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Clear blue lakes turning murky in USA

New research reveals that many lakes in the continental United States are becoming murkier, with potentially negative consequences for water quality and aquatic life. These are the findings of a study published in Limnology and Oceanography.

From blue, clear lakes to greenish brown

In the 5 years between 2007 and 2012, the dominant lake type in the United States shifted from clear, blue lakes to greenish-brown, murky lakes. Blue lakes declined by 18% while murky lakes increased by 12%. 




Overall, “blue” lakes decreased by ~ 18% (46% of lakes in 2007 to 28% in 2012) while “murky” lakes increased by almost 12% (24% of lakes in 2007 to 35.4% in 2012).  So, the majority of lakes are now murky.

Regionally, murky lakes significantly increased in the Northern Appalachian, Southern Plains, and Xeric ecoregions.

In the Northern Appalachians, blue lakes decreased by 41.4%, brown lakes increased by 17.8%, and murky lakes increased by 26.8%. In the Northern Plains, green lakes significantly increased by 18.9% and in the Southern Plains, blue lakes significantly decreased by 25.6% and murky lakes increased by 29.8%. in the Upper Midwest, blue lakes significantly decreased by 25%, and in the Xeric region, green lakes significantly decreased by 30% while murky lakes increased by 34.2%
 

So, what is making clear blue lakes murky?

The investigators cannot definitively say what is causing this shift, but they suspect that land cover and land use patterns within a watershed, as well as changes in climate, may be important factors.

Lead author Dina Leech, of Longwood University in FarmVille, Virginia, tells us
Blue lakes typically are those that do not show evidence of nutrient pollution or elevated organic matter while murky lakes have high levels of both. 

Does it matter?

The answer to that question is a resounding yes.  It is indicative of profound changes occurring in the ecosystem and the complex network of life that sustains it.  A shift toward murkiness is a management concern because murky lakes tend to have more algae, including potentially harmful cyanobacteria. And with poor food quality at the base of the food web, over time murky lakes may not be able to support a healthy fishery.  The highest recorded concentrations of the toxin microcystin occurred in murky lakes.

Once lakes become murky it is difficult for them to reverse the process.


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