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Use of man-made impoundment in mitigating acid mine drainage in the North Branch Potomac River 总被引:1,自引:0,他引:1
The US Department of the Army, Baltimore District Corps of Engineers, oversees a long-term monitoring study to assess and
evaluate effects of the Jennings-Randolph reservoir on biota in the North Branch Potomac River. The reservoir was intended,
in part, to mitigate effects of acid mine drainage originating in upstream and headwater areas. The present study assessed
recovery of benthos and fish in this system, six years after completion of the reservoir. Higher pH and lower iron and sulfate
concentrations were observed upstream of the reservoir compared to preimpoundment conditions, suggesting better overall water
quality in the upper North Branch. Water quality improved slightly directly downstream of the reservoir. However, the reservoir
itself was poorly colonized by macrophytes and benthic organisms, and plankton composition suggested either metal toxicity
and/or nutrient limitation. One large tributary to the North Branch and the reservoir (Stony River) was shown to have high
(and possibly toxic) levels of manganese, iron, zinc, and aluminum due to subsurface coal mine drainage. Macroinvertebrate
diversity and number of taxa were higher in sites downstream of the reservoir in the present study. Compared with previous
years, the present study suggested relatively rapid recovery in the lower North Branch due to colonization from two major
unimpacted tributaries in this system: Savage River and South Branch Potomac. Abundance of certain mayfly species across sites
provided the most clear evidence of longitudinal gradients in water quality parameters and geomorphology. Fish data were consistent
with macroinvertebrate results, but site-to-site variation in species composition was greater. Data collected between 1982
and 1987 suggested that certain fish species have unsuccessfully attempted to colonize sites directly downstream of the reservoir
despite the more neutral pH water there. Our results show that recovery of biota in the North Branch Potomac was attributed
to decreased acid inputs from mining operations and dilution from the Savage River, which contributed better water quality.
Continued improvement of North Branch Potomac biota may not be expected unless additional mitigation attempts, either within
the reservoir or upstream, are undertaken. 相似文献
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