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Lecture 92

GGR202H5 Lecture 92: Chapter-11-ENV-1

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Nicole Laliberte

Chapter 11: Fresh Water - Blue Planet Water is what makes us unique: - shapes the surface of the Earth o affects morphology of earth - allows for life - makes Earth different from all other planets! - exists in all 3 states o atmosphere o on surface o under the ground In Atmosphere: - important in moving heat from equator to the poles - rises as vapour; falls as rain/snow On Surface: - Ocean currents - Sculpts terrestrial landscape - Carrier for many substances (nutrients & pollutants) Water is locked up in Minerals in the Earth’s Mantle: - Makes the mantle elastic; affects the dynamics of plate tectonics o allows the plates to move - May be largest water reservoir on the planet - Unknown how much cycles between internal & surface reservoirs through tectonics Hydrology is “water science” - Study of water in the hydrosphere, both on and under the ground - Movement, distribution, quantity, quality - Reservoirs, processes, ecosystems Fresh Water = few dissolved salts - Only 2.5% of earths water is fresh - Most of this is tied up in the glaciers, ice caps, aquifers - Reservoirs differ in the amount of water they store, transmit, and how long they hold it - Largest reservoir has the longest residence time 1. Water molecule stored in ocean ▪ +3000 Years 2. Water stored in Glaciers/Ground Water ▪ 100-1000 years 3. Atmosphere (large container but small reservoir) ▪ Days Hydrologic Cycle: - Precipitation - Transpiration Hydrologic cycle from a Systems Perspective: Reservoirs: - Ocean; ice caps and glaciers; and then groundwater Processes: - Precipitation, surface runoff, infiltration, percolation, evaporation, transpiration Fluxes: - The global hydrologic cycle maintains mass balance (water is never consumed or destroyed but it is always present) – total amount of water is fixed - Local variations affect supply, and cause problems like floods and droughts - Solar Energy and Gravity DRIVE the Hydrologic Cycle: Solar energy: evaporation, transpiration, condensation ▪ Sun heats the earth unevenly and drives the change of water from one state to the next Gravity: precipitation, runoff, groundwater percolation ▪ Physical movement in liquid water - Water Molecule forms into condensation nucleus - Condensation Nucleus is what vapor condenses around - Form Droplets that compose the clouds - Condenses into Raindrop which is large enough for gravity to pull it down Surface Freshwater: - Rivers and streams Springs - Lakes and ponds Wetlands 2 Rivers shape the landscape: - Water from rain, snowmelt, and springs runs off over the surface - Surface runoff (sheetflow) organizes into rills and gullies, then streams and rivers o Largely driven by Topography – height of the land o Tributary = a smaller river flowing into a larger one - Erosion is the work of rivers carrying sediment to the ocean Drainage Basin is a Local Hydrologic Unit: - Drainage basin = Catchment = Watershed = area drained by one river o Draining an area of land o Water flows in SAME direction - Well defined in areas of Topography (mountains) - Catchments are separated from one another by Divides (line on a map where the water goes in different directions) o Catches the water in one area o Input = Precipitation o Output = Runoff, Evaporation, Aquifers o P (precipitation) = R (runoff) + ET(evaporation + transpiration) + dS (storage) Floodplain: region of land over which a river has historically wandered; periodically inundated o Agriculture thrives o Riparian (riverside) forests are protected o Demonstrated that flowing of water is only one part of a riparian system o Erosion, transport, deposition of sediment o Any changes in upstream areas (near source) will have impacts on downstream ▪ Changes in water quality, clarity, level, temperature, sediment carried Groundwater: - water located beneath the Earth's surface - in soil pore spaces; fractures of rock formations - largest unfrozen freshwater reservoir - aquifers store and transmit water aquifer: underground layer of water-bearing permeable rock, gravel, sand, or silt confined aquifer: between impermeable layers (in-between layers or rock) unconfined aquifer: water seeps in from above (soil on top and rock on bottom) 3 unsaturated zone: some air, some water saturated zone: completely filled with water water table: top of saturated zone aquiclude: zone that prevents water from moving among aquifers - (layer of rock that prevents water from moving) - can create Perched Water Table – Water table was high but lowered and the rock did not for all the water to go down – Spring is formed - residence time may be thousands of years o Changing because humans are withdrawing a lot of water - Canada: much more water underground than on the surface - 26% of Canada’s population