The hydrology of interconnected bog complexes in discontinuous permafrost terrains

Abstract

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. Copyright © 2015 John Wiley & Sons, Ltd.

Water flow in the active layer along an arctic slope – An investigation based on a field campaign and model simulations

“…The effect observed here is conceptually similar to the observations on larger scale as described by Connon et al (2015), who 5 focused on the interconnectivity of wetlands. The flow on the top of the permafrost follows a fill and spill behaviour that is similar to the processes occurring on hillslopes with bedrocks topography (Wright et al, 2009).…”

A Synthesis of Three Decades of Eco-Hydrological Research at Scotty Creek, NWT, Canada

“…Although isolated collapse scars are large in number, they account for less than 5% of the Scotty Creek 5 catchment, while the area occupied by connected collapse scars is more than five times larger and roughly equivalent to the area occupied by channel fens (Quinton et al, 2009a). This conceptualisation of the form and hydrological functioning of collapse scar wetlands was modified again by Connon et al (2015) who demonstrated that many of these features that were assumed to be hydrologically isolated, can form ephemeral connections with a fen (either directly or via another collapse scar or series of them) during periods of high moisture supply, such as during the snowmelt runoff period. (A more detailed 10 discussion on the development and hydrological functioning of such connections is presented below in the context of permafrost thaw).…”

“…This process the authors referred to as 'bog capture' transforms internally drained bogs to 'open bogs' that are 5 hydrologically connected to fens. Bog capture increases basin runoff by adding to it the runoff from direct precipitation onto captured bogs, and the runoff entering such bogs from their local contributing areas, termed "bogsheds" (Connon et al, 2015). As captured bogs expand due to permafrost thaw at their margins, they merge into other bogs, a process that further expands the basin runoff contributing area, and therefore basin runoff as well.…”

“…The cascading wetlands operate in a manner similar to the 'fill-and-spill' principle, where wetlands are not capable of shedding water until their storage capacity has been filled (Connon et al, 2015), similar to hydrological systems in the Prairie Potholes Region 25 and the Canadian Shield (Spence and Woo, 2003), though driven by a somewhat different phenomenon. Connon et al (2015) also showed that the storage deficit of an individual wetland complex is highly dependent on the plateau:wetland ratio: wetlands with more plateaus yield considerably more runoff. Large wetlands with a low plateau:wetland ratio can act as 'gatekeepers' (see Phillips et al, 2011), preventing the transmission of water to downstream wetlands.…”

“…However, the collapse scar wetlands can and likely should be further sub-classified by geochemical function and groundwater connection. Gordon et al (2016) investigated the production of methylmercury (MeHg) along the same 5 toposequence studied by Connon et al (2015). The authors found that the lower three collapse scar wetlands were more appropriately described as "minerotrophic poor fens", due to the higher pH of their pore water, and presence of graminoids and sedges.…”