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Climate change is expected to profoundly affect both temperature and net precipitation, with implications for lake water level. We describe the design of a harmonized, simultaneous, cross-European mesocosm experiment to elucidate the effects of climate change on community structure, functioning, and metabolism in shallow lakes at low and high nutrient levels with contrasting depths (1 and 2 m). We used cylindrical (D = 1.2 m) tanks that were either 1.2 or 2.2 m high, each having a 10-cm sediment layer. We inoculated the mesocosms with a mixed sample of sediment and plankton from lakes with contrasting nutrient concentrations and added macrophytes and planktivorous fish. Sediment was pre-equilibrated to the required experimental nutrient concentration. During the experiment the water level decreased with increasing temperature (up to 90 cm in the Mediterranean mesocosms) while conductivity increased. The average chlorophyll a concentration increased with temperature in the deep mesocosms but was more variable in the shallow mesocosms. Macrophyte abundance increased with temperature, while the oxygen data suggest that net primary production peaked at intermediate temperatures. We conclude that our experimental design has the potential for tracking the interacting effects of global warming and eutrophication in shallow lakes. [ABSTRACT FROM AUTHOR]

The wastewaters of an iron mining company in NW Russia have changed the water quality in some forest lakes to be hard with a high pH, in contrast to the soft water and low pH in natural lakes. Two impacted lakes and a reference lake were sampled once in early August in three successive years for water quality, plankton communities, and fish. The concentrations of potassium, lithium, and sulphate were high in the impacted lakes. Total phosphorus was low (~10 µg L-1) in all lakes. The primary producers' biomass and chlorophyll a content in the impacted lakes were high because of high densities of autotrophic picocyanobacteria (Synechococcus spp.). All planktonic communities showed a changed taxa composition and lower species richness. Zooplankton was predominantly Rotatoria in all the lakes. In the impacted lakes, Cladocera was represented by Bosmina, and Copepoda by small cyclopoids. The most obvious substance to be harmful to some planktonic species was potassium. The high pH and high mineral content of the water obviously lower both the toxicity and the bioavailability of heavy metals in the impacted lakes. [ABSTRACT FROM AUTHOR]