Water storage and release dynamics in nested prairie watersheds

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Date
2019-06
Authors
Bansah, Samuel
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Abstract
Precipitation falling on a watershed can be stored above ground as well as in the vadose zone in the shallow subsurface or the deeper saturated zone. Examining the dynamics pertaining to the storage and release of water from these different zones is essential, not only for better hydrological process understanding, but also for biogeochemical reasons. Indeed, there are strong linkages between water storage dynamics and the persistence of contaminants in runoff and groundwater and their timing of release from terrestrial to aquatic environments. When it comes to the release of water from storage zones, two main types of dynamics are generally considered; (1) active storage release, which relates to the fast release and transfer of water from surface sources and the vadose zone, and (2) passive storage release, which rather refers to the slow release and transfer of water from the saturated zone to streams. While the literature is rich in theoretical, field and modelling studies targeting the assessment of water storage and release dynamics, few have attempted to compare different storage assessment approaches at the same site, i.e., hydrometric approaches, isotopic approaches only, or approaches that combine hydrometric and isotopic data. Undertaking a study of this nature in the Canadian prairie region is especially important in view of the numerous surface storage depressions that are naturally present, the man-made ponds built for stormwater control purposes, and the many bridges and ditches that all together modify the release and transport of water to streams in ways that are not yet fully understood. The overall goal of this PhD thesis was, therefore, to assess water storage and release dynamics within a nested system of eight prairie watersheds located in Manitoba, Canada. Through the synthesis of hydrometric and isotopic data analysis results, a conceptual framework detailing the dominant flow processes prevailing in each of the studied watersheds has been suggested. Most importantly, this thesis showed value in combining many different assessment approaches when characterizing water storage and release dynamics, as the plausibility of different hypotheses could be evaluated on the basis of convergent and divergent conclusions reached via these approaches.
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Hydrometric, Stable Isotopes, Old water fractions, Water ages, Mean transit time, Nested watershed
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