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Lake Management - Lecture 19 Lake Management EVPP/BIOL 350...

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Lecture 19 – Lake Management EVPP/BIOL 350 Fall 2011
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Management of Lakes and Freshwater Systems Freshwater is a valuable resource for ecosystem services like: Drinking water Living resources Food supplies Irrigation Transportation Other functions (see previous lecture) I t s u s e m a y b e i m p a
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Management of Lakes and Freshwater Systems Despite the value of freshwater and freshwater ecosystems, this resource is being intensely modified and degraded More than half of all accessible surface freshwater is used directly or indirectly by humanity In addition to use, human activity in watersheds (such as agriculture and urbanization) changes land cover, lake stratification, and streamflow characteristics Global warming will affect all aspects of the hydrological cycle The need for management of our freshwater systems (or management of our impacts?) is evident
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Management is managing our own impacts
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Excess Nutrients – N&P Natural Eutrophication Productivity of lakes are determined by a number of factors: Geology and soils of watershed Water residence time Lake morphometry Water mixing regime Over thousands of years these factors gradually change resulting in lakes becoming more productive
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Cultural Eutrophication Human activities can alter the balance of these factors, esp. when excess nutrients (P in freshwater) are introduced Untreated sewage for example has a TP conc of 5-15 mg/L Even conventionally treated sewage has about ½ that. Compare that with inlake concentrations of 0.03 mg/L that can cause eutrophic conditions So, even small amounts of sewage can cause problems
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Cultural Eutrophication Problems associated with cultural eutrophication include Anoxic hypolimnion Part of lake removed as habitat Some fish species eliminated Chemical release from sediments Toxic and undesirable phytoplankton Blooms of toxic cyanobacteria Phytoplankton dominated by cyanobacteria and other algae that are poor food for consumers Fewer macrophytes Elimination of habitat for invertebrates and fish
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Cultural Eutrophication - Management Source controls Diversion One of the first methods tried Sewage captured and diverted outside lake to say large river or ocean Advanced wastewater treatment More desirable now that technology exists
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Management – Decomposable Organics Human and animal waste is very rich in partially decomposed organic matter and other substances When placed in a water body either directly or via a conveyance system (sewer) this can be very destructive
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Managemenent – Decomposable Organics The input of raw or poorly treated sewage creates a whole chain reaction of problems downstream Immediately below the release, BOD (decomposable DOC) and ammonia are highly elevated which stimulates bacteria and causes rapid depletion of DO, often to 0 As water moves farther downstream, the BOD is used
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