Vegetation restoration and agricultural management to mitigate nitrogen pollution in the surface waters of the Dan River, China

Non-point source pollution in rivers is an important factor affecting water quality. Quantifying the load of non-point source pollutants in the water and implementing improvement measures are critical for guaranteeing drinking water quality. In this study, the Dan River watershed, which is an important water source for Beijing, was investigated. Through a combination of water sampling and numerical simulations, the temporal and spatial distributions of nitrate nitrogen (NO₃^--N) and ammoniacal nitrogen (NH₄⁺-N) loads in the watershed were determined, and the effects of vegetation restoration and agricultural management on reducing nitrogen pollution in the river were predicted. The NO₃^--N and NH₄⁺-N loads in the watershed were higher during the wet season (July-September), accounting for more than 50% of the annual nitrogen output. The Soil and Water Assessment Tool (SWAT) was used to simulate the nitrogen load in the watershed. Pollution from nitrogen loading was serious in the lower reaches of the river; however, vegetation restoration can reduce the nitrogen output. Through scenario simulations, we found that an increase in forestland in the watershed would reduce the NO₃^--N and NH₄⁺-N loads. The nitrate and NH₄⁺-N loads in the watershed also decreased with reduced fertilizer use and reduced irrigation application in the watershed. Thus, reasonable land planning and agricultural management measures can effectively reduce nitrogen loss, which is an effective way to control non-point source pollution in watersheds and ensure river water quality.

Examination of mercury contamination from a recent coal ash spill into the Dan River, North Carolina, United States

Coal ash spills occasionally occur due to the accidental failure of surface impoundments, and toxic metal-laden ash can pose a serious health threat to adjacent aquatic ecosystems. Here, we performed an investigation into longitudinal variations of mercury (Hg) contamination in the Dan River (North Carolina, United States) about 17 and 29 months after a February 2014 coal ash spill incident, in which the reported Hg concentrations in the spilled coal ash (210 ng/g) were 1-2 orders of magnitude higher than the river sediments (2-61 ng/g). We examined total Hg (THg) and methyl Hg (MeHg) in sediments from 0 to 65 km downstream of the spill, and found that most of the variations of THg and MeHg in surface sediments (0-16 cm) could be well accounted by the organic matter content and appeared to be not contaminated by Hg derived from coal ash. In examining MeHg bioaccumulation in invertebrates (aquatic and riparian) and fish in the Dan River and fish in a reservoir downstream of Dan River, we found no evidence of elevated MeHg bioaccumulation due to the 2014 coal ash spill. Thus, we concluded that Hg contamination from the coal ash spill is largely absent in the Dan River for both surface sediments and biota within the first three years of spill (until 2017), even though the majority of coal ash may be buried deeper in the sediment in the river channel and/or the downstream reservoir. Alternatively, the Hg associated with the coal ash is largely not bioavailable for extensive microbial Hg methylation. The findings provide useful insights into remediation strategies for this incident and other coal ash spills.

Damage cost of the Dan River coal ash spill

The recent coal ash spill on the Dan River in North Carolina, USA has caused several negative effects on the environment and the public. In this analysis, I report a monetized value for these effects after the first 6 months following the spill. The combined cost of ecological damage, recreational impacts, effects on human health and consumptive use, and esthetic value losses totals $295,485,000. Because the environmental impact and associated economic costs of riverine coal ash spills can be long-term, on the order of years or even decades, this 6-month assessment should be viewed as a short-term preview. The total cumulative damage cost from the Dan River coal ash spill could go much higher.