Soil partitioning and surface store controls on spring runoff from a boreal forest peatland basin in north-central Manitoba, Canada

The mid- to high-boreal forest in Canada occupies the discontinuous permafrost zone, and is often underlain by glaciolacustrine sediments mantled by a highly porous organic mat. The result is a poorly drained landscape dominated by wetlands. Frost-table dynamics and surface storage conditions help to control runoff contributions from various landscape elements, hydrological linkages between these elements, and basin streamflow during spring snowmelt. Runoff components and pathways in a forested peatland basin were assessed during two spring snowmelts with contrasting input and basin conditions. Runoff from relatively intense melt (up to 16 mm day(-1)) on slopes with limited soil thawing combined with large pre-melt storage in surface depressions to produce high flows composed primarily of meltwater (78% of the 0.29 m(3) s(-1) peak discharge) routed over wetland surfaces and through permeable upper peat layers. Melt intensity was less in the subsequent year (maximum of 10 mm day(-1)) and active layer development was relatively greater (0.2 m deeper at the end of spring melt), resulting in less slope runoff. Coupling of reduced slope contributions with lower storage levels in basin wetlands led to relatively subdued streamflows dominated by older water (73% of the 0.09 m(3) s(-1) peak discharge) routed through less-permeable deeper peat layers and mineral soil. Interannual differences in runoff conditions provide important insight for the development of distributed hydrological models for boreal forest basins and into potential influences on biogeochemical cycling in this landscape under a warming climate. Copyright (C) 2001 John Wiley & Sons, Ltd.