Estimation of sources of total phosphorus in a river basin and assessment of alternatives for river pollution reduction.

The methodology of material flow analysis is presented and applied to developing a phosphorus balance in a river basin and evaluating different scenarios for pollution reduction. The method is based on the balance principle: inputs and outputs of each phosphorus-related subsystems were balanced. The application of the methodology strategies was illustrated by means of a case study of the Krka River, Slovenia. The results showed that besides effluents from wastewater treatment plants, agriculture contributed significantly to the total annual phosphorus load. After establishing the present levels of phosphorus balance, different scenarios were considered: different stages of wastewater treatment as well as management of agricultural activities. The present emission of phosphorus is estimated to be 81.8 tons/year; after implementation of measures, it would be 48.6 tons/year, a total reduction of 40%. Besides reduction of point sources by means of wastewater collection and implementation of nutrient removal technology, managing agricultural phosphorus to protect water quality should become a major challenge in the Krka river basin.