Quantifying Water Pollution Sources in a Small Tile-drained Agricultural Watershed

This paper evaluates the quantity and quality dynamics of surface and drainage waters in a small, 7.1 km(2) agricultural watershed, located in the crystalline complex of the Czech Republic. Concentrations and monthly solute loads of amonium nitrogen (NH4-N), nitrate nitrogen (NO3-N), phosphate phosphorus (PO4-P) and total phosphorus (P-tot) from ten watershed's subcatchments with different soil, land use and tile drainage characteristics were compared for the period March-October from 2009 to 2011. The results and relevant processes were described using regular monitoring as well as event-based sampling approaches, methods of runoff separation and regression techniques. The average baseflow comprised 35-50%, whereas interflow and overland flow were 50-65% of the total runoff. The highest concentrations of NO3-N were detected in waters originating from cultivated and tiled subcatchments; those of NH4-N, PO4-P and P-tot came from subcatchments containing settlements and water ponds. In the monitored sites within the watershed, non-point pollution sources produced on average 23% of NH4-N, approximately 45% of NO3-N, 24% of PO4-P and about 26% of P-tot of total monthly solute loads. The differences in the share of monitored subcatchments in the total load from non-point pollution sources varied from month to month and were caused mainly by miscellaneous hydrological conditions and natural as well as man-altered runoff characteristics. The obtained results confirmed that used methods count for a useful approach for discerning water pollution sources and their dynamics in small, tile drained watersheds.