Assessing the Biometeorology of a Newly Established Reclamation Soil Cover in Fort McMurray, Alberta
Several experimental watersheds have been established in the Fort McMurray region as part of a risk-based assessment of various reclamation strategies for oil sands mining. This study has been undertaken to specifically evaluate if the most cost-effective reclamation option (minimal soil depth) can retain sufficient moisture to promote plant development and return the area to a functional boreal ecosystem. The eddy covariance technique was used during the second post-reclamation growing season to quantify the exchange of energy and water vapour atop a 25 cm soil cover, situated on a south facing slope. The 2008 growing season was both hotter and wetter than normal, resulting in large seasonal evapotranspiration (ET) values (309 mm from May 10th - Oct 8th). The majority of available energy was partitioned into latent heat, resulting in a mean Bowen ratio of 0.75 and a Priestley-Taylor alpha coefficient approaching unity (mean = 0.87). A low mean daytime (0900 to 1700 hrs) decoupling coefficient (Ømega = 0.31), which decreased bi- weekly with increasing LAI, suggests that ET at this site was predominantly controlled by canopy resistance (rc). A total derivative analysis of the Penman-Monteith equation was used to demonstrate the sensitivity of ET to changes in available radiation (Ra), vapour pressure deficit (D) and rc between months. Results indicate that ET was particularly influenced by rc during the driest month of July when soil moisture became limited and the vegetation became stressed. ET was more sensitive to changes in D prior to leaf-out and during senescence. Although too early to predict whether this soil cover will be successful in sustaining regeneration, this study provides some insight into the unique biometeorology of the initial stages of engineered soil covers. Over time, this may allow for the detection of specific environmental indicators that may preclude the impending success or failure of reclamation efforts.
Uptake and Hydraulic Redistribution of Soil Water in a Natural Forested Wetland and in two Contrasting Drained Loblolly Pine Plantations: Quantifying Patterns over Soil-to-Root and Canopy-to-Atmosphere Interactions
The conversion of wetlands to intensively managed forest lands in eastern North Carolina is widespread and the consequences on water and carbon balances are not well studied. Quantification of evapotranspiration (ET), tree transpiration and their biophysical regulation are needed for assessing forest water management options. We characterized vertical variation in the diurnal and seasonal soil volumetric water content at 10 cm intervals to evaluate changes in water availability for root uptake and monitored eddy covariance ET and tree transpiration (sap flux) in three contrasting loblolly pine (Pinus taeda L.) stands. Those stands included a 50- yr-old wetland natural regeneration (NG), a 17-yr-old drained mid-rotation plantation (MP) and a 5-yr-old drained plantation (YP) in eastern North Carolina. We also quantified the magnitude of hydraulic redistribution (HR), the passive movement of soil water from deep to shallow roots, to identify factors affecting the seasonal dynamics of root water uptake, root and plant water potentials and stomatal conductance. In NG, soil water content was always at full saturation and total tree water use peaked between 6-7 mm/day, and this stand was used as reference. In MP, soil water content varied with soil depth and total water use from the upper 1m peaked between 4 and 6.5 mm/day during the growing season and was strongly correlated and similar to ET (ET represented 90-95% of total water depletion). In YP, soil water used was limited to the upper 30 cm and was strongly affected by summer drought by declining progressively from 0.9 mm/day in spring to 0.4 m/day in September. After periods of more than 10 days without rain, water extraction in MP shifted to the deeper layers, and recharge from HR approached 20% of ET. During days of high evaporative demand, water use in MP was comparable to NG thanks to HR and to the contribution of deeper roots to water uptake. In YP, HR never contributed for more than 8% of ET. There was no HR in NG. Tree transpiration represented on average 60% and 40% of ET in MP and YP, respectively. However, in MP it represented only 50% of ET on days following rain events and up to 80% of ET after prolonged periods without rain. In MP, we propose that HR prevented soil water potentials from decreasing during periods of increasing soil water deficit, therefore maintaining a constant driving force for water uptake. In MP, HR was an important mechanism for maintaining shallow root function during drought and preventing total stomatal closure. Our study shows that HR prevented soil water potentials from dropping below -0.6 MPa, and played a role in wetland hydrological balance by increasing water uptake in MP to level close to those of trees growing on pure wetlands (NG).
