Land degradation impact on soil carbon losses through water erosion and CO 2 emissions
Soil Fertility and Analytical Services, KwaZulu-Natal Department of Agriculture and Environmental Affairs, Private Bag X 9059, Pietermaritzburg, 3200, South Africa; IRD - BIOEMCO c/o School of Bioresources Engineering and Environmental Hydrology, Rabie Saunders Building, University of KwaZulu-Natal, Box X01, Scottsville, 3209, South Africa
Worldwide concerns with global change and its effects on our future environment require an improved understanding of the impact of land cover changes on the global C cycle. Overgrazing causes a reduction in plant cover with accepted consequences on soil infiltration and soil erosion, yet the impact on the loss of soil organic carbon (SOC) and its associated processes remain unaccounted for. In this study performed in South Africa, our main objective was to evaluate the impact of plant cover reduction on (i) SOC erosion by water in both particulate (POC) and dissolved (DOC) forms, and (ii) soil CO 2 emissions to the atmosphere. The study performed under sandy-loam Acrisols investigated three proportions of soil surface coverage by plants (Cov), from 100% (Cov100) for the "non-degraded" treatment to 25-50% (Cov50) and 0-5% (Cov5). POC and DOC losses were evaluated using an artificial rainfall of 30mmh -1 applied for a period of 30min on bounded 1×1m 2 microplots (n=3 per treatment). CO 2 emissions from undisturbed soil samples (n=9) were evaluated continuously at the laboratory over a 6-month period. At the "non-degraded" treatment of Cov100, plant-C inputs to the soil profile were 1950±180gCm -2y -1 and SOC stocks in the 0-0.02m layer were 300.6±16.2gCm -2. While soil-C inputs by plants significantly (P<0.05 level) decreased by 38.5±3.5% at Cov50 and by 75.4±6.9% at Cov5, SOC, the losses by water erosion of 0.75gCm -2 at Cov100 increased from 66% at Cov50 (i.e. 3.76±1.8gCm -2) to a staggering 213% at Cov5 (i.e. 7.08±2.9gCm -2). These losses were for the most part in particulate form (from 88.0% for Cov100 to 98.7% for Cov5). Plant cover reduction significantly decreased both the cumulative C-CO 2 emissions (by 68% at Cov50 and 69% at Cov5) and the mineralization rate of the soil organic matter (from 0.039 gC-CO 2gC -1 at Cov100 to 0.031gC-CO 2gC -1 at Cov5). These results are expected to increase our understanding of the impact of land degradation on the global C cycle. Further in-situ research studies, however, need to investigate whether or not grassland degradation induces net C-emissions to the atmosphere. © 2012 Elsevier B.V..
Global c Cycle; Land use change; Particulate and dissolved SOC forms; South Africa; Water erosion; Air pollution; Erosion; Forestry; Rating; Soils; Vegetation; Carbon dioxide; Acrisol; air-soil interaction; carbon cycle; carbon dioxide; carbon emission; infiltration; land degradation; land use change; mineralization; overgrazing; rainfall; sandy loam; soil carbon; soil emission; soil erosion; soil organic matter; soil profile; soil surface; vegetation cover; water erosion; South Africa