The aim of the study was the long-term observation of changes in the trophic status of the Great Masurian Lakes versus changes in the management of lakes’ watershed. The Great Masurian Lakes (GML), a system of interconnected glacial lakes, were, until the 80s, receivers of untreated and partially treated sewage from cities and diffuse sources, particularly in the tourist season. In the 90s, state farm areas turned into fallow land, which reduced the input of nutrients from diffuse sources. In the late 90s municipal sewage plants began to be systematically built in cities and the larger villages of the region. An analysis of changes in the trophic status of the GML hydro-system during the period of 35 years was based on rotifer indices of lake trophy. Results of the analysis show that in 1976 lakes in the northern and southern part of the GML system were mesotrophic or meso-eutrophic, while in the central part, in the triangle formed by three cities, the beginning of eutrophication was observed. After several years of increased inflow of nutrients due to the impact of tourism, a marked increase in the trophy of lakes was noticed in the central part of the system. In the 90s, after the collapse of large-scale agriculture and the installation of modern sewage treatment plants, the trophic status of nearly all lakes in the central and southern parts of the system ranged between meso-eutrophy and low eutrophy. The exceptions were Lake Nidzkie, whose trophy increased and Lake Niegocin, which became mesotrophic. Changes in the trophic status of the studied lakes indicate high sensitivity of the GML system to anthropogenic changes in their watershed.
Studies were carried out in September 2007 at a set of stations called RIVERS located on two tributaries of the Narew River, and six stations on the tributaries of the Supraśl River. Concurrently, rotifers were sampled at nine stations of the River Rudnia (called RUDNIA). The aim of the research was the verification of the hypothesis on the uniforming effect of the river drift on rotifer communities inhabiting aquatic vegetation. The total numbers of all monogonont species inhabiting aquatic vegetation of RUDNIA and RIVERS were 83 and 107, respectively. The percentage similarity of rotifer communities from aquatic vegetation and river current at the same stations was relatively low and only slightly higher in RIVERS (21.7%) than RUDNIA (17.1%), which suggests that species composition of communities of epiphytic rotifer fauna has a rather low impact on species structure of rotifer communities in water drift. The set of individuals of different species carried with the water current was random and various at different stations. Although the percentage similarity of rotifer communities in the river drift calculated for all possible pairs of the stations was relatively lower in RIVERS than in RUDNIA, it was not reflected in the similarity of epiphytic rotifer communities, which were similar in both sets of stations. Thus, the hypothesis cannot be confirmed by the results of this research.
Jolanta Ejsmont-Karabin, Andrzej Górniak and Maciej Karpowicz
Studies of summer rotifer fauna of 11 shallow and 6 deep lakes of the Suwałki Landscape Park were conducted in an aim to assess the role of lake depth and biotic and abiotic factors in determining the diversity of rotifer communities in lakes undergoing a natural rate of eutrophication not accelerated by anthropopression. Some differences were observed when the group of shallow lakes was compared with that of deep lakes. The former were more differentiated as regards a list of rotifer species, partly due to the high proportion of species with low frequency. Consequently, their faunal originality was markedly higher and values of the percentage similarity of rotifer communities were much lower than in deep lakes. Species richness of rotifer fauna was also dependent on the trophic state of the studied lakes, the character of a nutrient limiting primary production, as well as biomass of diatoms and green algae.
Jolanta Ejsmont-Karabin, Andrzej Górniak, Elżbieta Jekatierynczuk-Rudczyk, Maciej Karpowicz and Adam Więcko
Rotifer abundance and species composition in lakes of the Suwalki Landscape Park were studied in the years 1983–1985, 2009, 2012 and 2015. Rotifer trophic state indices (TSIROT) were used to assess changes in the trophic state of the studied lakes. In most lakes of the Suwalki Landscape Park, there were no changes in rotifer communities over the 25–32 year period to indicate a decline in trophy of the lakes. However, in lakes with the strongest decline in TSIROT values, the values of indicative parameters widely varied in 2015, which may indicate that the status of rotifer communities in the lakes may be dependent on non-trophic factors.