The water clarity of Polish lakes with charophyte vegetation in the years 1953-1968

A total of 313 lakes with charophyte vegetation were identified based on the data presented in 1111 manuscripts under the shared title of “Assumptions for the fisheries management project in Lake (lake name)”, based on the results of an environmental inventory carried out by the Inland Fisheries Institute in 1953-1968. The lakes’ morphological characteristics were described, hydrophyte species that most frequently accompanied charophytes were identified, differences in summer water transparency were analyzed in 281 lakes with charophyte vegetation and the results were compared with the observations made in 657 other lakes, and the potential trophic state of lakes with charophyte vegetation was determined using Carlson’s trophic state index (1996). More than half (54%) of 171 dimictic lakes with charophyte vegetation were classified as mesotrophic and 31% as oligotrophic, whereas 50% of 110 polymictic lakes were classified as eutrophic, and 40% as mesotrophic. The frequency of taxa that contribute to the eutrophication (degradation) of water bodies, including Ceratophyllum spp. Myriophyllum spp. and Elodea canadensis, increased with a decrease in the percentage of charophytes in communities of submerged hydrophytes. Regardless of the proportion of charophytes in submerged hydrophyte communities, water in the lakes colonized by charophytes was more transparent than in the 659 lakes without charophytes. Water in many polymictic and dimictic lakes with charophyte vegetation, including lakes with a small contribution of charophytes, was more transparent than in lakes without charophytes, which suggests that charophytes are sensitive indicators of water quality and are components of ecological memory in aquatic ecosystems.

Assessment of selected physicochemical properties of restorated water of the Mogileriskie Lake

Excessive supply of nutrients contributes to gradual eutrophication of water. This process can happen fast, especially in shallow lakes which are more prone to degradation. This also causes deterioration of settlement conditions of many organisms and limits economic use of water. Eutrophication can lead to gradual shallowing and shrinking of water reservoirs and subsequently disappearance of lakes. Therefore, appropriate diagnosis and reduction of the amount of pollutantsflowing into lakes are crucial for the water quality improvement and prevention from further degradation. The Mogileńskie Lake, like many other town lakes was supplied with sewage. As a consequence, the reservoir stopped being an attractive urban element, and became an object cumbersomeaud dangerous to the residents health. For this reason the lake has been subjected to many protection and reclamation processes.The water samples were taken 10 times from 3 sampling points between September 2014 and June 2015. The contents of total phosphorus, phosphorates, total nitrogen, nitrates, nitrites, and ammonium nitrogen was measured in the tested water. The results obtained from the water analyzed for biogenic elements, and their compounds indicate low effectiveness of the carried out reclamation. According to many authors, the choice of artificial aeration as a reclamation process for the Mogileńskie Lake was a mistake.This cleaning method does not provide the expected results when used for shallow and polymictic lakes, especially in combination with an invasive method of dredging and the controversial deposing of the extracted residues in the direct proximity of the lake.

Overgrowing of two polymictic lakes in Central-Western Poland

Overgrowing of two polymictic lakes in Central-Western PolandThis study examined the overgrowth in two eutrophic lakes during the period 1961-2008. In addition, for comparative studies, analyses of plant community structures in these lakes were performed to assess the effects of human pressure, such as water level reduction and increase of nutrient availability on changes in the range of the littoral zone surface. To achieve these aims aerial photos, ortophotmaps, GPS measurements were used to evaluate changes in plant cover in two lakes: Niepruszewskie and Tomickie. Considerable differences between the studied lakes located in an agricultural catchment were observed. Lake Niepruszewskie was characterised by a threefold higher rate of overgrowing, measured per hectare, in comparison with Lake Tomickie. Moreover, in comparison with lake areas, rates of overgrowing were substantialy higher in Lake Tomickie than Lake Niepruszewskie, which is almost seven times bigger. The littoral zones of both lakes are dominated by emergent vegetation. Compared to the data from 1961, the zone of Lake Niepruszewskie increased almost threefold. The biggest changes in overgrowing were observed after reduction of water level (>2002) which was 1.30 ha yr-1. During almost 50 years, emergent vegetation in Lake Tomickie increased more than fivefold. The most intensive growth was observed in years from 1961 to 1986, which amounted to 0.73 ha yr-1. Probably, water level reductions in Lake Niepruszewskie and high eutrophication in Lake Tomickie were recognised as major factors causing intensive overgrowing in the studied lakes.