Lake disappearance is one of the results of water eutrophication which leads to lake shallowing and overgrowth, and small and shallow lakes are the most threatened with degradation. We studied the effect of lake shallowing on its overgrowth, taking into account the morphometric parameters of water bodies. The study was performed in 20 lakes located in the central west part of Poland. The degree of lake shallowing was evaluated on the basis of bathymetric maps made in the 1960s and studies carried out presently. Additionally, an analysis of littoral coverage and macrophyte growth forms was investigated. Moreover, the composition, intensity of phytoplankton blooming, and physico-chemical parameters of the lake water were analyzed. Redundancy analysis shows that the lake volume, average depth, shallowing rate, and change in volume were the parameters that most strongly correlated with the share of macrophytes in the lakes. According to the regression analysis, the share of emergent macrophytes was significantly correlated with lake shallowing. No relation was found between phytoplankton abundance and lake shallowing. Conversely, the lakes with the highest rate of shallowing were characterized by the greatest share of vegetation, which suggested that vegetation growth had a significant impact on lake shallowing.

Lake overgrowth is one of the mechanisms affecting the gradual disappearance of lakes in the temperate zone caused by excessive eutrophication of waters. The aim of this study was to assess the possibility of using helophytes as bioindicators of lake overgrowth based on long-term changes based on the cartographic maps studies and field analyses of plant form growth cover (2012)(2013)(2014). Additionally, water and sediment chemistry in overgrowing lakes were investigated. The study comprised a total of 33 eutrophic lakes characterized by varying degrees of vegetation development. Based on discriminant analysis, four groups of lakes with diverse degrees of vegetation growth were distinguished. The group comprising the most overgrown water bodies was found to have the greatest percentage of helophytes, with a considerable proportion of submerged and floating-leaved macrophytes. Based on a review of archival materials, lakes which currently exhibit the highest degree of overgrowth were shown to have been affected by intensive littoral growth for over 100 years, which confirms bioindicator properties of helophytes in the assessment of the degree of lake overgrowth. In addition, lakes with the highest rate of overgrowth were characterized by a high content of nitrogen in sediment, with a concurrent high concentration of potassium.

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Changes in water levels in lakes play an important role in the development of their coastal zones and water trophy. The aim of this study was to assess the role of changes in hydrometeorological conditions in the development of littoral and riparian vegetation of a meromictic lake during the last half-century. The study was carried out in Lake Powidzkie, one of the largest water reservoirs located in central Poland. Water level and meteorological conditions were analyzed in the period 1961–2015. Modifications in the range of plant communities were analyzed on the basis of cartographic materials and field studies. Meteorological conditions, especially precipitation and evaporation, were found to strongly affect the lake's water retention, whilst they had less of an effect on water levels. A significant effect of the lowering of the water level in Lake Powidzkie on the development of the littoral zone, whose area more than doubled over the last half-century, from 41.5 to 118.8 ha, was noted. The most dynamic development of the littoral was observed in the last quarter of the century, in which three of several years of low-flow were recorded. The occurrence of periods with an increased amount of precipitation, after dry periods, did not contribute to the reduction of the size of the rush zone and limitation of the development of woody vegetation.

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Over a period of 30 years, the surface water level in the north-west of Konin, in the east of the Wielkopolska region, decreased by almost 6 m, resulting in a reduction of the surface area of the majority of nearby lakes, the disappearance of smaller water bodies and wetlands, and the drying out of streams draining the area. The causes of the decrease in the surface and groundwater level in the region are complex. They include both natural and anthropogenic factors, among others broad-scale mining activity. Based on knowledge of the hydrostructural composition of the analysed region and the functioning drainage system of opencast lignite mines, a concept was developed of a change in water supply to the flooded opencast lignite mine, Kazimierz Północ. The task of redirecting waters from the drainage of a nearby opencast mine, Jóźwin IIB, was implemented in 2020. Current observations and forecasts suggest that, owing to the applied solutions, the analysed opencast mine will be flooded in 2023, and not, as previously assumed, at the end of 2021. As a result, groundwater levels in the vicinity of the opencast mine as well as in lakes and rivers within the range of impact of the related depression cone will be restored faster, particularly in the Lake Powidzkie catchment. The objective of the study is to present stages of flooding of the former opencast lignite mine Kazimierz Północ, identify factors determining the process, and describe solutions accelerating it, with a simultaneous environmental impact assessment of the undertaken activities.

