Water and nutrient inputs, outputs, and storage in Canadian boreal forest wetlands: a review

Boreal wetlands, primarily peatlands, are important global carbon (C) reservoirs and integral components of regional hydrological networks. This paper summarizes our current state of knowledge regarding components of water and nutrient budgets in northern wetlands, with a focus on Canada. Boreal wetland water budgets are strongly influenced by the following: seasonal weather patterns as they relate to the timing of precipitation and meltwater inputs and evapotranspiration (ET) losses; vegetation cover in the wetland and surrounding uplands as it relates to rain and snow interception and evapotranspiration; and connectivity of the wetland to the regional hydrological network. Key factors that influence boreal wetland phosphorus (P) budgets are: spatial and temporal variability in the water table as they relate to reduction-oxidation conditions and rewetting of highly decomposed peat; concentrations of metals and ions involved in P complexation and release; vegetation age and type (herbaceous versus woody); and seasonal weather patterns as they relate to water retention time. As with other components of the boreal forest, wetlands are often limited in bioavailable nitrogen (N), therefore bulk deposition and symbiotic fixation are key N sources. Within many wetlands, N is rapidly cycled through vegetation and microbial communities, and converted to gaseous N or exported as organic N in outflows. In terms of C budgets, boreal wetlands are important reservoirs, converting inorganic and organic C inputs to peat. Climate change and anthropogenic N loading threaten the water and C balance in boreal wetlands.