MODELING SEDIMENT YIELD AND PHOSPHORUS TRANSPORT IN FINNISH CLAYEY SOILS

Abstract

A mathematical simulation model (ICECREAM), describing the phosphorus cycle in the soil and its losses fromsoil to water, was developed and applied to clayey soils in Finland. The model is based on the CREAMS and GLEAMS model,with some modifications to adapt it to local (climatic) conditions. The original erosion submodel (USLE) highly overestimatederosion for Finnish agricultural clayey soils with relatively steep slopes (i.e., 7%8%). The calibration of poorly knownand/or spatially varying input parameters, such as Mannings n, soil erodibility, and field capacity, did not sufficientlyimprove the agreement between simulated and measured data. Therefore, a sensitivity analysis of the erosion equations wascarried out using Monte Carlo methods, varying both input and noninput parameters. This analysis showed that parametersin equations dependent on the slope, such as rill and interrill detachment rates, peak runoff rate, and equations related tosediment transport capacity were the most sensitive. Thus, those parameters were recalibrated, resulting in simulated annualsediment yields that approached the measured erosion rates, which ranged from 200 to 5000 kg ha 1 yr 1 . Since the amountof phosphorus bound to sediments is closely correlated with the amount of eroded soil material, simulated sedimentboundphosphorus also corresponded better to the measurements.