Environmental Impacts and Problems on the St. Lawrence

Metal Pollution Organic Waste Microbial Contaminants Visual or Aesthetic Pollution Organic Chemicals Acidification Thermal Pollution Exotic Species Species Loss Selected Bibliography

The St. Lawrence region is the most populated and developed area in Canada. The area includes 36 million people (8 million Canadians),1,300 industries and many temporary residents, such as ships that travel the river to reach central North America. Many local anthropogenic activities result in severe damage to the St. Lawrence ecosystem (the biological and physical environment). The damage is caused by diffuse pollution sources, such as car exhaust and residential waste, and point sources, e.g, industrial effluents. The main compartments of the river ecosystem are water, biota, air and sediments. Different pollutants tend to accumulate in each compartment. The main types of pollutants are metals, organic waste, microbes, visual or aesthetically displeasing waste, organic chemicals, acidification, thermal waste and exotic species. The affects of these pollutants are cumulative and inter-related. They all result in environmental deterioration, and habitat and species loss.

Metal levels in the St. Lawrence River have increased.

Metals vary in their properties and toxicity.

The fate of metals in the environment is complex.

Organisms uptake metal pollution.

Metal pollutants have many health affects.

Metals are natural components of all ecosystems. They are released from sinks (e.g., rocks) by natural weathering processes and distributed in the environment by ecological cycles. In the St. Lawrence River, human activities, such as agriculture, mining and industry, have significantly increased natural metal levels. These activities make metals more available by removing them from sinks, altering their chemical structure and changing ecosystem conditions.

Metals can be classified in three main groups:

1. light metals, such as sodium, magnesium and calcium, are essential macro/meso- nutrients (nutrients needed in large quantities), relatively non-toxic, and soluble in water;
2. metals, such as cobalt, copper, zinc and iron, are important micro-nutrients (nutrients needed in trace amounts), not very water soluble, and toxic in high concentrations; and
3. heavy metal (e.g., cadmium, lead, silver and mercury) are highly toxic and not water soluble.

The fate of metal pollutants in aquatic environments is complex. It depends mainly on water pH, hardness, temperature, salinity and organic content. pH is the concentration of hydrogen ions (H+) in the water (measure of acidity or alkalinity). The pH scale goes from 0 to 14, 7 is neutral, below 7 is acidic, and above 7 is alkaline. Hardness is the amount of calcium and magnesium ions in the water. It is expressed as calcium carbonate concentrations. In general the following rules hold:

• high temperatures increase the solubility of metals in water;
• metals precipitate in hard water (clump together);
• metals are less soluble in salt water; and
• metals are most soluble in acidic water.

Metals that are not dissolved in the water column collect in river sediments and organic debris.

Organisms (biota) in the river system uptake metal pollutants from water, organic matter and/or sediments via eating or respiration. The uptake of metals by biota also varies with environmental conditions. Benthic organisms and their predators usually accumulate the most metals. Some metals may lead to biomagnification. Biomagnification means that an organism and its predators accumulate a toxin via the food chain, and the concentration of the toxin increases in organisms of higher trophic levels. The table below indicates mercury levels found in several river biota. Recently, mercury levels in many river organisms have dropped significantly, e.g., Saguenay shrimp.

The main metal contaminants in the St. Lawrence River are are iron, nickel, copper, zinc, lead, aluminum, barium, cadmium, molybdenum, vanadium and arsenic. Also, the toxic metals cadmium and lead are often detected in the St. Lawrence River system, particularly near Quebec City. The table below indicates the concentration of various metals in the St. Lawrence water, and the metal levels that are safe for human consumption, recreation, and aquatic life.

The main metal content of St. Lawrence River sediments in each hydrographic region is indicated in the table below. Also, identified in the table is the toxic effect threshold (TET). The TET is the concentration of a metal that is detrimental to bottom organisms.

Metal pollution is dangerous to the health of all life forms (including humans). Many metals cause cancer, tissue damage and inhibit essential biological functions. For example, cadmium and lead are cancer causing agents (carcinogens), and mercury causes neurological damage to organisms. The St. Lawrence Beluga is particularly sensitive to metal poisoning. Contaminated Beluga have a shorter life span and fewer young.

Humans have increased the river's organic load.

Decomposition can deplete river oxygen levels.

Organic material can also cause eutrophication.

Adding phosphorus usually leads to eutrophication.

Ecosystem changes occur due to eutrophication.

Organic waste is dead matter derived from plants and animals. It is a natural component of all ecosystems and a food source for decomposer organisms. Decomposers break down and recycle the nutrients and energy contained in dead materials. Decomposition is essential to renew an ecosystem and ensure a continuos flow of nutrients and energy. The main decomposer organism in the St. Lawrence River are bacteria, fungi and benthic organisms. Many of these organisms use dissolved oxygen to degrade organic matter.

