The Influence of the Przebędowo Reservoir on the Water Quality of the Trojanka River in the First Years of its Functioning

Agriculture, mainly biogenic compounds (nitrogen and phosphorus) and plant protection products are one of the sources of environmental pollution. The sources of pollution are both farm buildings and intensively used agricultural land. Therefore, a crucial element of the environment contributing to the improvement of surface water quality are the aforementioned shallow reservoirs covered by vegetation that act as biofiltres or reservoirs such as dammed reservoirs. The analysed reservoir is located in the Greater Poland Province, about 25 km to the north from Poznań, in Murowana Goślina commune. The research on the analysed reservoir was conducted during the growing seasons, from 2016 to 2018, at three measurement and control points: at the Przebędowo reservoir inflow, it the Przebędowo reservoir and at the Przebędowo reservoir outflow. They included determining 4 groups of physico-chemical indicators supporting biological elements, including indicators characterising aerobic conditions, salinity, acidification (pH) and indicators characterising biogenic conditions. Based on the conducted research, a great influence of the reservoir was proven, especially in the context of the concentration of dissolved oxygen at the outflow, where, concerning this indicator, the reservoir was classified as water quality class I. The presented research results also confirmed that in the context of the complexity of hydrological and physico-chemical processes taking place in dammed reservoirs, it is necessary to continuously control them both in terms of water quantity and quality.