake size and catchment area, the faunal parameters exhibited a clearer pattern along altitude. Macroinvertebrates per sample increased with higher elevation, reached their maximum in lakes between 2400 and 2600 m a.s.l., but decreased strongly above 2600 m. The altitudinal pattern of species richness and Shannon diversity resembled each other being highest between 2001 and 2200 m a.s.l., but decreased when going lower and higher, respectively. Various patterns and trends along altitude were also evident when individual groups were analysed within the individual sampling regions. The somewhat conflicting trends of various biocoenotic indices let assume that factors other than altitude are also responsible for the structure of faunal assemblages in the littoral of alpine lakes. Six variables (“bare rocks” and “nitrate”, “alkalinity”, “ammonia” and “peat bog”) were selected by the CCA analysis where these three groups of lakes were identified: (1) lakes with a higher alkalinity (higher pH, conductivity, ion concentration), a higher relative vegetation cover (compared to the “bare rocks” on the opposite side) and lower nitrate levels; (2) lakes with a higher portion of “bare rocks” in their catchments and higher nitrate levels; and (3) a smaller group of lakes with higher ammonia levels and a boggy environment. Geographical patterns seemed to have weak effects on the presence of taxa while catchment properties had evident impacts on macroinvertebrate communities in these lakes. In this way, the present study contributes to the overall understanding of environmental settings and effects on high mountain lake ecosystems and assists in refining research and conservation strategies for an important landscape aspect in the Alps. [ABSTRACT FROM AUTHOR]

This work introduces an interpretational key to quantify and understand how much of variations among lakes in fundamental ecosystem characteristics that may be related to lake morphometry, catchment area features, measurement uncertainties and other factors (mostly climate). The size and form of lakes regulate many general transport processes, such as sedimentation, internal loading and outflow, which in turn regulate many abiotic state variables, such as concentrations of phosphorus, colour, water chemical variables and water clarity, which regulate primary production, which regulate secondary production. This paper discusses relationships between key abiotic state variables, lake morphometry and catchment area characteristics using empirical/statistical analyses based on data from 95 lakes. It has been shown that of the studied variables Secchi depth depends most on morphometry (34%); 31% of the variations among the lakes in Secchi depth may be related to catchment area characteristics, 1% to uncertainties in empirical data and 34% to “other” (climatological) factors. The corresponding figures for alkalinity, which depends least on lake morphometry are, 0% related to morphometry, 34% to catchment conditions, 1% to empirical uncertainty and 58% to other causes. For all other studied variables, i.e., conductivity, hardness (CaMg), calcium, iron, colour, pH and phosphorus the corresponding figures vary between these values. The interpretational key helps to explain the mechanistic reasons for these statistical/empirical results. [ABSTRACT FROM AUTHOR]

This work introduces an interpretational key to quantify and understand how much of variations among lakes in fundamental ecosystem characteristics that may be related to lake morphometry, catchment area features, measurement uncertainties and other factors (mostly climate). The size and form of lakes regulate many general transport processes, such as sedimentation, internal loading and outflow, which in turn regulate many abiotic state variables, such as concentrations of phosphorus, colour, water chemical variables and water clarity, which regulate primary production, which regulate secondary production. This paper discusses relationships between key abiotic state variables, lake morphometry and catchment area characteristics using empirical/statistical analyses based on data from 95 lakes. It has been shown that of the studied variables Secchi depth depends most on morphometry (34%); 31% of the variations among the lakes in Secchi depth may be related to catchment area characteristics, 1% to uncertainties in empirical data and 34% to “other” (climatological) factors. The corresponding figures for alkalinity, which depends least on lake morphometry are, 0% related to morphometry, 34% to catchment conditions, 1% to empirical uncertainty and 58% to other causes. For all other studied variables, i.e., conductivity, hardness (CaMg), calcium, iron, colour, pH and phosphorus the corresponding figures vary between these values. The interpretational key helps to explain the mechanistic reasons for these statistical/empirical results. [ABSTRACT FROM AUTHOR]