Decreased water levels due to climate change cause many negative effects on lake ecosystems. The aim of this study was to (a) assess the effect of the reduction of water levels on nutrient availability in the sediment in the littoral zone; (b) evaluate the effect of changes in water level on biomass productivity and nutrient concentrations in the aboveground biomass of four emergent species: Phragmites australis (Cav.) Trin. ex Steud., Typha angustifolia L., Carex acutiformis L., Glyceria maxima (C. Hartm.) Holmb; and (c) assess the efficiency of the littoral zone in the reduction of nutrient pollution. The study hypothesis was that water level reduction has a positive effect on the plant biomass of high productive species. The study was carried out in the littoral zone of Tomickie Lake, situated in the western part of Poland. This lake is located in the protected area—the buffer zone of Wielkopolska National Park, and at the international level—Natura 2000. Six transects, perpendicular to the shoreline, were selected at two subzones—permanently and seasonally flooded. Analyses of nutrient concentrations in sediments and plant species were performed. The results show the higher productivity of reeds in the zone where water occurs seasonally at the site through the year, which reached 1193 g dry weight/m2. The decline of the water level may lead to the increased growth of highly productive species as emergent vegetation with a broad ecological scale in terms of nutrient concentrations and changes of water depth, i.e., Phragmites australis (Cav.) Trin. ex Steud. Species that prefer growth in the deeper part of the lake will be characterized by lower productivity, despite the high availability of nutrients. Changes in the availability of nutrients may cause the intensification of lake overgrowth by very productive species, which may affect biodiversity, which is particularly high in protected areas.

Changes in nutrient concentrations in groundwater were investigated to determine the impact of agriculture on water quality in artificial lakes. The study covered three reservoirs in an agricultural area of Wielkopolska (central-western part of Poland). Assessing the agricultural impact required a network of piezometers around the reservoirs, used to determine the degree of groundwater pollution from nutrients supplied to the reservoirs. Moreover, the analysis covered the quality of water in streams flowing into the reservoirs, and in the reservoirs themselves. Field research was conducted every month of the growing season from March to November. The analysis covered land inclination, ground permeability, and soil type. Detailed objectives included: (1) assessment of the agricultural impact on the chemical parameters of ground and surface water quality, and (2) evaluation of the impact of different sources of agricultural pollution on water quality in artificial reservoirs in regards to their management. This study revealed high dynamics of nutrient concentrations, particularly for nitrates and phosphates, in groundwater and surface water. A significant effect of maize cultivation on an increase in nitrate concentrations in the groundwater of the catchment of the Przebędowo Reservoir was evidenced, as well as a substantial effect of the functioning of an animal farm on the quality of groundwaters in the catchment of the Lachotka Reservoir. The nutrient load of agricultural origin in the catchment of the Miedzichowo Reservoir was relatively low. Our study revealed elevated amounts of nutrients such as nitrogen and phosphorus, detected more frequently in groundwater than in running waters, which confirms our hypothesis of the importance of groundwater analysis in detecting the source of pollution of the studied lakes. High nutrient concentrations recorded in groundwater leached from arable fields were also observed in the summer period, failing to confirm the hypothesis that the greatest effect of factors would be related to the spring effect of arable fields on water quality (lack of compact vegetation cover, high water level, etc.). Our study also indicated a greater importance of the type of land use than lithology or permeability of deposits.