Relationship between catchment characteristics and nutrient concentrationsin an agricultural river system

We examined the effects of catchment characteristics and riverine processes on the concentrations of nutrients and total suspended solids (TSS) using data from the outlets of 12 tributaries (9-139 km(2)) and 22 main channel s ites of a river draining an intensely cropped area of 1088 km(2) in SW Finl and. For the tributaries, the flow-weighted mean concentrations of TSS and total phosphorus (TP), which both reflect erosion, were best explained by f ield percentage and the mean slope of the fields of the catchment. The best model describing the concentration of dissolved reactive P (DRP) included field percentage and catchment area. Total nitrogen (TN) and nitrale + nitr ite-nitrogen (NOx-N) correlated only with field percentage. Except for DRP, the regression models derived from the tributary data rather accurately pr edicted the concentrations in the main river channel. Our results suggest t hat, with regard to lakeless catchments of 10-1000 km(2), the export of TP, TSS and N per unit area remains constant. Furthermore, although some P in eroded soil particles may be released into dissolved, algal-available form during the river transport, erosion control appears not to efficiently redu ce dissolved P. (C) 2000 Elsevier Science Ltd. All rights reserved.