Relationships among groundwater age, denitrification, and the coupled groundwater and nitrogen fluxes through a streambed
Relationships among groundwater age, denitrification, and the coupled groundwater and nitrogen fluxes through a streambed
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DOI：
10.1029/2008wr007400
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发表时间：
2009-09
影响因子：
5.4
通讯作者：
C. Kennedy;D. Genereux;D. Corbett;H. Mitásová
中科院分区：
文献类型：
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作者：
C. Kennedy;D. Genereux;D. Corbett;H. Mitásová
以美国北卡罗来纳州沿海平原的农业河流西熊溪为例，研究了地下水与氮通量耦合、地下水年龄与反硝化作用之间的关系。对水力传导率（K）和水头梯度（J）以及地下水中NO3−（[NO3−]）、溶解气体和氯氟烃浓度的河床同步测量值进行插值、绘图，并在河床区域进行积分（对于水通量v = KJ和硝酸盐通量fNO 3 = v[NO3−]）。硝态氮和溶解性有机氮分别占河床氮通量的92%和8%。河床图显示了一条地下水年龄较大、[NO3−]和fNO 3较低的带，贯穿大部分研究河段的中心。硝酸盐通量（fNO 3）显示出这种“中心低”模式，即使其控制因素之一，地下水通量（v），平均具有相反的“中心高”模式。[NO3-]与年龄之间的反比关系表明肥料是地下水NO3-的主要来源。反硝化作用使fNO 3平均值降低了约50%，从370 mmol m−2 d−1（没有反硝化作用时的值）降至173 mmol m−2 d−1（实际值）。地下水年龄和v的测量使得估算流量加权平均地下水年龄（τFWM）的新方法成为可能，τ FWM是与地下水储存和补给速率相关的重要含水层水力特征。该方法得出τFWM = 30年，这与地下水年龄的总体分布沿着，表明氮肥施用量的变化与地下水向西熊溪的NO3−通量之间可能存在显著的时间滞后。河床左右两侧的河床地下水化学差异表明，河流两侧的农业实践存在差异。
The relationships among coupled groundwater and nitrogen (N) fluxes, groundwater age, and denitrification were examined for a section of West Bear Creek, an agricultural stream in the coastal plain of North Carolina, United States. Simultaneous streambed measurements of hydraulic conductivity (K) and hydraulic head gradient (J) and the concentrations of NO3− ([NO3−]), dissolved gases, and chlorofluorocarbons in groundwater were interpolated, mapped, and (for water flux v = KJ and nitrate flux fNO3 = v[NO3−]) integrated over the streambed area. Nitrate and dissolved organic N accounted for 92 and 8% of N flux through the streambed, respectively. Streambed maps show a band of greater groundwater age, and lower [NO3−] and fNO3, running through the center of most of the study reach. Nitrate flux (fNO3) exhibits this “center‐low” pattern even though one of its controlling factors, groundwater flux (v), has on average the opposite “center‐high” pattern. An inverse relationship between [NO3−] and age is indicative of fertilizer as the primary source of groundwater NO3−. Denitrification reduced mean fNO3 by ∼50%, from 370 mmol m−2 d−1 (what it would have been in the absence of denitrification) to 173 mmol m−2 d−1 (what it actually was). Measurement of both groundwater age and v made possible a new method for estimating flow‐weighted mean groundwater age (τFWM), an important aquifer hydraulic characteristic related to groundwater storage and recharge rate. This method gives τFWM = 30 years, which, along with the overall distribution of groundwater ages, suggests the possibility of a significant time lag between changes in N fertilizer application rates and NO3− flux from groundwater to West Bear Creek. Differences in streambed groundwater chemistry between the left and right sides of the streambed suggest differences in agricultural practices on opposite sides of the stream.