Predicting storage dynamics based on landscape setting in a boreal, Precambrian Shield catchment

As part of a whole-ecosystem mercury addition experiment, a 7.5 ha zero-order Precambrian Shield catchment was intensively monitored from August 2007 to October 2008 to characterize its hydrological and biogeochemical behaviour across a range of wetness conditions. Hydrometric observations were used in combination with a detailed depth-to-bedrock survey and digital terrain analysis to examine spatio-temporal dynamics in catchment storage, hydrologic connectivity, and event runoff response. Using a 1m resolution LiDAR digital elevation model, the landscape was partitioned into hydrologic response units (HRUs) on the basis of local drainage conditions. The HRUs were subsequently classified using various quantitative indices of slope, drainage conditions, contributing area, patch geometry, and topological connectivity to examine first-order controls on water table dynamics. The storage dynamics in different HRUs follow a predictable trajectory based on their topographic setting and local drainage conditions. Connecting midslopes and ridge tops quickly transmit water to depression storage areas that then control the delivery of water to downslope elements through a fill-and-spill process of hydrologic connectivity. During rain events the runoff response is controlled by antecedent storage deficits generated within depressional HRUs having deeper soil depths and poorer drainage conditions. In particular, a large depression storage area located at the bottom of the catchment covering 10% of the total area ultimately controls the runoff response at the outlet such that when the water table falls below the elevation of the downslope bedrock sill the flow of water ceases. Moreover, the combined analysis of subsurface hydrology and topographic structure provides further insight into how landscape elements govern the runoff response of Shield dominated catchments, and provides a promising scaling framework for quantifying storage dynamics in these topographically complex landscapes.