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Plants play an important role in fishpond littorals, but little is known about factors influencing their presence and growth patterns. We surveyed vegetation of reed bed and exposed bottom zones in ponds used for rearing of common carp fry (nursery pond) and ongrowing to market size (main pond). Plant species diversity and functional diversity and plant species cover and functional cover were assessed. We found no significant differences in spring and summer surveys. When data of the analysed vegetation zones were combined, nursery and main ponds showed significant differences in plant species diversity and species cover. Analysis of the vegetation zones revealed that (i) regardless of fishpond management type, exposed bottoms and reed beds significantly differed in plant species cover and functional cover; (ii) plant species diversity and species cover of exposed bottom zones differed between nursery and main ponds; and (iii) no assessed characteristics differed significantly between nursery pond reed bed and main pond reed bed zones. Zone width and shoreline slope exerted greatest impact on development of reed beds, whereas fishpond management type and surrounding land use were the most important factors determining vegetation of exposed bottoms. Partial summer drainage supported plant species diversity and functional diversity as well as cover of typical species of reed beds and exposed bottoms in both fishpond types. Our results are applicable to preservation of fishpond biodiversity as well as to the management and conservation of other shallow water bodies.

Pathways of photochemical degradation of a cardiovascular drug verapamil under conditions relevant to natural waters and the toxicity of the photoproducts to Daphnia magna were investigated. Photodegradation was shown to proceed via photocatalysed mechanism. Two main photodegradation pathways were recognised: the first leading to hydroxylation at the methylamino position followed by splitting of verapamil molecule into two fragments, and the second providing the main active metabolite of verapamil, norverapamil, and a series of norverapamil isomers, followed again by their splitting at the amino group position. Twenty-two products of photodegradation were identified. Toxicity assays in sublethal concentrations of the parental drug, of the photoproduct mixture, and of norverapamil revealed no direct negative response in Daphnia magna to verapamil. On the other hand, photochemical products significantly lowered the number of juveniles, number of clutches, and body size of Daphnia. The exposition of Daphnia to norverapamil showed the same but even more pronounced effects than its exposition to the mixture of photoproducts, which leads to the conclusion that norverapamil is mainly responsible for the toxicity of photoproduct mixture and represents a noteworthy threat to aquatic invertebrates.

Fishponds form substantial part of standing water ecosystems in the landscape of the Central Europe. We studied the effects of fish production and environmental parameters on phytoplankton in fifteen fishponds of various size, fish production and situated at different altitudes. Water and plankton samples were collected from April to October 2018 and 2019. Phytoplankton abundance, zooplankton biovolume, total phosphorus, total nitrogen, ammonia-nitrogen, nitrites, nitrates, phosphates, and total iron concentration were determined. Based on average values of total nitrogen (8.53 mg.l-1), total phosphorus (0.399 mg.l-1), and chl-a (180 µg.l-1) all fishponds were classified as hypertrophic. Fish production was significantly correlated only with altitude. With increasing altitude, fishponds have a lower nutrient content, lower temperature, and hence lower production. The direct effect of fish production on phytoplankton was not observed. Two environmental parameters significantly explained the variability in phytoplankton - altitude and total iron concentration. Our results indicate that besides traditionally monitored parameters like nitrogen and phosphorus concentration, the attention should also be focused on other factors potentially affecting studied ecosystems, hypertrophic fishponds. info:eu-repo/semantics/openAccess

