Denitrification and mixing in a stream-aquifer system: Effects on nitrate loading to surface water

被引:112
作者
McMahon, PB [1 ]
Bohlke, JK [1 ]
机构
[1] US GEOL SURVEY,RESTON,VA
关键词
D O I
10.1016/S0022-1694(96)03037-5
中图分类号
TU [建筑科学];
学科分类号
0813 ;
摘要
Ground water in terrace deposits of the South Platte River alluvial aquifer near Greeley, Colorado, USA, had a median nitrate concentration of 1857 mu mol l(-1). Median nitrate concentrations in ground water from adjacent floodplain deposits (468 mu mol l(-1)) and riverbed sediments (461 mu mol l(-1)), both of which are downgradient from the terrace deposits, were lower than the median concentration in the terrace deposits. The concentrations and delta(15)N values of nitrate and N-2 in ground water indicated that denitrifying activity in the floodplain deposits and riverbed sediments accounted for 15-30% of the difference in nitrate concentrations. Concentrations of Cl- and SiO2 indicated that mixing between river water and ground water in the floodplain deposits and riverbed sediments accounted for the remainder of the difference in nitrate concentrations. River flux measurements indicated that ground-water discharge in a 7.5 ion segment of river had a nitrate load of 1718 kg N day(-1) and accounted for about 18% of the total nitrate load in the river at the downstream end of that segment. This nitrate load was 70% less than the load predicted on the basis of the median nitrate concentration in the terrace deposits and assuming no denitrification or mixing in the aquifer. Water exchange between the river and aquifer caused ground water that originally discharged to the river to reenter denitrifying sediments in the riverbed and floodplain, thereby further decreasing the nitrate load in this stream-aquifer system. Results from this study indicated that denitrification and mixing within alluvial aquifer sediments may substantially decrease the nitrate load added to rivers by discharging ground water.
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页码:105 / 128
页数:24
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