by Erin McDonnell
What are zebra mussels?
Zebra mussels (Dreissena polymorpha) are small mollusks which have invaded the freshwaters of North America. While these creatures are no bigger than the end of your thumb, they have turned into a big problem. They probably hitched a ride on a ship from Eastern Europe through the St. Lawrence Seaway to Lake Erie, where they found plenty of nutrients in the North American waters and decided they liked the New World. Unfortunately, there were no predators or other means of naturally limiting their growth, and they spread through the tributaries of the Great Lakes and grew prolifically in places where they were not welcome. They clogged water intake pipes for power and water treatment plants. Divers were needed to scrape them off surfaces, and then the mussels were dumped on land to be hauled to landfills. But the wet creatures, which are mostly shell, were heavy and expensive to transport and dispose of, so some folks started looking for a more beneficial way to use them; enter composting.
Why compost them?
Shells have been used to lime, or raise the pH, of soils for years, so it wasn't so far fetched to think that a useful compost could be made from Zebra Mussels. In fact, Ontario Hydro of Toronto and the Monroe Power Plant in Michigan collected zebra mussels for composting for several years. Ontario Hydro layered the zebra mussels to form windrows with debris also removed in cleaning out its pipes, periodically turned the windrows, and eventually used the compost to cover a landfill on the property. At Detroit Edison's Monroe Power Plant, the zebra mussels and debris were mixed together, piled into windrows, and eventually spread onto grounds where coal used to be piled to encourage grass growth and discourage an overwhelming population of nesting seagulls.
Cornell researchers wanted to see if they could make a recipe for folks who might want to compost anywhere from 100 to 1000 pounds of zebra mussels. Since a zebra mussel is mostly shell and hardly any organic matter, you probably need to mix mussels with some other organic material to provide the right nutrients for compost microorganisms. After a number of small tests, the researchers found that a co-composting mixture of 1:14:17:18 parts by weight of peat, sawdust, poultry litter and water could be made and then mixed 1:1 with zebra mussels for composting. An equal volume of wood chips for bulking was then added. Two compost piles were built, each containing one cubic yard of zebra mussels supplied by Rochester Gas and Electric on a bed of wood chips and perforated PVC drainage pipes. In monitoring the compost, it was observed that the shells probably help maintain good pore structure for air flow.
After three months of composting and maturing, the wood chips were screened out, the compost was mixed with various ratios of topsoil, and tomatoes and radishes were grown in the mixtures. All seedlings did as well or better than the topsoil alone.
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Cornell Waste Management Institute ©1996
Department of Crop and Soil Sciences
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