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 km2 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 (Ptot) 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 Ptot 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 Ptot 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.