Lake Ontario - Ecology and Environmental Concerns

Ecology and Environmental Concerns

The Great Lakes watershed is a region of high biodiversity, and Lake Ontario is important for its diversity of birds, fish, reptiles amphibians and plants. Many of these special species are associated with shorelines, particularly sand dunes, lagoons, and wetlands. The importance of wetlands to the lake has been appreciated, and many of the larger wetlands have protected status. However, these wetlands are changing in part because the natural water level fluctuations have been reduced. Many wetland plants are dependent upon low water levels to reproduce. When water levels are stabilized, the area and diversity of the marsh is reduced. This is particularly true of meadow marsh (also known as wet meadow wetlands); for example, in Eel Bay near Alexandria Bay, regulation of lake levels has resulted in large losses of wet meadow. Often this is accompanied by invasion by cattails, which displace many of the native plant species and reduce plant diversity. Eutrophication may accelerate this process by providing nitrogen and phosphorus for the more rapid growth of competitively dominant plants. Similar effects are occurring on the north shore, in wetlands such as Presqu'ile, which have interdunal wetlands called pannes, with high plant diversity and many unusual plant species.

Most of the forests around the lake are deciduous forests dominated by trees including maple, oak, beech, ash and basswood. These are classified as part of the Mixedwood Plains Ecozone by Environment Canada, or as the Eastern Great Lakes and Hudson Lowlands by the United States Environmental Protection Agency, or as the Great Lakes Ecoregion by The Nature Conservancy. Deforestation in the vicinity of the lake has had many negative impacts, including loss of forest birds, extinction of native salmon, and increased amounts of sediment flowing into the lake. In some areas more than 90 percent of the forest cover has been removed and replaced by agriculture. Certain tree species, such as hemlock, have also been particularly depleted by past logging activity. Guidelines for restoration stress the importance of maintaining and restoring forest cover, particularly along streams and wetlands.

The open water is less-affected by shoreline features, such as wetlands, and more affected by nutrient levels that control the production of algae. Algae are the basis of the open water food web, and the source of primary production that ends up as Lake Trout and Walleye at the top of the open water food web.

Like the other Great Lakes, Lake Ontario used to have an important commercial fishery. It has been largely destroyed, mostly by over-fishing. Consider the Lake Sturgeon as but one example. Lake sturgeon are huge fish—they can grow up to three meters long and exceed 190 kg in weight. The females maturely slowly and require decades to reach sexual maturity. It was once an abundant species in Lake Ontario. "In 1860, this species, taken on incidental catches of other fishes, was killed and dumped back in the lake, piled up on shore to dry and be burned, fed to pigs, or dug into the earth as fertilizer." It was even stacked like cordwood and used to fuel steamboats. Once its value was realized, "They were taken by every available means from spearing and jigging to set lines of baited or unbaited hooks laid on the bottom to trapnets, poundnets and gillnets." Over 5 million pounds were taken from adjoining Lake Erie in a single year. The fishery collapsed, largely by 1900. They have never recovered. Like most sturgeons, the lake sturgeon is rare now, and is protected in many areas. Populations in the Oswego River are being actively managed for recovery.

This food web has been damaged not only by over-fishing, and changes in nutrient levels, but also by other types of polluted from industrial chemicals, agricultural fertilizers, untreated sewage, phosphates, such as from laundry detergents, and chemicals. Some pollutant chemicals that have been found in the lake include DDT, benzopyrene and other pesticides; PCBs, aramite, chromium, lead, mirex, mercury, and carbon tetrachloride. The International Joint Commission has identified areas where pollution is particularly intense (point sources) and mapped them as Areas of Concern. A Remedial Action Plan has been developed for each area. Some Lake Ontario areas of concern include the Oswego River and Rochester Embayment on the American side, and Hamilton Harbour and Toronto on the Canadian Side.

By the 1960s and 1970s, the increased pollution caused frequent algal blooms to occur in the summer. These blooms killed large numbers of fish, and left decomposing piles of filamentous algae and dead fish along the shores. At times the blooms became so thick that waves could not break. Fish eating birds such as osprey, bald eagle and cormorant were being poisoned by contaminated fish. Since the 1960s and 1970s, environmental concerns have forced a cleanup of industrial and municipal wastes. Cleanup has been accomplished through better treatment plants, tighter environmental regulations, deindustrialization and increased public awareness. Today, Lake Ontario has recovered some of its pristine quality but regional airshed pollution remains a concern. For example, walleye, a fish species considered as a marker of clean water, are now found. The lake has also become an important sport fishery, although with introduced species (Coho and Chinook salmon) rather than the native species. Bald eagle and osprey populations are also beginning to recover.

Invasive species are a problem for Lake Ontario, particularly lamprey and zebra mussels. Lamprey are being controlled by poisoning in the juvenile stage in the streams where they breed. Zebra mussels in particular are difficult to control, and pose major challenges for the lake and its waterways.

Thermal pollution from the Pickering Nuclear Generating Station and Darlington Nuclear Generating Station just east of Toronto has become a concern in recent years, with the warm wastewater released from the plant being a problem year-round. Radioactive and heavy metal contamination from these nuclear plants, as well as nuclear-industry fuel manufacturing in Port Hope, Ontario, is also an ongoing concern.