WATERSHED CONTROLS ON SUMMER STRATIFICATION OF MAINE SUBALPINE PONDS

The Mountain Ponds Project has been collecting high-resolution water temperature data in subalpine ponds in the state of Maine over the last five years. Most of the ponds are situated between 600 and 1000m elevation and are located along or near the Appalachian Trail. Using the surface and bottom water temperature records at each site, we can identify the timing and frequency of turnover events. The ponds can be classified into three summer stratification types: strongly stratified, weakly stratified, and ponds that show intermittent, short duration mixing events. Previous work on these data suggested that transparency was a significant factor in determining pond mixing behavior. We collected water samples from a ten pond subset of the project locations and analyzed them for color and dissolved organic carbon (DOC). Preliminary results show higher DOC levels in sites with lower secchi depths, which are ponds exhibiting strong stratification during summer months. The ponds with the lowest DOC values are showing deeper secchi depths and are more weakly stratified during the summer. Given the similarities of watershed characteristics among the sample sites, the variability may be explained by contrast in underlying bedrock. Better understanding of the controls on stratification will help predict how these ponds respond to future climate change.