Scott J. Ketcheson

Water Relations in Cutover Peatlands

Sphagnum mosses, the dominant peat-forming plant in many northern peatlands, generally do not regenerate spontaneously in mined peatlands because water transfer between the cutover peat and incipient moss diaspores cannot overcome the capillary barrier effect between the two hydraulically distinct layers. Artificial drainage networks established throughout peatlands, coupled with the removal of the acrotelm during the peat extraction process, drastically alter the natural system function through the exposure of more decomposed catotelm peat and increased compression, oxidation, and shrinkage, subsequently decreasing average pore diameter and enhancing this capillary barrier effect. Water table (WT) fluctuations, constrained within the reduced specific yield of the altered catotelm, exhibit increased variability and rapid decline. The increased effective stress caused by a declining WT can result in seasonal surface subsidence of 8 to 10 cm, thereby reducing saturated hydraulic conductivity by three orders of magnitude. Restoration efforts aim to alter the disturbed hydrological regime, creating conditions more favorable for the recolonization of Sphagnum mosses and the ultimate reestablishment of an upper acrotelm layer. Due to the large areal coverage and high organic carbon content, the response of peatlands to disturbances caused by resource extraction, and their return to functioning ecosystems, must be thoroughly addressed. This paper integrates both published and unpublished work to facilitate an overview of our understanding of the hydrological impact of peat cutting and its implications for restoration.

The hydrological functioning of a constructed fen wetland watershed

Mine reclamation requires the reconstruction of entire landforms and drainage systems. The hydrological regime of reclaimed landscapes will be a manifestation of the processes operating within the individual landforms that comprise it. Hydrology is the most important process regulating wetland function and development, via strong controls on chemical and biotic processes. Accordingly, this research addresses the growing and immediate need to understand the hydrological processes that operate within reconstructed landscapes following resource extraction. In this study, the function of a constructed fen watershed (the Nikanotee Fen watershed) is evaluated for the first two years following construction (2013-2014) and is assessed and discussed within the context of the construction-level design. The system design was capable of sustaining wet conditions within the Nikanotee Fen during the snow-free period in 2013 and 2014, with persistent ponded water in some areas. Evapotranspiration dominated the water fluxes from the system. These losses were partially offset by groundwater discharge from the upland aquifer, which demonstrated strong hydrologic connectivity with the fen in spite of most construction materials having lower than targeted saturated hydraulic conductivities. However, the variable surface infiltration rates and thick placement of a soil-capping layer constrained recharge to the upland aquifer, which remained below designed water contents in much of the upland. These findings indicate that it is possible to engineer the landscape to accommodate the hydrological functions of a fen peatland following surface oil sands extraction. Future research priorities should include understanding the storage and release of water within coarse-grained reclaimed landforms as well as evaluating the relative importance of external water sources and internal water conservation mechanisms for the viability of fen ecosystems over the longer-term.

The distribution and migration of sodium from a reclaimed upland to a constructed fen peatland in a post-mined oil sands landscape

Post-mine landscape reclamation of the Athabasca Oil Sands Region requires the use of tailings sand, an abundant mine-waste material that often contains large amounts of sodium (Na+). Due to the mobility of Na+ in groundwater and its effects on vegetation, water quality is a concern when incorporating mine waste materials, especially when attempting to construct groundwater-fed peatlands. This research is the first published account of Na+ redistribution in groundwater from a constructed tailings sand upland to an adjacent constructed fen peat deposit (Nikanotee Fen). A permeable petroleum coke layer underlying the fen, extending partway into the upland, was important in directing flow and Na+ beneath the peat, as designed. Initially, Na+ concentration was highest in the tailings sand (average of 232mgL-1) and lowest in fen peat (96mgL-1). Precipitation-driven recharge to the upland controlled the mass flux of Na from upland to fen, which ranged from 2 to 13tons Na+ per year. The mass flux was highest in the driest summer, in part from dry-period flowpaths that direct groundwater with higher concentrations of Na+ into the coke layer, and in part because of the high evapotranspiration loss from the fen in dry periods, which induces upward water flow. With the estimated flux rates of 336mmyr-1, the Na+ arrival time to the fen surface was estimated to be between 4 and 11years. Over the four-year study, average Na+ concentrations within the fen rooting zone increased from 87 to 200mgL-1, and in the tailings sand decreased to 196mgL-1. The planting of more salt-tolerant vegetation in the fen is recommended, given the potential for Na+ accumulation. This study shows reclamation designs can use layered flow system to control the rate, pattern, and timing of solute interactions with surface soil systems.

Transport and Retention of Water and Salt within Pervious Concrete Pavements Subjected to Freezing and Sand Application

AbstractPervious concrete pavement can effectively reduce both the volume of water and the concentration of many sediment-associated contaminants in urban runoff. However, chloride from road salt is recognized as a threat to surface and groundwater resources because it is a conservative ion and does not readily bind to soil particles. To better understand and manage water resources in urban environments experiencing annual freeze-thaw cycles, this study examines the impact of road salt (sodium chloride) and sand applications on water and chloride movement in pervious concrete structures in a laboratory setting. Water movement and salt retention were characterized within pervious concrete slabs under frozen and thawed conditions. Laboratory experiments were repeated using both brine (23% salt solution) and fresh water as well as varying additions of sand (typical of winter sand application rates in Canada) to provide a range of temperatures experienced in cold-climate urban environments. Performance testin...