Influence of Long-Term Land Use and Land Cover (LULC) Changes on Soil Loss, Sediment Export, and Deposition in the Ungauged Bontanga Watershed

Soil loss due to surface runoff is a natural phenomenon accelerated by anthropogenic activities. The study attempted to evaluate soil loss, sediment export, and deposition as influenced by changes in land use and land cover (LULC) in the Bontanga watershed. The InVEST-SDR model integrated with RUSLE was used in soil loss assessment. Results revealed that agricultural land produced 11,365.39 tons/year of soil loss in 1997, followed by 17,476.85 tons/year in 2002. In 2013, agricultural land experienced a soil loss of 5,391.98 tons/year, which finally increased to 91,274.53 tons/year in 2022. Agricultural land exported 56.16% of sediment, 13.39% of dense forest, and 13.30% of grassland. Dense forest deposited 41.54% of the sediment load, 30.49% of mixed shrub and grassland, and 10.85% of grassland. Over a long period, agricultural land is anticipated to contribute soil loss of 2,347,414.04 tons/year and sediment export of 388,497.56 tons/year. Sediment deposition amounting to 1,048,258.78 tons/year is anticipated to be deposited within the agricultural field. Both MAE and MAPE statistical measurements indicate a good model prediction performance for soil loss and sediment export. Understanding where sediments are produced and delivered will guide decision-makers, land use planners, and watershed managers in monitoring and planning the Bontanga watershed.