N2O as a sensitive indicator of denitrification in groundwaters

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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.