Carbon and nitrogen cycling in watersheds and wetlands

The role of greenhouse gases (GHGs) in affecting climate remains a global concern and a high research priority. In the past 15 years our research has focussed on using the isotopes of carbon (¹³C and ¹⁴C) to examine the source, transport and fate of the various forms of carbon in watersheds and wetlands.

Isotopic analysis of CO₂ and CH₄ are currently being used to develop new predictive models of the processes governing release of greenhouse gases following two large ecosystem scale flooding experiments conducted at the Experimental Lakes Area near Kenora, Ontario. Carbon isotopes yield information that is not obtainable from the study of carbon mass and flux alone.

Recently, we have explored the potential of δ¹⁸O-O₂ in five different aquatic environments; lakes (small lakes and Great Lakes), rivers, groundwaters, constructed wetlands and reservoirs. We demonstrated that this simple but powerful technique for science and management of aquatic systems was been even more fruitful than originally anticipated. Our research showed that δ¹⁸O-O₂ can be used to quantify in situ rates of P and R, gas exchange coefficients, whole ecosystem respiratory quotients (CO₂/O₂) and re-aeration rates in rivers, lakes and reservoirs. In wetlands and groundwater, δ¹⁸O-O₂ can quantify O₂ translocation by macrophytes and chemical transformations in aquifers. We built and tested a dynamic model for δ¹⁸O-O₂ and O₂ in water that includes P, R, and gas exchange (GE). The next step is to translate this demonstrated scientific potential into applications to benefit scientific advancement and environmental policy and management.

To this end, we have prepared a research proposal to concentrate on the Grand River watershed, a highly impacted system in Southern Ontario. The overarching goal of this proposal is to develop the δ¹⁸O-O₂ tool for science and science-based management of rivers Nitrous oxide (N₂O) is a potent greenhouse gas, having a global warming potential of approximately 300 times that of CO₂. Although N₂O has been increasing in the atmosphere, the sources are not well known. Rivers are supersaturated with N₂O, but emissions of N₂O from Canadian rivers have not been measured.

There are two main sources of N₂O in human-impacted rivers; application of N fertilizer in agriculture and N released from wastewater treatment plants (WWTPs). The processes of nitrification and denitrification can result in the creation of N₂O from NH₄+ and NO₃- depending on environmental conditions including O₂ concentration. Isotopic analysis will allow these two processes to be separated facilitating research into the processes controlling N₂O release and possible mitigation measures. Applications have been submitted to CFCAS and NSERC to assess the magnitude and importance of N₂O flux from Canadian rivers. These projects are possible due to UW-EIL’s recent acquisition of a trace gas analyzer and development of new techniques for the analysis of the isotopic composition of dissolved N₂O.

During the past five years I have supervised 7 PhD. and 12 MSc. students all with an isotopic component to their thesis research. In addition, 2 Post Doctoral Fellows, 7 undergraduates, 9 technicians, and 14 undergraduates (non-thesis) have been trained in preparing samples for ¹³C, ¹⁴C, ¹⁵N, ³⁴S and ¹⁸O analysis. The UW-EIL is crucial to our success. All our isotope measurements are completed in the EIL. Most of our samples in environmental research are not “routine”, and UW-EIL provides the expertise required for developing the new techniques we require. Ready access to well maintained world-class instrumentation and quick turn-around is crucial to timely technique development especially where graduate student projects are concerned.

Selected Publications

• Schiff, S., J. Spoelstra, R. Semkin, D. Jeffries. 2005. Drought induced pulses of SO4 from a Canadian Shield wetland: Use of δ34S and δ18O in SO42 to determine sources of S. Applied. Geochemistry. 20 691-700.
• Venkiteswaran, J. and S. Schiff. 2005. Methane oxidation: isotopic enrichment in boreal reservoirs. Applied Geochemistry. 20 4 683-690.
• Matthews CJD, Joyce EM, St.Louis VL, Schiff SL, Venkiteswaran JJ, Hall BD, Bodaly RA, Beaty KG. 2005. Carbon Dioxide and Methane Production in Small Reservoirs Flooding Upland Boreal Forest. Ecosystems 8: 267-285.