Devils Lake in northeastern North Dakota (USA) is a terminal lake of glacial origin with a substantial sulfate content. Since 1940, the lake water level has risen over 13.5m and salinity has decreased. Devils Lake consists of a series of interconnected basins with sulfate concentration increasing in an eastward direction from 450mg/l in West Bay to 3000mg/l in East Devils Lake. Using sulfate as a tracer and linking measurements of specific conductance with observed time series of water surface elevations, wind, and water velocity, this paper illustrates the magnitude and dynamics of mass transport and exchange processes between the multiple basins of Devils Lake. Measurements show small horizontal salinity gradients within the lake basins, but large salinity gradients in some of the exchange zones connecting basins. Vertical salinity gradients were observed in small basins and near exchange zones with strong horizontal salinity differentials. These instances of vertical stratification were associated with buoyancy driven exchange flows and wind sheltering. Exchange flow velocities between selected basins were correlated with wind direction and speed. Interbasin exchange flows were found to reverse direction frequently in response to the prevailing wind direction. Flow direction frequencies in one specific exchange zone were 31% west to east, 48% east to west, and 21% bidirectional (stratified). At the lake level observed in 2000, time averaged, measured interbasin exchange flow rates were 30--40m3/s compared to tributary inflow rates to the lake of 3--9m3/s. [ABSTRACT FROM AUTHOR]

The present paper focuses on the biological properties of Lake Chapo prior to the installation of a hydroelectric power station. Most of the biological parameters indicate that the lake is oligotrophic, i.e., it has very low values of chlorophyll a and primary production. The phytoplankton community of 73 species shows a predominance of only a few species in terms of density and biomass. The zooplankton community is poor in species, with one of the lowest densities measured in the North Patagonian lakes. The fish community is dominated by two introduced salmonid species. Comparison with other North Patagonian lakes reveals that Lake Chapo is the most oligotrophic. [ABSTRACT FROM AUTHOR]

This paper presents data on the diversity of cyanobacteria and algae of nine gravel pit lakes situated within the city boundaries of Bratislava, W Slovakia. During more than 30 years of investigations 187 genera and 591 infrageneric taxa were determined, of which 40 genera and 58 species belong to Cyanobacteria, and 147 genera, 492 species, 2 subspecies, 35 varieties and 4 forms belong to various groups of algae. From gravel and sand pit lakes in Slovakia several new taxa were established, e.g. Cyanocatena planctonica Hindák, 1975 and Planktocyanocapsa stagnalis Hindák, 2002 from the cyanobacteria, or Catenococcus tortuosus Hindák, 1977, Posonia sestonica Hindák, 1982 and Catenocystis gerulata Hindák, 1988 from the chlorophytes. Many taxa found were new records for this country. The floristic composition of the lakes investigated was rich but due to the uniformity of environmental conditions more or less similar. The majority of the taxa were diatoms, while the chlorophytes represented about 22%. As a whole, the taxonomic structure is typical of mesotrophic to eutrophic, slightly saline water of temperate zones, but some taxa may be considered characteristic of oligotrophic lakes. [ABSTRACT FROM AUTHOR]

This paper analyses the life strategies, the dominance patterns and the diversity in phytoplankton communities in large and deep lakes. The study was carried out on the largest Italian Lake (Lake Garda) from 1995 to 2000. Different statistical analyses were applied. For phytoplankton the time variable represents a complex environmental gradient driving annual succession; this gradient was made explicit by the application of PCA analyses to the environmental data. The use of Non Metric Multi Dimensional Scaling applied to Bray-Curtis dissimilarity matrices revealed an ordered and cyclic development of phytoplankton every year; the Bray-Curtis index, calculated between pairs of chronologically contiguous samples, was also used as a measure of the community change rate (βt) over the temporal succession. A significant relationship between βt and the complex environmental gradient was assessed. Finally, for every phytoplankton species, the optimum conditions for growth and the realised niches were determined. The positioning of the species on the complex environmental gradient, and the contemporaneous application of cluster analysis based on the different specific environmental optima, highlighted primarily the existence of two groups at the extreme of the complex environmental gradient. The first group included the large late winter/spring diatoms, which developed during high water turbulence and strong physical control, high nutrient concentrations, low light conditions and reduced competition. The second group was composed by many heterogeneous summer species characterised by the ability to contrast losses by grazing and sinking in stratified and stable conditions, and the ability of tolerating nutrient deficiency. A third group of species developed during environmental conditions in the middle of the two previous extremes. These included the three master species Mougeotia sp., Fragilaria crotonensis and Planktothrix rubescens/agardhii. The endogenous and exogenous mechanisms promoting species coexistence are discussed, along with the applicability of competitive and equilibrium/non-equilibrium theories to phytoplankton dynamics. [ABSTRACT FROM AUTHOR]

