SEVERN SOUND WATER QUALITY
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Severn Sound has experienced
excessive phosphorus enrichment since the 1960s. This resulted in
excessive algae growth, leading to poor water quality conditions for
recreational uses such as swimming, and low oxygen conditions for cold
water fish communities.
In 1985, Severn Sound was listed as an Area of Concern (AOC), one of the most polluted on the Great Lakes.
Led by Environment Canada and the Ministry
of the Environment, the communities surrounding
Severn Sound developed a Remedial Action Plan (RAP), the goals of which were to improve water quality and restore a
healthy ecosystem in Severn Sound. Over
the past 20 years, implementation of the RAP resulted in reduced
phosphorus loads through sewage
treatment plant upgrades, agricultural projects, private sewage system
upgrades, and stormwater treatment. This in turn led to significant
improvement in the water quality of
the Sound. In 2003, restoration targets had been met, and Severn Sound
was delisted as an AOC. The RAP continued as the Severn Sound
Environmental Association (SSEA),
which monitors 11 stations throughout the Sound in an effort to detect
long-term changes in water quality. SSEA continues to monitor water
quality and work with municipal
partners to ensue that the quality of Severn Sound is maintained.
These are essential for growth and reproduction of living organisms. Two key nutrients are phosphorus and nitrogen. Although naturally found in the environment, excessive amounts create imbalances in plant and animal communities and can adversely affect our recreational water use. Phosphorus is the most limiting nutrient for algal growth, so increases will lead to increased densities. Phosphorus concentrations have decreased below the target of 15 µg/L for Severn Sound and 20 µg/L for Penetang Harbour, set in the Remedial Action Plan. Reduced phosphorus loads from upgrades to sewage treatment plants, agricultural stewardship projects, private system upgrades and stormwater treatment have played an important role in reducing nuisance algae growths and restoring the water quality of Severn Sound. Nitrogen is also an important nutrient for algal growth. Sources can be both natural (air and soil) and anthropogenic (fertilizers, animal and human waste). Nitrate, the form of nitrogen most available to algae, has been increasing since 1970. However, since phosphorus concentrations have declined, and it is the limiting nutrient, increased levels of nitrate are unlikely to lead to increased algal biomass.
Water clarity Measured using a Secchi disk, this is a measure of the amount of particles (sediment and algae) and colour in the water column. Over the last decade, clarity has increased at all stations and target levels of 3 m for Severn Sound and 2 m for Penetang Harbour have been achieved. The large increase in clarity around 1994 coincides with the zebra mussel invasion, as well as several major upgrades to sewage treatment plants that discharge to Severn Sound. A slight decrease in recent years may be related to lower water levels in Georgian Bay-Lake Huron.
Chlorophyll This pigment is found in both plants and algae and is related to the amount of algae in the water column. Over the last decade, chlorophyll concentrations have decreased, reaching target levels of 5 µg/L for Severn Sound and 7 µg/L for Penetang Harbour. This has resulted in increased water clarity, and indicates that fewer algal blooms are occurring.
Phytoplankton (Algae) These microscopic plants grow suspended in the water column. Population densities can vary throughout the season depending on light, temperature, and nutrient availability. The right combination of these factors can result in algal blooms, which can affect the taste and odour of drinking water, and cause beach fouling. All stations have shown a decrease in the total biovolume of algae.
Zooplankton These microscopic animals live suspended in the water column. Most feed on algae and other particles found in the water column. They are important food for larval stages of all fish and for adult forage fish. Despite normal annual fluctuations, the number of zooplankton species, or diversity, has increased, which is a healthy sign. Zooplankton help keep algal populations in check through their grazing activities.
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