Despite the importance of shallow lakes worldwide, knowledge of microbial components, the base of their food webs, remains scarce. To close this gap, we investigated planktonic microbial food webs, in particular protistan bacterivory (for both ciliates and heterotrophic nanoflagellates [HNF]), in 10 shallow hypertrophic fishponds in South Bohemia (Czech Republic). We used fluorescently labeled bacteria as bacterivory tracers to estimate how abundant protistan populations in fishponds (4–25 × 103 HNF mL−1 and 55–770 ciliates mL−1) contribute to total bacterial mortality. Fluorescence microscopy, innovative image processing tools, and quantitative protargol staining were combined to detect major bacterivorous and omnivorous ciliate taxa. We quantified bacterial production, bacterivory by individual ciliate species, total ciliates, and total protistan bacterivory in all fishponds. On average, ciliate bacterivory was comparable to that of HNF, accounting for 56% and 44% of total protistan grazing, respectively. We found that primarily bacterivorous Peritrichia (genera Vorticella, Epistylis) and Scuticociliata (Cyclidium spp.) contributed only moderately (mean 26%) to total ciliate bacterivory. Unexpectedly, but highly abundant omnivorous Halteria/Pelagohalteria (Stichotrichia) and, to a lesser extent, also omnivorous Rimostrombidium spp. (Oligotrichia) contributed significantly more (mean 71%) to total ciliate bacterivory than typical bacterivorous taxa. This suggests that unselective grazers, which feed on a broader size spectrum from bacteria to small algae, may have a considerable competitive advantage in hypertrophic environments rich in small particles. Moreover, a meta‐analysis of available literature data supports our hypothesis that the role of ciliate bacterivory increases significantly, relative to HNF bacterivory, along a trophic gradient toward hypertrophic habitats.

Submerged macrophytes are of key importance for the structure and functioning of shallow lakes and can be decisive for maintaining them in a clear water state. The ongoing climate change affects the macrophytes through changes in temperature and precipitation, causing variations in nutrient load, water level and light availability. To investigate how these factors jointly determine macrophyte dominance and growth, we conducted a highly standardized pan-European experiment involving the installation of mesocosms in lakes. The experimental design consisted of mesotrophic and eutrophic nutrient conditions at 1 m (shallow) and 2 m (deep) depth along a latitudinal temperature gradient with average water temperatures ranging from 14.9 to 23.9°C (Sweden to Greece) and a natural drop in water levels in the warmest countries (Greece and Turkey). We determined percent plant volume inhabited (PVI) of submerged macrophytes on a monthly basis for 5 months and dry weight at the end of the experiment. Over the temperature gradient, PVI was highest in the shallow mesotrophic mesocosms followed by intermediate levels in the shallow eutrophic and deep mesotrophic mesocosms, and lowest levels in the deep eutrophic mesocosms. We identified three pathways along which water temperature likely affected PVI, exhibiting (a) a direct positive effect if light was not limiting; (b) an indirect positive effect due to an evaporation-driven water level reduction, causing a nonlinear increase in mean available light; and (c) an indirect negative effect through algal growth and, thus, high light attenuation under eutrophic conditions. We conclude that high temperatures combined with a temperature-mediated water level decrease can counterbalance the negative effects of eutrophic conditions on macrophytes by enhancing the light availability. While a water level reduction can promote macrophyte dominance, an extreme reduction will likely decrease macrophyte biomass and, consequently, their capacity to function as a carbon store and food source. Eesti Teadusagentuur, Grant/Award Number: PRG709; Türkiye Bilimsel ve Teknolojik Araştirma Kurumu (TÜBİTAK), Grant/Award Number: BIDEB 2232, 2211 and ÇAYDAĞ 110Y125; CLEAR2 (a Villum Kann Rasmussen Centre of Excellence project); AU Centre for Water Technology; EU FP-7 Theme 6 projects REFRESH (Adaptive Strategies to Mitigate the Impacts of Climate Change on European Freshwater Ecosystems), Grant/Award Number: 244121; Orta Doğu Teknik Üniversitesi BAP Programme Eesti Teadusagentuur, Grant/Award Number: PRG709; Türkiye Bilimsel ve Teknolojik Araştirma Kurumu (TÜBİTAK), Grant/Award Number: BIDEB 2232, 2211 and ÇAYDAĞ 110Y125; CLEAR2 (a Villum Kann Rasmussen Centre of Excellence project); AU Centre for Water Technology; EU FP-7 Theme 6 projects REFRESH (Adaptive Strategies to Mitigate the Impacts of Climate Change on European Freshwater Ecosystems), Grant/Award Number: 244121; Orta Doğu Teknik Üniversitesi BAP Programme