Survey samplings on late summer phytoplankton communities were carried out on 48 high mountain lakes located on the Austrian and Italian slopes of the Eastern Alps. The lakes of North Tyrol (A) and South Tyrol (I) were sampled in 2000 as part of the EU project EMERGE (EVK1-CT-1999- 00032). The lakes of Trentino (I) were investigated in other research projects during 1996 and 1997 (Adamello mountain range) and 2000 (catchment of the River Avisio), respectively. The objectives of this paper are: (1) to study taxonomy and biodiversity of Chrysophyceae, Dinophyceae and Cryptophyceae in high altitude lakes of the Eastern Alps; (2) to identify functional flagellate groups characterising lakes with similar habitat properties, (3) to identify the environmental variables driving abundance and distribution of the three selected algal groups, thus contributing to the selection of sensitive bioindicator taxa. The lakes investigated show rather wide morphological, chemical and trophic state gradients. Flagellate algae account for a median relative abundance (R.A.) of 68%. Chrysophyceae are the most important group in terms of biodiversity and R.A.. Special flagellate associations could be related to lake features, like catchment geology, mineralization level and nutrient concentrations. However, the distribution of flagellate algae did not allow a complete geographical separation of the lakes studied in the different districts. Multivariate canonical analyses indicate that the distribution of Chrysophyceae is mainly driven by NO3-N concentration and thermal conditions, while Dinophyceae are driven by a combination of alkalinity, altitude, thermal condition and, less importantly, nutrient concentration. Physical properties of the lakes, such as thermal condition and lake depth, represent the principal driving variables for Cryptophyceae. The responses to the different environmental variables suggest that the three flagellate groups analysed might be used as indicators for environmental changes in high mountain lakes of the Eastern Alps. [ABSTRACT FROM AUTHOR]

This paper summarises the outcomes of the 13 th Workshop of the International Association of Phytoplankton Taxonomy and Ecology (IAP). The authors mostly addressed their contributions on the following topics: the effect of trophic state on the attainment of a steady-state; the establishment of equilibria in deep and shallow lakes; the role of spatial heterogeneity, disturbance, and stress in the establishment of equilibrium assemblages; the mechanisms leading to the steady state; the frequency and longevity of equilibrium phases, and the role of morphological and physiological plasticity of phytoplankton in maintaining the (apparently) same populations under different environmental conditions. The composition of steady-state assemblages is compared to that of phytoplankton functional groups (coda). Those functional associations recognised as steady-state assemblages appear to be strongly K-determined in many instances. [ABSTRACT FROM AUTHOR]

The temporal and spatial distribution of total nitrogen and total phosphate in the sediments of a shallow eutrophic Chinese lake (Lake Chao), and their relationships with the physical and chemical features of sediments, and their effects on the lake water quality and trophic state, are presented in this paper. The following results were obtained: (1) higher concentration of Tot-N and Tot-P in the sediments occurred in the summer and the autumn seasons; (2) higher annual average Tot-N and Tot-P concentrations were observed in the sediments near the various river mouths and in the western part of the lake; (3) Tot-N and Tot-P concentration in the lake sediments generally increased with increase in lake sediment Eh, pH, and Al2O3, and declined with decrease in lake sediment size diameters and SiO2; and, (4) correlations were observed in both the temporal and spatial distributions between the trophic state, Tot-N and Tot-P concentration in the lake water, and the Tot-N and Tot-P concentration found in the lake sediments. [ABSTRACT FROM AUTHOR]

In temperate shallow lakes, submerged macrophytes facilitate zooplankton development by providing refuge against fish predation and, thereby, indirectly contribute to maintaining a clear-water state through enhanced zooplankton grazing. The role of macrophytes for zooplankton and their grazing potential is less clear for tropical lakes. We investigated crustacean zooplankton in a phytoplankton-dominated basin (algal basin) and two restored basins dominated by macrophytes (macrophyte basins) in the shallow Huizhou West Lake in tropical southern China. We found that copepods prevailed in all basins, but the dominant taxon differed, with omnivorous cyclopoids dominating in the algal basin and herbivorous calanoids in the macrophyte basins. Moreover, the biomass ratios of calanoid:copepod and zooplankton:phytoplankton were higher in the macrophyte basins than in the algal basin. Our results suggest that restoration measures involving macrophyte transplantation and fish removal lead to reduced fish predation on zooplankton, which help to maintain the clear-water state when macrophytes are established due to higher control on phytoplankton. However, unlike in temperate lakes, large-bodied Daphnia were generally absent and the zooplankton:phytoplankton ratio was overall low, indicating a weaker top-down control in tropical lakes, which is likely due to higher fish predation. [ABSTRACT FROM AUTHOR]