depends on groundwater (mostly rural) Groundwater flow is Controlled by Gravity: o where water table intersects surface = Surface Water o Recharge = water flows into aquifer via precipitation/infiltration o Discharge = water flows out of aquifer via percolation/streams/springs/ocean o in many regions, water table; recharge & discharge vary seasonally Water: o supplies houses, agriculture, and industry o is Unequally Distributed: o Many areas with high population density are water- poor and face serious water shortages o 1.2 billion people, (20% world pop’n), live in areas of physical scarcity (500 million people are approaching this situation) o 1.6 billion people, (~25%) face economic water shortage (lack necessary infrastructure to take water from rivers and aquifers). o ~ 800 million people do not have access to safe drinking water o > 3.5 million people die each year from preventable water-related disease o Areas with high population density are water poor o Water holds value on in situ (in place) in undistributed fresh water systems o Rivers/Lakes: transportation, boating and recreation, cultural and spiritual uses and freshwater fishing There is (already) a global water crisis o By 2025, the world’s population could increase to almost 9 billion people o According to the UN, 2/3 of those people will be living in conditions of serious water shortage o Global demand for fresh water will exceed availability by 56 percent o 43 countries (1.2 billion people) today already face water scarcity (United Nations, 2011) o “The wars f the 21 century will be fought over water” 4 Climate Change will cause changes to Hydrologic Cycle: o Altering precipitation patters, melting glaciers, intensifying droughts/flood, decreasing river flows, lowering ground water levels, raising sea levels o Water levels drop = dredge channels to accommodate shipping o Canada: snowmelt and spring runoff can occur earlier o rain belts will shift o continental interior will experience drier summers Global Water Management Challenges Include: o Urban and rural drinking water and sanitation o Water for industry and agriculture o Protection of aquatic ecosystems o “Holistic” watershed management o Impacts of environmental change on water resources Canada is Criticized for WASTEFUL Water Consumption o Per capita water use is 28% higher than the average OECD country o Since 1980, Canada’s water use has increased 5x faster than OECD ave. rate of increase Human use of surface water has environmental impacts: o Downstream and transboundary impacts o Decreased flow o Changes in erosion and siltation rates – change speed and yearly cycle o Changes in water salinity o Impacts on local climate o Evaporative loss from reservoirs and irrigation o Impacts on habitat, wildlife, ecosystems o Pollution, eutrophication o Salinization o Waterlogging We have erected thousands of dams: o Dam = obstruction to block the flow of water in a river so the water can be stored in a reservoir o Slowing down/impeding the flow of a river o Diversion Dam = water is diverted but not stored in reservoir o Functions: prevent floods, provide drinking water, allow irrigation, generate electricity o 45,000 large dams have been erected in more than 140 nations o 60% of the world’s largest rivers have been intensively or moderately affected by dams, canals, and diversions o Diversion drastically alters a river’s ecology o Ex: Colorado River – Hoover Dam = flow rate decreased; almost to 0 now Benefits Drawbacks o Power generation o Habitat alteration o Emission reduction (Hydro energy is cleaner o Fisheries declines – less fossil fuels) o Population displacement o Crop irrigation o Sediment capture (accumulates at dam) o Drinking water o Waterlogged land o Flood control o Risk of dam failure o Shipping (canals created) o Lost recreational opportunities o New recreational opportunities 5 Dam Removal (decommissioning): o Removing dams restores riparian ecosystems, fisheries, river recreation o In Canada only a few dams removed; >500 dams have been removed in the U.S. Inefficient irrigation wastes water: o Today, 70% more water withdrawn for irrigation than in 1960 o Consumptive use (removes the water from that drainage basin) o The amount of irrigated land has doubled o Water vapor is a huge part of global warming and irrigation is increasing the amount The Aral Sea is a case study of diversion o once the 4th-largest lake on Earth o 80% loss of volume in 45 years due to diversion of two input rivers o 60,000 fishing jobs lost o pesticide-laden dust blows from the lake bed o cotton cannot bring back the region’s economy Environmental impacts of groundwater use: o Depletion of aquifers o Take a long time to discharge and recharge o Declining water tables o Ground subsidence o There is an empty space that collapse o Sink holes: ground gives away with little
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