Event-based analysis of wetland hydrologic response in the Prairie Pothole Region

Abstract

Previous studies in the Prairie Pothole Region mainly assessed wetland hydrologic function at seasonal, annual and decadal scales. While many studies have looked at water balance dynamics and local flow generation processes in wetlands, no study looked at hydrological dynamics in response to individual rainfall events in prairie pothole wetlands (here after referred as wetlands) across a gradient of alteration. The present study aimed to investigate: (1) the most important metrics needed to characterize the spatial variability of wetland hydrologic response to rainfall-runoff events; (2)the temporal variability of individual wetland hydrologic response; (3) the spatial and temporal variability of wetland-stream interaction; and (4) the temporal persistence of various spatial controls on individual wetland hydrologic response characteristics. High-frequency water level data was collected over two years for ten intact, three consolidated, and seven drainage ditches associated with fully drained wetland(s), as well as a creek located in southwestern Manitoba, Canada. The hydrologic response of the studied wetlands to individual rainfall-runoff events was characterized using a range of metrics. Several data analysis methods were used, including principal component analysis, graphical assessments of wetland-stream hysteresis dynamics, and correlations analyses between wetland response metrics and spatial characteristics. Results suggested that wetland alteration status (i.e., drained versus intact, open-water wetlands) plays an important role in explaining differences in the event-scale hydrologic behaviour of wetlands. Climatic and antecedent storage conditions (i.e., surface and subsurface storage in wetland basin) also had a strong influence on the hydrologic responses of wetlands during individual rainfall-runoff events and appeared to override the influence of spatial controls such as wetland area, volume or catchment area. Antecedent storage also seemed to be the driving factor of wetland-stream interactions. A lack of persistent correlations between wetland spatial characteristics and response metrics was observed and suggested nonstationary wetland hydrological behaviours and controls, a conclusion that has significant implications for wetland classification and modelling.