An introduction is presented which discusses various topics within the issue including shallow lakes of the Central Plains of Argentina, reviews of Pampean shallow lakes and effect of the light limitation on the phytoplankton assemblages in a turbid shallow lake.

Lake browning is expected to change aquatic ecosystems considerably. The changes that may occur in zooplankton communities with a high concentration of dissolved organic carbon (DOC) are little studied and not yet sufficiently understood. We studied zooplankton communities in Finland in 27 lakes with a wide DOC range. We explored how zooplankton diversity and biomass vary along a DOC gradient and how species belonging to different functional groups respond to varying DOC concentrations. The total biomass of zooplankton was not related to DOC concentration, but diversity decreased and the negative linear trend in diversity coincided with an increase in omnivorous zooplankton taxa, whereas several other herbivorous zooplankton taxa were displaced from the community along the gradient of DOC. The results of our study suggest that some well-adapted taxa, especially omnivorous taxa, can benefit from lake browning, but a larger number of taxa suffer from unfavourable conditions caused by high DOC concentration. DOC-induced changes in predation pressure and changes in phytoplankton community in terms of resource availability for zooplankton should be emphasized in future research to understand the effects of lake browning on zooplankton. [ABSTRACT FROM AUTHOR]

The East African Great Lakes are inhabited by impressive radiations of cichlids that display a large variation in morphology, diet, colour pattern, and behaviour and have adapted to a large array of niches. Whilst most of these cichlids are bottom dwellers, a number of species have adapted to a pelagic environment and inhabit open waters. From the Lake Edward system, one pelagic species had been previously described, the zooplanktivorous Haplochromis pappenheimi. Our sampling revealed the Lake Edward system to be inhabited by two more pelagic species that were unknown to science and are formally described here, the zooplanktivorous Haplochromis pelagicus sp. nov. and the insectivorous H. aureus sp. nov. All three species seem mostly restricted to deepwater regions where the depth exceeds six metres in Lake Edward, except for H. pelagicus sp. nov., which also occurs in shallower regions of Lakes Edward and George and of the Kazinga Channel. Sexual dimorphism, mainly in head shape, was discovered in H. pappenheimi and H. pelagicus sp. nov. These differences suggest that females of these species have larger buccal cavities than males, which is most likely linked to female mouth brooding behaviour. [ABSTRACT FROM AUTHOR]

Mouthbrooding in cichlids is a behaviour that protects vulnerable offspring. However, the efficacy of this behaviour has not been properly estimated in mouthbrooders that spawn on the bottom or in open water. The present study examined changes in brood size during mouthbrooding in two open-water spawning cichlids from Lake Tanganyika, Cyprichromis coloratus and Cyprichromis leptosoma, using a large number of samples and accounting for the mouth size of mouthbrooding females. Analyses of 279 and 263 mouthbrooding females showed that the average egg number decreased by 22.8% and 11.2% from spawning to hatching and average larval number decreased by 11.6% and 16.2% from hatching to independence in C. coloratus and C. leptosoma, respectively. Future studies should compare these egg and larval mortality rates with those of bottom-spawning mouthbrooders to assess the relative efficacy of this behaviour amongst mouthbrooding species in different aquatic environments. [ABSTRACT FROM AUTHOR]

