Abstract

Investigation into the effects of beaver dams on hyporheic fluxes in channelled peatlands is needed to better understand how biological processes drive stream-riparian area connections and thus nutrient export, and to improve our overall conceptual model of water storage and flow through peatlands. The objective of this study was to determine the influence of beaver dams on vertical and lateral hyporheic exchange. Hydrometric methods were used to determine subsurface flow pathways and estimate hyporheic water fluxes for a third-order stream draining a Canadian Rocky Mountain peatland in 2006 and 2007. Three sites were studied two contained small, in-channel beaver dams and the third was a control. Vertical hyporheic fluxes equaled or exceeded lateral hyporheic fluxes despite the fact that hydraulic conductivity of the stream bed tended to be lower than the banks, suggesting peat hydraulic properties were not the dominant factor in the development of hyporheic exchange in stream systems draining peatlands as has been reported for streams underlain by mineral substrates. Instead, vertical fluxes were partially influenced by the presence of a mineral lens 0.65 m below the ground surface. As well, high riparian water tables in relation to stream stage were key to limiting lateral fluxes. Steep hydraulic gradients above the two dams created looping flow pathways beneath and around them. However, little water actually flowed along these pathways. Measures of larger fluxes of water to the riparian area above the dams than those returning to the stream below the dams suggests either that hyporheic flow paths are longer than those measured in other studies or that the beaver dams generated recharge to the groundwater flow system.