Lake Management – Plants & Heat

Lake Management – Plants & Heat

Aug 11, 2012

Aquatic Plants and Summer Heat

By Mike Pehanich

The phones are ringing off the hook Herman Brothers Pond Management in Peoria, Ill., during this protracted heat wave, and most of the calls are prospects for new business.

But these aren’t owner Nate Herman’s happy times.

“Fish are dying in lakes and ponds all over the state,” said Herman, noting that calls for his company’s services climb during conditions that add up to bad times for fish. “We are getting fish-kill calls like crazy!”

Fish kill reports are coming in across the country during the extended heat wave.

The problem relates to very warm water temperatures and reduced levels of dissolved oxygen in the water.

It’s a compound problem. Fish metabolism speeds up as water temperatures increase. But warmer water carries less dissolved oxygen (DO) than cold water. As a result, the fish have trouble breathing.

Most species of sport fish are at risk when water temperatures climb and the waters they inhabit don’t get adequate oxygen replacement from wind and wave action or the photosynthesis of plants.

So-called “cool water” and “cold water species of fish like northern pike, muskellunge, and trout are at greatest risk. They have lower thermal tolerance and greater oxygen demands than warm water species like largemouth bass. But bass, too, will suffer catastrophic die-offs in waters where oxygen levels are unduly depleted.

Plant life

Many pond and lakefront owners wage an ongoing battle with aquatic vegetation in their home waters, scheduling regular chemical “weed kills” to solve or prevent a problem.

Cool water species like northern pike can be especially vulnerable when thermal stress and oxygen depletion are compounded with chemical herbicide treatment.

For some, it is a legitimate concern as certain types of aquatic plants can make navigation and fishing difficult or displace more favorable plant habitat – or even choke the lake with dying vegetation.

For others, it’s a misguided effort to produce a “swimming pool” lake. In short, they don’t what that danged “sea weed” to get between their toes when they swim!

The irony is that, when they kill off too much favorable aquatic vegetation, the nutrients in the lake go quickly into other forms of plant and animal life that suspend in the water. Generally, this means their lake water gets darker and less favorable as a “swimming hole” – and often as a fishing lake, too — than a lake with a desirable amount of vegetation.

What’s worse, they deprive the lake of its oxygen producers – the plants themselves. Like terrestrial vegetation, aquatic plants generate oxygen, which fish require in increasing amounts as water temperatures climb.

And as the plant life decays, oxygen levels drop further.

The 25 percent solution

As a general rule, Herman targets rooted aquatic vegetation coverage over 25 percent of the acreage of waters he manages. The ideal figure will vary with the specific features of the lake, he notes, but the “25 percent solution” generally will make for a healthy, self-sustaining lake system without additional management and mechanical solutions, such as aeration.

Nate Herman recommends a "25 percent" formula -- keeping one quarter of a lake's acreage covered with healthy and favorable aquatic plant life to provide good habitat and to produce a self-sustaining oxygen supply to fish.

“People don’t understand how important plants are to the ecosystem,” he emphasizes.

Timing chemical treatment

If chemical herbicide treatment becomes necessary, time that treatment so that it has the least deleterious effect on fish and their living conditions.

For Nate Herman, that means no major chemical applications when water temperatures rise above 80 degrees F. “Above 80 degrees, water can’t saturate with oxygen,” he explains. “Oxygen levels are already less than what the fish prefer. Chemical ‘weed kill’ in warm water temperatures stresses the lake too much. Dying plants take up oxygen that the fish need.”

The sudden die-off of plant life forces nutrients in the water to convert into the simplest available life forms, which can darken the water.

Now Herman does recommend regular algae treatment on many waters before it reaches “nuisance levels.” “You do that like you would weed your garden,” he says.

Help your lake sustain a healthy fish population with sound management decisions.

But careful and calculated algae treatment should not be equated with wholesale eradication of a lake’s plant life.

“You can manage a pond without any vegetation by adding amino acids, trace minerals, key bacteria…,” he says. “But that takes constant management. Rooted plants help sustain a lake during stressful times.”



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