Modeling sediment yield and phosphorus transport in Finnish clayey soils

A mathematical simulation model (ICECREAM), describing the phosphorus cycle in the soil and its losses from soil 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, overestimated erosion for Finnish agricultural clayey soils with relatively steep slopes (i.e., 7%-8%). The calibration of poorly known and/or spatially varying input parameters, such as Manning's n, soil erodibility, and field capacity, did not sufficiently improve the agreement between simulated and measured data. Ther, fore, a sensitivity analysis of the erosion equations was carried out using Monte Carlo methods, varying both input and non-input parameters. This analysis showed that parameters in equations dependent on the slope, such as rill and interrill detachment rates, peak runoff rate, and equations related to sediment transport capacity were the most sensitive. Thus, those parameters were recalibrated, resulting in simulated annual sediment yields that approached the measured erosion rates, which ranged from 200 to 5000 kg ha(-1) yr(-1). Since the amount of phosphorus bound to sediments is closely correlated with the amount of eroded soil material, simulated sediment-bound phosphorus also corresponded better to the measurements.