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In this study, pressure driven ceramic membranes for microfiltration (MF) and ultrafiltration (UF) were used to improve the quality of waters in lakes. Four urban lakes located in the city of Olsztyn and belong to the Masurian Lake District: Track (53°47′21″N; 20°32′24″E), Podkowka (53°47′2″N; 20°27′1″E), Tyrsko (53°48′18″N; 20°25′21″E), and Redykajny (53°48′55″N; 20°25′4″E) were examined. The effects of the composition of lake water from different photic zones and of the type of membrane on the efficiency of removal of total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) were investigated. The average efficiencies of rejection were 71.6 ± 5.8% (TOC), 16.0 ± 5.7% (TP) and 19.6 ± 9.3% (TN), independently of the composition of the feed and the type of membrane. Due to the similar average permeate fluxes of 2.2 ± 0.1 L/(m2 min) and water recoveries of above 85% in MF and UF, the use of MF is suggested because it has lower operational costs than UF. Because membrane filtration of waters from the zones with the highest chlorophyll contents was very effective both in terms of efficiency of pollutant rejection and hydraulic parameters of membranes, this technology can be used for selective treatment of parts of water with the highest phytoplankton abundance.

The authors acknowledge COST Action ES 1105 "CYANOCOST Cyanobacterial blooms and toxins in water resources: Occurrence impacts and management" and COST Action Global Change Biology ES 1201 NETLAKE -Networking Lake Observatories in Europe" for contributing to this study through networking and knowledge sharing with European experts in the field. We acknowledge the members of the Global Lake Ecological Observatory Network (GLEON) for their collaborative spirit and enthusiasm that inspired the grassroots effort of the EMLS. E.M. was supported by a grant from the Swiss State Secretariat for Education, Research and Innovation to Bas Ibelings and by supplementary funding from University of Geneva. We thank Wendy Beekman for the nutrient analysis. We thank Pieter Slot for assisting with the pigment analysis. We thank Dr. Ian Jones for valuable feedback on an earlier version of the manuscript. We thank the Leibniz Institute of Freshwater Ecology and the Aquatic Microbial Ecology Group for logistic and technical support of J. Fonvielle and H.-P. Grossart, and the Leibniz Association for financial support. H.P. was supported by the US National Science Foundation (1840715, 1831096). A.C.'s work was funded by the Spanish Agencia Estatal de Investigacion and EU funds through the project CLIMAWET (CGL2015-69557-R). The collection of data for Lough Erne and Lough Neagh were funded by the Department of Agriculture, Environment and Rural Affairs, Northern Ireland. We are grateful to Kristiina Vuorio from the Freshwater Centre of the Finnish Environment institute for her help in organizing, collecting and analysing samples by the University of Jyvaskyla and to Gerald Dorflinger from the Water Development Department of Cyprus for his assistance with the sampling in Cyprus and for granting the CUT team permission to use WDD's equipment. Finally, we would like to thank the numerous other assistants that helped realizing each local survey. Open access funding provided by Universite de Geneve., To determine the drivers of phytoplankton biomass, we collected standardized morphometric, physical, and biological data in 230 lakes across the Mediterranean, Continental, and Boreal climatic zones of the European continent. Multilinear regression models tested on this snapshot of mostly eutrophic lakes (median total phosphorus [TP] = 0.06 and total nitrogen [TN] = 0.7 mg L-1), and its subsets (2 depth types and 3 climatic zones), show that light climate and stratification strength were the most significant explanatory variables for chlorophyll a (Chl a) variance. TN was a significant predictor for phytoplankton biomass for shallow and continental lakes, while TP never appeared as an explanatory variable, suggesting that under high TP, light, which partially controls stratification strength, becomes limiting for phytoplankton development. Mediterranean lakes were the warmest yet most weakly stratified and had significantly less Chl a than Boreal lakes, where the temperature anomaly from the long-term average, during a summer heatwave was the highest (+4 degrees C) and showed a significant, exponential relationship with stratification strength. This European survey represents a summer snapshot of phytoplankton biomass and its drivers, and lends support that light and stratification metrics, which are both affected by climate change, are better predictors for phytoplankton biomass in nutrient-rich lakes than nutrient concentrations and surface temperature., European Cooperation in Science and Technology (COST) ES 1105 ES 1201, Swiss State Secretariat for Education, Research and Innovation, University of Geneva, Leibniz Association, National Science Foundation (NSF) 1840715 1831096, Spanish Agencia Estatal de Investigacion, European Commission CGL2015-69557-R, Department of Agriculture, Environment and Rural Affairs, Northern Ireland

