HR: 0800h
AN: H31B-1308    [Abstracts]
TI: Pathways of DOC Export From Wetland-Dominated Catchments on the Boreal Shield
AU: * Beall, F D
EM: fbeall@nrcan.gc.ca
AF: Great Lakes Forestry Centre, Canadian Forest Service, 1219 Queen St. E, Sault Ste. Marie, ON P6A 2E5 Canada
AU: Creed, I F
EM: icreed@uwo.ca
AF: Dept. of Biology, Univ. of Western Ontario, 1151 Richmond St., London, ON N6A5B7 Canada
AU: Bourbonniere, R A
EM: rick.bourbon@ec.gc.ca
AF: National Water Research Institute, Environment Canada, 867 Lakeshore Rd., Burlington, ON L7R4A6 Canada
AB: The proportion of catchment area covered by wetlands has repeatedly been shown to control the flux of DOC from headwater catchments. However, it is not clear where, i.e. surface layers or from deeper in the peat, the source of DOC enriched water observed in streams originates within the wetland. Two wetland-dominated catchments at the Turkey Lakes Watershed, north of Sault Ste. Marie, Ontario, were instrumented with tension lysimeters in upland areas and piezometers of varying depth in wetland areas to sample soil water. Soil and stream water was sampled with a seasonally variable regime, varying from daily to monthly, in 2003 and 2004. Catchment 38 (c38) has an area of 6.32 ha with 17% of its area covered by wetlands and c60 has an area of 3.5 ha with 14% wetlands. Forests in upland areas are a mature, uneven age tolerant hardwood forest, dominated by sugar maple, while wetland forest are a mixture of black ash, yellow birch, eastern white cedar and balsam fir. In c38 during winter baseflow conditions, DOC concentrations were similar in the stream and at a depth of 3 m in the peat. Winter DOC concentrations in the stream draining c60 were intermediate between the concentrations observed at 0.5 and 1m. During snowmelt, DOC concentrations in stream water dilute but begin recovering quickly. Stream water DOC concentrations during snowmelt are most similar to those observed in upland mineral soils. Over the course of the growing season, DOC concentrations increase in all samplers, with the greatest increases observed in stream water and 0.25 m piezometers in the wetlands. DOC in tension lysimeters in the upland areas showed the smallest increases. In c60, the increase in stream water DOC preceded the increase in all other samplers and reached a higher value, indicating that an important source of DOC was not sampled. Stream water DOC was most similar to 0.15 m piezometers along the wetland margins in c60 during the fall, suggesting a flow path along the surface of the wetland was the most significant contributor to stream DOC. In contrast, stream water DOC in c38 was intermediate between the 0.15 m piezometers along the wetland margins and the deeper piezometers at 0.5 and 1 m. This suggests that stream water in c38 is composed of a mixture of near surface water and deeper soil water. These results demonstrate the variability between two apparently similar catchments with respect to the sources of DOC in stream water.
DE: 1806 Chemistry of fresh water
SC: Hydrology [H]
MN: Fall Meeting 2005