EFFECTS OF DAM ONBIODIVERSITYRENJITH R KFRM PA2 02
Humans have divertedwater from its naturalchannels throughout history.240 BC – Gukov riverChina ( 98 feet high, 985 ftlong).Many small earthen damsbuilt in Sri Lanka during 5thcenturySumerians built irrigationbased civilizations betweenTigris and EuphratesHISTORY OF DAMS
About 60% of the world’s river flow is regulated.There are more than 40,000 large dams with heights >150 m.Reservoirs cover a total area in excess of 500,000 km2.Large hydroelectric dams are among the most controversial of alltypes of development projects.Focus - criticism of the World Bank and other internationalfinancing agencies.Critics point out - destruction of biodiversityDAM & RESERVOIR
Advantage – economically least-cost source of electric power available, especiallyto large urban centers they are a renewable electricity sourceSignificant Adverse Environmental Impacts.
Anthropogenic alterations that disrupts dynamic processes and soimpact on ecological integrity of natural system.Dams disrupt the river continuum and cause upstream anddownstream shifts in biotic and abiotic parameters.WHAT DAMS DO?
IMPACT ORDER OF DAM ONENVIRONMENT• 1storder impacts Immediate abioticeffects• 2ndorder impacts Changes in channeland floodplainbiology• 3rdorder impacts Long term bioticchanges and “newequilibrium”
freshwaters are home to a relatively high proportion of species,with more per unit area than other environments (10% more thanland and 150% more than the oceans).only about 45,000 species of freshwater animals, plants andmicroorganisms have been scientifically describedat least an additional million more species remain to be named.BIODIVERSITY
•Freshwater biodiversity is unevenly distributed.•‘Hotspots - High numbers of species or endemics are found inhotspots
Blocking migratory species.Changing turbidity.Filtering out of woody debriswhich provides habitat andsustains a food chain.Trapping silt in reservoirs andreducing downstreamproductivity.Changing conditions ofunderwater terrain running water becomesstill deepwater zones, temperature and oxygenconditions changesBIOLOGICAL IMPACTS
Unstable for riverine species.Possibly fostering exotic species.Reservoirs may be colonised by species whichare vectors of human and animal diseases.Dam management diminishes or stops normalriver flooding and affecting biodiversity.Changing the normal seasonal estuarinedischarge which can reduce the supply ofnutrients, impacting the food chains that sustainfisheries in inland and estuarine deltas.Modifying water quality and flow patternsdownstream.
•anadromous fishes (salmon and hilsa) catadromous fishes (eels)•Many stocks of Salmonidae and Clupeidae have been lost as aconsequence.•Eg. Columbia River, USA, more than 200 stocks of anadromous,Pacific salmonids became extinct.•Sturgeon populations in the Caspian Sea rely on hatcheries mainlyin Iran, since Russian dams block natural spawning migrations.•Hydroelectric dams in the Amazon basin have halted the longdistance upstream migration of several species of catfishes andinterrupted the downstream migration of their larvae.MIGRATION
Araguaia-Tocantins River basin (Brazil) several species ofmigrating catfish have been drastically reduced in abundanceas a result of dams; catches in the downstream fisheries havebeen reduced by 70%.glochidia larvae of freshwater mussels ‘hitch rides’ on hostfishes.To help counteract the drift downstream of their larvae,some aquatic insect adults such as mayflies and stoneflies flyupstream to lay their eggs (Hynes 1970).about 250 species, <1.2% of all fishes faces migratoryblocks (McDowall,1992).
•Reservoirs trap suspended particles, reducing turbidity downstream.•Many species are adapted to natural turbidity.•Eg. turbid water catfishes have small eyes, refined senses of smell andtouch in their sensitive barbels.•Downstram biota changes• Clear water increases visual predator attack (birds).• Indigenous species affected adversely.• Other animal species may move in• filter feeders and aquatic vegetation may flourish.• Sediment burrowing species reduces due to lack of sediment•increased turbity, above natural levels, can interfere with primaryproduction (Arthington & Welcomme 1995).TURBIDITY
•branches and tree trunks that fall into the river because of age,storms, beaver activity and eroded banks (Maser & Sedell, 1994)•Trees can also play a complex role in creating habitats• divert, slow and speed up current flow,• shelter a variety of biota from currents and predators• create feeding stations•On land - LOD helps stabilize slopes and reduces erosion, and isconverted into humus which helps hold water and moderates therunoff.LARGE ORGANIC DEBRIS(LOD)
In the Santilla River (Georgia), wood represented 4% of the totalhabitat, yet supplied 60% of the invertebrate biomass and 78% ofthe drifting invertebrates (Bryant & Sedell 1995).The logs and branches may become waterlogged and sink, driftonto the shore. If the integrity of downstream ecosystems is to bemaintained, then LOD input must be sustained.