The object of the study was Tyrsko Lake (area 18.6 ha, max. depth 30.4 m), located in the western part of Olsztyn (Olsztyn Lakeland). This lake is one of the clear water lakes in Olsztyn, but the progressive deterioration of water quality is observed during last years. The phosphorus concentration in the water-sediment interface, phosphorus fractions quantity and the amounts of components which can bind this element was investigated in the upper (0-5 cm) layer of deposits. The aim of study was the analysis the potential influence of bottom sediment on the lake water quality. The obtained results revealed, that bottom sediment of Tyrsko Lake can be classified as mixed, silica-organic type, with quite high content of iron (over 4% Fe in d.w.). The total phosphorus content was ca. 3.5 mg P g-1 d.w. on average. Phosphorus in bottom sediment was bound mainly with organic matter (NaOH-nrP fraction), which had over 50% share in TP. Easy mobile fractions (NH4-Cl-P and BD-P) together included ca 5% to 7 % TP only. The obtained results show, that bottom sediment of Tyrsko Lake can bind phosphorus quite effectively. Calculated internal mineral phosphorus loading during summer stagnation period was 10.9 kg P and it was lower that the assessed annual external phosphorus load (22.6 kg P y-1). The assessed annual phosphorus loading from both sources still was lower than critical load according to Vollenweider criteria. But due to the fact that internal loading phenomenon is occurring in the lake it should be taken into consideration that the lake water quality can deteriorate gradually during the longer time perspective. These findings should be taken into consideration in the future if the potential protection and restoration procedures will be developed.

The experiment was established in a set of containers. Every container held a 10 cm thick layer of profundal sediments and water from a badly polluted lake. The following five preparations were tested (brand names): AQUAKALGON+, BIOGEN REMEDIANT, BIODENN K, ECOTABS 1(TABLETS), ECOTABS 2(POWDER). The biological preparations were applied twice: phase I lasted 56 days and phase II was continued for 21 days. The research results demonstrated that considerably higher values, compared to the control, were initially (day 3) obtained for TOC after the application of ECOTABS 1, for total nitrogen − after BIODENN K and ECOTABS 1, and for total phosphorus − after BIODENN K, ECOTABS 1 and BIOGEN REMEDIANT. Multiplying bacteria might have been an additional source of organic matter in water, which was subsequently deposited in the bottom sediments as implicated by a higher percentage (by 1 to 7% of d.w.) of organic matter in the sediments at the termination of the experiment. Our preliminary experiment did not provide any justification for using the tested preparations in lake restoration efforts. Subsequent studies should focus on the question whether mineral phosphorus released to the lake water or a drastic change in the environmental conditions would not lead towards the dominance of invasive and highly toxic cyanobacteria.

Insight into how environmental change determines the production and distribution of cyanobacterial toxins is necessary for risk assessment. Management guidelines currently focus on hepatotoxins (microcystins). Increasing attention is given to other classes, such as neurotoxins (e.g., anatoxin-a) and cytotoxins (e.g., cylindrospermopsin) due to their potency. Most studies examine the relationship between individual toxin variants and environmental factors, such as nutrients, temperature and light. In summer 2015, we collected samples across Europe to investigate the effect of nutrient and temperature gradients on the variability of toxin production at a continental scale. Direct and indirect effects of temperature were the main drivers of the spatial distribution in the toxins produced by the cyanobacterial community, the toxin concentrations and toxin quota. Generalized linear models showed that a Toxin Diversity Index (TDI) increased with latitude, while it decreased with water stability. Increases in TDI were explained through a significant increase in toxin variants such as MC-YR, anatoxin and cylindrospermopsin, accompanied by a decreasing presence of MC-LR. While global warming continues, the direct and indirect effects of increased lake temperatures will drive changes in the distribution of cyanobacterial toxins in Europe, potentially promoting selection of a few highly toxic species or strains. © 2018 by the authors. Licensee MDPI, Basel, Switzerland., The authors acknowledge COST Action ES 1105 “CYANOCOST—Cyanobacterial blooms and toxins in water resources: Occurrence impacts and management” and COST Action ES 1201 “NETLAKE—Networking Lake Observatories in Europe” for contributing to this study through networking and knowledge sharing with European experts in the field. Evanthia Mantzouki was supported by a grant from the Swiss State Secretariat for Education, Research and Innovation (SERI) to Bas Ibelings and by supplementary funding from the University of Geneva. We thank Clare Ahnlund, Ena Suarez and Irene Gallego for helping out with the Swiss survey. We thank Wendy Beekman and Els J. Faassen for the nutrient and toxin analysis.

