Great Lakes water quality improvement The strategy of phosphonts discharge control is evaluated Jaseph X De Pinto Thomas c. Young Lyn M. MeILroy Ckukson Universiry Potsdam, N.P 13676
The impressive size of the Great Lakes has not been enough to shield
them from many of the water quality problems that have resulted from the tremendous human population explosion within their basin p h l e 1). Over the past 180 years the population residIn 1972 the United States and Canada ing within the Great Lakes basin has signed the Great Lakes Water Quality risen from approximately 300,000 to Agreement (GLWQA) to protect the more than 40 million. aquatic environment common to the The municipal, industrial, and comtwo countries, known geologically as mercial use of this water resource durthe Laurentian Great Lakes. This ing the development of urban society agreement expressed the intent of each has led to a concomitant deterioration country to restore and enhance the of Great Lakes water quality; so has the quality of a water resource that repre- extensive agricultural cultivation of the sents 20% of the world’s surface fresh surrounding land. This is prticularly water. The GLWQA was revised in the case in the lower Great Lakes ba1978 and is currentlyundergoing an ex- sins (involving 59% and 56% of land in tensive review. the Lake Erie and Lake Ontario basins, One of the major thrusts of the agree- respectively). Several studies have ment has been to solve the problem of linked the chemical and biological deteeutrophication and its environmental rioration of the Great Lakes to populaconsequences. The 1972 GLWQA and tion growth within the basii (1-3). its 1978 revision set forth an overall The importance of the Great Lakes policy of reducing phosphorus loadmg was recognizedlong before the signing and addressing the problem of eutro- of the Boundary Waters ’lteaty of 1909. phication. Eutrophication is a pmess The most significant provision of this by which increases in the population of maty, which is stiU in force today, is certain algae., encouraged by the pres- the establishment of the International ence of excess phosphorus in a lake, Joint Commission @C). Among the relead to the depletion of oxygen in the sponsibilities of the UC is that of underwater and the consequent deterioration taldng investigations into the prohlems of the lake. of specific boundary waters on the re-
quest of either the U.S. or Canadian government, or both. These. SNdieS, designed to formulate recommendations to the two governments, are known as “references.” Since its inception the UC has issued more than 50 references; some of its more important work, however, has been done .according to the functions given to it under the GLWQA. ltuo international hoards have been establ i i to assist the UC in its work relative to the GLWQA: the Great Lakes Water Quality Board and the Science Advisory Board. By the mid- to late 1960s members of the Great Lakes research and regulatory communities had documented serious eutrophication problems in the lower Great Lakes and had found cause for concern in parts of Lakes Michigan and Huron. They were particularly concerned with this phenomenon in the large embayments of Green Bay and Saginaw Bay. At about the same time scientists in general bad begun to agree that the most effective means of controlling eutrophication in lakes is to reduce phosphorus levels. On the basis of this conclusion and the 1970 annual report of the UC, the 1972 GLWQA set forth water quality objectives and recommended measures to control the discharge of phosphorus that fmds its way
fo the Great Lakes (4). The agreement contains a specific objective that states that phosphoms concentrations “. . . should be limited to the extent necessary to prevent nuisance growths of algae, weeds and slimes that are or may become injurious to any beneficial water use” (5).There has been some doubt as to the actual phosphorus concentrations that would meet this objective and the reduction in phosphorus loading necessary to achieve desii in-lake levels. Nevertheless, the authors of the agreement had the foresight to suggest phosphorus control measures that include a daily l i t averaging 1 mglL of phosphorus in effluent from municipal waste treatment plants discharging in excess of 1 million gdday into the lower Great Lakes (iilnding the international section of the St. Lawrence River). This effluent guideline is based largely on the level deemed to be achievable by available technology. As the United States and Canada began to implement the 1972 GLWQA phosphorus control program, the IJC and the various research agencies involved continued to refme knowledge of the relationships between phosphorus levels and eutrophication in the
Great Lakes. This knowledge was needed to cany out the comphnsive review of the operation and effectiveness of the agreement, which was to be made. during the fifth year after its establishment. (The review was q u i d by Section M of the 1972 GLWQA.) To conduct this review a bilateral technical task p u p (lbk Group III) was formed to establish Greet Lakes water quality objectives and to set target phosphorus loads and phosphorus loading reductions repuired to meet those objectives (6).The fmdings of this group, which made extensive use of a varie4y of water quality mcdels, are incorporated into the 1978 GLWQA (7). Also included in the 1978 revised agreement are the fmdings of the hternational Reference Group on Great Lakes pollution from Land Use Activities (PLUARG). Among the contributions of PLUARG to the Great Lakes phosphoms control program are the identification of the significance of nonpoint source phosphorus l d m g s to the Lakes and the development of a strategy for managing these diffuse