Pathways of photochemical degradation of a cardiovascular drug verapamil under conditions relevant to natural waters and the toxicity of the photoproducts to Daphnia magna were investigated. Photodegradation was shown to proceed via photocatalysed mechanism. Two main photodegradation pathways were recognised: the first leading to hydroxylation at the methylamino position followed by splitting of verapamil molecule into two fragments, and the second providing the main active metabolite of verapamil, norverapamil, and a series of norverapamil isomers, followed again by their splitting at the amino group position. Twenty-two products of photodegradation were identified. Toxicity assays in sublethal concentrations of the parental drug, of the photoproduct mixture, and of norverapamil revealed no direct negative response in Daphnia magna to verapamil. On the other hand, photochemical products significantly lowered the number of juveniles, number of clutches, and body size of Daphnia. The exposition of Daphnia to norverapamil showed the same but even more pronounced effects than its exposition to the mixture of photoproducts, which leads to the conclusion that norverapamil is mainly responsible for the toxicity of photoproduct mixture and represents a noteworthy threat to aquatic invertebrates.

Key life history parameters significantly differed between two different clones of Simocephalus vetulus originating from different habitats, i.e. a fishless pool and a fish pond. The following fitness-related traits were studied: lifespan, age at first reproduction, interclutch period, number of clutches, and number of embryos. In general, in relation to the fish pond clone the fishless pool clone revealed longer lifespan and higher fecundity due to more frequent clutches, contributing to a higher fitness. Higher food quantities decreased the lifespan but did not alter fitness-related traits except for a shorter interclutch period. The Simocephalus clone from the fishless pool matured earlier in low food conditions, while the fish pond clone matured earlier in the high food conditions. The switch in food concentration between the subsequent generations significantly shortened the lifespan in the fish pond clone but revealed no effect in the fishless pool clone.

Usage of atrazine, a widely used herbicide, is now banned in many countries. Although forbidden to use, significant concentration of this herbicide is still present in the environment. The study focused not only on the toxicity of atrazine itself but also on products of homogeneous photocatalytic degradation. Such degradation was very fast in given conditions (sufficient amount of Fe(III) in the reaction system)-more than 95% of the initial amount of atrazine was eliminated after 30 min of irradiation. The toxicity of atrazine and its photodegradation products were examined on the aquatic plant Lemna minor and microcrustacean Daphnia magna in both acute and chronic tests. While the growth inhibition assay of atrazine for Lemna minor revealed EC50 value of 128.4 μg dm-3, the herbicide did not affect Daphnia in the acute toxicity assay. A degradation product, desethyl-atrazine, has been demonstrated to have a pronounced negative effect on the plant growth. Both atrazine and desethyl-atrazine affect negatively the number of juveniles and number of clutches of Daphnia magna in the chronic toxicity assay. Photocatalytic degradation lowers the negative effect of atrazine in Daphnia magna while photodegradation products still negatively affect Lemna growth.

