Climate change in lakes
Gretchen Hansen's research on the effects of climate change on lakes in Wisconsin
How will climate change affect fish communities in lakes?
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Water temperature influences the suitability of a lake for walleye and largemouth bass. In general, walleye reproduce more successfully in cooler lakes, and largemouth bass populations are most abundant in warm lakes. Both species exhibit a threshold response to temperature, where small changes in temperature can produce big changes in the fish population.
The temperature threshold separating lakes with successful vs. unsuccessful walleye reproduction is approximately the same threshold separating lakes with low vs. high largemouth bass abundances. This means that lakes with the best habitat for natural walleye reproduction generally do not have the habitat to support high largemouth bass abundance, and vice versa.
In the future, we expect lakes will get warmer, although the magnitude of temperature increase varies among lakes. As water temperatures get warmer, many lakes that currently can support natural walleye reproduction will no longer have the habitat conditions to do so.
Although a relatively small number of lakes are predicted to support walleye natural reproduction in the future, the lakes where walleye are expected to persist are for the most part some of the state's largest and most popular lakes. When considered in terms of total lake area, walleye natural reproduction is predicted to continue in a large proportion of the state’s lake surface area. Most of the surface area of lakes that support natural walleye reproduction will also support high largemouth bass densities. The majority of Wisconsin lakes and total lake area are predicted to have habitat conditions suitable for high largemouth bass densities by the mid-21st century.
Hansen, G. J. A., J. S. Read, J. F. Hansen, L. A. Winslow. In press. Projected shifts in sport fish species dominance in Wisconsin lakes under climate change. Global Change Biology. doi: 10.1111/gcb.13462
How do diverse lakes across the landscape respond to climate?
Temperature is a critical driver of ecosystem processes and food web dynamics. Past water temperatures may provide insights into mechanisms behind observed trends in aquatic ecosystems, and projections of future water temperatures can help prioritize management actions. Unfortunately, very few lakes are monitored for water temperature on the spatial scale and resolution necessary for these types of research questions. Air temperatures are widely available, but lake temperatures do not track air temperatures linearly. The decoupling of air and water temperatures is especially apparent in deep waters that provide critical habitat for cool- and cold-water fishes.
Together with collaborators at the United States Geological survey and elsewhere, we have developed a mechanistic, thermodynamic model of lake temperatures to hindcast (from 1979-2012) and forecast (through 2089) water temperatures of >2,100 Wisconsin lakes. This model generates daily, depth-specific thermal profiles for the past and future that can be linked to critical ecosystem functions such as the abundance of walleye or other fish species. To date, we have demonstrated strong connections between modeled lake temperaturesand walleye recruitment in Wisconsin. Work is ongoing to improve model accuracy, add dissolved oxygen predictions, expand our model to include other states and provinces in the Great Lakes region, and to link model outputs to trends in other fish species.
Read J.S., L.A. Winslow, G.J.A. Hansen, J. Van Den Hoek, P.C .Hanson, L.C .Bruce, C.D. Markfort. 2014. Simulating 2,368 temperate lakes reveals weak coherence in stratification phenology. Ecological Modelling. 291C: 142-150. doi:10.1016/j.ecolmodel.2014.07.029
Winslow, L. A., J. S. Read, G. J. A. Hansen, and P. C. Hanson. 2015. Small lakes show muted climate change signal in deepwater temperatures. Geophysical Research Letters 42: 355-361. doi:10.1002/2014GL062325.