Keeping out the Zebra Mussel

ENVIRONMENT

Purple Loosestrife has taken over our meadows and wetlands across Canada; the Round Goby is proliferating in Lake Superior and Michigan; the Spiny Cladoceran has invaded Lakes Ontario; and all around the Great Lakes and as far south as the Mississippi River, the Zebra Mussel is infesting our waters.

The problem of aggressive plants, fish and other aquatic life being transported across the world and becoming nuisances where they settle is becoming worse as the years go by. Experts gathered in Toronto in February to look at the problem, and heard that in the Great Lakes alone we have seen one major invader every three years for the last 15 years.

The 10th International Aquatic Nuisance Species and Zebra Mussels Conference was a week-long event held by Canada’s Department of Fisheries and Oceans. Keynote speaker Herb Dhaliwal, the Minister of the department, told the attendees from Canada, the U.S. and elsewhere that the threat of invasive species to biodiversity is now second only to environmental degradation.

Exotic water species arrive in various vehicles, most often in the ballast of ships or by pet owners discarding their aquarium contents. Once here, the exotic visitors drive out indigenous species. The situation not only threatens the natural habitat and ecological balance, but also costs us money — $138 billion annually in North America according to some estimates.

Dhaliwal and the other opening speakers concentrated on how to prevent further invasions by education and prevention programs, but for consulting engineers the issue is how to deal with exotic species once they’re here. The biggest nuisance is the zebra mussel or Dreissena polymorpha, which was first discovered in Lake St. Clair around 1985. The question is how to keep these crusty little blighters out of industrial and power plant water intake plants and municipal water treatment works.

In Ontario the main treatment is still chlorine. Yet this chemical treatment is just a stop-gap, introduced as an emergency measure in 1989. It is opposed by environmental and health groups.

As alternative remedies, Ontario Power Generation is testing ozone at the Darlington and Bruce nuclear power plants, and, with help from Wardrop Engineering, is trying ultra-violet radiation at Bruce. A Canadian firm, Sparktek of Stoney Creek promotes a “pulsed power” technology where energy is focused on a pipeline to remove the mollusks. Other remedies presented at the Toronto conference are low frequency electromagnetic radiation, heat (to temperatures of about 37C) and filter assemblies. The latter have to filter out the mussel larvae since the species often invade systems at the veliger stage. They only begin to clog the pipes as they grow larger.

Biological approaches include biofilms and bacteria, although using nature to control nature has a habit of backfiring. On this front, some argue zebra mussels might not be such a bad thing. Researchers in the U.S. and Puerto Rico suggest that the mollusks have such an enormous filtering capacity they might be used to clean up another water organism that has become a nuisance, Cryptosporidium.