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 are