Integrated eco-hydrological modelling of soil organic matter dynamics for the assessment of environmental change impacts in meso- to macro-scale river basins

Abstract

A process-based extension of the eco-hydrological river basin model SWIM (Soil and Water Integrated Model) to simulate selected environmental change impacts on soil organic carbon (SOC) dynamics for environmental conditions in meso- to macro-scale river basins is proposed. The novel aspect and main advantage of the extended model is an integrated consideration of hydrological processes, vegetation dynamics and biogeochemical cycles (soil carbon, phosphorus, and nitrogen) in semi-closed systems (river basins) under environmental change. Thereby the extension was designed to integrate present-day understanding of soil organic matter dynamics under the constraints of data availability for parameterisation at the regional scale. A major advantage is less data and parameter necessary to run the model compared to state of the art SOC models and the availability of direct measurements of soil C carbon contents to test and validate the model. The model extension was tested regarding primary organic matter decomposition and long-term SOC dynamics using observed data sets. This test delivered similar quality as other SOC models. The new SOC model extension adequately represents these processes when compared to observed data on experimental field sites and literature studies. Application of the extended model to assess impacts of land management practices (different organic and inorganic fertilisation schemes, different crop rotations, inclusion of cover crops and harvest by-product returns) on long-term SOC dynamics is presented here at the experimental field and river basin scale. The simulated quantification at the field scale of different fertilisation regimes led to changes from −0.13 to +0.1 t C ha −1 year −1 in SOC, different types of crop rotations and cover crop impacts changed SOC between −0.13 and +0.07 t C ha −1 year −1 and incorporation of harvest by-products (grain straw residuals) led to changes between −0.1 and +0.027 t C ha −1 year −1 in SOC. It is shown on the river basin scale that harvest by-products quantity remaining on the field significantly impact regional SOC dynamics (loss of 0.26 t C ha −1 year −1 when exporting all harvest by-products). The modelled results are in general agreement with studies reported in literature. The extended model is hence able to quantify the impacts of selected land management practices on long-term SOC dynamics and allows land management practices and their impacts on water availability, water quality, carbon storage in soils, and vegetation growth to be assessed in an integrated way.