Assessment of water pollution with nitrogen and phosphorus along the course of a river: A case study from Northern Bulgaria

Abstract

The present article seeks to estimate water pollution with nitrogen and phosphorus and to analyse the territorial specifics in the content of those physicochemical variables along the length of a river. As a case area, the watercourse of the Osam River (Northern Bulgaria) is selected. Data concern the values of the following parameters: ammonium nitrogen (N-NH4), nitrate nitrogen (N-NO3), nitrite nitrogen (N-NO2), total nitrogen (N-tot), orthophosphates (P-PO4), and total phosphorus (P-tot), collected at four sampling points during the period 2015–2020. The assessment is based on the guidelines of Regulation 4/2012 for characterization of the surface waters. The spatial changes in the content of the examined variables are related to land use and for this purpose a map of CORINE Land Cover (2018) is prepared. The resulting information reveals that parameters with the most frequent excesses over the reference norm include N-NO3, N-tot, P-PO4, and P-tot, whose highest observed concentrations remain up to four times above the permissible limits for ”Good status” recommended in Regulation 4/2012. However, the reported values appear to be lower than those established for previous periods, which shows a positive tendency in water quality. There are also spatial features as moving from upstream to downstream – the upper part is contaminated with P-PO4 and P-tot due to the release of raw municipal and industrial effluents, while the lower section is loaded with N-NO3 and N-tot as a result of the excessive fertilization of arable lands. This work enriches past studies with new data for a recent period.

Keywords

• eutrophication
• nutrient components
• water quality