Seasonal changes of the concentrations of mineral forms of nitrogen and phosphorus in watercourses in the agricultural catchment area (Bay of Puck, Baltic Sea, Poland)

The Baltic Region countries are obliged to meet the stringent limits of N and P discharge set byHELCOM for 2021. Area sources of pollution, including agriculture, are considered the maincontributors of biogenic compounds. The Bay of Puck as an inner part of the Baltic Sea is particularlysensitive to eutrophication caused by nutrient inflow from agricultural lands. Rivers and streamsinflowing to the Bay of Puck transport nitrogen and phosphorus compounds washed out from fields. The article discusses concentrations of nitrogen and phosphorus compounds measured during annual research (VII.2017–VI.2018) at three watercourses: Plutnica, Reda and Bladzikowski Stream inflowing to the Bay of Puck. The concentrations ranged from 0.01 to 0.13 mg/L N-NO2, from 0.39 to 7.55 mg/L N-NO3, from 0.03 to 0.58 mg/L N-NH4, from 0.44 to 9.51 mg/L TN, from 0.05 to 0.45 mg/L P-PO4 and from 0.03 to 1.89 mg/L TP. Seasonal changes of nutrient concentrations were observed, with maximum concentrations of nitrates in August and September after application of fertilizers to arable land.