Long-term studies as frameworks for peering into the future: Climate forcing and ecological response in a set of Wisconsin lakes

Background/Question/Methods

In this presentation we draw on research from the North Temperate Lakes Long Term Ecological Research program in Wisconsin to show how long-term studies can provide a framework for predicting future ecological change. In particular, we focus on how climatic forcing has led to quasi-cyclical patterns of lake water levels over the past 75 years and how, in turn, these changes in water level have influenced lake ecology. We use downscaled climatic projections to assess likely scenarios for future water levels and subsequent ecological response.

Results/Conclusions

Over the 75-year period of observation, water levels of northern Wisconsin seepage lakes have fluctuated with a dominant period between successive low water periods of approximately 13 years and an amplitude of approximately one meter. In some lakes low water levels expose critical habitat and thus alter ecological dynamics. For example, in Sparkling Lake, cobble habitat preferred by crayfish is lost during low-water periods. Long-term records show that the abundance of Orconectes rusticus, an invasive crayfish species that decimates macrophyte beds, declines during low water periods owing to reduced recruitment. Similarly, in Little Rock Lake, littoral woody habitat formed by dead trees that have fallen into lakes is exposed during periods of low water levels. This habitat is critical for littoral fish foraging, recruitment, and growth. The loss of this habitat has been associated with declines in forage fish abundance and reduced growth of top piscivores. Fish and crayfish are important elements of littoral food webs, and changes in their abundance resulting from water level fluctuations can have strong effects on ecological processes in lakes.

The most recent low-water period in northern Wisconsin (1999 -- present) was more prolonged and severe than previous cycles. Downscaled climate projections suggest that over the next 50 years, we can expect increases in both water temperature and evaporation rates causing water levels of seepage lakes to decrease by up to an additional 1-2 meters. Given past observations of ecological change observed during periods of low water level, we predict that these changes in climatic forcing will have important, complex, and non-linear effects on the ecology of littoral zones.