sources (@. In addition to establishing target phosphoms loadings for the Great Lakes, the 1978 GLWQA provided for
the continued evaluation of progms toward the desii level of phosphorus control and for the further development of the most viable phosphorus management strategies for the Great Lakes. mosphonromaoPgen=tstrategy To establish goals of reducing algal
biomass and related nuisance conditions in Lakes Erie and Ontario, eliminating algal nuisance growths in Lake Michigan, and preventing the degrada-
tion of Lakes Huron and Superior from their current states of low biological productivity, Annex 3 of the 1978 GLWQA includes a proposal for the development of a phosphorus control p m gram that consists of the following elements (9): a maximum discharge concentration of I mglL total phosphoms for municipal wastewater plants discharging more than I million gdday into the upper Great Lakes (Superior, Michigan, and Huron)basins and a 0.5-mglL maximum for those plants located in the Lake Erie and Lake Ontario basins; regulation of industrialdischarges of phosphorus to the greatest extent practicable; reduction of phosphoms discharges Envimn. &I. Technol., MI.20, No. 8,1986 753
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from diffuse s o m s into the upper Great Lakes to the greatest extent practicable and reduction of phosphorus discharges from diffuse sources into the lower Great Lakes
by 30%;
reduction of phosphorus in detergents to 0.5% by weight; and maintenance of a viable research program to seek maximum efficiency and effectiveness in the control of phosphorus introductions into the Great Lakes. AU of these recommendations were dedicated to meeting the target loading reductions established in the 1978 agreement or to meeting local phosphorus load allocations (the permitted discharge quantities established by local authorities to meet local water quality objectives), whichever were more stringent. The actual 1978 GLWQA target loading reductions are discussed together with the phosphorus loading profiles for each lake given below. The 1978 GLWQA also provides for an 18-month period of review of the target loading reductions to confirm theii validity and to develop a strategy for achieving the reduced loadings. This c o n f d o n by the parties to the agreement is to “take into account the recommendations of the International Joint Commission arising from the Pollution from Land Use Activities Reference [Group]” (9). To assist PLUARG with this task the Science Advisory Board, supported by the Water Quality Board, appointed a joint task force called the Phosphorus Management Strategies Thsk Force (PMSTF). The final report of the PMSTF (la) and the suhsequent review and adoption of the task force’s recommendations by the ITC (11) c o n i i i the 1978 target loads, with the extion that the target for Lake Erie may have to be lowered in the future. The. reports laid the fonndation for the inclusion of a Phosphorus Laad R e 754
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duction Supplement to Annex 3 of the 1978 GLWQA (signed Oct. 7, 1983). The supplement not only confiimed the targel loads but estimated that further reductions would be required to achieve the targets in the lower lakes after all municipal heahnent plants with capities of more than 1 million gaV day have achiwed levels of 1 mg/L of phosphorus in theii emuent (2OOO metric tons per year [t/yr] for Lake Erie and 1210 t/yr for Lake Ontario). The Annex 3 supplement also recommended continued efforts to limit phosphorus content in household detergents and provided guidelines for the imple mentation of nonpoint source programs in the Great Lakes basin. The Phosphorus Load Reduction Supplement also proposed ways to evaluate how the bioavailability of phosphorus would influencethe organization Of PhOSphOruS control priorities and to assess the desirability and eficacy of addressing problems of eutrophication in near-shore waters. Moreover, recommendations were made to develop a better understanding of the socioeconomic factors involved in phosphorus discharge control and to consider hasmg all aspects of phosphorus management stmtegies on mass units of phosphorus (that is, loads) rather than on fixed effluent standards.
hmplisbments Adherence to the 1972 and 1978 agreements has resulted in significant reductions in total phosphorus loadings tlwughont the Great Lakes basm. Efforts have focused primarily on point source controls, such as discharges h m municipal wastewater treatmnt plants. During the decade following the 1972 GLWQA, more than 57 billion ($1.5 billionfromCanadaand$5.7billion from the United States) was canmitted to capital improvements of municipal sewage systems within the Great Lakes basin (12).
