Tracking the fate of a high concentration groundwater nitrate plume through a fringing marsh: A combined groundwater tracer and in situ isotope enrichment study
Tracking the fate of a high concentration groundwater nitrate plume through a fringing marsh: A combined groundwater tracer and in situ isotope enrichment study
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DOI：
10.4319/lo.2001.46.8.1977
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发表时间：
2001-11
影响因子：
4.5
通讯作者：
C. Tobias;S. Macko;I. Anderson;E. Canuel;J. Harvey
中科院分区：
文献类型：
--
作者：
C. Tobias;S. Macko;I. Anderson;E. Canuel;J. Harvey
富含15 NO3 −的地下水羽流是在中盐盐沼的梯度上形成的。通过测量浓度和同位素富集的NO3−，N2 O，N2，NH 4+，和颗粒有机氮（PON）在羽流传输通过沼泽，在原位速率的异化硝酸盐还原为铵（DNRA）和反硝化（DNF），以及氮储存在还原氮池估计。对于沼泽顶部10 cm内的地下水排放，NO3−去除在最靠近高地边界的沼泽50 cm内完成90%。烟羽的NO3−损失率峰值在208至645 µM d−1之间。DNRA（180 µM d−1）和DNF（387-465 µM d−1）分别处理了30%和70%的NO3−负荷。终端N2生产约等于N2生产率在DNF。从15 NO3 −库中损失的15 N和在每种还原产物中获得的15 N的比较仅占还原的15 N的22%，因此表明N从系统中输出。尽管DNRA的比率很高，但产生的NH 4+并不是地下水来源的N的长期储存库，而是迅速固定到沼泽PON中并在较长的时间尺度上保留。在N2和N2池相对于DNF率的15 N的小库存，与溶解的氩气的不饱和度相一致，表明在短时间尺度上被排出到大气中。DNF和DNRA的相对大小与NH 4+的固定和N气体的逃逸一起决定了地下水NO3−负荷的输出与保留的程度。
A groundwater plume enriched in 15NO3− was created upgradient of a mesohaline salt marsh. By measuring the changes in concentration and isotopic enrichment of NO3−, N2O, N2, NH4+, and particulate organic nitrogen (PON) during plume transport through the marsh, in situ rates of dissimilatory nitrate reduction to ammonium (DNRA) and denitrification (DNF) were estimated, as well as N storage in the reduced N pools. For groundwater discharge within the top 10 cm of marsh, NO3− removal was 90% complete within the 50 cm of marsh nearest the upland border. The peak NO3− loss rate from the plume ranged from 208 to 645 µM d−1. Rates of DNRA (180 µM d−1) and DNF (387–465 µM d−1) processed 30% and 70% of the NO3− load, respectively. Terminal N2 production was approximately equal to N2 production rates during DNF. Comparison of 15N lost from the 15NO3− pool and 15N gained in each of the reduced products accounted for only 22% of the reduced 15N, thus indicating N export from the system. Despite high rates of DNRA, the NH4+ produced was not a long‐term repository for the groundwater‐derived N but was instead rapidly immobilized into marsh PON and retained on longer timescales. The small inventory of 15N in the N2 and N2 pools relative to DNF rates, coincident with an undersaturation of dissolved argon, indicated that denitrified N was exported to the atmosphere on short timescales. The relative magnitudes of DNF and DNRA in conjunction with the immobilization of NH4+ and evasion of N gases dictated the extent of export versus retention of the groundwater NO3− load.