Reservoirs tend to serve as sediment traps since river velocitiesand carrying capacity for particles decrease in reservoirs (McCartneyet al. 1999)Sedimentation can degrade habitat both in the reservoir andbelow the dam, as well as reduce storage capacity.Many of the molluscan extinctions in the Mobile Bay (USA) dueto siltationSuspended silt may reduce the feeding efficiency of filter-feedingbivalves and other species.About 50 km3of sediment, nearly 1% of global reservoir capacity,was estimated in 1997 to be trapped behind dams.SEDIMENTATION
The pattern of flow of a river undergoes a regular series ofchanges with the seasons. The patterns can differ profoundlyfrom region to region e.g. in an Indian river the peak flow may be during the monsoon,in an Arctic river during snow-melt or ice breakup. The expansion and contraction of the river controls living spaceand access to particular habitats. species in a drainage basin adapt to the seasonal patterns . It is from river flow events that species take cues to migrate,spawn, etcSEASONAL VARIABILITY OF FLOW ANDFLOOD PLAINS.
Some species are adapted to strongly seasonal flow regimes withflooding.Drastic declines in the molluscs of the Murray-Darling Riversystem ( Australia) have been attributed to: predation andsediment disturbance by introduced fish such as the common carp,Cyprinus carpio (Fletcher et al. 1985)changes in flow patterns through intensive flow regulation afterimpoundments and possible changes in algae, bacteria and fungi,which form potential mollusc food sources.
Water diversion for irrigation may lower thedownstream water table adjacent to the river and reduceseasonal recharging of the water tableThe supply to springs and cave streams may also beaffected.According to David Culver there are 1,300 describedobligatory cave species in the United StatesWATER TABLE CHANGES
Of the world’s 110 described species of cave fishes, a high proportion arethreatened (Proudlove, 1997)Many cave organisms are restricted to a single cave or cave complex. Cutting offthe cave water supply, either temporarily or permanently, may lead to extinctions.When selecting potential dam sites, planners should be alert to known cavedwelling species or check for the presence of unknown species.
Naga Hammadi barrage area of the lower Nile, Egypt Perch- Zingel streber and Zingel zingel (IUCN -vulnerable) Salmonids- Hucho hucho, (endangered, and salmon -Salmo trutta. The European beaver, Castor fiber, has left the territoriesinfluenced by the dam. The mean annual fish catch has dropped by 87%.INLAND DELTAS.
Many of the effects in estuaries are similar to upstream,e.g. loss of habitat and changes in seasonal flow, turbidityand productivity.Total shifting of ecosystemESTUARINE AND MARINEIMPACTS
Water withdrawal on the North Caspian had the followingeffects(Rozengurt & Hedgepeth 1989) the mean salinity increased from 8 to 11ppt; the estuarine mixing zone was compressed and moved up to thedelta; the nutrient yield, especially phosphorus, and sediment load werereduced by as much as x2.5 and x3, respectively; biomass of phytoplankton, zooplankton, and benthic organismswere decreased by as much as x2.5; and a substantial part of the Volga flood plains that served as a nurseryground for many valuable fishes was transformed into dryingswamps or desserts.
Decreased discharge rates can result in an increase insalinity in estuaries and change the composition of speciesin this zone.47 commercial fish species in the Nile prior to theconstruction of the Aswan High Dam, only 17 were stillharvested a decade after its completion(Abramovitch,1996)SALINITY, NUTRIENTS AND REPRODUCTION
•Ranked second in Asia for length•UN commission plans 7 dam sites.•The Mekong, which courses through the very heart of inlandSouth-East Asia, is home to the world’s largest freshwater fisheries.•about 800 different native species.•Its rich biodiversity is second only to the Amazon’s.•Through fishing, aquaculture and irrigation, it sustains 65m people.RIVER MEKONG
protection from floods and droughts,increase agricultural production and employmentelectricity productionimproved navigation that benefits tourismResulted in relocation of 1 lakh people.coastline erosionhealth problems.
The standing water in irrigation canals is a breeding ground forsnails carrying the parasite Bilharzia (Schistosomiasis)Schistosomiasis is the second most socioeconomically devastatingparasitic disease after malaria.Sardine catch off the Egyptian coast declined from 18,000 tons in1962 to 8,590 tons in 199230 of 47 commercially exploited fish species becomingeconomically or biologically extinct
Mediterranean fishing and brackish water lake fishery declinedafter the dam was finished because nutrients that used to flow downthe Nile to the Mediterranean were trapped behind the dam.
Farakka Barrage is a barrage across the Ganges River, located inthe Indian state of West Bengal, roughly 16.5 kilometres (10.3 mi)from the border with Bangladesh near Chapai Nawabganj District.Construction was started in 1961 and completed in 1975.Operations began on April 21, 1975. The barrage is about 2,240metres (7,350 ft) long. The barrage was built to divert up to 44,000 cu ft/s (1,200 m3/s)of water from the Ganges River into the Hooghly River during thedry season ( Jan to June).In order to flush out the accumulating silt at the Port ofKolkata (Calcutta) on the Hooghly River.FARAKKA BARRAGE
have nearly eliminated the anadromous Hilsa ilisha (Clupeidae) in the riverinestretches.Other major carp species reduced (50% of 1964 levels) in the lower Ganges.
Dams alter river ecosystems and subsequently requiredevelopment of new relationships between humankindand natural resources associated with these ecosystems.dams built to receive benefits will accrue humans withenergy, water supply,transportation,flood control, fishing,recreation, aesthetics, and so on.CONCLUSION