Tom 16 (2016): Zeszyt 1 (March 2016)

Resuspension in lakes affects the quality of lake water. It is possible to model this process and visualize its outcomes using GIS tools. An assessment of the size of the zone of sediment resuspension was made for two lakes located in Northern Poland threatened by rapid eutrophication. For each of the lakes, four simulations using two methods for determining the effective wind length (F) (Model 1 and Model 2) and two methods for determining the wind wavelength (Lw) (Model A and Model B) were performed. The analysis, taking into account the morphometry of the studied lakes and anemometric conditions, indicated that the differentiator is the applied simulation method of calculating the wavelength caused by the wind. The analysis is theoretical in nature and the results need to be verified in the field..

In 2010-2013, 528 samples of surface sediments were collected from the profundal zone of lakes to determine concentrations of phosphorus, Al, Ca, Fe, K, Mn, Na and S, as well as trace elements (As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sn, Sr, Ti, V and Zn) using the ICP-OES method. Additionally, Hg concentration (by the TMA method) and organic carbon concentration (using the coulometric titration method) were also determined. Phosphorus concentration was found to range from 0.005 to 1.925% (0.109% on average). High phosphorus concentrations in sediments were reported in lakes located within and around urban areas, in lakes on which recreation centres and leisure facilities are situated, and in lakes adjoining special protection areas of birds. The phosphorus concentration in sediments shows a clear correlation with the contents of Al, Fe, Mn, S and TOC, which indicates the presence of phosphorus in both organic and inorganic forms. It also correlates with the contents of most of the trace elements examined for this study, including Zn, Hg and Pb. A certain regional variability was found; water sediments of lakes in the Masurian and Pomeranian lakelands, located in the area covered by the Pomeranian phase ice sheet, are characterised by a slightly higher phosphorus concentration compared with those from the Greater Poland Lakeland situated in the area of the Poznań phase glaciation.

The paper presents an analysis of water stages in Lake Wielki Staw based on observations by the Institute of Meteorology and Water Management conducted in the years 1968-1979. Water level (low and high) variability was determined in the annual cycle, together with the variability of annual stages in the analysed 12-year period, and their amplitudes. Moreover, water stage variability trends were identified. Due to the vicinity of Lake Morskie Oko, comparisons of water stages in both lakes were performed for the purpose of determining the degree to which water supply (water stages) is affected by local and climatic factors.

The study was carried out on Lake Rentyńskie (100.8 ha; 9.4 m) situated approximately 20 km to the west of Olsztyn, in the drainage basin of the rivers Giłwa and Pasłęka. The direct catchment area of the lake is 166.2 ha. Forests cover most of the drainage basin area (74%). As revealed in the study, Rentyńskie is a highly eutrophic reservoir. The lake waters were characterized by a high content of nutrients, up to 1.508 mg P dm^-3 and 11.7 mg N dm^-3. The high fertility of the lake was also evident in the values of chlorophyll a - 75.4 μg dm^-3, and low water transparency - average 1 m. The total annual phosphorus and nitrogen load to Lake Rentyńskie, calculated according to Giercuszkiewicz-Bajtlik (1990) equals 759.0 kg of phosphorus and 31869.7 kg of nitrogen, or per unit surface 0.753 g P m-2 yr^-1 and 31.611 N m^-2 yr^-1. Allowable and critical load levels to Lake Rentyńskie calculated according to the hydrological model of Vollenweider (1976) equal (respectively) 0.090 g P m^-2 yr^-1 and 0.189 g P m^-2 yr^-1. From a comparison between the actual phosphorus load and the values calculated according to Vollenweider it can be concluded that the loads not only exceed the allowable values by several times but also the critical values responsible for advanced eutrophication. The study showed that the River Giłwa, which flows through the reservoir, posed a major threat to the analysed lake . In order to improve the water quality in Lake Rentyńskie drastic protective measures should be taken in the basin of the River Giłwa, which is intensively used for agriculture, and also, at the point where the river enters the lake a special system to reduce the level of phosphorus compound concentrations should be set up.

Stawy Dojlidzkie (The Dojlidy Ponds) are located in the north-eastern part of Poland, near the capital of the Podlasie province, in Białystok. The Dojlidy Ponds (DP) are a complex of more than 20 reservoirs arranged adjacent to one another in an area of about 140 hectares. The largest recreation reservoir (Plażowy) is located within the city limits. Its total area is 34 hectares, it has a capacity of 597 040 m3 and a maximum depth of approximately 2.5 m. DP are supplied by a tributary of the Dojlidy Górne and the River Biała, the principal river of Bialystok. Water tests of a limnic and lenitic character in the upper part of River Biała catchment in Bialystok were conducted from March to October 2014. Referring the obtained results to the actual norms, it can be concluded that most of the parameters analyzed in DP can be assigned to the first class of surface waters. Exceptions were the iron ions, orthophosphates (SRP), total phosphorus (TP), Kjeldahl nitrogen, and also water color and DOC. According to the evaluation of trophic status, the water of DP is eutrophic. The average value of TSI was 55 in the water of the tested objects. The obtained results show that the ecological status of water in the largest pond within the DP complex, in accordance with, the Ecological State Macrophyte Index (ESMI) represent to the good state.

The aim of this study was to determine the relationship between the development of rush zones in small lakes and the utilization and condition of surrounding lands. Generally, the width of the helophyte zone increased along shores with gentle slopes (>5˚) that were covered with vegetation. The most favourable conditions for rush development and spread were along sloped areas bordered by farmlands and rural developments. In addition, pasturelands that developed on top of peat accumulation adjacent to lakes were found to facilitate the development of rushes. We observed a positive effect of anthropogenic development, especially agriculture and infrastructure, on stem density and total biomass of Phragmites austalis populations in the lakes studied. However, individual stem biomass of plants was lower. In different parts of the studied lakes, macrophyte distribution patterns were influenced by environmental conditions including nutrient availability, wind exposure, and bottom slope. The poorest macrophyte communities were found in areas within the lakes that were shaded by trees growing on neighboring banks and where slopes were forested rush zones were absent altogether.