Changes in the Dynamics and Nature of Sedimentation in Mill Ponds as an Indicator of Environmental Changes in a Selected Lake Catchment (Chełmińskie Lake District, Poland)

The article presents the changes in a hydrographic network resulting from the construction and functioning of nine water mills located in the Struga Rychnowska catchment (Poland). Two ponds (Bierzgiel and Oleszek) have been chosen for a detailed study—both with similar basin origins and morphological settings, but different morphometries, paths of water delivery and discharges from the mill, and water retention times. An attempt was made to restore the course of the deposit sedimentation process in mill pond basins on the basis of historical sources, archived cartographic materials, fieldwork, and laboratory analyses (sedimentology, palynology, and 14C dating). The studies allowed determining the scope of anthropogenic impact on the environment on the example of small river catchment, both when the ponds were in use, and afterwards. Decommissioning of water mills induced a number of serious changes in water resources. The most important of them include: the loss of water retention capacity in the Struga Rychnowska catchment, and decreased ground water level in immediate vicinity of former water reservoirs. Currently, a renewed interest in the old locations of water mills is present, in order to restore retention, and use them for the purposes of modern small hydropower plants (SHP).