Impacts of Watershed Management Interventions on Bio-Physical Environment and Ecosystem Service valuesin Yezat Watershed, Upper Blue Nile Basin, Ethiopia

Abstract

This study was aimed at assessing the impacts of watershed management interventions on the bio-physical environment and ecosystem service values in the Yezat Watershed, Upper Blue Nile Basin, Ethiopia. Landsat images of 1990, 2000, 2010, and 2021 were employed and analyzed to produce maps of the respective years using GIS and remote sensing techniques. The normalized difference vegetation index (NDVI) was also employed to detect vegetation greenness. A revised universal soil loss equation model was also used to estimate soil loss. Additionally, a modified ecosystem services valuation model (InVEST) was employed to estimate sediment export. A one way ANNOVA was also used to evaluate the mean variances of crop yield and soil moisture for each treatment group in the study area. A paired-samples t-test was also applied to evaluate the amount of teff crop yield before and after watershed management interventions.An integrated valuation of the modified ecosystem service value coefficient was also applied to estimate ecosystem service values and functions. The results of the study showed that between 1990 and 2021, built-up area, plantations, natural forests, shrubland, and grasslands increased by +254ha, +712.3ha, 196.3ha, +1070.8 ha, and +425.3 ha, respectively, due to watershed management interventions. Conversely, cultivated land decreased at a rate of -2658.7hain the study area. However, the reverse was true between 1990 and 2000 due to large-scale land degradation. Due to the expansion of cultivated land and built-up area at the expense of forest, shrubland, and grassland, the mean annual soil loss of the study area increased by 111 tons per year in2000. However, the mean annual soil loss decreased from 111 tons per year in 2000 to 79 tons per yearin 2021. Regarding sediment export, a high amount of mean annual sediment yield was observed (35 tons per year) in 20000 due to the expansion of cultivated land and built-up area. Conversely, it decreased from 35 tons per year in 2000 to 18.4 tons per year in 2021. In the case of soil moisture, the results of the study indicated that bio-physical types of watershed management interventions have a high moisture status (43.6%), followed by physical types (38.63%) of watershed management interventions, while low amounts of soil moisture potential (30.16%) were observed from untreated (control) parts of the watershed, which was statistically significant at P≤ 0.05 in soil moisture status between the treated (physical and bio-physical) and untreated (controlled) farmlands in each cycle of soil moisture status. The longest teff height was observed in bio-physical watershed management interventions followed by physical treatments, while the shortest teff height was observed in untreated sites of the watershed. Similarly, the longest spike length (47.4 cm) was recorded from farmlands treated with bio-physical treatments, followed by areas treated with physical interventions (44.4 cm), whereas the shortest spike length (30.3cm) was recorded from untreated farmlands. In addition, the numbers of productive tillers counted in a 25-m2 area, above-ground biomass yield, straw yield, and crop yields were significantly affected by watershed management interventions at a P-value ≤ 0.05. Between 1990 and 2000, the ecosystem service values of natural forests, shrubs, and grassland were reduced, whereas the ecosystem service values of plantations and cultivated land were increased. However, between 2010 and 2021, the ecosystem service values of natural forest, shrubland, grassland, and plantations increased. Conversely, the ecosystem service value of cultivated land was reduced between 2010 and 2021.