Seasonal and Event-based Hydrological Response in a Hillslope-Riparian Zone setting of the Temperate Beverly Swamp
Mills, Angela Jennifer Rebecca
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Wetland ecosystems are an integral part of the landscape, providing vital habitat for species at risk, while providing important services in hydrological and biogeochemical cycling. Since many of the habitats and biogeochemical processes depend on hydrology, it is important to first understand hydrological functioning of these systems. Past studies have largely focused on one or two variables such as topography or antecedent moisture conditions, but fail to assess the complex interconnected factors that produce hydrologic responses of wetlands. This thesis examines the combined influence of topography, seasonal variability in antecedent moisture conditions, and natural (climatic) and anthropogenic (upstream reservoir release) event responses along the hillslope-riparian zone continuum of a temperate deciduous swamp. Results demonstrate seasonality in hydrological processes within the hillslope-riparian zone continuum where, water table position rises in response to the spring snowmelt freshet, declines gradually through the summer and subsequently rises again as evapotranspiration decreases in the autumn. During this time, event hydrologic responses vary with event properties (intensity, duration, etc.) and antecedent moisture conditions. These responses vary spatially throughout the study site, both with riparian zone topography, and with distance from the Spencer Creek that receives inputs from the Valens Reservoir, upstream of the study site. Upland sites more actively respond to precipitation events in comparison to low lying topographic positions. Low-lying sites in the riparian zone in close proximity to Spencer Creek are more temporally variable than low-lying wetlands further away from the stream; however, wetland responses at the same sites to precipitation events are dampened during flooded conditions following dam releases from the upstream Valens reservoir. Hydraulic gradients across the sites are more spatially variable than they are temporally variable. However, sites located in the middle of the riparian zone-hillslope continuum (located at the break in slope) have highly variable vertical hydraulic gradients, much more so than those of upland or riparian sites, suggesting that they could be important sites for biogeochemical processes. This thesis combines the influence of physiological, climatic and watershed management variables within one wetland to further knowledge of hydrological response along the hillslope-riparian zone continuum.