Important drivers of gross primary production (GPP) and ecosystem respiration (ER) in lakes are temperature, nutrients, and light availability, which are predicted to be affected by climate change. Little is known about how these three factors jointly influence shallow lakes metabolism and metabolic status as net heterotrophic or autotrophic. We conducted a pan-European standardized mesocosm experiment covering a temperature gradi- ent from Sweden to Greece to test the differential temperature sensitivity of GPP and ER at two nutrient levels (mesotrophic or eutrophic) crossed with two water levels (1 m and 2 m) to simulate different light regimes. The findings from our experiment were compared with predictions made according the metabolic theory of ecology (MTE). GPP and ER were significantly higher in eutrophic mesocosms than in mesotrophic ones, and in shallow mesocosms compared to deep ones, while nutrient status and depth did not interact. The estimated temperature gains for ER of ~ 0.62 eV were comparable with those predicted by MTE. Temperature sensitivity for GPP was slightly higher than expected ~ 0.54 eV, but when corrected for daylight length, it was more consistent with predictions from MTE ~ 0.31 eV. The threshold temperature for the switch from autotrophy to heterotrophy was lower under mesotrophic (~ 11 C) than eutrophic conditions (~ 20 C). Therefore, despite a lack of signifi- cant temperature-treatment interactions in driving metabolism, the mesocosm’s nutrient level proved to be cru- cial for how much warming a system can tolerate before it switches from net autotrophy to net heterotrophy. We thank the technical staff at the various experimental sites for their support. We thank Alena S. Gesell, Deniz Özkundakci, Jan-Hendrik Schlei- mer, Silke Schmidt, Torsten Seltmann, and Tom Shatwell for their helpful discussions during the preparation of this manuscript. We thank Anne Mette Poulsen, Adam Wilkins, and Michael Thayne for their valuable edit- ing of the manuscript. We are also grateful to reviewers for their valuable comments on the manuscript. This study was supported by FP-7 REFRESH (Adaptive strategies to Mitigate the Impacts of Climate Change on European Freshwater Ecosystems, Contract No. 244121) and the MARS project (Managing Aquatic ecosystems and water Resources under multi- ple Stress), funded under the 7th EU Framework Programme, Theme 6 (Environment including Climate Change), Contract No. 603378 (http:// www.mars-project.eu), TUBITAK- ÇAYDAG (projects No. 105Y332 and 110Y125), the Middle East Technical University (METU)-BAP program of Turkey. EJ was further supported by AU Centre for Water Technology and A_lÇ was also supported by TUBITAK (project 296 Nos. 105Y332 and 110Y125). We thank the technical staff at the various experimental sites for their support. We thank Alena S. Gesell, Deniz Özkundakci, Jan-Hendrik Schlei- mer, Silke Schmidt, Torsten Seltmann, and Tom Shatwell for their helpful discussions during the preparation of this manuscript. We thank Anne Mette Poulsen, Adam Wilkins, and Michael Thayne for their valuable edit- ing of the manuscript. We are also grateful to reviewers for their valuable comments on the manuscript. This study was supported by FP-7 REFRESH (Adaptive strategies to Mitigate the Impacts of Climate Change on European Freshwater Ecosystems, Contract No. 244121) and the MARS project (Managing Aquatic ecosystems and water Resources under multi- ple Stress), funded under the 7th EU Framework Programme, Theme 6 (Environment including Climate Change), Contract No. 603378 (http:// www.mars-project.eu), TUBITAK- ÇAYDAG (projects No. 105Y332 and 110Y125), the Middle East Technical University (METU)-BAP program of Turkey. EJ was further supported by AU Centre for Water Technology and A_lÇ was also supported by TUBITAK (project 296 Nos. 105Y332 and 110Y125).

Aerobic Anoxygenic Phototrophic (AAP) bacteria are bacteriochlorophyll (BChl) a -containing organisms which use light energy to supplement their predominantly heterotrophic metabolism. Here, we investigated mortality and growth rates of AAP bacteria in three different freshwater lakes in Central Europe: the mountain lake Plesne, the oligo-mesotrophic Lake Stechlin and the forest pond Huntov. The mortality of AAP bacteria was estimated from diel changes of BChl a fluorescence. Net and gross growth rates were calculated from the increases in AAP cell numbers. The gross growth rates of AAP bacteria ranged from 0.38 to 5.6 d−1, with the highest values observed during summer months. Simultaneously, the rapidly growing AAP cells have to cope with an intense grazing pressure by both zooplankton and protists. The presented results document that during the day, gross growth usually surpased mortality. Our results indicate that AAP bacteria utilize light energy under natural conditions to maintain rapid growth rates, which are balanced by a generally intense grazing pressure. This article is protected by copyright. All rights reserved.

The response of planktonic (phytoplankton, ciliates, rotifers and crustaceans) and littoral (Ephemeroptera, Plecoptera, Trichoptera and Heteroptera: Nepomorpha) assemblages to chemical recovery was studied over a twelve-year period (1999–2011) in eight glacial lakes in the Bohemian Forest (central Europe). The region suffered from high atmospheric pollution from the 1950s to the late 1980s, but has since been recovering from acidification due to 86% and 44% decrease in sulphur and nitrogen deposition, respectively, during the 1990s–2000s. Despite the rapid improvement in water chemistry of all the eight studied lakes, only four have partly recovered so far (low-aluminium lakes), while the other four lakes still remain strongly acidic (high-aluminium lakes). Although biotic responses (especially in the low-Al lakes) showed important signs of recovery, such as reappearance of some indigenous or acid-sensitive species, decline in eurytopic acid-tolerant species and colonisation by vagile species, the assemblages of all the lakes still suffer from acid stress. Our results also indicate an increasing role of biotic interactions between colonisers and residents leading to the reconstruction of aquatic food webs in the low-Al lakes.

