The Great Lakes Atlas

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Western University
Geography 2011A/B
Wendy Dickinson

THE GREAT LAKES AN ENVIRONMENTAL ATLAS AND RESOURCE BOOKCHAPTER 1 INTRODUCTIONTHE GREAT LAKES Physical Characteristics of the System 32 Lakes contain about 23000 km of water covering a total of 244000 kmLargest system of freshwater on earth 18 of the world supplySensitive to effects of many pollutants o Runoff of soils and farm chemicals from agricultural lands o Waste from cities discharges from industrial areas and leachate from disposal sites o Atmospheric pollutants that fall with rain or snowOutflows from Great Lakes are relatively small 1 per yearo Pollutants that enter lakes are retained in system and become more concentrated over time o Also remain in system due to resuspension of sediment and cycling through food chainsNorthern Great Lakesclimate is cold terrain is dominated by granite bedrock Canadian ShieldSouthern Great Lakesclimate is warmer lands are fertile and agriculturalLake Superiorlargest deepest and coldest of the fiveo Retention time of 191 years Retention timemeasure based on the volume of water in the lake and the mean rate of outflow o Most of the basin is forested little agriculture because of cool climate and poor soils o Forest and sparse population result in few pollutants except via airborne transportLake Michigansecond largest entirely within the United States o Northcolder less developed and sparsely populated Green Bayhas one of the most productive Great Lakes fisheries but receives wastes from worlds largest concentration of pulppaper mills o Southtemperate urbanized and home to about 8 million people 15 of the total population of Great Lakes basinLake Huronthird largest by volume o Saginaw River Basinintensively farmed very productive fisheryLake Eriesmallest and exposed to greatest effects of urbanization and agriculture o Fertile soils surround the lake intensively farmed o 17 metropolitan areas with populations over 50000 located within Lake Erie basin o Average depth is only about 19 m 62 ftshallowest of the five lakes o Shortest retention time of 26 yearsLake Ontarioslightly smaller than Lake Erie but average depth of 86 m 283 ft and retention time of 6 years o Major industrial centers such as Toronto and Hamilton located on its shore SettlementExploitationFirst European arrivals had limited impactexploitation of some furbearing animalsHowever later immigrants logged farmed and fished commercially in the regionbrought about ecological changesAs settlement and exploitation intensified parts of the system were greatly changed o Loggingremoved protective shade from streams and left them blocked with debris o Sawmillsleft streams clogged with sawdust o Farmingexposed soils washed away more readily burying stream and river habitats o Exploitive fishingreduced endless abundance of fish IndustrializationAdded to degradation of water qualitybacterial contamination putrescence and floating debrisAlso resulted in contaminated drink watercontributed to fatal human epidemics of waterborne diseaseAs industrialization and agriculture intensified use of PCBs and DDT and other chemical substances came into use o Used to enrich fertile soils to enhance productionCombination of fertilizers nutrientrich organic pollutants and phosphate detergentscaused acceleration of biological production eutrophication in lakeso 1950sLake Erie showed first evidence of lakewide eutrophic imbalance algal blooms and oxygen depletion The Evolution of Great Lakes Management1970smajor reductions in pollution dischargesProblem of algal growth required lakewide approach to measure amount of phosphorus entering and leaving each lake from all sources
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