Modelling Chemical Weathering in Different Scales

Abstract: Chemical weathering is one of the most important processes supporting life on Earth. Chemical weathering continuously contributes macronutrients and micronutrients to the soil solution. These recycling, essential elements are used as building blocks for all organic living matter. Chemical weathering is a vital factor in the analysis and understanding of a large number of important environmental issues, acidification and nutrient cycling in managed forests and agro-ecosystems. The main research objectives forming the basis of this thesis were to: 1. Improve the numerical estimations of the reaction coefficients in the mathematical biogeochemical soil model PROFILE by dissolution experiments of epidote and clay-size soil minerals using fluidized bed flow-through reactor, 2. Use the PROFILE model to estimate the potential weathering rate in agricultural soils/systems and to assess the contribution of weathering to mass balances and field budgets in agricultural systems and forest ecosystems 3. Develop a technique to estimate the weathering-related limits for regional sustainable biomass production in a forested area in southern Sweden. The conclusions from the thesis work can be summarized as: –Kinetic processes must be seen as whole system. It requires holistic view for the system of simultaneous chemical reactions and all chemical participants in promoting and retarding effects; –PROFILE could be adapted to calculate the weathering rate in agricultural soil system with reasonable accuracy; –Spatial distribution of weathering rate is possible using kriging interpolation with nested sampling strategy in the same forested area; –By using the Liebig “Law of the Minimum” is possible to estimate the long-term sustainable biomass production in 3,500 ha large forested area in southern Sweden, based on mineral nutrient mass balances; –Forestry is not always sustainable with respect to Ca and Mg in the investigated area; –The stand quality (Swedish;Bonitet) is not good predictor of long-term sustainable yield. For successful modelling, it is important to have holistic approach to model development of ecosystems due to the complexity of the model system. Therefore there must be close connection and feedback between: 1) model use and development, 2) experimental studies, and 3) practical use and field experiments, according to our experience of modelling events in different ecosystems.