Foestland-Peatland Hygrologic Connectivity in Water-Limited Environment: Hydraulic Gradients Often Oppose Topography

Authors
K.J. Hokanson
E.S. Peterson
Kevin Devito
Carl Mendoza
Contacts
Resource Date:
February
2020
Page Length
12

It is common to conceptualize the water table as a subdued replica of surface topography, where groundwater recharges at, and flowsfrom, topographic highs and flows to, and discharges at, topographic lows, in humid (i.e. wetter) environments. This concept is also regularly applied to peatland hydrology, where hydraulic gradients are shown to be towards the peatland. However, this may not be a realistic representation of hydrologyfor low-relief and sub-humid regions.While it is widely accepted that peatlands maintain internal water tables in drought conditions through a system of autogenic negative feedback loops, there is a general lack of knowledge concerning the controls on, and patterns of,forestland hydrologic process that drive the hydraulic gradients between wetlands and their adjacentforestlands in water-limited conditions in low-relief areas. This study identifies the hydrologicfunction (i.e. source or sink of water) offorested uplands and peatlands in the Boreal Plains region of Canada and demonstrates that during a mesic (non-drought) year most peatlands are, infact, potential sources of groundwater to adjacentforestlands. Sixteenforestland-peatland pairs were selected to represent a spectrum offorested hummock and peatlandmorphometries, topographic positions, and geologic settings. Hydraulic gradients determinedfor each well pair during the ice-off season demonstrate that the dominant gradient under mesic climatic conditions isfrom peatlands to adjacentforestlands, opposite of the topographic gradient, and that the sink-sourcefunction of each land unit does not change seasonally.Water table depressions under eachforested hummock indicate that borealforestlands are not reliable sources of groundwater recharge, spatially or temporally, which supports previous research showing that peatlands are the primary water sourcefor runoff; illustrating the needfor alternative conceptualizations of catchment hydrology in water limited regions of the boreal.

Social Media Summary: Forests are poor sources of water to boreal peatlands and landscapes due to water table depressions.