Environmental implications of soil erosion and sediment yield in Lake Hawassa watershed, south-central Ethiopia

Abstract

Background Assessing soil erosion, sediment yield and sediment retention capacity of watersheds is one of the under-researched areas in watersheds of developing countries like Lake Hawassa watershed. The study examined soil erosion and sediment yield and their environmental implications in the Lake Hawassa watershed. The quantification and mapping were carried out using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model. Data such as Land Use Land Cover (LULC), Digital Elevation Model (DEM), rainfall, soil, and management practice were used as input parameters. Results The empirical analysis confirmed that the watershed has a total soil loss of about 5.27 Mt annually. The mean annual erosion rate from the watershed was estimated to be 37 t ha−1 year−1. The estimated erosion rate was greater than the maximum tolerable erosion limit in Ethiopia (2–18 t ha−1 year−1). The total amount of sediment which was exported to the nearby streams and lakes in the watershed was estimated to be 1.6 t ha−1 year−1. The water bodies receive a total of 226,690.3 t of sediment annually. Although higher soil loss and sediment export per unit of area were estimated from the highest slope gradients, greater contributions to the total soil loss and sediment export were computed from slopes with 5–30% gradients. In terms of LULC, the highest contribution to the total soil loss was computed from cultivated land while the highest rate of soil loss per hectare was observed from bare land. Due to the existing vegetative cover, a total of 18.65 Mt (130.7 t ha−1 year−1) of sediment was retained. Vegetation-covered LULCs such as forest, woodland, shrubland, and agroforestry revealed the highest sediment retention capacity. As a result of the increased soil erosion and sediment yield in the watershed, the drying-out of a small lake and the rise in the water level of Lake Hawassa were identified. Conclusion Most of the soil loss and sediment yield were contributed by a small part of the watershed. Thus, the results underscore the urgent need for targeted soil and water conservation measures of various types to ensure the sustainability of the watershed resources.

Suitable Land-Use and Land-Cover Allocation Scenarios to Minimize Sediment and Nutrient Loads into Kwan Phayao, Upper Ing Watershed, Thailand

“…At the same time, evergreen forest generated the lowest average sediment export, with a value of 0.01 tons/km 2 , in the Klong U-Tapao watershed, Songkhla Province, Thailand. Likewise, Degife et al [74] found that the highest sediment export per unit of area was observed from miscellaneous land (bare land), while the highest contribution of the total sediment that reached the surrounding water bodies was from cultivated land (40.7%). Similarly, Zhou et al [75] found that decreases in miscellaneous land (bare land) significantly reduced sediment export in the Qiantang River Basin, China.…”

“…Annual land requirements under Scenario III for each LULC type.As a result, under Scenario III, economic crop areas, precisely paddy field, field crop, para rubber, and perennial trees and orchards were located based on suitability classes of economic crop zonation. Paddy fields expanded from 220 74. km 2 in 2019 to 280.20 km 2 in 2029, and field crop areas increased from 21.84 km 2 in 2019 to 34.11 km 2 in 2029.…”

Mapping Land Use Land Cover Changes and Their Determinants in the Context of a Massive Free Labour Mobilisation Campaign: Evidence from South Wollo, Ethiopia

“…A study done in the Northern Gojam sub-basin by [59] ascertained that agricultural land had exhibited a gross increase of 17.2% between 1994-2007. Findings by many other scholars at different temporal and spatial dimensions have put forward similar results [56,[60][61][62]. High population growth and the emerging landless youth have forced the community to plough forest, area closures and grazing lands.…”

“…It is inevitable to observe LULCC occurring in non-linear form due to complex and interweaved anthropogenic and natural processes. Transformation of land is a trend that will continue to unfold, as most of the intervention was raised from the very egocentric nature of human beings and their descendants [56][57][58]. Ever since the history of humanity, land devoted to human use has grown considerably, and increases in the production of commodities have further accelerated the use and abuse of land resources [51].…”

Estimating the Best Exponent of the Modified Universal Soil Loss Equation and Regionalizing the Modified Universal Soil Loss Equation under Hydro-Climatic Condition of Ethiopia

“…128 However, the USLE/RUSLE was applied at different parts of Ethiopia following similar 129 or different approaches to estimate any of its factors (e.g, [28,[33][34][35][36][37][39][40][41][42][43][44]46,48]).…”