Application of two-component model of drainage discharge to nitrate contamination.

A conceptual two-component model of drainage discharge based on delta(18)O, nitrate content and delta(15)N data was constructed. It comprises the infiltrated precipitation and the local groundwater, both discharging into the drainage system. The movement of the water via the unsaturated zone is described as a piston-like flow with a varying amount contributing to the total drainage. Two tile drainage systems were studied for nitrate loss. The transit time between the rainfall infiltration and the drainage into the tile system is estimated to be approximately one year. This process is strongly dependent on the duration of the infiltration and its magnitude, and thus on the discharge dynamics in general. The local groundwater contribution to the system formed a significant part of the drainage discharge (varying as 65-98% of the whole drained amount). Nitrate content and delta(15)N data were used for the specification of the nitrate flux and nitrate origin in the drainage discharge.