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Green water, chemicals: lake worries and theories
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| By: Anita Zimmerman |
July 29, 2009 |
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Algae growth, fed by the phosphorus-rich lakes, are part of the story–but analyzing the lakes’ entire ecosystem has so far been time- and cost-prohibitive, so other unrecognized factors could be influencing the coloration.
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If you're looking to explain the green water in the Chetek chain, there are theories out there.
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The Cary Institute of Ecosystem Studies in New York hypothesizes that green lake water is attributable to a bounty of small fish. When small fish consume too many of the zooplankton (pronounced "zoh-plankton") that should be eating algae, the water grows green.
There is a solution, the institute's researchers say. Adding big fish reduces the number of small fish, thereby reversing the process and inhibiting the greening of lakes.
'Course, not everyone is buying the theory. Department of Natural Resources wildlife biologist Larry Damman characterizes it as "pretty much hogwash."
Asked why the Chetek chain has turned green so early this year, Damman says the real culprits are a combination of weather and the nature of the lakes.
This summer, there's been very little rain to flush out the lakes, he comments. "Weather is probably the biggest factor-internal cycling, shallow lake and the lack of rain" all affect how quickly algae grows.
Last week, The Alert reported on Xcel Energy's use of herbicides to reduce vegetation near power lines, some of which was sprayed directly into the chain.
For those locals concerned about the negative effects of chemicals in the water, Damman expects few repercussions and no changes in lake coloration.
Fish along that shoreline at the time might be affected, but the chemicals-present only in miniscule amounts-are soon diluted and mixed with organic materials, rendering them nontoxic.
Nor will herbicides bioaccumulate in fish, he adds, nor will they kill monocots (the majority of aquatic plants fall into this category) if designed to eliminate dicots.
"Only a few species would be affected," he says.
Besides, when someone wants to kill aquatic plants, they have to try harder than that, Damman adds. In Cumberland, for example, Beaver Dam Lake is sprayed with chemicals to reduce the growth of Eurasian milfoil.
To target the invasive species, boats spray herbicides over acres of water. It takes many, many gallons of chemicals to kill the weeds, and the water has to be sprayed periodically to control growth.
Green water is the chain's native state, he says. As hypereutrophic lakes, the Chetek chain is naturally rich in nutrients that promote plant growth.
When water is murky, as in this time of year, the algae is in full bloom. When water is clear, aquatic plants are winning the competition for sunlight and food. Locals who see the water greening faster or taking on a new hue might be witnessing the growth of different kinds of algae; blue-green algae is coming into season in August, Damman adds.
Not everyone at the DNR is so quick to dismiss ecosystem-based thinking. Water resources biologist Jim Cahow says studies have shown the top-down influence of the food chain, but the DNR's current focus on preventing and controlling invasive species demands a lot of time and money.
So, what's really clouding the lakes? Indirectly, lack of money and time might be factors. Unlike other geographic regions, Northern Wisconsin is rich with water, and that means each lake and river gets less attention.
Cahow is personally responsible for more than 2,000 lakes, some of which he's never seen. If he spends 200 hours a year on the Chetek chain, it's a disproportionate amount, and other lakes suffer.
Financial resources are also limited, he says, and that prevents the kind of full-scale studies done on bodies of water in other areas.
For example, an imbalance of organisms affects how much algae (and which types) grow; certain zooplankton, like daphnia, consume more algae than others. Studies of the chain haven't been in-depth enough to identify which zooplankton are present in which levels, nor have researchers had time to devote to broader study of the fish population, temperature or other characteristics.
While the chain's hypereutrophic tendencies are longstanding, other factors still influence the annual greening.
Agricultural practices have changed over time, eliminating a lot of the phosphorus runoff, but Cahow agrees historical septic tank bypasses have permanently altered the nutrient content of the chain and are now part of internal loading.
Currently, the DNR is trying to educate lakefront property owners not to mow their lawns all the way to the shore, and that kind of prevention is designed to aid in keeping the whole lake system from "crashing," as Cahow calls the potentially fish-killing danger of dramatic daily pH and oxygen swings.
Barring entrance to exotic species is important because they may not be digestible to zooplankton, so the populations could get out of control and cause the food chain to collapse, he adds.
Before he worries about crystal-clear water, Cahow says he wants to see the lakes' balance restored. When that happens, a clearer, healthier chain should be a byproduct.
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©The Chetek Alert 2009
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