Pastuszak, Marianna, et al. “Reduction of Nutrient Emission from Polish Territory into the Baltic Sea (1988–2014) Confronted With Real Environmental Needs and International Requirements”. Oceanological and Hydrobiological Studies, vol. 47, no. 2, June 2018, pp. 140-66, https://czasopisma.bg.ug.edu.pl/index.php/oandhs/article/view/8618.