Great Lakes found to ‘exhale’ pollutants as governmental report paints a largely negative picture of their environment

A Canadian and US governmental research body has discovered that the world’s biggest fresh water system is cleansing itself of pollutants as the surrounding air becomes less loaded with contaminants, while the annual report on the Great Lakes by both governments reveals that great environmental threats remain.

The bi-governmental Integrated Atmospheric Deposition Network (IADN) found that between 1992 and 1996 Lake Ontario, the smallest of the five Great Lakes, released almost two tonnes of polychlorinated biphenyls, or PCBs, into the air, as well as “significant amounts” of dieldrin, a widely banned insecticide. Data showed that during the same period the level of PCBs in the lake decreased by about 10 tonnes while dieldrin levels decreased by four tonnes. Dr. Keith Puckett, the Canadian environment ministry’s manager of the IADN said that since atmospheric levels of pollutants began dropping following increased regulation, the lakes began expelling contaminants at twice the rate they took them in.

“As air pollutants over the air drop, this then allows the lakes the opportunity to cleanse themselves, and they do this through a process of volatilisation or out-gassing of these compounds into the air,” Puckett said, comparing the process to giant lungs breathing out the pollutants that have been inhaled for the past 50 years, now that atmospheric levels have dropped to enable them to do so. The IADN tracks levels of 20 pollutants from stations around the lakes and is trying to determine what percentage come from local sources and the amount coming from far afield. Puckett estimates that only 30 to 40% of dioxins in the lakes come from local pollution, and says that toxaphene, a pesticide banned in the area, is carried to the lakes from the southern US. “There is still material going into the lakes, but there is more coming out,” Puckett said. “In order to stop the material going in we have to ensure that material still being used in Canada and elsewhere is sort of limited and international agreements are put in place. With that, pollution levels will go down faster.”

The researchers now plan to extend their research to discover sources of pollution in the Arctic and how waters are coping with a high level of imported contaminants.

There is little positive news, however, in the State of the Great Lakes 2001 report, compiled by the US Environmental Protection Agency and Environment Canada. One area of excellence is that the surface waters of the five lakes remain “amongst the best sources of drinking water in the world”, and continue to serve a large part of the 33 million people who live in the Great Lakes basin. However, despite contaminant levels continually decreasing in most species of fish, advisories related to humans eating fish from all of the lakes remain in place. Contaminant levels will need to continue to decline for “many more years” before advisories can be lifted, or, in some areas, even modified.

Invasive, non-native aquatic species are the greatest biological threat to the lakes aquatic ecosystems, other factors replacing contaminants to stress fish populations. Weakening of the forage base, food chain disruptions, habitat loss and competition with invasive species are the major threats. Sea lamprey controls since the 1960s have allowed the rehabilitation of the Great Lakes fishery, however populations of the species in Northern Lake Huron and the St. Mary’s River continue to pose a problem, the report says.

There is bad news for the coastal wetlands, as the report shows that four of five indicators for assessing their quality have shown a continual decline in both quality and quantity. Over two-thirds of the Great Lakes wetlands have already been lost and many of those remaining are threatened by pressures such as development, drainage and pollution.

Urban sprawl is the greatest physical threat to high quality natural areas, rare species, farmland and open space in the Great Lakes basin, the report concludes. It also advocates special protection for “extraordinary biologically diverse” natural areas such as the coastline of northern Lakes Michigan and Huron, Georgian Bay, and the St. Mary’s River.

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