Global Climate Change and Lakes

While some still debate the causes of global climate change, there is strong scientific consensus that the earth’s climate is getting warmer. A recent volume of the scientific publication “Limnology and Oceanography” deals specifically with the role that lakes and reservoirs play in climate change. The lakes of the world are not only susceptible to the influences of climate change; they provide a record of and ultimately influence it.

Three themes were prominent throughout the volume. Theme one investigated lakes and reservoirs as sentinels of present climate change and examined which physical, chemical, or biological properties of lakes can help quantify aspects of climate change. Theme two analyzed fossil organisms in lake sediment layers, allowing scientists to speculate on the environmental conditions that existed throughout the past. Finally, theme three considered the role of lakes and reservoirs as regulators of future climate change, which primarily involved tracking the present flow of carbon into and out of lakes and predicting the future flow.

Lakes as sentinels

As air temperatures continue to rise, arctic and alpine lakes may be the hardest hit. Currently, some lakes that were perennially covered in ice are experiencing only seasonal ice cover. One result of the loss of ice cover is that more UV rays are penetrating deeper into the water column, potentially affecting organisms at the cellular level. In addition to the loss of ice cover, surface waters will also warm, but at a rate faster than deeper, hypolimnetic waters. As a result of warming, the temperature differential between the two layers intensifies, hastening the onset of stratification and increasing its stability. The subsequent changes in the rates of nutrient cycling and food web dynamics can be dramatic. In one example, the mean surface temperature in Italian Lake Maggiore rose by about 6 °F over the last 25 years. This warming increased the depth of the epilimnion, thus providing deeper and darker waters with oxygen. The dark, oxygenated water provided the spiny water flea (Bythotrephes longimanus) daytime refuge from sight-feeding predators. The spiny water flea continued to migrate to the surface at night (with the rest of the zooplankton community) to feed on other zooplankton. Numbers of the spiny water flea have increased 10-fold in the lake, and the population of its preferred prey species have declined significantly as a direct result of the increased epilimnion depth caused by the warming water.

Bythotrephes longimanus
(aka Spiny Water Flea)
Spiny Water Flea

 

 


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