Under ongoing climate change and increasing anthropogenic activity, which continuously challenge ecosystem resilience, an in-depth understanding of ecological processes is urgently needed. Lakes, as providers of numerous ecosystem services, face multiple stressors that threaten their functioning. Harmful cyanobacterial blooms are a persistent problem resulting from nutrient pollution and climate-change induced stressors, like poor transparency, increased water temperature and enhanced stratification. Consistency in data collection and analysis methods is necessary to achieve fully comparable datasets and for statistical validity, avoiding issues linked to disparate data sources. The European Multi Lake Survey (EMLS) in summer 2015 was an initiative among scientists from 27 countries to collect and analyse lake physical, chemical and biological variables in a fully standardized manner. This database includes in-situ lake variables along with nutrient, pigment and cyanotoxin data of 369 lakes in Europe, which were centrally analysed in dedicated laboratories. Publishing the EMLS methods and dataset might inspire similar initiatives to study across large geographic areas that will contribute to better understanding lake responses in a changing environment., The authors acknowledge COST Action ES 1105 “CYANOCOST – Cyanobacterial blooms and toxins in water resources: Occurrence impacts and management” and COST Action ES 1201 “NETLAKE – Networking Lake Observatories in Europe” for contributing to this study through networking and knowledge sharing with European experts in the field. Evanthia Mantzouki was supported by a grant from the Swiss State Secretariat for Education, Research and Innovation (SERI) to Bas Ibelings and by supplementary funding from University of Geneva. We thank Wendy Beekman for the nutrient analysis and the University of Wageningen for covering the costs of this analysis from the personal funding of dr. Miquel Lürling. We thank Pieter Slot for assisting with the pigment analysis and the University of Amsterdam for covering the costs of the analysis through funding from the group of Prof. Jef Huisman and dr. Petra Visser (IBED). We would like to thank the Environmental Data Initiative for covering the cost of archiving the EMLS dataset. We would like to thank the Leibniz Institute of Freshwater Ecology and Inland Fisheries, Dept. of Experimental Limnology and the Aquatic Microbial Ecology Group for logistic and technical support of J. Fonvielle and H.-P. Grossart; and the Leibniz Association for financial support. The collection of data for Lough Erne and Lough Neagh were funded by the Department of Agriculture, Environment and Rural Affairs, Northern Ireland.

We investigated changes in the spatial distribution of phosphorus (P) and nitrogen (N) in the deep, mesotrophic Lake Hańcza. The raw data collection, supported by global navigation satellite system (GNSS) positioning, was conducted on 79 sampling points. A geostatistical method (kriging) was applied in spatial interpolation. Despite the relatively small area of the lake (3.04 km2), compact shape (shore development index of 2.04) and low horizontal exchange of water (retention time 11.4 years), chemical gradients in the surface waters were found. The largest variation concerns the main biogenic element – phosphorus. The average value was 0.032 at the extreme values of 0.019 to 0.265 mg L−1 (coefficient of variation 87%). Smaller differences are related to nitrogen compounds (0.452–1.424 mg L−1 with an average value of 0.583 mg L−1, the coefficient of variation 20%). The parts of the lake which are fed with tributaries are the richest in phosphorus. The water quality of the oligo-mesotrophic Lake Hańcza has been deteriorating in recent years. Our results indicate that inferences about trends in the evolution of examined lake trophic status should be based on an analysis of the data, taking into account the local variation in water chemistry.

