The snowmelt as a critical period for the quality of surface water in the agricultural catchment

The research on the quality of the water of a small watercourse was conducted in the agricultural catchment in north-eastern Poland. The water quality was analyzed in the hydrological year and in the period of increased discharge, which in these hydro-meteorological conditions occurs in the snowmelt period. Nutrients get from agricultural land to surface water during the snowmelt or precipitation period. Therefore, the chemical composition of the water of the studied watercourse was subject to intense seasonal fluctuations. The concentration of nitrates, phosphates and ammonium ions increased with discharge. The snowmelt lasted for several days. However, as research has shown, this is a critical period for the quality of surface water in the agricultural landscape. During this period, the water of a small watercourse transported about 36% of annual nitrate load, over 45% of phosphate load and as much as 66% of ammonium ions