The top-down effect of fish predation on reproduction success of Daphnia females was investigated in an outdoor mesocosm experiment with natural (oligotrophic) food conditions. The planktivorous fish, sunbleak (Leucaspius delineatus, 4.9 individuals m–3) was introduced into a half of mesocosms after the first sampling of zooplankton to compare daphnid life-history traits with and without fish predators. Our results showed selective fish predation on the daphnid females with advanced developmental stages of embryos. The Daphnia populations exposed to fish exhibited a lower proportion of females with advanced embryos over those with earlier embryonal stages. Fish predators obviously were attracted to more visible females bearing larger embryos, with well-developed pigmented eyes. Simultaneously, we found a smaller daphnid body length in the mesocosms with fish than in those that were fishless. However, the daphnid clutch size did not reflect their body-length pattern and, surprisingly, decreased regardless of fish presence or absence since the first sampling day, probably owing to deterioration of food quality (mean seston carbon:phosphorus ratio ~238). Nevertheless, this selective elimination of the females with advanced embryos, together with the overall decrease in daphnid fitness, can strengthen the deceleration of its population growth under fish predation.

Seasonal and inter-annual macrophyte assemblage dynamics were surveyed in ten nursery and ten main fishponds stocked primarily with common carp Cyprinus carpio fry and with common carp being reared to market size, respectively. The results indicate a significant difference in macrophyte species number and abundance between the nursery and main fishponds, with up to 24.5% of the variation in macrophyte species distribution patterns explained by fishpond management type (nursery or main) and up to 6.7% by water transparency. Fish biomass used as a fish stock proxy explained up to 13.9% of variability. Although not significant, differences in species number and abundance were found (i) between spring and summer survey periods during the growing season with both species number and abundance usually decreasing in summer, and (ii) between years of the farming production cycle with a higher species number and abundance typically found in the first year of the farming cycle in the nursery fishponds. The results increase knowledge of fishpond macrophyte assemblages and may be of interest for conservation of aquatic habitats.

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.

Zooplankton community response to the combined effects of nutrients and fish (hereafter N + F) at contrasting temperatures was studied in a long-term experiment conducted in 24 shallow lake mesocosms with low and high nutrient levels. We found a positive effect of N + F on zooplankton biomass, chlorophyll-a and turbidity. In contrast, zooplankton species and size diversity decreased with added N + F, as did submerged macrophyte plant volume inhabited (PVI). The community composition of zooplankton in high N + F mesocosms was related to chlorophyll-a and turbidity and to macrophyte PVI in the low N + F mesocosms. Macrophytes can protect zooplankton from fish predation. Compared to N + F effects, temperature appeared to have little effect on the zooplankton community. Yet analysis of community heterogeneity among treatments indicated a significant temperature effect at high N + F levels. The results indicate an indirect temperature effect at high N + F levels that can be attributed to temperature-dependent variation in fish density and/or chlorophyll-a concentration.

The impact of fish and cyclopoid copepod predation on zooplankton communities was evaluated using large-volume mesocosms (depth 9.5 m; volume 13 m 3 ) in the R ˇ imov reservoir (Czech Republic). Two yearling roach and perch individuals introduced into mesocosms represented the fish treatment, which was com- pared to cyclopoid copepods (initial abundance of 2 ind.L x1 ) and a control with no initial addition of pre- dators. Our results clearly support the hypothesis that planktivorous fish feeding leads to the suppression of large-bodied cladocerans. In the presence of fish, the cladoceran community changed from a dominance of large-bodied Daphnia spp. at the beginning to dominance by the smaller Bosmina longirostris at the end of the experiment. Chlorophyll-a concentration and rotifer abundances increased in the absence of daphnids. In the absence of fish, the presence of large-bodied cladocerans resulted in decreasing chlorophyll-a concentration. Although no significant differences were observed between cyclopoid abundances in treatments stocked with cyclopoids and the control, the proportion of large cladocerans clearly showed the effect of the manipulation. The similar trends in both of these treatments did not confirm the importance of cyclopoid predation in our experiment. The overall strong effect of fish over cyclopoid predation suggests the main role of fish predation in the forming of zooplankton communities and in turn impacting phytoplankton biomass in mesocosms.

