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Extreme precipitation is occurring with greater frequency and intensity as a result of climate change. Such events boost the transport of allochthonous organic matter (allo-OM) to freshwater ecosystems, yet little is known about the impacts on dissolved organic matter (DOM) quality and seston elemental stoichiometry, especially for lakes in warm climates. A mesocosm experiment located in a Turkish freshwater lake was designed to simulate a pulse event leading to increased inputs of allo-OM by examining the individual effects of increasing water colour (HuminFeed®, HF), the direct effects of the extra energetic inputs (alder tree leaf leachate, L), and the interactions of the single treatment effects (combination of both sources, HFL), along with a comparison with unmanipulated controls. Changes in the DOM quality and nutrient stoichiometry of the allo-OM treatment additions was examined over the course of the experiments. Results indicated that there was an increase of high recalcitrant DOM components in the HF treatment, in contrast to an increase in less aromatic microbially derived molecules for the L treatment. Unexpectedly, seston C:P ratios remained below a severe P-limiting threshold for plankton growth and showed the same temporal pattern in all mesocosms. In contrast, seston N:P ratios differed significantly between treatments, with the L treatment reducing P-limiting conditions, whilst the HF treatment increased them. The effects of the combined HFL treatment indicated an additive type of interaction and chlorophyll-a was highest in the HFL treatment. Our results demonstrate that accounting for the optical and stoichiometric properties of experimental allo-OM treatments is crucial to improve the capacity to explain extrapolated conclusions regarding the effects of climate driven flooding on freshwater ecosystems in response to global climate change. [ABSTRACT FROM AUTHOR]

Shallow lakes in the semi-arid climate zone of the Mediterranean are sensitive to drought due to the low annual precipitation and high evaporation. Changes in precipitation and temperature as projected by climate change scenarios will have an effect on the hydrology of these shallow lakes with secondary effects on nutrient dynamics and ecological state. In this study, we used a combined modelling approach that included the catchment model Soil and Water Assessment Tool (SWAT) and the lake model PCLake to study the possible effects of several climate scenarios on a shallow lake in semi-arid central Anatolia, Turkey. Our results show that lower precipitation and higher temperatures may reduce inflow rates and water levels drastically. Diffuse nutrient loading depended highly on precipitation and thus decreased as well. The lake model predicts an interaction between external nutrient loading and water levels. Low water levels benefited submerged macrophytes if nutrient concentrations were low, but low inflow rates and high evaporation during dry periods increased in-lake nutrient concentrations and chlorophyll-a. Cyanobacteria biomass was also higher in the drier and warmer scenarios. Overall, the results show that lower hydraulic loads and reduced flushing rates as a result of drier and warmer conditions lead to lower water levels and higher in-lake nutrient concentrations unless nutrient loading decreased as well. This implies that catchment-scale nutrient management is essential to maintain low nutrient concentrations in the lakes with increasing temperature and decreasing precipitation in a dry climate. [ABSTRACT FROM AUTHOR]

To elucidate the specific and combined effects of bottom-up and top-down control on the microbial community in warm lakes, we sampled microbial community along with physical-chemical and biological variables and performed in situ food web experiments, in 14 Turkish shallow lakes with contrasting nutrient levels and predation pressures. Our field results revealed that differences in microbial communities correlated with differences in zooplankton community structure, temperature (increasing nutrient concentrations, change in zooplankton composition), nutrient concentrations (increasing bacteria and heterotrophic nanoflagellate abundances with increasing nitrogen concentrations and temperature) and macrophyte coverage (ciliates as potential consumers of bacteria and HNF was strongest in macrophyte-dominated lakes). Our in situ experimental study revealed that the zooplankton not only affect the biomass and composition of microbial communities but also alter the microbial structure and trophic relationships. Our results therefore indicate that both bottom-up factors and top-down effects were important for the efficiency of the carbon transfer from bacteria to higher trophic levels in the study lakes. Due to an anticipated increase in eutrophication, temperature and alteration of the classical food web with climate warming, major changes in the microbial community of lakes are, therefore, expected in a warmer future in semi-arid Mediterranean climatic regions. [ABSTRACT FROM AUTHOR]

