Landuse/cover change and its impact on Carbon Stocks in Sezibwa River micro-catchment, Uganda

Abstract

Significant land use/cover changes have been reported in the central region of Uganda. The land cover changes involve conversion of forests and grasslands as well as wetlands into agricultural lands in order to meet the needs of the growing population. Changes in land use/cover directly impact on carbon stocks and crucially expose the organic-rich soil surfaces to the atmosphere. This study assess the extent of land use/coer change and its impact on carbon stocks in Sezibwa River Micro-catchment in central Uganda. Specifically the study i) determined the trend in landuse/cover changes in the catchment, ii) determined the trend in carbon stock in the catchment, and iii) determined the drivers of carbon stock change in the catchment. The change in land use/cover for the period 1995, 2005, 2015 and 2020 was assessed using landsat 7 and 8 satellite imagery, while the total carbon density in the various land use/cover types and soils at different soil depth was assessed with field measurements and allometric biomass functons. Finally, the mean carbon densities of land use/cover types were combined with land cover maps resulting in carbon stocks values for a given land use/cover type for each time period studied. Across-sectional research design using both quantitative and qualitive approaches was adopted to determine the drivers of carbon stock change within the catchment. Results indicate negative changes in forest cover, Bushland and Grasslands in the catchment at the expense of small scale and large scale farming, built up areas, plantations and woodlands between 1995 and 2020. Soil organic carbon is highest along the 100 cm soil profile compared to the top soil (0-30 cm) in the catchment. Forest cover has the highest above ground carbon density (127.2 t/ha) followed by woodland (90.0 t/ha), Small scale farming (41.2 t/ha) and Bushland (23.7 t/ha). Total Carbon Stock at the top soils increased from 1995 to 2020 for all the land use/cover types and decreased for the deeper soils except for builtup areas and large scale farming and wetlands. Small scale farming and woodland have a positive effect on total carbon stock at the top soils compared to other land use/cover types. Demographic pressure is the overall driver to Total Carbon Stock change through its effects such as intensification and expansion of farming, builtup infrastructure development, firewood and charcoal burning, and corruption in catchment conservation of natural resources. The Total Carbon Stock changes are complex in such a way that the factors keep interacting whose magnitude differs in time and space to cause change. The finding of this study contribute to the proper planning for designing catchment management plans which ensure carbon sequestration to combat climate change effects.