Human activities have significantly increased the organic load of the St. Lawrence River. Agriculture, industry and consumers release various forms of organic matter to the river. Organic pollutants found in the river include human and animal excreta, food, dead plant and animal matter, and debris from forestry operations. The St. Lawrence River is most affected by organic pollution near urban areas and agricultural zones. Decomposers require a large amount of oxygen to degrade this extra organic input. If biological oxygen demand exceeds natural oxygen replenishment rates, low oxygen environments develop. Many aquatic species cannot tolerate low oxygen levels, thus, have disappeared from section of the river. Good quality water contains about 9 parts oxygen per million.

Also, the build up of organic materials can cause noxious odors and alter the nutrient content of the water system. Organic pollution increases the flow of nutrients into the water system, causing eutrophication. Eutrophication is the process by which a body of water becomes nutrient rich and more productive. It is a natural process that occurs over many years, but is significantly accelerated by human activities and the generation of organic waste.

The main nutrients that humans add to ecosystems are phosphorus and nitrogen. Phosphorus concentrations usually limit productivity in water systems. Thus, the addition of phosphorous is mostly responsible for eutrophication. However, nitrogen pollution is the main cause of eutrophication in many salt water areas.

In a eutrophic body of water primary production increases significantly, transparency decreases, biological diversity decreases and species composition changes. For example, White fish are replaced by coarser fish, such as Bass, and the water is filled with algae blooms. Eutrophication makes water less attractive to humans for recreation. Also, eutrophic water may be unsafe to drink. For example, algae blooms may release toxins into the water.

Many microbes inhabit polluted water.

Coliform bacteria are used to determine water quality.

Several microbial populations contaminate the water of the St. Lawrence River. Microbes are microscopic organisms, such as bacteria and viruses. Some microbes are pathogens or agents that cause sickness. High levels of microbial contaminants occur in highly polluted are of the river. Microbes can make water unsafe for human consumption and recreation, and aquatic life. Also, contaminants can destroy economically important seafood crops. For example, mussels that accumulate microbes are unfit for human consumption.

One type of bacteria that contaminate the St. Lawrence River are Coliform (e.g., Escherichia coli). These bacteria naturally inhabit the intestine of mammals (including humans) and are excreted in their feces. They enter the river via raw sewage. Coliform are not pathogens, but are useful indicators of water quality. Water is unsafe for human consumption when coliform counts exceed 100 per 100 ml. When coliform levels exceed 200 per 100 ml, water is unsuitable for human recreational use. Water coliform counts usually parallel increases in pathogenic bacteria and viruses. The table below has data for 1990 to 1993, indicating the frequency that coliform counts for the St. Lawrence water system exceeded 100 and 1000 per 100 ml.

Aesthetic pollution is displeasing to human senses.

Waste that is displeasing to human senses is called visual or aesthetic pollution. In the St. Lawrence River, aesthetic pollution may alter ecosystem appearance or generate odors. It may consist of suspended solids, floating objects, debris, oily matter and/or algae. The main sources of aesthetic pollution along the St. Lawrence River are pulp and paper mills, petroleum and textile industries, raw sewage and farming. Aesthetic pollution can make some recreation activities unappealing and destroy the spawning ground of aquatic species. The areas most affected by this form of pollution are regions near industrial discharge points, urban areas and agricultural zones.

Organic chemicals contain carbon and hydrogen.

Oils contaminate the St. Lawrence River.

Organochorines persist in the environment.

Organophosphates and carbamates also contaminate the river.

Many organic chemical contaminate the St. Lawrence River. Organic chemicals contain carbon and hydrogen atoms. In general, the most toxic organic chemicals also contain chlorine. Organic chemicals are released to the St. Lawrence River by agriculture, industry and municipalities. The main types of organic chemicals found in the river are oils, organophosphates, carbamates and organochlorines. These chemicals are released at various sources along the river and are exported downstream.

Oils are chemicals, such as benzene and polyaromatic hydrocarbons (commonly called PAHs). These chemicals are not water soluble. They collect in organic matter and sediments. Organisms collect these chemicals via the food chain, and on the surface of their skin. Fish may accumulate oil via their gills. Oil can permanently damage gills, making fish susceptible to other environmental stresses and illness. Oils are carcinogenic and cause many health problems in all life forms. For example, small PAHs can cause respiratory or skin problems.

