The Hamilton Harbour remedial action plan: eutrophication

In the late 19~0s ~nd earl~ 1970s, concern grew abo~t the detenoratmg qualny of water in the Laurennan Great Lakes. In 1972, the Canadian and U.S .. governments began the Great Lakes Water Qualny Agreement (GLWQA) which sought to enhance and restore water qualiry in the Great Lakes systems. Initially, advancing eutrophication in the lower lakes (Erie and Ontario) was the main concern. Subsequently, the agreement dealt with toxic contamination of water and sediment. Controls on nutrients and organic contaminants were largely successfu! as phosphorus levels declined by 50% and colomal .sea bird populations returned. Despite p~ogress m the open waters of the lakes, pollurion ~nll ~ccurs. ~?e 1987 iteration of the agreement 1dennfied 43 areas of concern" (AOCs) in which conditions were unacceptable or beneficial uses were impaired. Most of the areas are enclosed embayments ~r connecting channels with eutrophication, contammant loadings, and contaminated sediments. Th~ two countries undertook to rectifY the problems m the 43 areas by the construction of "remedial action plans" (RAPs). The plans were to be based on an "ecosystem concept" that included multiple stresses and brought communiry decision-making into contact with scientific investigation of problems and potential solutions. See ZARuLL & HARnG (2000) for more background. The Hamilton Harbour AOC is at the western tip o f Lake Ontario. The harbour is separated from the l~e ~y a natural sand bar, ~hich is penetrated by a sh1ppmg canal through wh1ch flow exits. The harbaur is triangular with an east-west dimension of 8 km and a north-south dimension of 5 km. The surface area is 2150 ha with a mean depth of 13 m and a maximum depth o f 26 m. The theoretical hydraulic residence time is about 500 days but this may be reduced during periods of intense exchange with Lake Ontario. About half of the hydraulic load is treated sewage from the local communities, which comprise about 500,000 people in a drainage basin of 49,400 ha. The quantiry and qualiry of the treated sewage causes eutrophication problems of too much algae, turbidiry restricting aquatic plants, and severe oxygen depletion. Beginning in the mid 1980s, a combination of public. processes and scientific investigations culminated m reports on conditions and problems (RooGERS et al. 1992a) and on goals and recommendations (Ro~G.ERS et al. 1992b). Federal, provincial, and muntcipallevels of government endorsed the plan in 1992 ~d . the implementation phase began. Eutroph•canon.aspects are.important for the plan to restore aesthencs, recreanonal uses, hypolimnion oxyge~, and. plant/fish habitat. The plan called for reducnons m sewage phosphorus and ammonia loads in stages corresponding to optimized convent!onal treatment with phosphorus precipitation (ininai goa!) and then with the addition of tertiary filtration and nitrification (final goa!). The loads from the two largest sewage p' ants were to be reduced by 23o/o and then 67% for r nosphorus and by 23o/o and then 82o/o for ammoni ,, Initial and final goals for phosphorus for ambient water are 0.034 and 0.017 mg P/ L. Initial and final goals for chlorophyll are 15-20 and 5-1 O pg chl.a/L, respectively, and initial and final goals for Secchi transparency are 2 m and 3 m, respectively. Un-ionized ammonia is to be less than 0.02 mg/L. Measurements of water qualiry variables have been conducted as in other reports (CHARLTON & LESAGE 1996, CHARLTON 1997). This paper assesses progress towards the eutrophication goals of the plan.