Water transit time estimates for 13 forested headwater catchments based on comprehensive and long-term observations from the Turkey Lakes Watershed Study

The time it takes water to travel through a catchment, from when it enters as rain and snowmelt to when it leaves as streamflow, can influence water quality and catchment sensitivity to environmental change. Most estimates of catchment transit times are based on relatively short data records (<10 years) and often from only a few catchments within a region. A better understanding of how catchment transit times vary over time and across a landscape would help inform effective management of forest water resources. We used comprehensive and long-term observations from the Turkey Lakes Watershed Study, one of the longest running forest watershed studies in Canada, to estimate water transit times for 13 headwater catchments. Chloride, a natural water tracer, was measured in streams, rainfall, snowfall and as dry atmospheric deposition over a 31 year period. These data were used to fit a number of models to estimate transit time distributions. Our results show that transit times can be variable through time and between adjacent catchments and are influenced by catchment characteristics, such as slope, wetland cover and forest change. Although the Turkey Lakes Watershed Study was initiated in 1979 to focus on ecosystem response to acid rain, our study highlights the often unforeseen added value of long-term monitoring to understand a broad range of ecosystem processes.