Issues in Ecology Number 10 Winter 2003 BOX 3:THE GREAT LAKES ECOSYSTEMS The Great 5一8eMgn地omEe0.6号20 itrof亚 water supply The a 25 218 of the U.S.popula and al pro ruc on has been si been gu nd cli mate ch t samepo,hehntaned by the er e of the Great Lak Water Quality.Water quality in the Great Lakes has improved dramatically from the eutrophic conditions that p the 1980s This has been achieved throua ato ation of point-source pollution.Ho ever,water quality restored to "natural condition"Years of n h for exam nutriont for diato Without enough silica.natural algal assemblages and the zooplankton that feed upon them have been severely altered.Today cultural eutrophication may actually be masked by the filtering activity of zebra mussels,which in ases water clarity by shifting nutrients from the water column to the lake sediments.Nonpoint source pollutants,including fertilizers.pesticides,sediment.an bacteria,still significantly impair Great Lakes water quality. Invasive Species Non-native sp cies have modified habitats.reduced native biodiversity and alterec food webs.An estimated 162 exotic species now reside in the Great Lakes,including introduced spor fish.Although the zebra mussel and sea lamprey have received the most attention,many other less apparent species profoundly affect the ecosystem,including quagga mussels.predatory zooplankton such as Cercopagis pengoi and Bythotrephes cederstroemi,the benthic amphipod Echinogammarus schnus,and the round and tubenose gobies.In addition to their ecological impacts,lamprey cost $10 million in control efforts each year,and zebra mussel control has totaled some $4 billion as of 2001. oxic Chemicals.The sediments in the Great Lakes store organic and inorganic contaminants coming from industrial,urban,and agricultural runoff as well as atmospheric deposition (including mercury and PCBs).Contaminants from sediments accumulate in aquatic species,affecting fish and wildfowl health and even the health of humans who eat contaminated fish.Contaminants also affect shipping.a major industry on the Great Lakes,because of potential restrictions on dredging of channels and harbors (which can release contaminants into the water column)and on disposal of dredged sediments. Habitat Destrction Land use changes have resulted in habitat oss throughout the Great Lakes basin.Urban sprawl continues to replace natural areas,farmland,and open space.The quality and quantity of coastal wetlands are declining:and the extent of hardened shorelines (that is.reinforced by sheet pilingor rip rap)appears to be increasing.thus isolating wetlands from lakes. destroying habitat,and altering natural sediment movements. Cmate Change.Implications of future cimate change in the Great Lakes region are profound.Some cmate change modeks suggest that will lead to lower lake levels,creating problems for the shipping industry as well as changes in water supply and environmental conditions in the lakes.Current climate models also suggest more extreme swings in climate,and unusually wet years may lead to periodic flooding.It is important to note that the 35 million people in the Great Lakes Basin are unprepared for arge changes in lake level in either direction. represent a permanent change from:and the plant and anima and expense are now required to maintain water quality a neanmehMgnoe elegacies of past colf-s Perhaps the aminated by toxins 11 BOX 3: THE GREAT LAKES ECOSYSTEMS The Great Lakes – Superior, Michigan, Huron, Erie, and Ontario – hold 20 trillion cubic meters of fresh water, approximately 18 percent of the planet’s fresh water supply. The overall basin is home to 35 million people, including 10 percent of the U.S. population and 25 percent of the Canadian population. Nearly 25 percent of agricultural production in Canada, and 7 percent of the agricultural production in the United States occurs in the basin. In addition, the Great Lakes provide drinking water for 40 million people and supply 210 million cubic meters of water per day for municipal, agricultural, and industrial use. Poor water quality caused by excessive inputs of phosphorus and nitrogen is one of many serious problems affecting the Great Lakes. Some basins of the lakes also contain exceedingly high concentrations of toxic chemicals; habitat destruction has been significant and is increasing; native fisheries have been greatly altered or intentionally replaced; invasive species have altered native food webs and water quality and also damaged human infrastructure; and climate change is expected to alter lake levels. Although freshwater environments the world over share many of the same problems, their significance is heightened by the sheer size of the Great Lakes and the quantity and quality of their waters. Water Quality. Water quality in the Great Lakes has improved dramatically from the eutrophic conditions that prevailed prior to the 1980s. This has been achieved through greater regulation of point-source pollution. However, water quality has not been restored to “natural condition.” Years of phosphorus enrichment in Lake Michigan, for example, increased the growth of diatoms and depleted lake silica concentrations (silica is a necessary nutrient for diatoms and sinks to the lake bottom when diatoms die). Without enough silica, natural algal assemblages and the zooplankton that feed upon them have been severely altered. Today, cultural eutrophication may actually be masked by the filtering activity of zebra mussels, which increases water clarity by shifting nutrients from the water column to the lake sediments. Nonpoint source pollutants, including fertilizers, pesticides, sediment, and bacteria, still significantly impair Great Lakes water quality. Invasive Species. Non-native species have modified habitats, reduced native biodiversity, and altered food webs. An estimated 162 exotic species now reside in the Great Lakes, including introduced sport fish. Although the zebra mussel and sea lamprey have received the most attention, many other less apparent species profoundly affect the ecosystem, including quagga mussels, predatory zooplankton such as Cercopagis pengoi and Bythotrephes cederstroemi, the benthic amphipod Echinogammarus ischnus, and the round and tubenose gobies. In addition to their ecological impacts, lamprey cost $10 million in control efforts each year, and zebra mussel control has totaled some $4 billion as of 2001. Toxic Chemicals. The sediments in the Great Lakes store organic and inorganic contaminants coming from industrial, urban, and agricultural runoff as well as atmospheric deposition (including mercury and PCBs). Contaminants from sediments accumulate in aquatic species, affecting fish and wildfowl health and even the health of humans who eat contaminated fish. Contaminants also affect shipping, a major industry on the Great Lakes, because of potential restrictions on dredging of channels and harbors (which can release contaminants into the water column) and on disposal of dredged sediments. Habitat Destruction. Land use changes have resulted in habitat loss throughout the Great Lakes basin. Urban sprawl continues to replace natural areas, farmland, and open space. The quality and quantity of coastal wetlands are declining; and the extent of hardened shorelines (that is, reinforced by sheet piling or rip rap) appears to be increasing, thus isolating wetlands from lakes, destroying habitat, and altering natural sediment movements. Climate Change. Implications of future climate change in the Great Lakes region are profound. Some climate change models suggest conditions that will lead to lower lake levels, creating problems for the shipping industry as well as changes in water supply and environmental conditions in the lakes. Current climate models also suggest more extreme swings in climate, and unusually wet years may lead to periodic flooding. It is important to note that the 35 million people in the Great Lakes Basin are unprepared for large changes in lake level in either direction. As an example of freshwater integrity, the Great Lakes fail on most accounts: shoreline hardening affects connectivity of the lakes with their wetlands; the current chemical and nutrient conditions represent a permanent change from natural conditions; and the plant and animal assemblages have been highly modified by human intervention. Constant effort and expense are now required to maintain water quality at acceptable levels, remove the legacies of past toxic inputs, control harmful non-native species, and restock valued recreational fisheries with exotic game fish that do not naturally reproduce in the lakes. Perhaps the Great Lakes can never be “restored” to the point where they are functionally self-sustaining, and therein lies a hard lesson. Many goods and services valued by society are no longer available (such as fisheries uncontaminated by toxins), and others are possible only through continuing expenditures of millions of dollars in remediation. Zebra mussel photo courtesy USGS. 11 Issues in Ecology Number 10 Winter 2003