Lentic ecosystems act as sentinels of climate change, and evidence exists that their sensitivity to warming varies along a latitudinal gradient. We assessed the effects of nutrient and water level variability on zooplankton community composition, taxonomic diversity and size structure in different climate zones by running a standardised controlled 6-months (May to November) experiment in six countries along a European north-south latitudinal temperature gradient. The mesocosms were established with two different depths and nutrient levels. We took monthly zooplankton samples during the study period and pooled a subsample from each sampling to obtain one composite sample per mesocosm. We found a significant effect of temperature on the community composition and size structure of the zooplankton, whereas no effects of water depth or nutrient availability could be traced. The normalised size spectrum became flatter with increasing temperature reflecting higher zooplankton size diversity due to higher abundance of calanoid copepods, but did not differ among depths or nutrient levels. Large-bodied cladocerans such as Daphnia decreased with temperature. Taxonomic diversity was positively related to size diversity, but neither of the two diversity measures demonstrated a clear pattern along the temperature gradient nor with nutrient and water levels. However, genus richness decreased at the warm side of the temperature gradient. Our experiment generally supports recent empirically based findings that a continuing temperature increase may result in lower genus richness and lower abundance of large-sized zooplankton grazers, the latter likely resulting in reduced control of phytoplankton. [ABSTRACT FROM AUTHOR]

Losses of phosphorus (P) and nitrogen (N) have important influences on in-lake concentrations and nutrient loading to downstream ecosystems. We performed a series of mesocosm experiments along a latitudinal gradient from Sweden to Greece to investigate the factors influencing N and P loss under different climatic conditions. In six countries, a standardised mesocosm experiment with two water depths and two nutrient levels was conducted concurrently between May and November 2011. Our results showed external nutrient loading to be of key importance for N and P loss in all countries. Almost all dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) were lost or taken up in biomass in all mesocosms. We found no consistent effect of temperature on DIN and SRP loss but a significant, though weak, negative effect of temperature on total nitrogen (TN) and total phosphorus (TP) loss in the deeper mesocosms, probably related to higher organic N and P accumulation in the water in the warmer countries. In shallow mesocosms, a positive trend in TN and TP loss with increasing temperature was observed, most likely related to macrophyte growth. [ABSTRACT FROM AUTHOR]

Cladocerans are increasingly used in palaeolimnological studies as their community composition is sensitive to both anthropogenic and natural forces in lakes. We present the results of a palaeolimnological investigation of three Turkish shallow lakes located in cold dry steppe and semi-dry Mediterranean climatic regions. The aim was to elucidate historical changes in environmental conditions by analysing sub-fossil cladocerans in Pb-dated sediment cores. Sub-fossil cladoceran remains from the surface sediment of 40 Turkish lakes were analysed to examine the environmental factors that most correlated with variation in the cladoceran assemblage. Redundancy analysis showed that salinity, macrophyte abundance, fish density, depth and total phosphorus were the most correlated with change in cladoceran assemblage composition with eigenvalues for the first and the second axes being λ = 0.312 and λ = 0.061, respectively. Sedimentary cladoceran assemblages from three cores were placed passively within the framework of the surface sediment ordination. The results reveal a prevalent impact of salinity, fish abundance and water level changes from the past to present. Thus, using cladoceran-based inferences, we traced key environmental changes related to variation in climate change, restoration and water level regulation over the last century. [ABSTRACT FROM AUTHOR]

We conducted a fish survey in 40 lakes in western and central Turkey. Fifty species (one to eleven per lake) were recorded, including eighteen endemic and seven alien species. We investigated which local geo-climatic and other environmental variables shaped the fish assemblages. Altitude and temperature turned out to be the most important factors for total species richness as well as richness of omnivorous and zooplanktivorous species and the Shannon-Wiener diversity index, with more species and higher diversity occurring in the warmer lowland lakes. Altitude may affect the fish assemblage directly through dispersal limitation or indirectly by creating a gradient in temperature with which it was strongly correlated. Cyprinidae was the most species-rich and widespread family. Atherinidae, Gobiidae, and Mugilidae (families of marine origin) were mainly found in the lowland regions, while Salmonidae exclusively appeared in the high-altitude lakes. The presence of widely distributed translocated native and alien species revealed a large human impact on the fish assemblages, potentially threatening the rich endemic fish fauna in lakes in this region. [ABSTRACT FROM AUTHOR]

Periphyton communities play an important role in shallow lakes and are controlled by direct forces such as temperature, light, nutrients, and invertebrate grazing, but also indirectly by planktivorous fish predation. We performed a pan-European lake mesocosm experiment on periphyton colonization covering five countries along a north/south geographical/temperature gradient (Estonia, Germany, Czech Republic, Turkey, and Greece). Periphyton biomass on artificial polypropylene strips exposed at 50 cm water depth at low and high nutrient regimes (with mean total phosphorus concentration of 20 and 65 µg L, respectively) was compared during mid-summer. No significant effect of nutrient loading on periphyton biomass was observed as nutrient concentrations in the mesocosms were generally above limiting values. Water temperature significantly enhanced summer periphyton biomass development. Additionally, direct and indirect top-down control of snails and fish emerged as a significant factor in periphyton biomass control. [ABSTRACT FROM AUTHOR]

