Nitrous oxide processing in carbonate karst aquifers
Nitrous oxide processing in carbonate karst aquifers
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DOI：
10.1016/j.jhydrol.2020.125936
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发表时间：
2021-03
影响因子：
6.4
通讯作者：
M. Flint;Jonathan B. Martin;T. Summerall;A. Barry-Sosa;B. Christner
中科院分区：
文献类型：
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作者：
M. Flint;Jonathan B. Martin;T. Summerall;A. Barry-Sosa;B. Christner
人为活性氮（Nr=铵[NH4+]、亚硝酸盐[NO2−]和硝酸盐[NO3−]）丰富度的增加可能增加大气中氧化亚氮（N2O）的浓度，从而导致全球变暖和平流层臭氧消耗。碳酸盐岩溶含水层的氮循环和N2O的产生、减少和排放可能会被放大，因为碳酸盐岩溶含水层的分布范围广泛，易受氮污染，地下水和地表水的混合会改变含水层的氧化还原条件。然而，我们对喀斯特含水层中N2O循环的强度知之甚少，因此我们选取了13个从喀斯特上佛罗里达含水层（UFA）流出的泉水来评估N2O循环。根据地下停留时间的变化、地表水相互作用的差异以及溶解有机碳（DOC）和溶解氧（DO）浓度的变化，可将泉水分为三大类。这些温泉为含氧至亚氧，NO3 -浓度范围为< 0.1至4.2 mg N-NO3 - /L， DOC浓度范围为< 0.1至50 mg C/L。泉水N2O的最大浓度为3.85µg N-N2O/L，比与大气N2O平衡的水高约12倍。N2O浓度越高，NO3−浓度越低。当回灌水停留时间为几天时，对N2O发生部分反硝化作用，而在地下停留时间较长的泉水中，对N2O的完全反硝化作用更为突出。停留时间较短的泉水地下水排放因子大于全球平均值0.0060，反映了N2O的产量，而停留时间为月至年的泉水地下水排放因子小于全球平均值。这些发现表明，喀斯特含水层的N2O循环取决于补给地表水中DOC和DO的浓度以及随后用于地下N处理的时间。
The increased environmental abundance of anthropogenic reactive nitrogen species (Nr= ammonium [NH4+], nitrite [NO2−] and nitrate [NO3−]) may increase atmospheric nitrous oxide (N2O) concentrations, and thus global warming and stratospheric ozone depletion. Nitrogen cycling and N2O production, reduction, and emissions could be amplified in carbonate karst aquifers because of their extensive global range, susceptibility to nitrogen contamination, and groundwater-surface water mixing that varies redox conditions of the aquifer. The magnitude of N2O cycling in karst aquifers is poorly known, however, and thus we sampled thirteen springs discharging from the karstic Upper Floridan Aquifer (UFA) to evaluate N2O cycling. The springs can be separated into three groups based on variations in subsurface residence times, differences in surface–groundwater interactions, and variable dissolved organic carbon (DOC) and dissolved oxygen (DO) concentrations. These springs are oxic to sub-oxic and have NO3−concentrations that range from < 0.1 to 4.2 mg N-NO3−/L and DOC concentrations that range from < 0.1 to 50 mg C/L. Maximum spring water N2O concentrations are 3.85 µg N-N2O/L or ~ 12 times greater than water equilibrated with atmospheric N2O. The highest N2O concentrations correspond with the lowest NO3−concentrations. Where recharge water has residence times of a few days, partial denitrification to N2O occurs, while complete denitrification to N2is more prominent in springs with longer subsurface residence times. Springs with short residence times have groundwater emission factors greater than the global average of 0.0060, reflecting N2O production, whereas springs with residence times of months to years have groundwater emission factors less than the global average. These findings imply that N2O cycling in karst aquifers depends on DOC and DO concentrations in recharged surface water and subsequent time available for N processing in the subsurface.