Monday, November 13, 2006 - 1:15 PM
109-1

Long-Term Changes in Nutrient Cycling and Soil Chemistry at the Turkey Lakes Watershed.

Paul Hazlett and Neil Foster. Canadian FS, Nat'l Res. Canada, 1219 Queen Street East, 1219 Queen Street East, Sault Ste Marie, ON P6A 2E5, Canada

Acid deposition has been implicated as a factor contributing to the depletion of base cations in forest soils of eastern North America. Reductions in S emissions in this region during the past 25 years have resulted in declines in precipitation SO4- deposition at the Turkey Lakes Watershed, located on the Canadian Shield in central Ontario. While declining inputs of atmospheric acids should reduce soil acidification and cation leaching rates, natural production of NO3-, the release of adsorbed SO4- and soil base cation content could influence long-term trends. The Turkey Lake site supports a mature sugar maple dominated tolerant hardwood forest with acidic podzol soils that have developed in shallow glacial till deposits. In spite of similarity in profile morphology across the 10 km2 research watershed there was a large range in the soil reserves of exchangeable base cations. Our objectives were to examine how solution chemistry in soils with varied base contents responded to changing deposition and to determine if there were detectable changes in soil base reserves at the Turkey Lake Watershed over a 20-year time period. We measured ion concentrations in forest-floor and mineral soil percolate during periods of high and low deposition at two stands in the watershed that represented soils with different base saturations (30 % and 10 % in the B horizon). Base cation contents were determined for mineral soils sampled from the same two stands in the mid-1980’s and again in the mid-2000’s. Archived soil samples were used to compare laboratory methodologies over the study period.