Severn sound Open Water
In the past, Severn Sound experienced excessive phosphorus enrichment. 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.
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 14 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 ensure that the quality of Severn Sound is maintained.
Monitoring in the open waters of Severn Sound began in 1973 by the Ontario Ministry of Environment. Five stations were regularly sampled – one in each bay of Severn Sound, and one in the open waters. In 1997, the Severn Sound Environmental Association (formerly the Severn Sound Remedial Action Plan) took over regular monitoring, which continues today. The Severn Sound RAP Stage 3 Report called for continued monitoring of Severn Sound in order to assess changes in trophic status in relation to remedial actions and other ecosystem changes in the area (e.g. invasive species, water level changes).
Factors Affecting Water Quality
Severn Sound is a dynamic system that is influenced on a regional scale by the entire Great Lakes system (e.g. introduction of invasive species like zebra and quagga mussels (Dreissena spp) and spiny water flea (Bythotrephes), climate change, fluctuating water levels), and on a local scale by its surrounding watershed (point and non-point additions of nutrients and other contaminants).
Severn Sound Water Quality and Lower Food Web:
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.
Spring concentrations of nitrate, the form of nitrogen most available to algae, are highly variable but have been increasing in Midland Bay and inner Penetang Harbour since 1970. Following spring melt, concentrations decline rapidly as nitrate is taken up by plants and algae, so spring levels are a better indicator of watershed sources. However, since phosphorus concentrations have declined and it is the limiting nutrient, increased levels of nitrate are unlikely to lead to increased algal biomass of most types of algae. Increased nitrate in some parts of the Great Lakes has been linked to increases in blue green algae blooms. Ammonia concentrations are low in Severn Sound and have fluctuated around a fairly consistent level.