The influences of catchment geomorphology and scale on runoff generation in a northern peatland complex

We computed daily discharge (Q) versus gross drainage area (GDA) regression analyses for the 2009 and 2010 growing seasons for six small to medium headwater catchments at a northern peatland complex in the James/Hudson Bay lowlands. Temporal dynamics of the daily goodness of fits (R ²) between Q and GDA were then examined to identify the most relevant conceptual model of runoff generation in this landscape. We observed high R ² values during low flow conditions (mean R ²=0.93 for 2009 and 2010). During wetter periods and in particular during large runoff events, the relationship degraded rapidly and consistently, suggesting differences in quickflow response among the gauged catchments. At low flows, the six catchments generated equivalent amounts of runoff (mm), leading to a strong Q-GDA relationship. During high flows, total growing season runoff increased systematically with GDA between 8 and 50km ² and then decreased with further increases in GDA. These differences were responsible for the observed breakdown in the daily Q-GDA relationships and also resulted in significant differences in total runoff among the six catchments during the wetter year. Quantitative landscape analysis using a 5-m resolution Light Detection and Ranging (LiDAR) digital elevation model revealed that near-stream zone characteristics vary systematically with scale in a manner that is consistent with the observed patterns of quickflow runoff response. In this northern peatland complex, fast-responding flowpaths in the spatially discrete near-stream zones may be the key determinant of catchment runoff efficiency at the small to medium (~10 to ~200km ²) headwater catchment scales analysed here. Moreover, the relatively organized drainage patterns observed in this study are consistent with our understanding of ecohydrological feedbacks driving geomorphic evolution of northern peatlands.