We compared median runoff (R) and precipitation (P) relationships over 25 years from 20 mesoscale (50 to 5,000 km2) catchments on the Boreal Plains, Alberta, Canada, to understand controls on water sink and source dynamics in water‐limited, low‐relief northern environments. Long‐term catchment R and runoff efficiency (RP−1) were low and varied spatially by over an order of magnitude (3 to 119 mm/year, 1 to 27%). Intercatchment differences were not associated with small variations in climate. The partitioning of P into evapotranspiration (ET) and R instead reflected the interplay between underlying glacial deposit texture, overlying soil‐vegetation land cover, and regional slope. Correlation and principal component analyses results show that peatland‐swamp wetlands were the major source areas of water. The lowest estimates of median annual catchment ET (321 to 395 mm) and greatest R (60 to 119 mm, 13 to 27% of P) were observed in low‐relief, peatland‐swamp dominated catchments, within both fine‐textured clay‐plain and coarse‐textured glacial deposits. In contrast, open‐water wetlands and deciduous‐mixedwood forest land covers acted as water sinks, and less catchment R was observed with increases in proportional coverage of these land covers. In catchments dominated by hummocky moraines, long‐term runoff was restricted to 10 mm/year, or 2% of P. This reflects the poor surface‐drainage networks and slightly greater regional slope of the fine‐textured glacial deposit, coupled with the large soil‐water and depression storage and higher actual ET of associated shallow open‐water marsh wetland and deciduous‐forest land covers. This intercatchment study enhances current conceptual frameworks for predicting water yield in the Boreal Plains based on the sink and source functions of glacial landforms and soil‐vegetation land covers. It offers the capability within this hydro‐geoclimatic region to design reclaimed catchments with desired hydrological functionality and associated tolerances to climate or land‐use changes and inform land management decisions based on effective catchment‐scale conceptual understanding.
Abstract:While previous boreal peatland wildfire research has generally reported average organic soil burn depths ranging from 0.05 to 0.20 m, here, we report on deep burning in a peatland in the Utikuma Complex forest fire (SWF-060,~90 000 ha, May 2011) in the sub-humid climate of Alberta's Boreal Plains. Deep burning was prevalent at peatland margins, where average burn depths of 0.42 ± 0.02 m were fivefold greater than in the middle of the peatland. We examined adjacent unburned sections of the peatland to characterize the hydrological and hydrophysical conditions necessary to account for the observed burn depths. Our findings suggest that the peatland margin at this site represented a smouldering hotspot due to the effect of dynamic hydrological conditions on margin peat bulk density and moisture. Specifically, the coupling of dense peat (bulk density >100 kg m À3 ) and low peat moisture (m <250%) at the peatland margin allowed for severe smouldering to propagate deep into the peat profile. We estimated that carbon release from this margin 'hotspot' ranged from 10 to 85 kg C m À2 (mean = 27 kg C m À2 ), accounting for 80% of the total soil carbon loss from the peatland during the wildfire. As such, we suggest that current estimations of peatland carbon loss from wildfires that exclude (and/or miss) these 'hotspots' are likely underestimating total carbon emissions from peatland wildfires. We conclude that assessments of natural and managed peatland vulnerability to wildfire should focus on identifying dense peat on the landscape that is vulnerable to drying.
Abstract:Wetlands in the Western Boreal Plain (WBP) of North Central Alberta exist within a moisture-deficit regime where evapotranspiration (ET) is the dominant hydrologic flux. As such these systems are extremely susceptible to the slightest climatic variability that may upset the balance between precipitation (P) and ET. Wetland ET is predominantly controlled by vegetation composition but may also vary due to moisture regimes and microclimatic factors. To address this variability in moisture regimes, ET was examined in a typical moraine-wetland-pond system of the WBP during the 2005 and 2006 snow-free seasons. Closed dynamic chamber measurements were used to gather data on plant community-scale actual evapotranspiration (ET) in an undisturbed natural bog with varying degrees of canopy cover surrounding a shallow groundwater-fed pond. For the purposes of scaling plant community ET contributions to those of the wetland, potential ET (PET EQ ) was measured using a Priestley-Taylor energy balance approach at three separate wetland sites with varying aspects surrounding the central pond, along with actual evapotranspiration using a roving eddy covariance (EC) tower. Growing season peak ET rates ranged from 0Ð2 mm/h to 0Ð6 mm/h depending on the location, vegetation composition and time period. Sphagnum contributions were the greatest early in the growing season, reaching peaks of 0Ð6 mm/h, while lichen sites exhibited the greatest late season rates at 0Ð4 mm/h. Thus, Sphagnum and other nonvascular wetland plant species control ET differently throughout the growing season and as such should be considered an integral part of the moisture and water balances within wetland environments at the sub-landscape unit scale.
Abstract:The relative contributions to total actual evapotranspiration (AET) from pond and riparian areas in a pond-wetland complex in the Western Boreal Plain (WBP) of northern Alberta are measured using the Bowen ratio energy balance technique. Measurements show that a pond typical of the WBP evaporates at a rate more than twice that of the adjacent riparian peatland. Relating the actual to potential evapotranspiration over both surfaces yields Priestley-Taylor˛coefficients of 0Ð69 and 1Ð11 for the peatland and pond respectively. Further results demonstrate that the sheltering and turbulent influences of the adjacent forested areas must be considered in the processes governing the permanence of WBP ponds. That is, forestry practices may inadvertently enhance the evaporative losses from the ponds, over and above the controls exerted by the regional climate.
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