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This study is the first attempt at the European scale to make an inventory of ecosystem services (ESS) of a large lake. We analysed a set of ESS indicators against the annual mean values of environmental parameters for 2006–2013. According to principal component analysis, the trophic state- and hydrology-related factors explained about 70% of the environmental variability of the lake and showed strong relationships with some ESS. Among the provisioning ESS, the annual eel catch and the total fish catch were positively related to different eutrophication indicators while the catches of pike, bream, and burbot depended rather on hydrological factors. Reed harvesting efficiency was related to the lake’s water level. The indicators of regulating, maintenance, and cultural ESS showed very high variability in different years, the latter depending on socio-economic conditions rather than environmental factors. We discovered numerous trade-offs between ESS benefitting from higher trophic state or regulated water level of the lake and the goals of good ecological status of the lake. Our analysis showed a clear need for rules prioritizing life supporting regulatory services against other ESS.

Different sources of particulate organic matter (POM) as well as its composition affect the biological food web and hence the self-purification potential and water quality of rivers. We studied the effect of a large shallow lake on the POM pool of the water passing through it. Over four years, we analysed monthly the amount and composition of POM and a set of environmental variables in the inflows and in the outflow of Lake Võrtsjärv (Estonia). In the inflows, the live pool of POM consisted of phytoplankton – small crypto-, dino-, and chlorophytes. The concentration of chlorophyll a (Chl a), as a proxy of phytoplankton biomass, was positively correlated with temperature and total phosphorus and negatively with dissolved silica, total nitrogen, and discharge. In the outflow, the share of the live component of POM was much larger than in the inflows but was also dominated by phytoplankton represented by grazing resistant filamentous cyanobacteria. Chl a was positively correlated with total phosphorus, temperature, pH, and precipitation, and negatively with dissolved silica, total nitrogen, and discharge in the outflow. The different amounts, composition, and seasonal dynamics of POM in the inflows and in the outflow have potentially substantial impacts on the food web with a predominating classical pathway in the inflows versus a detrital pathway in the outflow. This study was supported by the institutional research funding (IUT 21-2) of the Estonian Ministry of Education and Research and by the MARS project ‘Managing Aquatic Ecosystems and Water Resources under Multiple Stress’ funded under the 7th EU Framework Programme, Theme 6 ‘Environment including climate change’ (Contract No. 603378). We are grateful to Dr. Jonne Kotta and to the two anonymous reviewers for valuable comments on the manuscript. Mrs Ester Jaigma kindly revised the English text of the manuscript. The publication costs of this article were covered by the Estonian Academy of Sciences. This study was supported by the institutional research funding (IUT 21-2) of the Estonian Ministry of Education and Research and by the MARS project ‘Managing Aquatic Ecosystems and Water Resources under Multiple Stress’ funded under the 7th EU Framework Programme, Theme 6 ‘Environment including climate change’ (Contract No. 603378). We are grateful to Dr. Jonne Kotta and to the two anonymous reviewers for valuable comments on the manuscript. Mrs Ester Jaigma kindly revised the English text of the manuscript. The publication costs of this article were covered by the Estonian Academy of Sciences.

For the first time, a general survey is presented of the temporal and spatial patterns of the phyto- plankton community in the River Emajogi, one of the largest Estonian rivers. The species compo- sition of phytoplankton in the River Emajogi resembles that of Lake Vortsjarv from which the river arises. The cyanobacteria Limnothrix planctonica (Woooszynska) Meffert, Limnothrix redekei (Van Goor) Meffert and Planktolyngbya limnetica (Lemmermann) Komarkova´-Legnerova et Cronberg dominated the phytoplankton biomass. Phytoplankton abundance, biomass and chloro- phyll a concentration showed an increasing trend from spring to late autumn. The results of princi- pal component analysis revealed that the first and the second axes explained 43.6% and 14.5% of total variance, respectively. The first principal component was positively correlated with pH, O2, BOD5 as well as with phytoplankton parameters, and negatively correlated with water level, transparency and concentrations of nitrite and carbonate. The second principal component was positively correlated with chemical oxygen demand and negatively correlated with the concentrations of ammonium and total phosphorus. Projection of the cases on the factor plane indicated that the water of the upper reach of the river and the water of the River Pedja differed significantly from each other as well as from the waters of a majority of other rivers.

The material for the present phytoplankton study was collected from 427 reaches of 162 Estonian rivers during the period of 1991–1997. Sampling was carried out at the end of June and in July. A total of 402 taxa of algae were identified in phytoplankton. The most numerous were diatoms (180), followed by green algae (125) and cyanobacteria (45). The phytoplankton of the Estonian rivers is sparse and heterogenous: only 13 species of algae were recorded in more than 50% of streams. Pennate diatoms dominate most frequently in phytoplankton biomass, while tiny flagellates dominate in phytoplankton abundance. The nonparametric means (medians) of phytoplankton biomass, abundance and number of taxa per sample in the lower reaches of the Estonian streams were 0.2 mg l−1, 0.4×106 cells l−1 and 19, respectively; the highest mean values (0.3 mg l−1, 0.6×106 cells l−1 and 23, respectively) were observed in the rivers of the drainage basin of Peipsi-Vortsjarv and the lowest ones (0.1 mg l−1, 0.2×106 cells l−1 and 13, respectively), in the streams of Hiiumaa. Phytoplankton biomass was correlated with content of chlorophyll a according to Lorenzen (L chl a) (Spearman r=0.72) and Jeffrey & Humphrey (JH chl a) (Spearman r=0.70) at the confidence level P

We determined the incoming fluxes of total organic carbon (TOC), dissolved inorganic (DIC) and organic carbon (DOC), nitrogen, phosphorus, and silicon via four main inflows into Lake Vortsjarv and compared these with the outgoing fluxes from the lake during 2008-2009. The discharge and loads of the studied substances from the four main rivers alone were higher than the amounts carried out of the lake in 2008. In 2009, the outflow of water exceeded the inflows and this was the case with the amounts of TOC, DIC, and DOC as well. However, the incoming load of nutrients was continuously higher than the outgoing load. The lake accumulated nutrients (nitrogen, phosphorus, and silicon) irrespective of whether water retention was positive or negative, but the balance between carbon accumulation and carbon emission depended on the lake's water budget.

Phytoplankton is one of the four biological elements used for the assessment of the water quality of surface water bodies. In rivers phytoplankton-based assessment of water quality has not been conducted in Estonia up to now. The aim of the present study was to test a new Hungarian potamoplanktic method for the assessment of the water quality of the Narva River, a large river on the Estonian-Russian border. For testing the method, algal species in the phytoplankton of the Narva River were classified into functional groups. Then the Ecological Quality Ratio (EQR) was calculated and its value was compared with the corresponding values for different water quality classes given in the literature. The mean value of the EQR for the Narva River revealed seasonal variation: in most cases it indicated 'good' or 'excellent' quality classes in spring and summer and 'very bad' quality class in autumn. The median value for the vegetation period of 2001-2008 indicated 'moderate' quality class. Variation in the functional groups of phytoplankton and in the EQR values reflected the seasonal dynamics of phytoplankton and the impact of Lake Peipsi. Comparison of the results of the assessments made by using the phytoplankton EQR and benthic diatom indices revealed agreement between the two metrics in the summer period: both were sensitive to the water quality and indicated at least 'good' quality class. The new Hungarian method appears to be suitable for the assessment of water quality in this Estonian large river. However, the numerical boundaries of the EQR for different water quality classes should be specified in the future on the basis of a larger Estonian phytoplankton database.