The Hydrology of Interconnected Bog Complexes in Discontinuous Permafrost Terrains

In the zone of discontinuous permafrost, the cycling and storage of water within and between wetlands is poorly understood. The presence of intermittent permafrost bodies tends to impede and re-direct the flow of water. In this region, the landscape is characterized by forested peat plateaus that are underlain by permafrost and are interspersed by permafrost-free wetlands. These include channel fens which convey water to the basin outlet through wide, hydraulically rough channels and flat bogs which are typically thought to retain moisture inputs as storage. Field studies conducted at a peatland-dominated landscape near Fort Simpson, Northwest Territories, Canada, indicate the presence of ephemeral drainage channels that form a cascade of connected bogs that ultimately discharges into a channel fen. Consequently, understanding bogs as dynamic transmitters of surface and subsurface flows, rather than simple storage regions, calls for further examination. Whether bogs act as either storage features or flow through features has a direct impact on the runoff contributing area in a basin. Here, two adjacent series of bog cascades were gauged over two consecutive years to determine spatial and temporal changes in effective runoff contributing areas. It was found that runoff varies significantly between two adjacent bog cascades with one cascade producing 125 mm of runoff over the 2-year period, while the other yielded only 25 mm. The bog cascades are primarily active during the snowmelt season when moisture conditions are high; however flows can also be generated in response to large rain events. It is proposed that bog cascades operate under an ‘element threshold concept’ whereby in order for water to be transmitted through a bog, the depression storage capacity of that bog must first be satisfied. Our work indicates that whether bogs act as storage features or flow-through features has a direct impact on the runoff contributing area in a basin. Neglecting to represent connected bogs as dynamic transmission features in the landscape is shown to underestimate water available for streamflow by between 5 and 15%, and these systems are therefore a key component of the water balance in discontinuous permafrost regions. C