Long-term changes in nitrogen and phosphorus emission into the Vistula and Oder catchments (Poland)-modeling (MONERIS) studies.

Modeling (MONERIS) studies allowed calculation of nitrogen (N) and phosphorus (P) emission into the Vistula and Oder basins (Poland), and facilitated estimation of N and P retention in these catchments in 1995-2015. In the discussion of results, data of other authors were used in order to get an insight into N (1880-2015) and P emission (1955-2015) into the Oder basin. Population growth and agricultural intensification were responsible for respective 5.3-fold and 3.5-fold increase in N and P emission into the Oder basin, with the maximum (135,000 tons N year; 14,000 tons P year) observed at the turn of the 1980s/1990s. Pro-ecological activities during the economic transition period (since 1989) covered various sectors of the economy including agriculture, environmental protection related to, e.g., construction of a large number of waste water treatment plants (WWTPs). Consequently, in 1985-2015, the emission into the Oder basin decreased from the abovementioned maxima to 94,000 tons N year and to 5000 tons P year, whereas in 1995-2015, the emission into the Vistula basin decreased from 170,000 to 140,000 tons N year and from 14,200 to 10,600 tons P year. In 1995-2015, groundwater, tile drainage, and WWTPs played a key role in N emission, while erosion, overland flow, WWTPs, and urban areas played a predominant role in P emission. The relative shares of nutrient emission pathways in overall N and P emission were considerably changing over time. Extreme weather conditions have a great impact on increased (floods) or decreased (droughts) nutrient emission; particularly, N emission is susceptible to variable weather conditions. In total, approximately 91,000 tons of N and 7600 tons of P were retained annually in the river basins.