N2O as a sensitive indicator of denitrification in groundwaters

该提案旨在确定将N2O作为受硝酸盐(NO3-)污染的地下水含水层反硝化作用的敏感指标。NO3-是加拿大地下水中分布最广泛的污染物，主要是由于通过使用合成肥料和动物粪便向农田中广泛添加氮(N)。在过去30年中，农业用地的投入大幅增加，预计这一趋势将继续下去。化粪池系统也是NO_3~-地下水含水层的主要来源。在加拿大，NO3-的饮用水限值为10 mg N/L，加拿大水生生物指南中的N03-限值为2.9 mg N/L。地下水为河流和河流提供了基流，地下水的NO3-污染直接影响到地表水资源的质量和生态系统的健康。为了准确地评估和预测地下水中NO3-的去向，需要关于影响地下IS浓度的过程的详细信息。地下水中最重要的硝酸盐去除过程之一是反硝化作用，它将硝酸盐还原为无害的氮气(N2)。因此，了解地下水中反硝化的潜力及其速率，是制定有效的氮管理战略的核心内容，将氮源输送到地下。一氧化二氮(N2O)是硝酸根反硝化为氮气的双产物。溶解N2O的常规分析可以在比典型硝酸盐分析低10,000倍的浓度下进行。因此，通过过量N2O的积累来检测地下水中的反硝化作用比分析NO3-的消失要敏感得多。使用N2O来评估地下水系统中的反硝化活性以前从未被探索过。这一建议的结果将对地下水管理产生影响，特别是在设计井口保护方案时。预计这项研究将产生一种新的方法来确定含水层中的反硝化活动，否则对NO3-浓度的分析将是不确定的。

This proposal aims to determine the use of N2O as a sensitive indicator of denitrification in groundwater aquifers that are contaminated with nitrate (NO3-). NO3- is the most widespread contaminant of groundwater in Canada, largely due to the extensive addition of nitrogen (N) to agricultural lands through the application of synthetic fertilizers and animal wastes. N inputs to agricultural lands have increased dramatically within the last 30 years and this trend is expected to continue. Septic systems are also a major source of NO3- to groundwater aquifers. The drinking water limit for NO3- in Canada is 10 mg N/L and the Canadian aquatic life guideline for NO3- is 2.9 mg N/L. NO3- concentrations in excess of the limits threaten human health and aquatic life. Groundwater provides the baseflow to streams and rivers, thus NO3- contamination of groundwater directly affects the quality of surface water resources and the ecosystem health. In order to accurately assess and predict the fate of NO3- in groundwaters, detailed information is require on the processes that affect is concentration in the sub-surface. One of the most important NO3- removal processes in groundwater is denitrification, which reduces NO3- to harmless nitrogen gas (N2). Understanding the potential for denitrification in groundwater, and its rate, are thus central components in the development of effective N management strategies for sources of N to the sub-surface. Nitrous oxide (N2O) is produced as a bi-product of the denitrification of NO3- to N2. Routine analysis of dissolved N2O can be done at concentrations that are10,000 times lower than for typical nitrate analysis. Therefore, the detection of denitrification in groundwater by the accumulation of excess N2O is far more sensitive than analysing for the disappearance of NO3-. The use of N2O to assess denitrification activity in groundwater systems has not been previously explored. Results of this proposal will have implications for groundwater management, especially in designing wellhead protections schemes. It is expected that this research will produce a new method for the identification of denitrification activity in aquifers where analysis of NO3- concentrations would otherwise be inconclusive.