Monitoring Effects of Sedimentation in Wetlands

Under natural conditions, coastal wetlands intercept and trap sediments as water slows and moves through dense plant growth. But what happens when this sediment is excessive due to urban runoff or erosion from agricultural practices?

Researchers at Eastern Michigan University (EMU) and the University of Toledo suspect that accelerated rates of sedimentation inhibit the microbial activity associated with plant decay, which is vital to a healthy wetland. When plants such as cattails, bulrushes and sedges die and fall into the water, they eventually become colonized by algae, bacteria and other organic matter.

“This dead plant material is acted on by microscopic organisms, and together they form the basis of wetland food chains,” explains ecologist Dr. Robert Neely of EMU. In a project funded by Michigan Sea Grant, Neely and researcher Dr. Robert Sinsabaugh are measuring the effect of sedimentation on the rate of decomposition.

The experimental design includes a total of 30 enclosures at two locations—Winous Point in Maumee Bay, Ohio and Lake Erie Marsh in Gibralter, Michigan at the mouth of the Huron River. Project assistants have placed litter bags (mesh bags with carefully weighed aquatic plants) inside the enclosures. Over the past two years, each of the enclosures received one of three sediment treatments; some received no sediment at all, while others received a silt mixture or a clay mixture.

Researchers have periodically collected the litter bags to analyze the results. The complex part of the project, says Neely, is in the analysis, which measures growth rate and composition of various microscopic organisms such as fungi, bacteria and algae.

Although the data is plentiful, says Neely, the main question about sedimentation has yet to be answered. The drought this past summer has altered the wetland habitat, so that plant material could not be suspended in water and exposed to sediment as planned.

Still, the experiment has revealed other important information. “What’s really interesting,” says Neely, “is that the two sites are profoundly different.” For instance, enzyme activity and fungal biomass were much higher at the Lake Erie site. This site is drier than Winous Point, and Neely suspects sedimentation may not be as important for similar wetland types. “Our results thus far suggest that wetland attributes will vary tremendously with the characteristics of the site.”

For more information on preliminary results of the study, visit the EMU water resources website at www.emich.edu/wrc