DNR monitoring aquatic plants in lakes

A DNR study now in its fifth year is focusing attention on the makeup of aquatic plant communities in northern Indiana natural lakes.

Biologists will use the results of the study to track long-term changes in the kinds of plants present, coverage, and their relative density. The results will also be used to monitor how changes in land use, water quality and aquatic weed control programs can affect plant communities on a region-wide basis.

“Aquatic plants are important to lake ecology,” said Jed Pearson, a DNR fisheries biologist. “They tie up nutrients in the water, buffer wave energy, and provide fish habitat. But aquatic plants can also be a nuisance and interfere with boating, swimming and fishing. Where they do, people forget the benefits and simply call them weeds.”

Pearson said maintaining healthy plant communities while trying to balance the interests of lake users is challenging. The study will serve as a benchmark to determine how well aquatic plants are managed.

To date, aquatic plants have been sampled in 48 randomly chosen lakes.

“Aquatic plants are too often managed on the basis of subjective opinions without any real data,” Pearson said. “Now we can look at them objectively.”

Based on results so far, a typical lake supports plants down to 13 feet. How deep they grow depends on sunlight penetration. They grow deeper in clean lakes and shallower in muddy lakes.

On average, seven species of aquatic plant are present. The number of species also depends on water clarity.

The most common species is coontail. It occurs in 88 percent of all lakes and usually covers about half of the area where plants can grow.

The second most common species is Eurasian water milfoil, a non-native plant that is often the target of weed control efforts. It occurs in 79 percent of northern Indiana lakes. Where present, Eurasian water milfoil typically covers a fourth of the plant-growing zone.

“This is just a glimpse of the amount of data we’re now getting from the surveys,” Pearson said. “As a result, we’ve never been in a better position to understand and manage aquatic plants — or weeds — whatever you call them.”