Hillslope hydrology and wetland response of two small zero-order boreal catchments on the Precambrian Shield

摘要

Two Precambrian Shield zero-order catchments were monitored from January 2003 to July 2004 to characterize their hydrological and biogeochemical characteristics prior to a forest management experiment. Hydrometric observations were used to examine temporal trends in hillslope-wetland connectivity and the hillslope runoff processes that control wetland event response. The hillslope groundwater flux from the longer transect (El) was continuous throughout the study period. Groundwater fluxes from a shorter and steeper hillslope (E0) were intermittent during the study period. Large depression storage elements (termed micro-basins) located on the upper hillslope of the El catchment appeared to be at least partly responsible for the observed rapid wetland runoff responses. These micro-basins were hydrologically connected to a downslope wetland by a subsurface channel of glacial cobbles that functioned as a macropore channel during episodic runoff events. The runoff response from the hilltop micro-basins is controlled by antecedent water table position and water is quickly piped to the wetland fringe through the cobble channel during high water table conditions. During periods of low water table position, seepage along the bedrock-soil interface from the hilltop micro-basin and other hillslopes maintained hillslope-wetland connectivity. The micro-basins create a dynamic variable source-area runoff system where the contributing area expands downslope during episodic runoff events. The micro-basins occupied 30% of the El catchment and are a common feature on the Precambrian Shield.