The pollution load by nitrogen and phosphorus in the Jadro River

The objective of the investigations of the Jadro River, located in Croatia, was to estimate the nitrogen and phosphorus loads in the Jadro River spring and its streamflow by calculating the load in kg/day or tons/year and to compare this with the load for the maximum allowed concentrations (MAC) for drinking water (Official Bulletin, No 46/94) expressed in kg/day or tons/year. Daily pollution loads at the Jadro River spring for total N ranged from 0 to 304 kg, for NH(3)-N from 0 to 38 kg, for NO(3)-N from 0-1321 kg and for PO(4)-P from 0-92 kg in the period from September 1993 to September 2003. When compared with MAC loads the results prove that the Jadro River spring is not polluted by nitrogen compounds and phosphorus. The average annual load for total N ranged from 10 to 33 t, for NH(3)-N from 0.25 to 5.15 t, for NO(3)-N from 40 to 190 t, and for PO(4)-P from 0.3 to 11.5 t. The nitrogen compounds and phosphorus loads vary from one year to another without any constant decreasing or increasing trends. The annual average loads compared with the average annual MAC loads (especially for NH(3)-N and PO(4)-P) show that there were no threats of constant pollution of the spring. The loads for total N and PO(4)-P along the Jadro River flow from the spring to the fishpond entrance were monitored over a five year period from September 1999 to September 2004. The results show no regularities. The highest annual total nitrogen load of 45 t was recorded at the entrance to the fishpond during the 2002/2003 period. The highest annual PO(4)-P load of 10 t was measured at the Vidovic Bridge during the 2003/2004 period; however, the concentrations of N and P did not exceed the MAC concentrations which are prescribed for drinking water. According to the investigation results of the daily and average annual loads compared with MAC loads for drinking water, it can be concluded that the Jadro River spring and its streamflow are not polluted by nitrogen and phosphorus.