Controversy over nutrient controls: Lake Erie

Controversy over nutirent controls: Lake Erie Phosphorus levels, and how they relate to zebra mussels, are the focus of some controversy in Lake Erie.

Excessive production of algae in Lake Erie has caused aesthetic problems over the years, and was the reason the lake was declared dead in the 1960s. The algal problem was caused by large amounts of phosphorus entering the lake from sewage and agricultural sources. At the same time, concerns were expressed about the taste and odour of Lake Erie water.

In response to those concerns, phosphorus loads to the lake were reduced by 50 per cent under the Canada/United States Great Lakes Water Quality Agreement. Long-term data (see chart) show that phosphorus in the central and east basins of Lake Erie is not stable; in fact, there was a decrease in concentrations from 1992 to 1995, and an increase in 1996 and 1997. Phosphorus in the west basin is near target.

Environment Canada research indicates that increasing phosphorus could increase the presence of zebra mussels, an alien species first discovered in North America in 1988, and a major concern in the Great Lakes. By 1990, zebra mussels were in each of the Great Lakes and had moved into many Ontario lakes. The mollusks can remove a large portion of the plankton and dissolved nutrients within water. While this makes the water clearer, it also alters the food chain. Zebra mussels also colonize water supply pipes of industrial facilities, reducing water intake by constricting flow. Navigational and recreational boating can be affected by increased drag from attached mussels.

The impact of zebra mussels is most pronounced in the lower Great Lakes, particularly in western Lake Erie, where the combination of relatively warm, shallow water and eutrophic conditions provide a suitable environment for population growth. Initially zebra mussels colonized hard substrates and artificially constructed coastal structures. More recently, mussels were observed in deeper waters on soft muddy sediments. The expansion of the mollusks into habitats that were once regarded as inhospitable is cause for additional concern, since it opens up the largest surface areas of the lakes for colonization. Scientists from Environment Canada's National Water Research Institute and the University of Guelph have determined that regular patterns of zebra mussel colonization exist.

Variability of phosphorus levels in Lake Erie central basin during summer

The decrease in phosphorus and the consumption of algae by zebra mussels have made the water clearer in the west basin of Lake Erie.

Some Lake Erie fishing interests have recently suggested that phosphorus controls have decreased lake algal production excessively, causing a reduction in desirable fish species. They advocate that nutrient loads to the lake be increased. At the same time, shoreline property owners are finding algae accumulations on their beaches. Increasing the phosphorus load would worsen this situation.

Approximately half of the Lake Erie shoreline is privately owned and/or used for recreation, and 13 million people live around the lake, so that any action taken to increase lake productivity will affect the various users in different ways. To restore the former algal production would require a massive "re-pollution" of the lake with phosphorus.

Scientists involved with the bi-national Lakewide Management Plan effort are considering the advisability of an "add phosphorus scenario". Environment Canada is not recommending any change in policy at this time, as increasing phosphorus would likely result in more zebra mussels, but not fish. It would be difficult to increase phosphorus levels in the central and east basins of Lake Erie without massive enrichment of the west basin. Meanwhile, Environment Canada scientists are continuing research on the role played by phosphorus and zebra mussels in algal productivity, and the link between phosphorus and fish production in Lake Erie.

  Home |  Air |  Atmospheric Science |  Climate Change |  Environmemental Action |  Habitat |  Pollution |  Species at Risk |  Technology |  Water |  Weather |  Wildlife