CHARACTERIZING AND PREDICTING MIXING EVENTS IN HIGH-ELEVATION MOUNTAIN PONDS IN MAINE

Global air temperatures, as well as those of the northeast United States, have been shown and predicted to be increasing due to the anthropogenic increase in global greenhouse gases in the atmosphere, and these increasing temperatures have already been shown to be altering the behavior of lakes in the form of decreasing duration of ice cover during the past century. Furthermore, it has been suggested that due to the sensitivity of inland water bodies, these locations may act as sentinels of climate change, and therefore should be closely monitored as these changes are taking place. Particularly, ponds at high elevations which are close to local elevation maxima provide limited options for species to relocate. This study is examining high-resolution water temperature data at the surface, bottom, and middle of nine small (<4 hectares) high-elevation (600 to 1000m) mountain ponds across western Maine. We seek to understand the mixing behavior of these ponds and how they may potentially respond to climate change, especially given the importance of mixing events to aquatic ecosystems. Mixing events are recognized in the data by sharp increases in the bottom temperature coupled with a corresponding decrease in the top temperature, often resulting in as much as 5 °C of total change. Unlike mixing in the spring and fall which continues for multiple days, summer mixing events are usually discrete and last less than a day before the pond again stratifies. There are conspicuous differences in hypolimnetic temperatures (up to 10 °C at times), timing of mixing events, and overall mixing behavior between the study ponds. Some ponds have been experiencing one or more summer mixing events each year, while others seem more resistant to these events. However, the data also show some simultaneous events at multiple locations, indicating that they are likely a response to a regional wind event. Characterization of these mixing behaviors based on location, volume, pond depth, basin shape and aspect, and clarity may help to explain the pattern of events and to predict the behavior of other regional subalpine ponds. By comparison of the water temperature data between ponds and to meteorological data, I plan to address what thresholds exist that control mixing, and if it is possible to use models to predict how these ponds may respond to a changing climate.