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Groundwater - surface water interactions in the Salmon River Watershed, BC : integrating spectroscopy, isotopes, water quality, and land use analyses

University of British Columbia

Understanding the sources and pathways of water pollutants is critical for protecting freshwater resources. Relationships between water quality and land use can be obscured by variable land use, seasonal variability, and interactions between surface water and groundwater. This research combines the tools of fluorescence spectroscopy, nitrate stable isotopes and water chemistry to better understand land use impacts on water quality. The Hopington aquifer, one of the most vulnerable aquifers in the Lower Fraser Valley, is a source of drinking water for the Township of Langley. This aquifer is also responsible for maintaining the summer stream flow in the Salmon River, a productive Coho salmon stream. Elevated nitrates in both ground and stream water are a concern. Twelve stream sites and eleven groundwater wells were sampled during 2006 to try and "fingerprint" different water sources. Samples were analyzed for: uv-visible absorbance, fluorescence, DOC, nutrients (ammonium, nitrate, ortho-phosphate), chloride, trace elements, and nitrate-isotopes (δ¹⁸0 and δ¹⁵N). The combination of these tools provided a more detailed look at the groundwater - surface water interactions and helped track pollutants within the system. Nitrate concentrations in the Salmon River increase where it cuts through the Hopington aquifer; concentrations peak in August when groundwater makes up the greatest proportion of the stream flow. Humic-like fluorescence was able to measure this groundwater influence because groundwater has much lower fluorescence. Nitrate isotopes showed that inorganic fertilizers were not a dominant source, but that soil N, septic tank leakage, and manure were possible sources. Stream sites influenced by groundwater had an isotopic fingerprint similar to nearby wells, showing that the nitrate source(s) were the same. A GIS-based land use analysis suggested that agricultural land use was having the greatest impact on local water quality, especially on surface waters in the wet season. Protein-like fluorescence showed potential as a tool for pollution monitoring and should be explored further.

Text

2011-02-25

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http://hdl.handle.net/2429/31782

Resource Management and Environmental Studies

University of British Columbia

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