In warm lakes, fish aggregate within macrophytes, thereby weakening the role of these as a daytime refuge for zooplankton and altering the zooplankton size structure, predation pressure, and water clarity. To elucidate the role of macrophytes as a refuge for zooplankton and their effect on zooplankton size distribution, we established three sets of strandardized artificial plant beds in 11 lakes in Turkey with contrasting fish predation risk and turbidity. Zooplankton were sampled within and outside of each plant beds during day and night. Fish, collected overnight in multimesh-sized gillnets, were abundant both inside and outside the artificial plant beds, impoverishing the usefulness of plants as a daytime refuge for particularly large-bodied zooplankton. Zooplankton size diversity was negatively related to fish abundance. Diel vertical migration was the frequent anti-predator avoidance behavior, but reverse migration was also observed when Chaoborus was present. In contrast to the small-bodied taxa, large- and medium-sized taxa showed intraspecific size-based migration (i.e., individuals of different sizes had different migration patterns). Predators influenced the size structure and diel movement of zooplankton, but the response changed with the size of zooplankton and water clarity. [ABSTRACT FROM AUTHOR]

According to the Intergovernmental Panel on Climate Change report released in September 2014, unprecedented changes in temperature and precipitation patterns have been recorded globally in recent decades and further change is predicted to occur in the near future, mainly as the result of human activity. In particular, projections show that the Mediterranean climate zone will be markedly affected with significant implications for lake water levels and salinity. This may be exacerbated by increased demands for irrigation water. Based on long-term data from seven lakes and reservoirs covering a geographical gradient of 52° of latitudes and a literature review, we discuss how changes in water level and salinity related to climate change and water abstraction affect the ecosystem structure, function, biodiversity and ecological state of lakes and reservoirs. We discuss mitigation measures to counteract the negative effects on ecological status that are likely to result from changes in climate and water abstraction practices. Finally, we highlight research required to improve knowledge of the impacts of anthropogenically induced changes on lake water level and consequent changes in salinity. [ABSTRACT FROM AUTHOR]

The body size of zooplankton has many substantive effects on the function of aquatic food webs. A variety of factors may affect size, and earlier studies indicate that water temperature may be a particularly important variable. Here we tested the hypothesis that the body size of cladocerans, calanoids, and cyclopoids declines with increasing water temperature, a response documented in an earlier study that considered only cladoceran zooplankton. We tested the hypothesis by comparing body size data that were available from prior studies of lakes ranging from 6 to 74 latitude and encompassing a temperature range of 2-30°C. Cladoceran body size declined with temperature, in a marginally significant manner ( P = 0.10). For cyclopoids, the decline was more significant ( P = 0.05). In both cases, there was considerably more variation around the regression lines than previously observed; suggesting that other variables such as fish predation played a role in affecting size. Calanoid body size was unrelated to temperature. In contrast with cladocerans and cyclopoids, perhaps calanoid body size is not metabolically constrained by temperature or is differently affected by changes in fish predation occurring with increasing temperature. The unexpected result for calanoids requires further investigation. [ABSTRACT FROM AUTHOR]

Cladocerans are valuable indicators of environmental change in lakes. Their fossils provide information on past changes in lake environments. However, few studies have quantitatively examined the relationships between contemporary and sub-fossil cladoceran assemblages and no investigations are available from Mediterranean lakes where salinity, eutrophication and top-down control of large-bodied cladocerans are known to be important. Here we compared contemporary Cladocera assemblages, sampled in summer, from both littoral and pelagic zones, with their sub-fossil remains from surface sediment samples from 40 Turkish, mainly shallow, lakes. A total of 20 and 27 taxa were recorded in the contemporary and surface sediment samples, respectively. Procrustes rotation was applied to both the principal components analysis (PCA) and redundancy analysis (RDA) ordinations in order to explore the relationship between the cladoceran community and the environmental variables. Procrustes rotation analysis based on PCA showed a significant accord between both littoral and combined pelagic-littoral contemporary and sedimentary assemblages. RDA ordinations indicated that a similar proportion of variance was explained by environmental variation for the contemporary and fossil Cladocera data. Total phosphorus and salinity were significant explanatory variables for the contemporary assemblage, whereas salinity emerged as the only significant variable for the sedimentary assemblage. The residuals from the Procrustes rotation identified a number of lakes with a high degree of dissimilarity between modern and sub-fossil assemblages. Analysis showed that high salinity, deep water and high macrophyte abundance were linked to a lower accord between contemporary and sedimentary assemblages. This low accord was, generally the result of poor representation of some salinity tolerant, pelagic and macrophyte-associated taxa in the contemporary samples. This study provides further confirmation that there is a robust relationship between samples of modern cladoceran assemblages and their sedimentary remains. Thus, sub-fossil cladoceran assemblages from sediment cores can be used with confidence to track long-term changes in this environmentally sensitive group and in Mediterranean lakes, subjected to large inter-annual variation in water level, salinity and nutrients. [ABSTRACT FROM AUTHOR]

