Compacted wheel tracks as underestimated structures in water erosion events in agricultural landscapes: Results of a first process-based model application at catchment level.

Soil erosion by water is one of the main causes of degradation of arable soils worldwide. Through the degradation of soil functionality and the long-distance effect of polluted soil particles, water erosion can severely limit soil fertility and the condition of aquatic ecosystems. Nowadays, a variety of different soil erosion models are used on different spatial and temporal scales to assess soil erosion risk, identify risk areas and support decision makers in adapting soil protection measures. Field studies show that highly compacted field areas such as wheel tracks, can have a major influence on the extent of soil erosion and runoff, but so far, they are not considered in any model-based soil erosion assessment.

The aim of this study is therefore to present an approach for integrating compaction effects of tramlines into process-based soil erosion models. Furthermore, the effects of tramlines on soil erosion and runoff processes within a watershed are to be identified. For this purpose, the soil erosion model EROSION 3D (E3D) was parameterized by accounting for soil conditions of compacted wheel tracks for a watershed in Norther Germany. In a further step, the modelling was conducted for a real heavy rainfall event and calibrated and tested with mapped runoff and soil erosion data. Additionally, a sensitivity analysis of the input parameters was conducted in order to assess soil properties which have a major impact on the model results.

The study shows that small-scale features such as tramlines can be integrated into soil erosion models and that this can significantly improves the spatial prediction of runoff and soil erosion. The model results also show that tramline tracks can have a significant contribution (up to 75 %) to total erosion as well as to sediment input into the water network, while bulk density of the wheel tracks is a major factor influencing modelled runoff and soil loss. The model results indicate that tramlines can play a key role in runoff and erosion processes and that the consideration of highly compacted areas in soil erosion assessments in agricultural landscapes is crucial. The results also indicate, that soil conservation measures may need to foster on tramlines and other compacted field areas such as headlands.