Variation in jaw protrusion is critical to cichlid fish trophic diversification. For instance, jaw protrusion distance can influence suction, attack speed, as well as bite force, and jaw protrusion angle is associated with exploiting prey from different substrates. Interestingly, premaxillary ascending process length has been shown to influence the maximum distance some cichlid fishes protrude their oral jaws, but its relationship to jaw protrusion angle is unclear. Using phylogenetic comparative methods, morphometrics, and field measurements in Malawi cichlid species, we tested the relationship between the length of the premaxillary ascending process and two components of jaw protrusion. In Malawi, the premaxilla's ascending process length ranged from 6.9 to 15.2% with respect to standard length. Maximum jaw protrusion ranged from 1.4 to 9.1% of standard length and jaw protrusion angle varied from 17° to 76°. Although jaw protrusion angle was not associated with premaxillary ascending process length, phylogenetically adjusted correlations between the ascending process and maximum jaw protrusion distance were highly significant. Evolutionary change in the premaxilla is likely critical for determining the maximum distance, but not the angle, of Malawi cichlid jaw protrusion. Examinations of this type of potential phenotypic multi-functionality will continue to illuminate the mechanisms contributing to cichlid fish diversity. [ABSTRACT FROM AUTHOR]

Smelting activities have strongly affected the Sudbury (Ontario, Canada) region since the late-nineteenth century, leading to acidification and metal contamination of local ecosystems. Regulations restricting acid deposition were enacted in the 1970s, after which many lakes exhibited increasing pH and decreasing metal concentrations. Given the documented chemical recovery and potential emergence of new stressors, we used paleolimnological tools to assess the biological recovery processes in three previously acidified lakes, and also to reconstruct the limnological histories of two reference lakes that were relatively unaffected by acidification. Using subfossil diatoms preserved in lake sediments, we show that assemblages from the acidified lakes have not returned to their pre-disturbance conditions but became dominated by an acidophilous planktonic taxon, Asterionella ralfsii var. americana Körner, during the past few decades. Considering that this taxon has a relatively low pH optimum and is mostly found in thermally stratified waters during summers, we suspect that the legacy effects of acidification and climate warming are the main factors driving its recent prosperity. Our study suggests that biological recovery lags chemical recovery in acid-impacted systems, and a return to pre-disturbance biological assemblages may be impeded by newly emerging environmental stressors. [ABSTRACT FROM AUTHOR]

Submersed aquatic vegetation (SAV) plays an important role in ecosystems. Inventories of SAV spatial distribution and composition are important for monitoring changes in SAV. In this study, we compared three common SAV sampling methods to quantify SAV in western Lake Erie. Aerial imagery of near-shore areas in western Lake Erie was classified using object-based image analysis (OBIA) and evaluated against field-based surveys using single-beam sonar or rake samples. To assess variation among methods, data were assigned either vegetation 'presence' or 'absence' and compared for simple correspondence and agreement (Cohen's Kappa, κ). The two field-based methods had the highest correspondence at 78% (n = 782) and the highest κ = 0.545. Correspondence between OBIA and rake surveys was 69% (n = 245) and κ = 0.36. Correspondence between OBIA and hydroacoustics was the lowest of 54% (n = 30,768) with an agreement of κ = 0.17. Environmental factors such as water turbidity may have played a role in reduced agreement between OBIA and field methods. Determining the optimal method or combination of methods will depend upon research goals, effort, and cost, but each method can provide reliable SAV information for resource management. [ABSTRACT FROM AUTHOR]

Benthic macroinvertebrate communities are useful indicators for biological assessment of environmental and anthropogenic stressors, but our ability to quantify benthic populations is constrained by small spatial scales of traditional grab sampling and labor-intensive processing. During the 2019 assessment of Lake Erie's benthic community we studied lake benthoscapes by enhancing the traditional collection of grabs at 68 stations with underwater imagery, water quality, and sediment nutrients data. Four major habitats were identified from video data including Dreissena aggregations, Hexagenia burrows, and biogenic structures ("chimneys" and "tubes"). All four habitats differed in near-bottom dissolved oxygen (DO) concentration, with the highest DO found above dreissenids and the lowest in chimney habitats. DO, turbidity, and chlorophyll concentration provided the largest contribution to the MaxEnt model and predicted benthoscape distribution. There was a significant separation of benthic species by selected benthoscapes confirmed by independent cluster analysis. Suitable habitat for Dreissena was limited to normoxic areas, and Hexagenia habitats to the western basin. The central basin, subject to summer hypoxia, was mostly characterized by tube and chimney habitats. The agreement among biological, video, and abiotic data confirmed that video analysis can provide a novel, quick, and reliable method to detect benthic habitats affected by periodic hypoxia. [ABSTRACT FROM AUTHOR]