Research ArticleQuantifying 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 (NH 4 -N), nitrate nitrogen (NO 3 -N), phosphate phosphorus (PO 4 -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 NO 3 -N were detected in waters originating from cultivated and tiled subcatchments; those of NH 4 -N, PO 4 -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 NH 4 -N, approximately 45% of NO 3 -N, 24% of PO 4 -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 mainlybymiscellaneous hydrologicalconditionsand naturalaswellasman-alteredrunoff 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.