Information on the effects of water level changes on microbial planktonic communities in lakes is limited but vital for understanding ecosystem dynamics in Mediterranean lakes subjected to major intra- and inter-annual variations in water level. We performed an in situ mesocosm experiment in an eutrophic Turkish lake at two different depths crossed with presence/absence of fish in order to explore the effects of water level variations and the role of top-down regulation at contrasting depths. Strong effects of fish were found on zooplankton, weakening through the food chain to ciliates, HNF and bacterioplankton, whereas the effect of water level variations was overall modest. Presence of fish resulted in lower biomass of zooplankton and higher biomasses of phytoplankton, ciliates and total plankton. The cascading effects of fish were strongest in the shallow mesocosms as evidenced by a lower zooplankton contribution to total plankton biomass and lower zooplankton:ciliate and HNF:bacteria biomass ratios. Our results suggest that a lowering of the water level in warm shallow lakes will enhance the contribution of bacteria, HNF and ciliates to the plankton biomass, likely due to increased density of submerged macrophytes (less phytoplankton); this effect will, however, be less pronounced in the presence of fish. [ABSTRACT FROM AUTHOR]

The article offers information on the 8th International Shallow Lakes Conference held on October 12-17, 2015 at Antalya, Turkey hosted by the Middle East Technical University in Ankara, Turkey. Topics discussed include description of limnological research over deep lakes, association of shallow lakes in development of disproportionate biodiversity, observation of shallow lakes in lowland areas and evolution of ecological theories with shallow lakes usage for environmental change response.

Net ecosystem production (NEP) is an important indicator of lake ecosystem function and integrity. An earlier study, restricted to one geographical region, indicated that oxygen saturation levels (DO%) might be used to predict daily NEP in shallow lakes. To test the generality of the method, we used DO% data collected in a standardised pan-European mesocosm experiment with contrasting trophic states and water levels covering a large climate gradient (from Sweden to Turkey). We corroborated these data with process-based DO simulations. The NEP ~ DO% relation depended on factors influencing gas transfer: water depth and wind. The NEP ~ DO% relation per volume became weaker with increasing depth (1–2 m) but was independent of depth when area based. Simulations indicated that the marginalisation of the depth was sensitive to wind conditions. Trophic status, temperature and light showed no or only marginal (climate zone) effects (experimental data), while the simulations indicated influence of those factors under particular wind–depth conditions. We confirmed that when considering also wind and depth effects, midday DO% potentially provides reliable estimates of daily NEP. Therefore, historical monitoring data of DO% might be used to estimate NEP, and process-based oxygen models may be valuable tool therein. We encourage further tests. [ABSTRACT FROM AUTHOR]

Climate and land-use change drive a suite of stressors that shape ecosystems and interact to yield complex ecological responses (that is, additive, antagonistic and synergistic effects). We know little about the spatial scales relevant for the outcomes of such interactions and little about effect sizes. These knowledge gaps need to be filled to underpin future land management decisions or climate mitigation interventions for protecting and restoring freshwater ecosystems. This study combines data across scales from 33 mesocosm experiments with those from 14 river basins and 22 cross-basin studies in Europe, producing 174 combinations of paired-stressor effects on a biological response variable. Generalized linear models showed that only one of the two stressors had a significant effect in 39% of the analysed cases, 28% of the paired-stressor combinations resulted in additive effects and 33% resulted in interactive (antagonistic, synergistic, opposing or reversal) effects. For lakes, the frequencies of additive and interactive effects were similar for all spatial scales addressed, while for rivers these frequencies increased with scale. Nutrient enrichment was the overriding stressor for lakes, with effects generally exceeding those of secondary stressors. For rivers, the effects of nutrient enrichment were dependent on the specific stressor combination and biological response variable. These results vindicate the traditional focus of lake restoration and management on nutrient stress, while highlighting that river management requires more bespoke management solutions.