Impacts of a Changing Climate on C and N Cycling in a Hardwood Forest Ecosystem at the Turkey Lakes Watershed.

The Turkey Lake Watershed (TLW) located on the Precambrian Shield in central Ontario, Canada has been the site of multi-discipline ecosystem research since 1979. An integrated research approach has enabled evaluations of the impacts of changing local climate on terrestrial and aquatic systems. The 10.5 km² watershed is positioned in uneven-aged tolerant hardwood forest with 90% of the basal area as mature to over-mature sugar maple. Podzolic soils with mor organic horizons have developed in thin glacial till deposits over predominantly metamorphic silicate bedrock.

While mean annual air temperatures at the TLW have increased at a rate of 0.75 ^oC per decade over the 30 years of the study, there has been significant inter-annual climate variability due to the influence of the El Niño/La Niña Southern Oscillation (ENSO). Winter precipitation was less and summer drought conditions were more frequent during El Niño phases. Organic matter decomposition and nitrogen mineralization in these soils is strongly influenced by soil temperature and moisture content. We used snowpack ablation dates, the Palmer Drought Severity Index and a Multivariate ENSO Index (MEI) to evaluate climate impacts on catchment biogeochemistry. Our objective was to examine relationships between these climate indices and dissolved organic carbon (DOC), nitrate (NO₃^-) and dissolved organic nitrogen (DON) concentrations in forest floor percolate, mineral soil percolate, first order streams and lake water.