INFLUENCE OF GROUNDWATER DISCHARGE ON THE THERMAL PATTERNS IN INLAND AND COASTAL WATERS

Abstract

River and coastal lagoon water temperatures are rising due to climate change, threatening cold-water biodiversity and altering aquatic habitat distribution. Groundwater discharge and hyporheic exchange buffer surface water temperatures and generate fine-scale thermal heterogeneity that aquatic species depend on during periods of thermal stress. Thus, understanding how groundwater discharge shapes thermal patterns in inland rivers and coastal lagoons is critical for evaluating cold-water habitat vulnerability and guiding restoration efforts. This dissertation investigates how groundwater discharge influences thermal regimes in inland rivers and a coastal lagoon and evaluates the design and performance of engineered cold-water habitat that promotes habitat resilience in a warming world.

Field monitoring, thermal infrared imaging, fiber-optic distributed temperature sensing, and process-based numerical modelling are applied across several study sites in Atlantic Canada. A regional analysis of shallow groundwater temperatures in Nova Scotia identifies the climatic, geologic, and hydrogeologic controls on shallow groundwater thermal regimes and their potential to buffer surface water temperatures. In a coastal lagoon located in Basin Head, Prince Edward Island, high-resolution thermal infrared imaging and distributed temperature sensing data reveal how tidal pumping and intertidal groundwater springs generate distinct spatiotemporal thermal gradients that influence cold-water habitat and ecosystem function. Experimental engineered cold-water habitat systems in Rights River and the Killag River in Nova Scotia demonstrate the feasibility of pumped groundwater and engineered hyporheic systems to create cold-water habitat, with modelling results demonstrating how discharge rate, thermal mixing, trench geometry, and residence time govern cooling magnitude and persistence. Collectively, the studies presented in this dissertation advance our understanding of how groundwater discharge creates and sustains thermal diversity in river and coastal systems and provides a basis for integrating natural and engineered groundwater systems into future thermal management and restoration practices to preserve cold-water biodiversity in a warming world.