An assessment of over 5000 lakes in Wisconsin revealed that nearly 25% of them have gotten more murky over the last twenty years. The study also indicates that things could get worse as a result of increased precipitation due to climate change.
The study, which was conducted by scientists from the University of Wisconsin-Madison in collaboration with the Wisconsin Department of Natural Resources, also suggests measures that can be taken to improve water quality, such as increasing the riparian buffer zone by restricting agriculture on land immediately bordering Wisconsin's rivers and lakes, which would limit nutrient runoff and thus improve the clarity of the water.
"In the face of increasing precipitation, this analysis provides empirical support for the fact that adapting our landscape is going to be important into the future," says co-author Monica Turner, a UW-Madison professor of zoology.
The authors suggest farming should be limited to within 10% of the riparian buffer zone surrounding lakes and rivers or streams that flow into those lakes. Leaving natural vegetation on the banks of rivers and lakes would reduce nutrient and sediment runoff during heavy rains, and would also benefit farmers who often suffer extensive damages to crops when rivers rise.
While the study shows that water clarity has remained unchanged for most of the lakes studied, with 6% actually showing an improvement in water clarity, the number of lakes where water clarity is getting worse is concerning, and indicates that preventative action needs to be taken to maintain water quality.
"If we want to maintain or improve water clarity, we need to think about trends in precipitation," says lead author Kevin Rose, formerly a postdoctoral researcher at UW-Madison and now an assistant professor of freshwater ecology at Rensselaer Polytechnic Institute in New York.
The studies findings, which were recently published in the scientific journal Ecological Applications, shows that water clarity in lakes that generally have clear water deteriorates during wetter years. Lakes with good water clarity tend to be more vulnerable to the torrent of nutrients and debris that flows in after heavy rainfall, which can result in the water turning murky or brown due to the increased sediment and debris, or even green due to an increase in algal growth fueled by excessive nutrients.
According to Turner, the study's results provide concrete evidence of what computer models predict, reflecting that water clarity in Wisconsin Lakes could decline as precipitation increases in the future unless measures are taken to improve landscape management, particularly in riparian buffer zones.
The study highlights the need to look ahead so that we can anticipate how changes to the landscape and climate may affect our lakes, Turner explains, which will in turn allow us to implement measures to protect both Wisconsin's lakes and farmers.
"It absolutely provides evidence for the importance of continuing to look for solutions to sustain the economy of Wisconsin without sacrificing the quality of our water," she says.
Kevin C Rose, Steven R. Greb, Matthew Diebel, Monica G. Turner. Annual precipitation regulates spatial and temporal drivers of lake water clarity. Ecological Applications, 2016; DOI: 10.1002/eap.1471