WILTON — In the summer of 2018, Wilson Lake joined the ranks of lakes across the world Lake which have a long-term deployment of environmental data loggers. For many decades, limnologists have been studying lakes by visiting during the summer months, but technology in remote sensors has exploded in the past decade and now allows a more comprehensive look at the lake environment. In particular, this allows a window into what is happening in lakes outside of the limited times when present to sample.

Most buoy deployments on northeast lakes (e.g. the buoys on Sebago Lake, Great Pond, and others) are seasonal: they only collect data during the summer, and are removed to avoid damage to sensitive equipment during freezing and ice breakup. While these buoys operate during the period when most biological growth takes place in lakes, they generally miss the spring and fall. In those dynamic seasons, lakes undergo changes such as rapid temperature fluctuation and water column mixing, which strongly influence biological organisms and nutrient cycling. The Wilson Lake buoy is unique in that it is constructed to freeze into the ice and collect data 12 months of the year, and is contributing valuable information to the emerging field of winter limnology. In addition to seasonal information, the buoy data will also establish a new data set alongside the long-term monitoring on Wilson Lake, which helps reveal climate change impacts on the lake and region.

The Wilson Lake buoy supports two types of sensors: temperature and dissolved oxygen (DO). These sensors are installed on a line that is suspended from the buoy to the lake bottom, and they record information at different locations along the water column. The temperature sensors allow us to identify when the lake is mixing or when it is stratified—that is, when a warm surface layer is floating on a denser, colder mass of water. In Wilson Lake, this “thermocline” occurs between 5 and 10 meters deep. During stratification, the lack of mixing may result in very different nutrient and dissolved gas conditions from the surface to the bottom. Temperature monitoring is also important to understand the habitat available to cold–water fishes. During peak stratification, surface waters may become too warm for many almonids.

The dissolved oxygen sensors are deployed in three locations: at the surface, at the thermocline (8m depth), and at the lake bottom. The benthic (bottom) sensor allows us to track hypoxia—a condition of low DO that arises from benthic microbial activity and a lack of lake mixing. This condition is of concern, as hypoxic lake sediments may release stored phosphorous into the water column and promote algal blooms. The other two sensors in the water column reflect cycles of DO that the lake experiences every day. During the day, DO increases as algae begin to photosynthesize. At night, DO declines due to respiration of algae and other organisms. Measuring the difference in concentrations between day and night allows an estimate of lake trophic status and algal biomass in the water column. A eutrophic lake (with a large amount of algal biomass) will undergo larger day-to-night fluctuations than an oligotrophic lake (a clear lake with little algae).

In addition to phytoplankton, other biological organisms undergo shifts in abundance and distribution in the lake. Currently, a UMF student is investigating how different species of zooplankton (essential prey for many fish species) increase in abundance during the winter to spring transition, and whether this response is due to temperature, phytoplankton abundance, or some other factor. So far, it is known that the winter zooplankton community in Wilson Lake is primarily dominated by copepods, and cladocerans (the larger-bodied taxa present in the summer) are primarily in a dormant “resting phase”.

The FOWL–UMF collaboration on the Wilson Lake buoy has already yielded new insights into northeast lakes, and looks forward to continuing to learn more about these important ecosystems. For more information, email rachel.hovel@maine.edu or dalyj@maine.edu.

From the Friends of Wilson Lake newsletter, written by Dr. Rachel Hovel (Biology, UMF) and Dr. Julia Daly (Geology, UMF).