Organochlorines (also called chlorinated hydrocarbons) in the St. Lawrence River include, chlordane, mirex, DDT and PCBs. Organochlorines are highly toxic. They accumulate in river sediments and organic matter. The chemical is uptaken by organism via their food and accumulated in fatty tissues. These chemicals are extremely persistent in the environment, i.e., they remain in the ecosystem for a long term. Organochlorines biomagnify in organisms. The use of many organochlorines is banned, but chemicals, such as DDT, are still found in the river's sediments. Organochlorine contaminants found in several sea mammals are indicated in the table below. The St. Lawrence Beluga accumulates large amounts of organochlorines. Beluga transfer contaminants to their young, and contaminant levels increase throughout their life. Many Beluga die due to tumors and lesions caused by organochlorine contamination. They accumulate many organochlorines from eels.

Organophosphates and carbamates include chemicals, such as diazinon. Many organophosphates are used as pesticides by farmers. These chemicals damage the nervous system and many are carcinogenic. Their slightly water soluble and can be de-toxified by many animals. These chemicals are not very persistent in the environment.

Acidification is the addition of acidic ions to an ecosystem.

Acidification is not a major problem in the St. Lawrence.

The pH of the water and land in the St. Lawrence is determined by the area's geology, ionic content, human activities and natural processes. Ions are atoms that have a positive or negative charge. Acidity (low pH) is caused by ions, such as nitrogen, sulfur and hydrogen. Alkalinity (high pH) is caused by ions, such as sodium, potassium, magnesium and calcium. Acidification is the addition of acidic ions to an ecosystem. Natural processes including precipitation, nutrient cycling and vegetation successional growth gradually lead to acidification. However, natural acidification rates in the St. Lawrence are now accelerated by human activities. For example, automobiles, industry and agriculture add sulfur and nitrogen to the environment. These acidic ions then move between water and land via natural processes.

The natural pH of fresh water is 7, and sea water is 8. In general, the pH of the St, Lawrence River is not yet affected by acidification. However, the area receives large amounts of acid rain, and parts of the river system risk alteration due to acidification. Acidification may be particularly problematic in drained swamp land. Acidification alters the species composition and diversity of an ecosystem.

Thermal pollution is heating water. It changes ecosystem structure.

Thermal pollution is the release of heat to bodies of water. The main sources of thermal pollution in the St. Lawrence area are power plants and water discharged from industrial cooling systems. Thermal pollution can significantly increase the temperature of water, particularly near its source. The warming increases the solubility of many chemical pollutants and decreases water oxygen levels. Also, it may cause ecosystem change. In the St. Lawrence river artificial heating generally lead to increased primary production (e.g., algae growth) and biomass (organic matter), and changes in species composition. Different species tend to have different optimum temperatures. Species diversity is usually greatest around 16 to 19 degrees Celsius. Blue green algae is commonly the dominant species in thermally polluted area.

Exotic species are found in the St. Lawrence River.

Zebra mussels cause environmental and economic damage.

Exotic fish also inhabit the river.

Exotic species are organisms that inhabit a foreign environment. Many exotic species are imported to an environment purposely or accidentally by humans. These species often have few competitors and predators in their new environment. Thus, if appropriate food and habitat are available, their populations may grow exponentially. They can take over the niche of native species, altering the ecosystem significantly. In the long term this may lead to widespread extinction or loss of native organisms, and significant environmental and economic concern.

Many exotic tubificids, molluscs, fish and plants inhabit the fluvial section and estuary of the St. Lawrence River. These species mostly originated in Europe. The Zebra mussels are most problematic exotic species that inhabit the river. Zebra mussels are small bivalve molluscs that originated in the Black and Caspian Sea. They reproduce quickly, tolerate desiccation and extreme temperatures, grow on hard substrate, live in dense colonies, taste poor and accumulate large amounts of toxins. Zebra mussels inhabit freshwaters, particularly near Montreal and Quebec city. They have caused several problems in the St. Lawrence water system. Exotic species may also carry diseases or parasites.

1. Mussels eat large amounts of phytoplankton, which can alter the food supply for other species. Reduced phytoplankton availability is connected to declining fish populations.
2. Toxin concentrations in Zebra mussels can be180 000 times greater than environmental levels. These toxins can be transmitted to predatory ducks, and humans who eat ducks.
3. Mussel colonies can block water flow.
4. mussel colonies that grow on boats and beaches are a nuisance.

Scientists estimate that during the next decade mussels will cause about 4.5 billion dollars of damage in Canada and the United States. The greatest damage will be due to fishery loss. Zebra mussels are now controlled using chlorine, but chemical control also impacts the environment. Other control methods, such as biological control, are not well developed. Biological control is the use of natural predators to limit mussel population levels. The extent of zebra mussel populations is estimated by determining mussel densities on sample navigation buoys. The mean density of zebra mussels on navigation buoys in 1991 is indicated on the map.

