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Chapter XII: Phosphorus Control under the 1978 Great Lakes Water Quality Agreement
- The University of Akron Press
- Chapter
- Additional Information
one of the stipulations of the Great Lakes Water Quality Agreement was that it be reviewed by the parties during its fifth year of operation (1976–1977). Another clause required that the effects of the agreement ’s phosphorus control program also be reviewed and modifications of it considered. To assist them in this latter task, the parties appointed a technical group, Task Group III (TG III). The task group was composed of eight Canadian and nine U.S. scientists and engineers intimately familiar with the Great Lakes phosphorus issue. They included some of the world’s foremost authorities on eutrophication and the role of phosphorus in it. The group was cochaired by the ubiquitous John R. Vallentyne, now senior scientist, Canada Center for Inland Waters, and N. A. Thomas, chief, Large Lakes Research Station, USEPA, Grosse Ile, Michigan. Its terms of reference were to prepare a report based on the latest information on “acceptable” total phosphorus loadings to each lake; to provide the best estimates of current phosphorus loadings from each country and each major source, including municipal, industrial, and tributary sources; to determine what control possibilities existed and what the costs of pursuing them would be; to develop for each lake several phosphorus loading levels and treatment strategies, the condiPhosphorus Control under the 178 Great Lakes Water Quality Agreement 210 C H A P T E R X I I tions which would result from these levels, and estimates of the response times of the lakes to these levels; and to determine what dissolved oxygen and other water quality objectives would be compatible with the proposed phosphorus loadings.1 At the time of signing the GLWQA, there had been some uncertainty about the efficacy of its phosphorus control program, but, on the basis of evidence accumulated since 1972, TG III unanimously endorsed the program .2 It reiterated that phosphorus was the single element for which all phytoplankton have an absolute requirement and for which there existed practical control measures. However, it entered a caveat regarding the excessive growth of Cladophora, an increasing problem in the Great Lakes. Although the growth was believed to be related to the general level of phosphorus enrichment, there was an insufficient understanding of the role of Cladophora in the Great Lakes ecosystem. More research was needed before effective strategies for controlling Cladophora could be developed . In considering the current state of, and recent trends in, the in-lake conditions of the Great Lakes, the group used total phosphorus concentration as the primary indicator and chlorophyll a concentration as the most important secondary indicator.3 The available data suggested that there had been few significant changes in either indicator during the preceding decade.4 The only trend observed in Lake Erie, reported by the Great Lakes Water Quality Board in 1976, was a significant upward trend for phosphorus concentration in the central basin.5 Yet no significant change in phosphorus loading had occurred during the period 1970–1976. TG III first determined desirable in-lake phosphorus concentrations for each Great Lake and then calculated external total phosphorus loadings which would yield those concentrations.6 Desirable in-lake conditions were based on annual average whole-lake (or open water) conditions. Although , in regard to human use, nearshore conditions were most critical in the short term, it was not possible to relate desirable nearshore conditions to total phosphorus loadings to the whole lake. Whole-lake conditions were important in determining long-term trends, which were used in developing the phosphorus management strategies designed to protect the lakes for future generations. Important advances had been made, since 1972, in developing mathePhosphorus Control 211 [34.230.66.177] Project MUSE (2024-03-19 12:30 GMT) matical models relating in-lake conditions to phosphorus loadings.7 The model created by Richard A. Vollenweider for his 1968 OECD report on eutrophication had been used by the IJC boards in their 1969–1970 reports on the lower lakes, by the IJC in its 1970 report on the lower lakes, and by the parties in drawing up the GLWQA. In 1978, TG III had, in addition, the use of more sophisticated models that allowed one to predict in-lake concentrations of phosphorus and chlorophyll a as well as the area of anoxia that would be produced in Lake Erie’s central basin by a given phosphorus loading.8 (Anoxia would be understood to occur when the concentration of dissolved oxygen fell to 4 mg/l or less...