Deep water lakes threatened by global warming

In an age of rapid global population growth, demand for safe, clean water is constantly increasing. In 2010 the United States alone used 355 billion gallons of water per day. Most of the available fresh water on Earth’s surface is found in lakes, streams and reservoirs, so these water bodies are critical resources.

Deep water lakes are often called “sentinels of change.” Like the figurative canary in the coal mine, lakes may experience change to their ecosystem dynamics before we start to see shifts in the greater watersheds around them.

Global warming may be threatening the health of deep water lakes.

In a recent study by scientists Goloka Behari Sahoo, S. Geoffrey Schladow, John Reuter, Robert Coats and Michael Dettinger, they reported that future climate change scenarios may significantly alter natural mixing processes in Lake Tahoe in the Sierra Nevada range that are critical to the health of the lake’s ecosystem.  Their findings would likely not be confined to these California lakes. Elevated global temperatures could potentially create a condition termed “climatic eutrophication.”

While many groups have studied the long-term impact of climate change on lakes, this process can now be added to the growing list of drivers of eutrophication: a potentially damaging phenomenon that could affect a number of vital deep-water lakes around the world, degrading water quality and harming fish populations.

Eutrophication is a condition that occurs when lakes and reservoirs become overfertilized. Cultural eutrophication is a well-understood process in which lake and reservoir ecosystems become overloaded with chemical nutrients, mainly nitrogen and phosphorus. These nutrients come from human activities, including fertilizer runoff from farms and releases from sewage systems and water treatment plants. Natural weathering processes, atmospheric deposition of air pollutants, and erosion also transport nutrients that are already present in the watershed into the water supply.

In water bodies, these heavy nutrient loads fertilize algae, causing surface algal blooms. When the algae die, they sink and are broken down as they decompose. This decomposition process consumes dissolved oxygen in the water. As oxygen levels become depleted, hypoxic (dead) zones develop in the bottom waters where oxygen levels are too low to support life. Dead zones harm fisheries and tourism, and algal blooms can contaminate drinking water.

Climatic eutrophication could potentially occur in deep water bodies throughout the Earth, depleting oxygen levels in lakes untouched directly by mankind.

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