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Lecture 42: Global Ecology and Pollution
Reading: None. Reminder: Final Examination.
El Niño-Southern Oscillation (ENSO) Origin: Tropical Pacific Ocean, south of the equator This is a natural phenomenon (causes unknown) occurring in a cycle of 2-7 years (Ricklefs, 1996, p 89, Fig. 4.13).
Warm Phase (=El Niño) Sea surface temperature increases, western trade winds collapse, and there is a shift in ocean currents and precipitation patterns. Cold Phase (=La Niña) Sea surface cools, and the western trade winds strengthen.
Normal Trade Winds Winds and surface currents are from the west coast of South America (eastern Pacific) toward the western Pacific. Sea level is 50cm higher in western Pacific than in the eastern Pacific (South American coast). Sea temperature 8°C warmer in west than east. There is a convective air flow loop with hot air rising in western south Pacific (low pressure) which causes heavy rainfall in the western Pacific. Deep ocean currents are upwelling in the eastern Pacific off the coast of South America (17°C isotherm at 50m), bringing nutrients to the surface waters of the eastern Pacific.
El Niño The convective air flow loop shifts east (central Pacific) causing droughts in western Pacific (Indonesia, Australia) and heavy rains in eastern Pacific. The deep ocean currents upwelling in the eastern Pacific collapses (17°C isotherm drops to 150m), so surface water primary production collapses. The convective air flow shift and resulting pressure shift changes the position of atmospheric circulation (jet stream shift), and changes global weather patterns.
La Niña This is the opposite of the El Niño phenomenon, an extreme version of the normal circulation pattern.
El Niño Impact in the United States
La Niña has the opposite effects El Niño Measurement and Prediction Tropical Atmospheric Ocean Array (TAO) 70 moored buoys measuring ocean temperature (surface to 500m), air temperature, precipitation, wind speed and direction, relative humidity, current direction communication from each buoy is by satellite TAO is maintained by a consortium involving the USA, France, Japan, Korea, and Taiwan. Check the following internet site for additional information: Acid Precipitation
pH scale (hydrogen ion concentration) pH scale is the positive exponents of H+ concentration, low pH is high acidity, high [H+]
Normal rain is slightly acidic due to atmospheric carbon dioxide forming carbonic acid in precipitation (pH 6). Acid rain is precipitation pH 4.5 or less. Sulfuric acid and nitric acid form in atmosphere from sulfur dioxide (SO2) and nitrogen oxides (NOx)
Sources Sulfur dioxide (SO2) 70% from electric utilities coal combustion, ore smelting gases Nitrogen oxides (NOx) 30% from electric utilities coal combustion, majority from internal combustion engines (automobiles) Atmospheric Transport Sulfur dioxide and nitrogen oxides transported 100’s miles by winds before deposition as acid precipitation National and international issue emissions in the midwestern U.S. causes deposition in N.E. U.S. and Canada emissions in England causes deposition in Scandinavia Effects Direct damage: foliage damage, high elevation trees Sensitive soils: poorly buffered (CaCO3) poor, soil parent rock granite (mountains) Non-sensitive soils: well buffered (CaCO3) rich, soil parent rock sedimentary limestone. Recall that limestone weathering results in acid neutralization, hydrogen ions (H+) are removed from water as carbonic acid dissociates to water and carbon dioxide (see below). Carbon Weathering (erosion and dissolution of carbonate rocks or sediments) Sensitive Soils Adirondacks, mid-Appalachian highlands, upper midwest, high elevation west, eastern Canada (Canadian shield region) Lakes and streams in sensitive soil areas are also poorly buffered
Effects on Sensitive Soils Terrestrial
Aquatic water pH decrease National Surface Water Survey (USA)
Eastern Canada Episodic acidification
Massive fish kills and sterile waters occur in sensitive areas.
Effects on Non-Sensitive Soil
Efforts to Reduce Emissions Clean Air Act Amendments 1990 Check the U.S. Environmental Protection Agency web site for more information of acid precipitation:
Stratospheric Ozone Depletion Ozone (O3) in stratosphere (6 - 20 miles elevation) absorbs 98% high energy UV (UV-B, UV-C) UV radiation dangerous
Ozone Depletion in Stratosphere Caused by Chlorofluorocarbons (CFC’s) and Halons (Bromine hydrocarbons) CFC and Halon uses: refrigeration, freezers, air conditioners, foaming agents, solvents, aerosol cans, fire extinguishers Unrelated Phenomena ground level ozone pollution (photochemical smog) global warming (but CFC’s are also greenhouse gases)
Ozone Formation and Destruction Natural Process in Stratosphere UV induced CFC Facilitated Destruction
Ozone Depletion Northern Hemisphere Depletion All halocarbons (CFC and halons) can cause ozone breakdown but some are more reactive than others. Halocarbons are also greenhouse gases. The lifespan of halocarbons in the stratosphere varies with each compound. The table that follows shows the reactivity of some halocarbons as relative ozone depletion potential (RODP) compared to CFC-12, the global warming potential (GWP) compared to CO2, and the lifetime in atmosphere.
International Protocols for the elimination of halocarbon emissions Montreal Protocol (1987) amended (accelerated schedules), London (1990), Copenhagen (1992) The scheduled phase-out and elimination of ozone depleting chemicals is resulting in a decrease in world CFC production, but notice that production is increasing in China. U.S. Congressional Research Service reports on stratospheric ozone depletion and the implications of the Montreal Protocol can be found at the Committee for the National Institute for the Environment (CNIE) web site at: www.cnie.org/nle/crsstrat.html. The CNIE web site (www.cnie.org) provides access to Congressional Research Service reports on a wide range of environmental issues, and links to many other sites.
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