Implications of changes in land use on soil and biomass carbon sequestration: a case study from the Owabi reservoir catchment in Ghana

Land use changes affect soil and biomass carbon sequestration potential of the agroecosystems of most Sub-Sahara Africa facing rising temperatures due to global climate change. One such ecosystem is the Owabi reservoir catchment in Ghana, which has undergone extensive changes in land use through urbanization. Our study aimed to determine the impact of the spatial and temporal variability of the different land uses on soil and biomass carbon storage in the Owabi catchment. Land use/cover maps were elaborated using SPOT satellite images of 30 x 30-m resolution and Erdas Imagine and ArcGIS Pro softwares. Soil and vegetation were sampled along three transects in the Y plane in early 2014. Nested plot design and temporary sample plots of 50 x 50 m were demarcated within a 1 ha plot in each of the land uses. Trees, herbs and litter were sampled to assess aboveground carbon, and soil samples were taken at 0-15 cm and 15-30 cm depth. Belowground (root) biomass was calculated using the root:shoot ratio. Seven (7) land use types - dense forest, sparse forest, grassland, cropland, wetland, settlement, and excavated land - were identified and differences in carbon stocks were assessed. Soil carbon stock (0-30 cm) ranged from 51.80 Mg/ha in dense forest to 7.00 Mg/ha in excavated land. Our study showed that the conversion of forest lands to other land uses through excavation resulted in about 30-folds loss in carbon and also a major loss of carbon in the catchment from c. 1.4 x 10(6) Mg C in 1990 to 0.55 x 10(6) Mg C in 2014. Enhancing forests or growing trees to sequester carbon seems to be the optimum choice among the seven land uses if the introduction of payment for environmental services options is considered.