Snow Accumulation and Spring Melt Rates of Bogs and Fens in the North Granny Creek Catchment Basin, Hudson Bay Lowlands, Ontario
The Hudson Bay Lowlands contain one of the most extensive, contiguous peatland complexes in the world. Interlinked patterned peatlands developed in this region because of the cool climate, low-gradient topography and an underlying layer of low conductivity marine sediments. There is currently little research regarding the mechanisms that control runoff and surface water connectivity in this region, especially the functions of different peatland types on runoff production and flow pathways. Runoff generation in these systems is dependent on several factors such as soil and pool storage capacity, snow accumulation and melt rates, and peatland morphometry. Snowmelt accounts for a major portion of total annual runoff in this region and the timing of the melt will determine effective runoff production from a peatland catchment. One of the objectives of this project is to identify the processes and mechanisms that generate spring snowmelt runoff in different peatland types (i.e. bogs and fens) and quantify the relative contribution of each type in a peatland-dominated catchment basin. This research is being conducted in a 30 km2 catchment basin located near the DeBeers Victor diamond mine, located 90 km west of Attawapiskat, Ontario. The North Granny Creek basin is located approximately 3 km from the mine pit and is comprised of several peatland types and forms. The surface hydrology of this area is expected to be affected by groundwater depressurization due to dewatering of the mine pit by deep groundwater pumping wells. Effects of this activity on surface hydrology could possibly include increased soil storage capacity due to drier conditions and decreased melt rates due to reduced inputs of warm groundwater. Surface water connectivity is usually at a maximum in the spring because of a relatively impermeable frost table and low soil storage capacity which reduces infiltration. These effects of melt will not be observed uniformly over the entire catchment because of the differing hydrological properties of peatland types. Fens are expected to experience melt quicker than bogs and will receive and convey most of the runoff waters. Snow survey data from the springs of 2008 and 2009 coupled with stream discharge measurements will be used to determine the characteristics of different peatland types that control snow accumulation, melt rates and runoff production and their respective contributions. Since it is expected that the surface hydrology of this area will change over time because of groundwater depressurization it is important to develop a base line characterization of runoff generation and flowpaths within and between peatland types. An examination of snow accumulation and melt characteristics is necessary in northern peatland complexes to fully understand the response of these environments to changes in hydrology.
Ecohydrological Processes in Cutover Peatlands: The Impact of Peatland Restoration (Rewetting) on the Site Hydrology and Water Balance of an Abandoned Block-cut bog in Quebec
Artificial drainage networks established throughout peatlands during the peat extraction process often remain active following abandonment, maintaining a water table relatively far from the surface of the peat and hindering the survival and reestablishment of Sphagnum mosses. In an effort to restore a suitable hydrological regime, the primary drainage network of an abandoned cutover peatland (the Cacouna bog) was blocked with a series of peat dams, resulting in a site-averaged water table rise of 32 cm. The components of the water balance and site hydrology were monitored over three consecutive study periods (2005-2006 prior to rewetting; 2007 following rewetting), permitting quantification of the altered hydrologic conditions due to rewetting. Following ditch blocking, runoff was reduced from 23 to 10% of precipitation during the 2005/2006 (two-year average) and 2007 seasons, respectively. The higher water table and blocked drainage network resulted in increased runoff variability, dependant upon antecedent conditions (capacity to retain additional water on-site) and event-based precipitation dynamics. Evapotranspiration (ET) remained the major water loss from the site in each year, comprising 91, 77 and 91% of total outputs during the 2005, 2006 and 2007 seasons, respectively. ET rates were 25% higher in 2007 following rewetting (3.6 mm/day), compared to pre-restoration ET rates of 2.7 mm/day during both the 2005 and 2006 study periods. Storage changes were restricted following rewetting, due to reduced runoff losses limiting water table drawdown, thereby constraining peat compression and preventing undue drying of the unsaturated zone. An average surface level rebound of 3 cm was observed, increasing the mean hydraulic conductivity by an order of magnitude. There is a need to understand the impact of site rewetting on the system hydrology, to facilitate a timely return to a functioning ecohydrological state following disturbance. The intention of this presentation is to provide an overview of the hydrological regime prior to, and following, rewetting.
Evaluating mechanisms and relationships between water and nutrient fluxes in Sphagnum mosses.
The dominant ground cover of fens and bogs are Sphagnum mosses. The mosses grow in colonies and physiochemical and morphological adaptations enable Sphagnum communities to occupy unique niches within a peatland. Raised above the water table, hummock-forming species contribute to the unsaturated zone, where the physical mechanisms governing water flow remain elusive. Evaluating unsaturated flow through Sphagnum mosses remains complicated because of multiphase flow (vapour and liquid), and the inherent difficulties in obtaining hydrophysical parameters of the moss. Further complications arise because diurnal moisture and temperature fluctuations likely provide the mosses with additional sources of water through dewfall and distillation. Though potentially minor contributions, at a diurnal scale they could be physiologically important to help alleviate the water stress incurred by the mosses during highly evaporative days. These two potential water sources have yet to be examined with scientific rigor. Water and heat, inputs and fluxes, are dynamic, shifting seasonally and daily, creating implications for nutrient distribution within the ecohydrological system. Examining the mosses at a small spatial (hummock), and temporal scale (diurnal), coupled with large-scale studies will help improve restoration and management techniques. Two 'study' hummocks from a fen in Parc du Bic, PQ, will be instrumented for measurements of moisture content, temperature, relative humidity and heat fluxes across a surface-to-depth profile, while a nearby meteorological station will provide measurements of ambient conditions. Sampling of nearby hummocks will provide a means for determining moss hydrophyscial properties as well as provide water samples which will be examined for ionic and isotopic composition. The objectives of the in situ experiments are: one; obtain a diurnal energy budget coupling heat and water fluxes and two; examine the diurnal moisture and temperature fluctuations within a hummock to assess and quantify moisture additions through dewfall and distillation. In addition to field studies, complementary laboratory column experiments will be conducted using hummock monoliths removed from the site. Advection and dispersion of a conservative tracer will help elucidate liquid and vapour flow under idealized conditions which, in conjunction of the fields will help assess the implications diurnal fluxes will have on the advection and dispersion of solutes.