Impacts of Land Use and Land Cover Changes on Land Surface Temperature, Soil Erosion and Soil Quality Deterioration in Suha Watershed, Northwestern Highlands of Ethiopia

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Date

2024-07

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Addis Ababa University

Abstract

Suha watershed found in the Upper Blue Nile Basin of Ethiopia is facing severe soil erosion and soil quality degradation problems due to its biophysical and socioeconomic characteristics. However, there is a lack of comprehensive data on the land use land cover changes and their impacts on land surface temperature, soil erosion risk and sediment yield, soil quality indicators as well as soil nutrient flows and balances in this watershed. Therefore, this study was undertaken to analyze the spatiotemporal changes in land use and land cover and to examine their impacts on the land surface temperature, soil erosion and sediment export, soil quality indicators and soil nutrient flows in the Suha watershed, northwestern highlands of Ethiopia. Multi-temporal Landsat images covering the periods from 1985 to 2019 were utilized to examine changes in land use and land cover (LULC) as well as land surface temperature (LST) variations with the application of GIS and remote sensing techniques. The process involved image preprocessing, supervised classification, accuracy assessment, and change detection. Quantification of soil loss and sediment export was carried out using the Revised Universal Soil Loss Equation (RUSLE) integrated with ArcGIS. Various data inputs, including digital elevation model, LULC, precipitation, soil types, and conservation strategies were used for this purpose. To evaluate the status of soil quality indicators, a total of 27 composite surface soil samples (0-30 cm) were collected from adjacently located land-use systems in three replications from each elevation gradient of the watershed. Standard procedures were applied to analyze selected physical and chemical soil quality parameters. The study also investigated soil nutrient depletion by quantifying nutrient flows and balances for macronutrients (N and P) in different elevation gradient of the watershed. Significant changes in land use and land cover were observed in the Suha watershed over the past 35 years. Agricultural land has increased by 15,418 hectares for the entire period at the expense of grazing and shrub lands. Barren land also expanded significantly due to cultivation of marginal and steep slope areas and poor land management. The study also revealed spatial and temporal variations in Land Surface Temperature (LST), with impermeable surfaces having the highest values. The average annual soil loss rate in this watershed varied over the years, with rates of 15, 22, 31, and 30 tons per hectare per year for the periods 1985, 1999, 2009, and 2019 respectively. The mean annual sediment yield was 4, 6, 8, and 8 tons per hectare per year for the same periods. Soil loss varied across different land use and land cover categories and landscape positions, with the highest mean value observed in bare land (54-103 t/ha/yr), followed by cultivated land (17-29 t/ha/yr). About 32% (25,660 ha) of the watershed experienced severe and very severe soil erosion in the past 35 years. The analysis of variance results of soil quality indicators showed significant changes in selected soil quality indicators across different land use systems. Specifically, the index of soil aggregate stability (ISS), organic carbon (OC), total nitrogen (TN), and C: N ratio revealed significant decreases in the cultivated land use system compared to other land use systems. Conversely, the content of available phosphorus (AP) was significantly higher in cultivated land. Moreover, the aggregated soil quality index (SQI) values have shown that soil quality is rated as low in cultivated fields, optimal in grazing land and high in forest land. The results of soil nutrient balances indicated that the rate of nutrient depletion is higher in the highland areas than the midland areas. N and P balances were -77.1 kg N /ha/yr and -11.9 kg P/ha/year for the wheat farming system (highland area), which are rated as one of the highest in Africa. For teff farming system, the values were -39.3 kg N/ha/yr and -1.4 kg P/ha/yr. The major negative drivers are removals in the harvested products (OUT1) and crop residues (OUT2) followed by soil erosion (OUT5). Overall, these studies provide valuable insights into the changes in land use/land cover, land surface temperature, soil erosion risk, soil quality and nutrient balances, contributing to a better understanding of the environmental dynamics. Sub watersheds that are found on the steep slope landscapes and are experiencing severe soil erosion that demand immediate interventions. effective soil and water management strategies should be established and integrated with vegetative measures to provide multiple benefits to the farmers. In order to reduce the volume of crop residue removal as household energy (OUT2), promoting energy saving technologies such as the use of fuel stoves, saving stoves and biogas is crucial.

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Keywords

LULC Change, LST, GIS & Remote Sensing, Landsat Image, RUSLE, Soil Erosion, Soil Quality and Soil Nutrient Flows

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