Traverse City Record-Eagle

Archive: Friday

March 19, 2010

Editorial: Watch plant growth in bays

Macrophyte beds in Grand Traverse Bay aren't necessarily a bad thing. Chara algae and milfoil plants are native to Michigan waters. They make great homes and food for fish.

Their presence in the bay takes on new meaning, though, when two things happen:

-- The number of algae beds jumps.

-- Phosphorous is hardly detectable in water tests but is found in sediment under the beds.

A 2009 study of macrophyte beds and sediment samples in the bay suggests, but does not yet prove, that both things may be happening now in the bay. That is not good news in the era of invasive mussels and bird die-offs.

The Watershed Center Grand Traverse Bay showed that the number of chara and milfoil beds leaped from 120 in 1998 to 400 last year -- most in areas near shoreline communities. A 1991 study, conducted when zebra mussels first were discovered in the bay, discovered only 60 sites.

The astounding increase can be attributed in part to aerial photography, used for the first time last year.

Zebra mussels probably also play a role, according to sediment samples taken in non-algae areas and in macrophyte sites. The mussels eat plankton and macrophytes. That clarifies the water and allows more sunlight to encourage plant and algae growth. The mussels also secrete phosphorous in their waste stream, in effect fertilizing the beds.

Study results plus reports of a few dead ducks and loons along bay shores last summer and in 2007 raise aesthetic concerns. Too many aquatic plants interfere with recreation and smell like raw sewage when they wash up on shore and rot.

Even so, algae mats are not harmful to birds or humans unless E. coli bacteria from decaying fish caught up in the tangles is present and eaten by diving and water birds -- as was the case in avian die-offs along Sleeping Bear Dunes. The algae there was cladorphora, which has not been found in the bay.

Phosphorous in the bay comes from three main sources: Wastewater, fertilizers in storm water runoff and the waste stream of zebra or quagga mussels.

Watershed Center staffers say Traverse City, Suttons Bay, Northport and Peshawbestown have done a good job of reducing phosphorous flow in the bay by upgrading wastewater and storm water systems in recent years. The focus now is aimed at lawn fertilizer run-off.

At this point, two things are clear:

Algae and aquatic plant growth in Grand Traverse Bay needs continued, careful monitoring and study.

More public education is a "must" to help homeowners and shoreline community leaders understand the link between phosphorous fertilizers and algae growth -- even when people live blocks away from the bay. Homeowners should buy phosphorus-free fertilizers.

The 2009 Watershed Center study is a benchmark. Its findings call for continued monitoring, testing and public support.

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