Water Quality and Groundwater Discharge in the Halton Region

The Halton Region in Ontario, Canada, lies along the Northwestern shores of Lake Ontario and has one of the fastest growing populations in the Province. In collaboration with Conservation Halton and the Halton Region, we assessed water quality in 21 of Conservation Halton’s watersheds at a high resolution (n>500 samples across n>40 streams) in 2022 to better understand nutrient, major and trace element dynamics and underlying controls in streams in this rapidly urbanizing region. This thesis presents the summary of this surface water quality monitoring data and its application for identifying groundwater discharge on a watershed-to-site-specific scale. In the second chapter of this thesis, field data from 2022 revealed significant variations in major and trace solute concentrations, not only between and within catchments but also over time and across water quality parameters: distinct hydrochemistries were observed for rural (upstream) creeks versus streams within and downstream of urban areas. Chloride and phosphate concentrations exceeded water quality guidelines often across the Halton region, especially within the urban reaches, in line with historic trends and their status as solutes-of-concern in southern Ontario watersheds. Investigated metal and trace element concentrations displayed concentration-discharge dynamics that were different from those of major water quality parameters, indicative of their distinct sourcing and mobilization that warrant further monitoring. In the third chapter of this thesis, interpolated groundwater discharge maps produced from >21,000 historic groundwater level measurements across the region were compared and contrasted to surface- and groundwater surveillance data that was aggregated to assess temperature gradients, hydrochemical (alkalinity, chloride) signatures, as well as stream ecology (water cress, fish taxa). Temperature gradients between air, streams, and groundwater were larger for downstream urban creeks than for upper reaches, and significantly correlated (p<0.05) to discharge locations predicted by interpolated groundwater mapping. In contrast, high alkalinity and low chloride levels in Halton Region groundwaters were visibly related to stream hydrochemical signatures in gaining versus losing stream sections but lacked statistical significance. Finally, strong links between the abundance of cold-water biota, thermal gradients and interpolated gaining stream sections (p<0.05) were observed, reflective of the upscaled spatiotemporal resolution presented by ecological parameters. Combined, these correlations helped identify sites with significant groundwater exfiltration across the watershed. This thesis shows that high-resolution stream monitoring data may be used to improve our understanding of spatiotemporal water quality variability and hyporheic exchange patterns at the watershed scale and optimize regional management of vulnerable streams and natural heritage systems.

Department dc:contributor.department

Geological Sciences and Geological Engineering

Year dc:date.issued

2024

Author dc:creator

• Beckner-Stetson, Nathan Dakota Kenneth Tanner

Advisor dc:contributor.supervisor

• Vriens, Bas

• Hydrogeology
• Hydrology
• Geology
• Environmental Science

Statement dc:rights

• Attribution 4.0 International

Licence dc:rights.uri

• http://creativecommons.org/licenses/by/4.0/

Language dc:language.iso

eng

Handle dc:identifier.uri

https://hdl.handle.net/1974/33350

OAI identifier oai:identifier

oai:queensu.scholaris.ca:1974/33350