To assist municipal treatment plants in complying with phosphorus control guidelines, all jurisdictions bordering on the Great Lakes, with the exception of Ohio and Pennsylvania, have enacted laws limitingthe amount of phosphorus in detergents. Illmois, Indiana, Michigan, Minnesota, New York, and Wisconsin are complying with the 1978 GLWQA requirement for a detergent phosphorus limit of 0.5% by weight (13).Canada has a federal law that limits the amount of phosphorus in lanndry detergents to 2.2% hy weight. Because of less favorable economics, the reduction of loadings from nonpoint sources (atmospheric, headwater, and tributary inputs) has received less attention than point source controls as a method of controlling eutrophication. Efforts toward agricultural runoff control, such as conservation tillage practices, have, however, recently been undertaken in Michigan and Ohio. For example, in 1980 EPA’s Great Lakes National Program Oflice began funding no-till demonstration projects in 30 counties in the western basin of Lake Erie and in several counties surrounding Saginaw Bay. Resented below is a sununary of the accomplishments of these phosphorus control measures in reducing total phosphorus loads to the
GreatLakes. Upper lakes. Phosphorus control policies for the upper Great Lakes are based on the principle of nondegradation of water quality. In general, there has been a decline in total phosphorus loadings in the upper Great Lakes since the early 1970s and’no deche in overall water quality. AU three lakes show total phosphorus levels at or below the 1978 GLWQA target loads (Figure 1). Some near-shore areas of Lake Michigan, however, such as Green Bay, are classified as mesotrophic (moderately productive of algae and other organisms) because they have been the primary recipients of phosphorus from urban and agricultural development. s i y , because of mass transport processes, Saginaw Bay, located in the southern portion of Lake Huron, has accumulated a significant portion of the wholelake phosphorus load. Evidence has been presented, howevet, that recent phosphorus load reductions in Saginaw Bay have diminished the effects of phosphorus-induced eutrophication on Lake Huron (14). Lower lakes. In contrast with the d e g r a d a t i o n approach that is used for the upper lakes, phosphorus control policies are applied to the lower Great Lakes. These policies have been d e signed to reversethe eutrophication that is caused hy phosphorus from manmade sources. Reductions in the total annual phosphorus load from 1972 to
1982 have been about 30% for Lake Erie (Figure 2) and 40%for Lake Ontario (Figure 3). Because Lake Erie supplies a major portion of the total phosphorus loading to Lake Ontario, loading reductions to Lake Erie have resulted in significant load reductions in Lake Ontario. The most intensive efforts to decrease phosphorus loadings from point and nonpint sources have concentrated on Lake Erie. The reduction of phosphorus loadings from municipal wastewater treatment plants has been the most important factor in decreasing phosphorus inputs to the lake (Figure 2). Phosphoms lnadings from municipal sources have declined to the point at which, as of 1983, both the United States and Canada have achieved the municipal point source phosphorus load for Lake Erie that would have been attained had the average effluent phosphorus level of all plants with discharges greater than 1 w o n gdday always been 1 mglL. In spite of this accomplishment, the total loading in Lake Erie nevertheless exceeds the 1978 GLWQA target loading of 11.000 t/yr. It has been estimated that to achieve this targel for Lake Erie a program intended to decrease phosphorus lnading from both urban and agricultural nnnpoint sources by approximately 2000 t/yr is necessary (13.15). Like Lake Erie, Lake Ontario has experienced a significant decrease in phosphorus lnadiig since 1972 (Figure 3). Although the combined U S . and Canadian phosphorus target loading from municipal point sources has not been achieved for Lake Ontario, Canada did reach compliice in 1983. If present trends continue, U S . municipal treatment plants could be in compliice in the near future. As is true for Lake Erie, the attainment of the 1978 GLWQA load target of 7000 t/yr in Lake Ontario will require the implementation of nonpoint source control programs in the basm (6).
