Bio E179 Lecture 3-5 Notes .doc

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Department
Biological Sciences
Course
BIO SCI 97
Professor
Rahul Warrior
Semester
Fall

Description
Notes for Lectures 3 4 and 5The Snake River in Idaho as a case study and an introduction to the impacts of dams and impoundmentsThe Middle Snake River is a tragic example of a river that had a very unique biology but because of dams eliminating the oceanmigratory salmon steelhead and several other fish species water pollution and water diversion this remarkable river habitat is now highly degraded and many of the species are endangered a number are already extinct The Middle Snake is the portion of the Snake that extends from roughly Boise to Twin FallsThis area was once one of the major fall chinook salmon producers in the Columbia Basin but dams have blocked their accessWhite sturgeon lived on dead salmon and steelhead as well as immature Pacific lamprey eelsall of which disappeared when ocean migration was blockedThe sturgeon are essentially endangered there today surviving as a tiny resident populationBecause of irrigation withdrawal during the summer the Snake River is almost completely dry by the time it reaches Shoshone Falls In addition to the vast historic salmon fishery before dams the Middle Snake River also sustained a remarkable freshwater snail fauna of which five species are listed as Threatened or Endangered due to habitat loss and pollutionThe snails are survivors from an ancient Pliocene lake Lake Idaho that covered southern Idaho 35 million years agoThis lake had the richest species diversity of any known freshwater lakeWhen the lake drained perhaps a million years ago all of the species became extinct except for a few that were able to survive till modern times in the freeflowing Middle Snake RiverToday they are endangered because of the dams habitat loss pollution and exotic species The fish fauna has transformed from a coldwater lotic fauna into that typical of a warm eutrophic lake The same thing has happened to the mollusks Most of the 18 mollusk species that were characteristic of the area prior to dams and pollution are either extinct or are declining They are being replaced by nonnative species that are very pollution tolerantI was able to identify half a dozen nonnative species that are inadvertently imported and spread by the fish farm industryThe New Zealand mudsnail is the worst of these exotics with populations reaching hundreds of thousands per square meterBecause they are parthenogenic females produce young from unfertilized eggs and live bearing a single snail can found a population This species is pollutiontolerant and is swamping out the natives simply by their sheer numbers in the habitats they shareEcological stressors in the Middle Snake River include irrigation diverting the Snake River for irrigation then returning the water to river after it has been flushed over southern Idahos agricultural lands five hydroelectric dams 140 private fish hatcheries the sewage effluent from two cities and over 500 cattle feed lot farms The phosphate and nitrate contributions of these combined influences including the changes caused by dams have transformed the Middle Snake River ecosystemState and federal efforts are being made to resolve many of these problems but in the meantime the ecosystem continues to declineImpacts of Dams and ImpoundmentsA dam is a barrier in a flowing water lotic system It can also be used to raise water levels in existing lakes For example Grant Lake in the Eastern Sierra has been deepened for water storage purposes by putting a dam at its outflowAll of these lentic bodies of water have three general layers verticalEpilimnion the top layerMetalimnion a zone of mixture between the epilimnion and the hypolimnionHypolimnion the lowest and by far the greatest layerThe flowing water stretch below downstream of a dam is called the tailwaterDams are used to store water divert water provide water for domestic and irrigation purposes for flood control for recreation and for navigation Flood control requires an empty basin that can accept and hold water that runs off the landscape after rains water storage is the opposite in that the basin retains water thus there isnt room for runoff after rain in the sense of an empty flood control basin There are two main theories of trying to structurally control flooding One is to build many small dams at the headwaters and the other is to construct a bigger dam in the middle portion of a river In a natural river without dams there is a natural flood control function in the spongelike quality of the flood plain and its riparian vegetation
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