Changes in Water Quality for Sprinkler Irrigation in Selected Lakes of the Poznan Lake District

The rapidly changing quality of irrigation water requires urgent attention to understand and predict the long-term effects on soils and food crops, especially in a situation of global freshwater scarcity. The aim of the research was to assess changes in water quality in two selected lakes located in Poland in 2009–2016. The study was carried out in terms of the possibility of using selected reservoirs as sources of water for sprinkler irrigation of agricultural crops. The presented analysis was compared with a similar one carried out in 1999–2006 and 2004–2009 to determine the historic and present water quality state. Results indicate, that the source of pollution of the lakes is most often outflows from sewerage systems, the precipitation and surface runoff from the catchment areas of these lakes, which are mainly used as agricultural land. In Lake Niepruszewskie, the oxygen conditions, water transparency, phosphorus content, sestone dry matter and coliform titre increased, while the biological oxygen demand (BOD5), nitrogen, and chlorophyll content decreased. According to present research, in the Strykowskie Lake, the phosphorus content and BOD5 decreased, while the sanitary condition, nitrogen content and oxygen conditions deteriorated. The reduction of mineral fertilization in recent years has reduced the degradation of the lakes and allowed the water quality to remain in Class III of purity. Despite the visible improvement in the general condition of both studied lakes, constant monitoring of their quality is necessary, which is obligatory for the water from these reservoirs to be used for sprinkler irrigation of crops.