『Abstract
　A conceptual two-component model of drainage discharge based on δ¹⁸O, nitrate content and δ¹⁵N 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 δ¹⁵N data were used for the specification of the nitrate flux and nitrate origin in the drainage discharge.

Keywords: Drainage recharge; Discharge model; Nitrate balance; Delta N-15; Delta O-18』

1. Introduction
2. Site description
3. Sampling and data analysis
4. Isotope data methodology
5. Dehtare catchment
6. Jenin catchment
7. Discussion
8. Implications
9. Conclusions
Acknowledgements
References