Assessment of pollution loads from point and diffuse sources in small river basin: Case study Ljubljanica River

The European Union Water Framework Directive (EU WFD) requires the identification of significant human pressures and impacts on water bodies. An important component in protecting the ecological quality of watercourses is the regulation of point sources of pollution. The purpose of this study is to determine the harmful effects of a point source of pollution on a small river and to assess their significance for distant aquatic systems and the receiving stream. The water quality of the Ljubljanica River (Slovenia) is described in terms of point sources (tannery and municipal effluents) and diffuse sources of pollution. Tannery wastewater is a complex mixture of biogenic matter from hides and a large variety of organic chemicals added during the tanning process. The municipal effluent contained higher amounts of organic pollutants and nutrients. The harmful substances from the effluents are traced in the receiving stream and sediments. Point sources of pollution dominate at the critical ecological low flow periods of high biological activity. The water quality is marked by several determinants diluting with increasing flow and, in many cases, they link to point source pollution (organic pollution, ammonia, Cr, sulphate, and chloride), whereas nitrate shows a mixed response of point and diffuse inputs possibly mediated with in-stream loss during the growing season.