By Laura Martin

Michigan is known as the Great Lakes state, but fertilizers from farms and lawns, discharges from sewage treatment plants and urban pollution mean that Michigan lakes may not always be in great condition.

Human activity increases the amounts of nutrients such as phosphorus in the water. Though phosphorus is a necessary and naturally occurring component of lakes, streams and wetlands, too much of it can cause excess aquatic plant growth and create poor water quality for other aquatic organisms.

Pat Soranno, a Michigan State University (MSU) fisheries and wildlife scientist, and a team of MSU researchers are collaborating with the Michigan Department of Environmental Quality (MDEQ) to develop a phosphorus standard for Michigan lakes.

“Every lake is different,” says Soranno, who is also a member of the MSU Center for Water Sciences scientific advisory board. “What is considered healthy for one body of water is not necessarily healthy for another. That’s why it’s important to develop a standard that takes water chemistry and biology differences into account.”

With 29,000 lakes in Michigan, figuring out how much phosphorus is healthy for each of them is a substantial challenge. By looking at patterns among hundreds of water bodies, Soranno and her team developed an approach that predicts healthy nutrient levels on the basis of lake characteristics and the surrounding land.

To create this database, the group examined several factors in each lake to determine how much phosphorus was present prior to human activity. Landscape data from 500 lakes—including information on soil, geology and water clarity—were collected and studied.

“Different landscapes contribute different amounts of nutrients and also determine what nutrient levels are healthy,” Soranno says.

Her team also looked at aquatic organisms and the effect that various amounts of phosphorus have on them. By comparing the conditions of the aquatic organisms to the landscape data, the group was able to determine a level of phosphorus that was healthy for a particular body of water. They then applied these findings to lakes with similar characteristics to estimate healthy phosphorus levels for them.

“Michigan has amazingly rich water resources,” she says. “If preserving the environment isn’t reason enough to support this research, there are also economic reasons. Healthy water is a valuable asset to tourism, land use, property value and industry. Michigan water quality is good right now, and it’s really important that it stays that way.”

Farmers can keep phosphorus out of lakes

By Wendy Powers
Products of human activities such as lawn fertilization, sewage and other urban pollution sources are no doubt important contributors to nutrients such as phosphorus in lakes and other surface waters. But farming plays a part as well through manure and fertilizer applications. As a phosphorus standard is developed for Michigan lakes and strategies are developed to meet the lake-specific standards, the contribution of agricultural inputs of P into the lakes will be considered. This means greater emphasis on good management practices to reduce soil losses and eliminate direct discharges of nutrients into waterways.

You can manage phosphorus output on your farm by:

• Maintaining vegetative filter strips or vegetative buffers along waterways.
• Restricting livestock access to waterways, including those used as a source of drinking water.
• Conducting routine soil testing to reduce unnecessary fertilization on crops (and keep your fertilizer bill lower, too!).
• Using feed formulations that match nutrient intakes of phosphorus with the nutrient needs of the animals, thereby reducing feed bills and excretion of unnecessary nutrients.

These practices are not one-time events. Maintenance is required for cattle restrictions and vegetative filter strips and buffers. Evaluate feed formulations periodically, and collect soil samples as frequently.

Michigan’s waters are vital to the state’s economy and to the day-to-day operation of your farm. Right now there is tremendous interest, statewide, in ensuring that we have adequate supplies of high quality water. Even if you have already considered how your operation may contribute to phosphorus loadings into Michigan’s waters, it is worth another look to see if plans are current and best management practices are maintained.

These articles are from the July 2008 issue of the Scoop. To read the entire issue, click here.