1 Introduction -- 1.2 Soil organic matter dynamics in terrestrial environments -- 1.3 SOM turnover modeling -- 2. RothC-calibration issues and uncertainty analysis -- 3. Carbon loss due to landuse change along a climatic gradient -- 4. Development of a coupled carbon, aggregation and structure turnover (CAST) model for topsoils -- 5. Synthesis: soil degradation in Koiliaris River basin critical zone observatory