lakewater phosphorus measured during the period 1974-76 (6)and that measured during the period 1979-83 (13, 14, 16, 17) for the Great Lakes and lake sub-basins of special interest with respect to phosphorus (Figure 4). No significant changes in phosphorus levels in the open waters of Lake Superior and Lake Huron have occurred. Small but significant decreases in phosphorus levels, however, have been detected between 1976 and 1983 in the open waters of Lake Michigan (13).
The total phosphorus concentrations in the open waters of the three upper lakes are at or withii the objectives proposed for the lakes: 5 pg/L of phosphorus for Lakes Superior and Huron and 7 pg/L of phosphorus for Lake Michigan (6). These data indicate that the policy of nondegradation, as set forth in the 1978 agreement, is successful for controlling phosphorus in the upper lakes. Some heavily affected local areas within the upper lakes have experi-
Effect on water quality Total phosphorus in the upper lakes. The upper lakes, historidy, have not received large quantities of phosphorus from anthropogenic sources except in a few, relatively lncalized regions or sub-basii. The most affected sites in the upper lakes have included portions of western Lake Superior near Duluth, Minn., Lake Michigan waters that are adjacent to Green Bay, Wis., and Chicago, U.,and Lake Huron’s Saginaw Bay. Since the imposition of controls over phosphorus inputs to the Great Lakes, little lakewide change has been observed in the upper lakes. This is indicated by a comparison between data on Emlron. W. Teohnol.,W.
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enced decreases in levels of total phosphorus. Annual measurements of total phosphorus during the spring in the inner bay of Saginaw Bay during the period 1974-80 (14)show a trend of declining concentration (Figure 4), but the levels have remained well above the concentration objective of 15 pg/L of phosphorus (6). Water quality in Sagiuaw Bay, nevertheless, has improved markedly in recent years. Lower lakes. The total phosphorus
in Lake Ontario has decreased steadily since the mid-1970s. This decline is clearly illustrated in Figure 5 by the time trend in lakewide average concentrations of total phosphorus measured during spring sampling periods. By way of comparison with Lake Ontario, the response in Lake Erie during the same period has been more complex, as indicated by the sub-basin annual average concentration series shown in Figure 6. Within Lake Erie,
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!Ontario (W
however, a trend toward decreasing concentration of total phosphorus is evident, especially in the western and central basiis. Nonetheless, the reductions in total phosphorus loadings to both lakes, and reductions in lakewater concentrations of phosphorus that have resulted, have not been sufficient to meet the lakewide objectives that have been proposed for each system. These are 15 pg/L of phosphorus for the westem basii of Lake Erie and 10 pglL of phosphorus for the central and eastern basins of Lakes Erie and Ontario (6). The resuspension of particulate matter in the internal load of phosphorus is a factor that is especially significant in the shallow, well-mixed waters of the western basin of Lake Erie (18, 19). Resuspension flux appears to he a significant factor in retarding the rate of decline in the concentration of water column phosphorus in the waters of Lake Erie. A greater decline in phosphorus OtherWiSe Would have been expected from the comparatively rapid decrease in external loadings (17).
Other variables Upper lakes. Although total phosphorus levels in the upper lakes generally have remained constant or decreased, concentrations of other anions and cations have tended to increase, according to such historical data as are available for comparison (13,16). This increase generally has included the algal nutrients nitrate and nitrite (NQand Na-) and silicon dioxide (Si@). It is plausible that increases in concentrations of NQ-, N a - , and Si@ may reflect decreased demand for these nutrients by phytoplankton populations growing with less bioavailable phosphorus. In Lake Michigan between 1976 and 1983, however, increased coIlcenttlttions were measured not only for NQ-, N@-, and Si@, but also for chloride (Cl-), sulfate (S0,2-), calcium (Ca2+), magnesium (Mgz+), sodium 7W Emimn. Sci. Rchnd., W. 20. No. 8,1988
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ma+), potassium (K
