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UBC Theses and Dissertations

The ecohydrology of coupled surface water - groundwater systems Neumann, Natasha Niki


Our ability as a society to responsibly manage water resources for both humans and the environment relies on accurate predictive models. Current hydrologic models are unable to simulate important biogeochemical reactions that occur in systems where surface water and groundwater are coupled, where flowpaths alternate between highly contrasting surface and subsurface environments. Informed and responsible aquatic ecosystem management requires an understanding of the complex feedbacks between ecological properties and functions in ponds, streams, rivers and lakes, and the catchment hydrological processes affecting the quantity and quality of water entering aquatic systems. The types of flowpaths and the duration of water flow in a catchment determine the physical and chemical characteristics of water entering aquatic systems, which in turn affect the natural range of ecological properties and functions. The primary objective of this work was to create capacity for better prediction of the impacts of hydrologic variability on aquatic ecosystems. Three field studies were undertaken, representing different aquatic ecosystems (a river, stream, and lake) and different ecological functions (salmon spawning habitat use, wetted habitat availability, and nutrient cycling) occurring at different scales (point, regional and catchment). For each study, a combined hydrochemical and hydrometric approach was developed to describe the variability in flowpaths over space and time, and to quantify or infer the relative transit times of water received from the catchments. Water exiting a catchment is the convergence of many different flowpaths with many different transit times. It was found that the selected ecological processes could be discussed in terms of transit time, specifically the ratio of long to short transit times of water delivered to an aquatic system. These results were used to propose a conceptual model capable of predicting the impacts of climatic variability and change and anthropogenic activities on aquatic ecosystems through their effects on hydrologic processes. Further work is needed to quantify the transit time ratio and test the efficacy of the predictive model.

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