The exotic fish found in the St. Lawrence water system include Salmonoids (e.g., Rainbow trout) and European carp. Many exotic fish have been stocked by humans for sport fishing. Some of these fish establish large populations in the river and compete with native species. For example, Rainbow trout competes with Atlantic salmon, resulting in reduced Salmon populations.

Many St. Lawrence biota risk extinction.

Several fish populations are declining.

For several reasons eel populations are reduced.

Sea mammals are also declining. Few Beluga remain in the river.

Bird populations along the river have also changed.

Human development has induced many changes in the St. Lawrence environment. These changes have severely impacted the river's biota. St. Lawrence biota now risk extinction due to pollution and habitat loss.

Many St. Lawrence fish populations have diminished significantly due to environmental toxins, competition with exotic species, disease, over harvesting and habitat loss. Fish habitat is destroyed by human activities that involve dredging, draining, dumping and altering the river's flow. Many fish spawning and feeding grounds have been lost, particularly during to the construction of the St. Lawrence Seaway (1954 to 1959). For example, an abundance of American shad once migrated from the Atlantic Ocean to spawn in the Ottawa River. The Seaway interrupted the migration route of the Shad, nearly eliminating its population. Several fish populations in the St. Lawrence are over harvested, e.g., Lake sturgeon. Striped bass was fished commercially in the 1960s, and now is almost non-existent in the river.

Recently, the American eel population in the St. Lawrence River has decreased substantially. In 1983 about 1,293,570 eels migrated upstream to lake Ontario, compared to 11,533 in 1992. This population decline is attributed to several factors.

• The population may have been over harvested by commercial fisheries.
• Eel habitat has been altered significantly. The eels may not be tolerant of the new chemical and temperature conditions in the river.
• Eels accumulate high concentrations of mirex, an organochlorine, that may reduce their life span and ability to breed.

Eels have complex life cycles and have been exposed to many environmental changes. For these reasons, it is difficult for scientist to know the precisely why their population is declining.

Sea mammal populations are also declining. Pre-European colonization many sea mammals were observed and hunted in the river. Today sea mammals are rare and hunting, except restricted seal hunting, is usually prohibited. Many fishers hold seals responsible for reduced fish stocks and hunt them to minimize their impact on St. Lawrence fisheries. Seals eat large amounts of fish. Also, some seals carry parasites that can attack fish and reduce their market value. However, many seal populations are also endangered.

Fish nets are a main cause of death for many St. Lawrence sea mammals, except the Beluga. The mammals get tangled in the nets and can't escape. Annually in the Lower Estuary and Gulf, about 100 Harbour porpoises are caught in nets and killed.

The St. Lawrence Beluga population is severely reduced. It is extremely sensitive to sickness resulting from environmental contamination. The Beluga is at the top of the food chain and tends to accumulate pollutants from its food (e.g., eel). When the population of an organism, such as the Beluga, is very small, the species risks extinction. The following are some reasons why small populations may be lost.

• Small populations have a limited gene pool. A gene pool is the total array of genes found in a population. These populations have less ability to cope with environmental change, risk inbreeding and may have high genetic mutation rates.
• Individuals in a small population may not be of breeding age, the appropriate sex to breed and/or may be unable to find mates. Thus, birth rates in a small population may fall. However, some species will have more young to compensate for a small population size or more eggs will survive. This is not the case for the Beluga.

Many St. Lawrence bird populations also have changed significantly due to human impacts. For example, Black ducks decreased from 1955 to 1988 due to urbanization. However, Mallards, a genetically similar species, have expanded their range along the St. Lawrence River. The Piping plover, which breeds on sandy shores, has been severely affected by human development, only a few individuals remain. The loss of riparian habitat (e.g., wetlands) is particularly difficult for bird populations.

• Harle, J.; Holdren, C.; Schneider, R.; and Shirley, C. 1991. Toxics a to z: a guide to everyday pollution hazards. University of California Press: Los Angeles.
• St. Lawrence Center. 1996. State of the environment report on the St. Lawrence River. Volume 1: the St. Lawrence ecosystem. Environment Canada -- Quebec region, Environmental Conservation, and editions MultiMondes, Montreal. " St. Lawrence UPDATE" series.
• St. Lawrence Center. 1993. St. Lawrence update: the river at a glance. Environment Canada: Quebec.

Related Web Sites

Canadian Environmental Links Environment Canada, Water Pollution Pathogens Nutrients Biochemical Oxygen Demand Exotic Species Great Lakes Environmental Information Network Natural Resources Canada Environnement et Faune Quebec Ontario Ministry of Environment and Energy Great Lakes Commission The Zebra Mussel Page St, Lawrence Belugas