Identification of wetlands on the Canadian boreal plain and their contributions to stream water chemistry

Abstract

The Alberta Wetland Inventory (AWI), which is used in a variety of applications across the province to estimate wetland cover from aerial photographs, detected only 34% of confirmed wetland field plots in boreal forest watersheds in the Swan Hills of Alberta. Given the association between wetland cover and runoff and surface water chemistry in western Canadian boreal forest (Boreal Plain) watersheds, accurate quantification of wetland cover is critical to efforts to model hydrologic processes and water quality. Therefore, as a component of the Forest Watershed and Riparian Disturbance (FORWARD) Project, the Wetland Inventory and Identification Tool (WIIT) was developed and successfully detected 81% of the wetland field plots. Application of both models across a variety of landscapes in the boreal forest of Alberta demonstrated that wetland cover estimates were 1.5 times higher with the new WIIT model than with the AWI. Also, the WIIT identified polygons that were both smaller and contained taller trees than those identified by the AWI, indicating that this computer model may be more effective than wetland identification methods that use only aerial photography. Results of this study show that careful interpretation of aerial photography at the 1:15 000 scale, coupled with ground truthing and computer models, can provide an accurate means of identifying wetlands on Boreal Plain landscapes. A preliminary annual (November through October water year) water and phosphorus (P) budget was also constructed for a 3-ha peatland in the Swan Hills, to quantify some aspects of peatland water and P cycling. Understanding the relationship between wetlands, and water and nutrient (P) inputs and outputs from watersheds is central to models being developed for stream water quality and quantity. The study wetland in the FORWARD Willow watershed retained 27% of the water collected through rainfall and runoff, and evapotranspiration represented the dominant route for water loss from the wetland, constituting 63% of rainfall inputs. The wetland retained (within soils, vegetation and microbial pools) approximately 77% of P entering the wetland via wet and dry atmospheric deposition and runoff.