Spatio-temporal Trends in Hydrology at the Turkey Lakes Watershed: Insights from 35 Years of Monitoring

Abstract:

The Turkey Lake Watershed (TLW) is located on the Precambrian Shield in central Ontario, Canada and has been the site of multi-discipline ecosystem research since 1979. The 10.5 km² watershed is within the Great Lakes - St. Lawrence forest region with an uneven-aged tolerant hardwood forest having 90% of the basal area as mature to over-mature sugar maple. Podzolic soils and small forested wetlands have developed in the complex topography of the watershed where variable glacial till deposits occur over predominantly metamorphic silicate bedrock. Within the watershed, 13 first-order catchments that vary in size and topography have been monitored to elucidate spatio-temporal processes controlling run-off patterns. Over the 35 year period mean annual air temperatures at the TLW have increased at a rate of 0.75 ^oC per decade, with large inter-annual climate variability due to the influence of regional climate oscillations. As a result of warmer climate there has been a decline in annual export of water, as well as, changes in the seasonal distribution of runoff, Snowmelt has been occurring earlier and the number of zero-flow days are increasing. Declines in runoff were greater for catchments with steep slopes and less for those with shallow slopes and wetland areas. The large year to year variability in weather conditions made detecting the impacts on runoff from different harvesting treatments in 1997 difficult. These changes and fluctuations in water yields induced by fluctuating and changing climate have been shown to have had large consequences on element (carbon, nitrogen and sulphur) cycling within and export from catchments.