The objective of this study was to evaluate the effect of lake restoration by the hypolimnetic withdrawal method on the intensity of ambient odour in the vicinity of the pipeline outlet. The study was carried out in 2012-2013 from the beginning of the summer stagnation period in Lake Kortowskie to complete overturn in fall. Samples of river water and ambient air were collected from two sites: near the pipeline outlet (PO) and behind the academic campus (AC). A total of 44 air samples and 44 water samples were analysed. Odour intensity was measured in samples of ambient air. The following physicochemical parameters of water were determined: flow rate, dissolved oxygen (DO), hydrogen sulphide (H2S), sulphate (SO4), ammonium nitrogen (NH4-N), total nitrogen (TN), dissolved nitrogen (DN), total particulate nitrogen (T-PN), total organic carbon (TOC), dissolved organic carbon (DOC) and total particulate organic carbon (T-POC). Water samples were also analysed to determine total bacterial abundance (TBA) and the counts of bacterial rods, cocci and spiral-shaped bacteria, and sulphate-reducing bacteria (SRB). Significant variations in odour intensity were noted between years and sampling sites. Odour was significantly determined by the proportion of lake water in river water. It was also significantly correlated (P2S, NH4-N, TBA and counts of SRB, rod- and spiral-shaped bacteria only in.

The aim of this study was to compare the concentration of nitrogen and trace the dynamics of its changes in two lakes with different intensity of anthropogenic pressure. The dominant land use of Lake Paskierz catchment is built-up areas, while in Lake Sajmino, wasteland is the dominant land use. The total amount of nitrogen in Lake Paskierz ranged from 1.68 to 6.58 g Ntot m-3, while in Lake Sajmino it was from 1.03 to 1.84 g Ntot m-3. The organic fraction was a dominant form in the surface water layers of the examined lakes. A slightly different situation was found in near-bottom water layers of Lake Paskierz, where ammonium nitrogen was the dominant form in the summer stagnation. In other cases organic nitrogen was a dominant form in each of the reservoirs. Concentrations of nitrites and nitrates were low and did not affect essentially the overall amount of nitrogen in the studied lakes. Based on the results, it can be concluded that Lake Paskierz is overfertilized. The high concentrations of ammonia measured in near-bottom layers of the lake indicate that the internal supply may be a very important process affecting the trophic status. Lake Sajmino was characterized by significantly less nitrogen abundance, although the periodically increasing nitrogen concentration reveals the presence of adverse anthropopressure on the lake.

Coagulation behaviour of polyaluminium chloride (PACl) was comparatively investigated in terms of the removal of turbidity and colour with surface water. The growth of flocs was also compared. The results show that the decrease in saturation and values of dissolved oxygen was ca. 20% for ALCAT and PAX 18 at both dosages and 15% for PAX XL 19H, respectively. The floc formation growth indicated that PACl coagulation occurred not only by charge neutralization but also by a form of sweep flocculation. Besides, flocs formed by ALCAT had better sizes than the flocs formed by PAX 18 and PAX XL19H. The rate of sedimentation was stable during coagulation with higher doses, and it was dependent on the substance used.

Sediments from hypereutrophic Lake Łajskie localized in northeastern Poland were examined on the basis of P-fraction. The sediments were collected at five sampling sites. In the investigated lake, the rank order of P-fractions was HCl-P > BD-P > NH4Cl-P > NaOH - nrP. The loosely sorbed phosphorus NH4Cl-P represented < 3% of the sedimentary inorganic phosphorus, while the reductant phosphorus (BD-P) ranged from 2 to 10%. The calcium bound phosphorus (HCl-P) showed considerable contribution (59-74%) to the sedimentary inorganic P-loads. BDP was the most reactive fraction in Lake Łajskie. Iron compounds and organic matter seem to play a significant role in regulating this labile P-budget.

The aim of this study was to determine the chemical composition of Lake Widryńskie bottom sediments (max. depth. 27.0 m, area 123.9 ha). The sampling of bottom sediments was conducted once, on 16 August 2010. Sampling was made in 10 specific areas. Among the 10 samples, 4 samples were taken from the littoral and sublittoral zones, while the rest were taken from the profundal zone. The dominant component of the sediments was silica and calcium carbonates were subdominant. Based on the survey, it was determined that silica occurred in greater numbers in littoral sediments, while in sublittoral sediments there was increased participation in the chemical composition of organic matter. The elements that build a capacity complex were a small percentage of the dry weight of sediment. Sediment from the vicinity of inflows contains higher amounts of silica, which confirmed the impact of the catchment on the chemical composition of sediments.