Aerobic Anoxygenic Phototrophic (AAP) bacteria are bacteriochlorophyll (BChl) a -containing organisms which use light energy to supplement their predominantly heterotrophic metabolism. Here, we investigated mortality and growth rates of AAP bacteria in three different freshwater lakes in Central Europe: the mountain lake Plešné, the oligo-mesotrophic Lake Stechlin and the forest pond Huntov. The mortality of AAP bacteria was estimated from diel changes of BChl a fluorescence. Net and gross growth rates were calculated from the increases in AAP cell numbers. The gross growth rates of AAP bacteria ranged from 0.38 to 5.6 d

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.

Summary 1. We followed microbial and other planktonic communities during a 4-month period (February–May) in 12 outdoor flow-through mesocosms designed to elucidate the effect of global warming and nutrient enrichment. The mesocosms were established in 2003. 2. Warming had a smaller effect than nutrients on the biomass of the microbial and planktonic communities, and warming and nutrients together exhibited complex interactions. 3. We did not find direct effects of warming on the biomass of bacterioplankton or ciliates; however, warming significantly added to the positive effect of nutrients on these organisms and on heterotrophic nanoflagellates (HNF). No warming effects on any of the other planktonic groups analysed were detected. 4. The zooplankton: phytoplankton biomass ratio was lowest, and the HNF: bacteria and rotifer: bacteria biomass ratios highest in the heated, nutrient-rich mesocosms. We attribute this to higher fish predation on large-bodied zooplankton, releasing the predation on HNF and competition for rotifers. 5. The proportion of phytoplankton to the total plankton biomass increased with nutrients, but decreased with warming. The opposite pattern was observed for the proportion of phytoplankton to the total microbial biomass. 6. As climate warming may lead to eutrophication, major changes may occur in the pelagic food web and the microbial community due to changes in trophic state and in combination with warming.

We studied potentially omnivorous feeding of the common limnetic calanoid copepod Eudiaptomus gracilis using feeding experiments with subsequent gut content analysis. Feeding experiments performed with a laboratory culture of the rotifer Brachionus calyciflorus established a daily feeding rate reaching up to 9.8 rotifers per day when a rotifer-only diet was offered. Addition of algae (Chlamydomonas sp.) to the calanoid diet decreased the ingestion rate of rotifers to near 0. Yet, gut content analysis regularly (though not very frequently) revealed the remains of a rotifer, B. calyciflorus, in the digestive tract of an E. gracilis. We thus proved the ability of E. gracilis to feed on rotifers, even when these were offered in a diet mixed with algae.

Seasonal dynamics of zooplankton were investigated in three different habitats of the shallow and temperate Kacležský pond (Czech Republic) during 2003–2004. The studied habitats included the limnetic zone and two littoral zones, each dominated by a different type of emergent macrophyte, reed grass (Glyceria maxima ) and common reed (Phragmites australis ). Species richness (calculated as number of taxa) was higher in both littoral zones than in the limnetic zone. The seasonal development of limnetic and littoral zooplankton communities differed. In contrast to the two littoral zones, close correlation with chlorophyll-a concentration was found for rotifers and cladocerans in the limnetic zone. Moreover, cladocerans inhabiting littoral areas (mainly Bosmina longirostris ) reached annual maxima during spring when chlorophyll-a concentrations were low.

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 mu g L-1, 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.

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

Water chemistry and fish occurrence in outflows from two lakes recovering from acidification were studied during 2005–2010. The two lakes represented the regional extremes: while Lake Laka (LA) was the least acidified among the Bohemian Forest lakes, Lake Certovo (CT) was the most acidified. Water chemistry improved downstream in either outlet due to mixing with less acidic water from tributaries. While pH of the LA stream was circumneutral and concentrations of ionic aluminium (Ali) were low ( 200 μg.l-1) throughout the year and was considered as a reference site. Brown trout (Salmo trutta s.l.) survived in the LA stream already at 0.7 km from the lake. A stable trout population, including young-of-the-year fish increasing in numbers, was found in the LA stream between 2005 and 2010 despite the spring short-term acid episodes. Any recovery of the CT stream is...