Recharge and drainage of lakes in the Powidzki Landscape Park in conditions of increased anthropogenic and environmental pressure (central-western Poland)

Abstract

The lakes of the Powidzki Landscape Park (Gniezno Lakeland) are known for their natural and recreational values. The majority of them are located within two large glacial tunnel valleys, that in many places cut through several levels of till and inter-till aquifers. Regional hydraulic linkage systems are developed where surface water and groundwater remain in direct contact. Smaller water bodies occur between the lakes, in other tunnel valleys, in isolated meltwater basins, or in river valleys. These water bodies constitute local drainage bases. The existence in the area of such morphologically diverse lakes with different flow rates, varied morphology, and heterogeneous geological structure permitted tracing of the hydrodynamic dependencies of lake catchments of various types. Hydrogeological cross-sections, comparative analyses of structural maps for successive aquifers, bathymetric plans of lakes, and piezometric contour maps were prepared. Surface and groundwater level fluctuations were investigated, as well as their response to changing atmospheric conditions. Water balances of lakes were also determined for selected lake catchments. The study showed that all the lakes analysed are closely related to groundwater, and that the deepest ones reach lower aquifers. The majority of the lakes drain the aquifers, but some of the lakes feed them. Such a situation was documented in coastal wetlands and in the eastern part of the Park, affected by a depression cone associated with a nearby lignite opencast mine. The study showed that the deepest of the lakes analysed have a very wide catchment area of groundwater recharge, expanding beyond the boundaries of their surface catchment areas. This is important for the development of their resources, especially in periods of hydrogeological low flow.