Development and Application of Novel Isotope Techniques for Tracing Nutrient Cycling in Watersheds

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Widespread application of nitrogen (N)- and phosphorus (P)-based fertilizers in industrial agriculture, but also N and P in urban runoff and wastewater effluents from cities and from industrial point sources, cause increasing nutrient releases into aquatic environments. In many countries including Canada this has resulted in nitrate loading of aquifers and eutrophication of surface water bodies causing problems such as drinking water deterioration and algae blooms, among others. The objective of this 5-year research program is to combine newly developed isotope tracers with established physical, chemical and isotopic approaches to gain new insights into N and P cycling in terrestrial and aquatic ecosystems. Novel isotope techniques will be developed and applied in order to obtain a better understanding of sources and processes in the N and P cycles that affect water quality in Canadian watersheds. These include 1) site-specific N isotope measurements on N2O; 2) the analysis of 17-O in nitrate and sulfate for tracing the fate of atmospheric nitrogen and sulfur; 3) the determination of oxygen isotope ratios of phosphate to identify sources and processes affecting phosphate in the environment; 4) determining the transit time of N in soils with isotopic labels, and 5) boron (B) isotope analyses for differentiating urban waste water effluents from agricultural return flows. Laboratory experiments, soil plot studies with agricultural soils characterized by different land use, controlled nutrient releases in artificial streams, and watershed wide studies will be conducted to test this novel multi-tracer approach using a combination of physical, chemical and isotopic techniques. It is anticipated that the research team will be able to differentiate nutrient inputs from atmospheric deposition, urban runoff and wastewater effluents, agricultural return-flows, and industrial point sources. The significance of this novel multi-tracer approach is that the impact of natural and different anthropogenic factors, including urban, agricultural, and industrial activities, on water quality of surface water bodies will be better quantified. This knowledge will be essential for developing future water management strategies for watersheds in Canada and elsewhere.