Erosión y desertificación.-Influence of land use changes on soil carbon stock and soil carbon erosion in a Mediterranean catchment

Abstract

ABSTRACT The effect of changing land uses on the organic soil carbon (C) stock and the soil C transported by water erosion and buried in depositional wedges behind check-dams was estimated in a Mediterranean catchment in SE Spain. The 57 % decrease in agricultural areas and 1.5-fold increase of the total forest cover between 1956 and 1997 induced an accumulation rate of total organic carbon (TOC) in the soil of 10.73 g m-2 yr-1. The mineralassociated organic carbon (MOC) represented the 70 % of the soil carbon pool, the particulate organic carbon (POC) represented a 30 % of the soil carbon pool. The average sediments/soil enrichment ratio at the subcatchment scale (8-125 ha) was 0.59 ±0.43 g kg-1. Eroded soil C accounted for between 2 % to 78 % of the soil C stock in the first 5 cm of the soil in the subcatchments. The C erosion rate varied between 0.008 and 0.2 t ha-1 yr-1. Observed changes in land use (decrease in agricultural areas) reduced soil C erosion, although sediments from non-agricultural sources are richer in organic C. At catchment scale from the 4 % of the soil C stock mobilized by water erosion, 77 % is buried in the sediment wedges behind check-dams. Soil C replacement due to increased vegetation cover between 1974 and 1997 represented a 36 % of the original soil organic C stock. All together represent an erosion-induced sink of soil organic C of 40 % compared to the original levels of 1974. We can conclude that the catchment is behaving as a soil C sink within the soil erosion subsystem as a consequence of the changes on the land use pattern that took place since the 1950’s. The meaning of this erosion-induced C sink in a wider C balance which takes into account soil respiration remains uncertain