Volume XV |

Pollution load released into the Bay of Gdańsk by small river catchments in the coastal city of Sopot

Abstract: The purpose of the study is to determine the quantity of wastewater entering the Gulf of Gdańsk, which is part of the Baltic Sea. The study area consists of small river catchments in the city of Sopot, which lies along the Gulf. The research also aims to determine wastewater release volumes over time, instead of focusing only on spatial distributions. Another aim is to identify main determinants potentially affecting water quality in rivers flowing across the city of Sopot. Land use is also considered as a factor. The study area consists of seven small river catchments in the city of Sopot, each with an open flow channel. The study period was 2014 – 2015. Laboratory tests were performed to determine the concentration of both total nitrogen and total phosphorus. Other metrics in the study included pH, specific conductivity, water temperature, dissolved oxygen content, and suspended matter content. Discharge was also measured for each studied river. Comparisons were then made with local meteorological data. Research has shown that none of the 6 studied rivers experienced concentrations of total nitrogen above the norm accepted in Poland for Class 1 water quality (5 mg·dm-3). Mean annual values ranged from 0.60 to 1.28 mg·dm-3. The Class 1 norm for phosphorus (0.2 mg·dm-3) was also not exceeded in the case of total phosphorus in any of the 6 studied rivers. Phosphorus values ranged from 0.066 to 0.1 mg·dm-3. The annual load supplied by all 6 rivers in the Sopot city area during the study period was 4,295.9 kg for total nitrogen and 370.2 kg for total phosphorus. For the purpose of comparison, the load supplied by Poland as a whole in the year 2012 was: 210,768,000 kg total nitrogen, and 15,269,000 kg total phosphorus. In summary, the 6 small rivers discussed in this paper contribute 0.002% of the biogenic load supplied to the Baltic Sea by Poland as a whole.