A higher forest coverage rate results in a lower soil erosion depth and SS concentration in water.
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Watershed health decreased as the cropland area and population density increased.
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The COD achievement rate is a suitable health indicator for outlying reservoirs.
Abstract
This study analyzed big data collected from 95 public water supply, power generation, and irrigation reservoirs in Taiwan and its outlying islands to establish and quantify the standards for seven watershed health indicators. The water supply reservoirs have high forest coverage and a low soil erosion depth; however, these reservoirs have a low water quality due to a low point source pollution was treated (9.1%–17.7%) and 44–65.8 kg nonpoint source pollution per area (km2). Most irrigation reservoirs are located in the flat plains, which have low forest coverage (50.5%) and high sediment accumulation (36.7%). The power generation reservoirs are located on steep mountains with high forest coverage and only natural soil erosion. The 30 outlying reservoirs have a Carlson’s trophic state index value higher than 50, which is primarily a function of transparency. The chemical oxygen demand achievement rate is a more suitable health indicator for the outlying reservoirs than the other aforementioned indicators. The forest coverage rate and point source pollution reduction were positively associated with watershed health, whereas sediment accumulation, nonpoint source pollution, and CTSI/RPI were negatively associated with watershed health. The results of this study suggest that management strategies need to be tailored to the type of watershed.
