The aim of the study was to develop a method for assessing phosphorus transport from a large drainage basin. A tentative conceptual model of watershed dynamics was developed consisting of two components: a runoff model and a phosphorus transport model. A similar approach has also been used in previous studies (e.g. Kallio 1992). As the runoff model, a modification of the HBV-model (Vehviläinen 1992) was used. The statistical P transport model was developed in this study. The models were tested against the data of eight subcatchments of the watercourse of Lake Längelmävesi, central Finland.

Runoff calibration was made against total discharges, though in the output data the runoff from forested and agricultural areas were presented separately. A good fit was obtained, the correlation coefficient squared R2 against water level being 0.964. The calibration against total phosphorus transport was made using simulated discharge values. In the present version the correlation coefficient squared R2 was 0.901.