Evaluation of Point and Diffuse Sources of Nutrients in a River Basin on Base of Monitoring Data

The methodology of materials accounting is presented and applied to developing nutrient balance (nitrogen and phosphorus) in a river basin. The method is based on the balance principle: inputs and outputs of each nitrogen and phosphorus related sub-systems were balanced. The application of the methodology strategies was illustrated by means of a case study of the Krka river, Slovenia. Different pathways of emission to surface waters were taken into account: WWTP discharges, direct discharges, erosion/runoff and baseflow. Total annual emission into the river Krka was estimated to be 362 tonnes N/year and 73.3 tonnes P/year. The main sources of nitrogen are diffuse sources, emitted via baseflow (52%). Other important sources are effluents from WWTP, which account for 36% of total emissions. Other sources like erosion and direct discharges to surface water (animal manure, industry, households) are of lower magnitude. Erosion is main source of phosphorus emission (55% of total emission), WWTP effluents account for 37% of total emission, while other sources are less important. Besides reduction of point sources by means of wastewater collection and implementation of nutrient removal technology, managing agricultural nitrogen and phosphorus to protect water quality should become a major challenge in the Krka river basin.     

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.