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Scientists think drought helped control algae

Link between algae and agriculture appears to grow more certain

Staff writer

Scientists who expressed puzzlement at the sudden lack of blue-green algae warnings for Marion County still aren’t certain of the cause, but it appears to them that what’s hurting farmers is helping lakes.

Even as new algae warnings and watches for 17 other lakes in Kansas were going out last week, experts from the Kansas Department of Health and Environment seemed to conclude that Marion County lakes have been spared because of a lack of runoff from farm fields.

The reverse, of course, might also be true: that a decade and a half of algae problems at the lakes were attributable mainly to agricultural practices.

According to Deputy Secretary Theresa Freed, the consensus of KDHE scientists is that lakes did not receive their normal big spring runoffs, providing nutrients algae need.

Drought conditions, which continue to rate as extreme for all but the southeast corner of the county, seem to be preventing or delaying algae blooms, she said.

Still, she said, high lake temperatures and stagnate water can at any time create conditions favorable for a bloom, especially if significant rainfall brings nutrients into the lakes. 

“Lakes are very dynamic, and water quality can vary considerably from year to year, particularly when impacted by either drought or wet weather,” she said.

For it’s part, the state has not implemented any new measures to control blue-green algae, but state officials suspect that a series of land management projects undertaken through the Marion Reservoir WRAPS program may have reduced nutrient runoff.

“At this point in the season I think there are still two scenarios that could contribute to a bloom,” Freed said. “The warmer weather will obviously warm the lake, but more so with the lake levels down. This could lead to a slower buildup of algae and possibly lead to a bloom – particularly in coves with more stagnant water. A large rainfall event also could introduce significant nutrient loading and fuel a bloom fairly quickly.”

Corps of Engineers records for rainfall in the watershed that feeds Marion Reservoir bear out the notion that lack of runoff may be the reason for no algae blooms this year.

From May through July last year, the watershed had three days with rainfall of greater than an inch, the largest being 1.72 inches, and 22 days with rainfall of at least a tenth of an inch.

This year, in contrast, it has had just two days with rainfall of greater than an inch, the largest being 1.32 inches, and just 13 days with rainfall of at least a tenth of an inch.

Timing of the rainfall may also be important. Last year, rainfalls of greater than an inch occurred May 20, June 16 and June 30. This year, they occurred much later, on June 25 and July 17, by which time most tilling and adding of nutrients to farm fields had ended.

The first blue-green algae warning last year was issued on the basis of weekly testing done nine days after the 1.72-inch rainfall.

Last modified Aug. 2, 2018

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