Zasilanie solińskiego zbiornika zaporowego związkami biogennymi - bilans masowy

The aim of this study was to find nitrogen and phosphorus retention in Solina man-made lake and nutrient loads and concentration in the watersheds of this reservoir. The mass balance was determined from the difference between tributaries input and nutrient amounts in the output of the reservoir. The retention time of the reservoir is 215 days. From February 1999 to June 2000 nutrient compounds (total phosphorus, phosphate, nitrate, nitrite, ammonium and Kjeldahl nitrogen) were measured monthly at estuary sections of the seven tributaries and in the output. The discharge in the rivers was measured by water level gauging at the time of sampling. Nitrogen retention (Nret) ranged between -24,6 and 410,7 mg N m-2d-1. Average Nret was 143,1 mg N m-2d-1 which was 43,5 % of nitrogen load. Phosphorus retention (Pret) ranged from - 24,4 to 16,1 mg P m-2d-1 which was average value of 1,2 mg P m-2d-1. This constituted 15 % of supplied phosphorus load. The greatest value of N and P retention were found in summer and the lowest ones in autumn when the low water level in the reservoir and extremely low fluxes in tributaries were observed. The results showed that two small tributaries were the richest in nutrient compounds. However, the two main tributaries had considerable influence nutrient level inputting together about 86% of phosphorus and 80% of nitrogen to the reservoir.