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Kruk MK, Mayer B, Nightingale M, Laceby JP. Tracing nitrate sources with a combined isotope approach (δ 15N NO3, δ 18O NO3 and δ 11B) in a large mixed-use watershed in southern Alberta, Canada. Sci Total Environ 2020; 703:135043. [PMID: 31759727 DOI: 10.1016/j.scitotenv.2019.135043] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Revised: 10/15/2019] [Accepted: 10/16/2019] [Indexed: 06/10/2023]
Abstract
Rapid population growth and land-use intensification over the last century have resulted in a substantial increase in nutrient loads degrading marine and freshwater ecosystems worldwide. In mixed-use watersheds, elevated nitrogen loads from wastewater treatment plant (WWTP) effluent or agricultural runoff often drive the eutrophication of waterways. Accordingly, the objective of this research was to identify sources of riverine nitrate (NO3), a deleterious dissolved species of nitrogen, with a combined isotopic tracing technique in the Bow River and the Oldman River in Alberta, Canada. Riverine NO3 and boron (B) concentrations, mean daily flux and δ15NNO3, δ18ONO3, and δ11B values were determined at 17 mainstem sites during high and low discharge periods in 2014 and 2015. The data for mainstem sites were then compared to results for effluent from seven WWTPs, eight synthetic fertilizers, cow manure, and three predominantly agricultural tributary sites to estimate point and non-point NO3 sources. The NO3 flux, δ15NNO3 and δ18ONO3 values indicated the city of Calgary's Bonnybrook WWTP effluent accounts for the majority of the NO3 flux in the Bow River downstream of Calgary. δ15NNO3 and δ11B values in the Bow River highlighted an increase in agricultural NO3 loading downstream of irrigation return-flows. A three-fold decrease in the NO3:B flux ratio indicated NO3-removal processes are active in the lower reaches of the Bow River. For the Oldman River, δ11B values revealed elevated nutrient loading from the Lethbridge WWTP effluent (10% of downstream B flux). Furthermore, the agricultural tributaries contributed 25% of the local B flux to the Oldman River. Overall, δ11B was proven to be an effective co-tracer for discriminating between urban and agricultural sources of NO3 in these large mixed-use watersheds. This combined isotope tracing approach has significant potential to identify point and non-point NO3 sources driving eutrophication around the world.
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Affiliation(s)
- M K Kruk
- Applied Geochemistry Group, Department of Geoscience, University of Calgary, Calgary, Alberta, Canada; Resource Stewardship Division, Alberta Environment & Parks, Government of Alberta, Calgary, Alberta, Canada.
| | - B Mayer
- Applied Geochemistry Group, Department of Geoscience, University of Calgary, Calgary, Alberta, Canada
| | - M Nightingale
- Applied Geochemistry Group, Department of Geoscience, University of Calgary, Calgary, Alberta, Canada
| | - J P Laceby
- Resource Stewardship Division, Alberta Environment & Parks, Government of Alberta, Calgary, Alberta, Canada
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Laceby JP, Kerr JG, Zhu D, Chung C, Situ Q, Abbasi S, Orwin JF. Chloride inputs to the North Saskatchewan River watershed: the role of road salts as a potential driver of salinization downstream of North America's northern most major city (Edmonton, Canada). Sci Total Environ 2019; 688:1056-1068. [PMID: 31726537 DOI: 10.1016/j.scitotenv.2019.06.208] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2019] [Revised: 06/11/2019] [Accepted: 06/13/2019] [Indexed: 05/27/2023]
Abstract
Multiple anthropogenic activities are driving the salinization of freshwater environments threatening water resources worldwide. Accordingly, this research will first examine the spatial and temporal variability of major ions (i.e. Ca2+, Mg2+, Na+, K+, SO42-, CO32-, and HCO3-) upstream and downstream of the northernmost major city in North America (Edmonton, Canada). Second, this research will estimate the relative contributions of the major sources of chloride (Cl), the main constituent of road deicers, to the sub-basin around Edmonton. Monthly water quality data was for three sites on the North Saskatchewan River (NSR): Rocky Mountain House (RMH - downstream of the Rocky Mountain headwaters), Devon Bridge (upstream of Edmonton) and Pakan Bridge (downstream of Edmonton). Change ratios investigate the downstream alterations of major ions at Pakan and Devon, relative to RMH. Seasonal Kendall tests examine temporal trends (1987-2017). A mass-balance approach then quantifies the major sources of Cl in the sub-basin of the NSR between Devon and Pakan. Progressing from the Rocky Mountain headwaters (at RMH) to downstream of Edmonton (at Pakan), Cl- increased by >5.5 times, Na+ by 4.8 times and K by 2.7 times. No significant temporal trends for Cl-, Na+ and K+ were evident at Devon (upstream of Edmonton), whereas all three significantly increased at Pakan (downstream of Edmonton). Deicers (54%), agriculture (20%), along with waste water treatment plant and industrial effluent (15%) were the largest Cl sources in the NSR Devon-Pakan sub-basin. In total, 77 Gg yr-1 of Cl (or 6 t km2 yr-1) is added to the Devon-Pakan sub-basin, of which, 43 Gg yr-1 is retained. Understanding and managing the major drivers of freshwater salinization will be of increasing importance in the 21st century owing to the potential salinization of freshwater resources in the context of a changing climate.
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Affiliation(s)
- J P Laceby
- Environmental Monitoring and Science Division, Alberta Environment and Parks, 3535 Research Rd NW, Calgary, Alberta T2L 2K8, Canada.
| | - J G Kerr
- Environmental Monitoring and Science Division, Alberta Environment and Parks, 3535 Research Rd NW, Calgary, Alberta T2L 2K8, Canada
| | - D Zhu
- Water Resources Branch, Environment, Government of Yukon, 419 Range Road, Whitehorse, Yukon, Y1A, 3V1, Canada
| | - C Chung
- Environmental Monitoring and Science Division, Alberta Environment and Parks, 3535 Research Rd NW, Calgary, Alberta T2L 2K8, Canada
| | - Q Situ
- Environmental Monitoring and Science Division, Alberta Environment and Parks, 3535 Research Rd NW, Calgary, Alberta T2L 2K8, Canada
| | - S Abbasi
- Environmental Monitoring and Science Division, Alberta Environment and Parks, 3535 Research Rd NW, Calgary, Alberta T2L 2K8, Canada
| | - J F Orwin
- Environmental Monitoring and Science Division, Alberta Environment and Parks, 3535 Research Rd NW, Calgary, Alberta T2L 2K8, Canada
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