Chapter 5 ENVIRONMENTAL CHALLENGES

A. Challenges To The Air 1. Air Pollution Air pollutants include heavy metals (lead), particulates (asbestos) & emissions from fossil fuel combustion (SO 2, NO 2, CO 2 ). When did we start polluting our air? Roman Empire (500BC-300AD) - metal smelters released lead into atmosphere.

Industrial smog - air pollution resulting directly from industrial & urban emissions. “London fog” incident (1952) made us aware of air pollution. Photochemical smog - air pollution resulting from vehicle emissions that react in the presence of sunlight. Ozone (O 3 ) is major component of photochemical smog.

2. Acid Deposition (rain, snow, fog, dew, particles) All precipitation is slightly acidic: CO 2 + H 2 O  H 2 CO 3 (carbonic acid) Burning of fossil fuels releases SO 2 & NO 2 SO 2 + H 2 O  H 2 SO 4 (sulfuric acid) NO 2 + H 2 O  HNO 3 (nitric acid)

Effect on lakes: lowers pH by 3.0 to 5.0 units toxic metals (aluminum & mercury) leach from sediments biodiversity plummets Effect on coniferous forests: thins trees & yellows needles Al 3+ released by soil blocks uptake of nutrients (Ca 2+ & Mg 2+ ) by roots Clean Air Act (1970) mandates reductions in sulfur & nitrogen oxides from autos, power plants & smelters.

4. Global Warming Primary cause is increase of CO 2 in stratosphere. Increase due to burning of fossil fuels & tropical deforestation. CO 2 traps infrared radiation (heat), preventing it from exiting the atmosphere.

B. Challenges to the Land 1. Deforestation Removal of all tree cover from a forested area. Tropical rain forests Cleared to harvest valuable timber, and to make way for subsistence farming. ~ ½ have already been cleared.

Temperate forest of North America Clearing began with arrival of European settlers. Cleared to harvest timber & turpentine, and to make way for agriculture. < 1% of the original temperate forest in southeast US survives.

2. Desertification Expansion of desert into surrounding areas. Cattle grazing is cause of expansion of Africa’s Sahara desert. Irrigation of cotton is cause of desertification of Asia’s Aral Sea.

D. Loss of Biodiversity Biodiversity is believed to be a critical factor in maintaining the stability of natural systems. Diversity-stability hypothesis proposes that an ecosystem with high biodiversity is better able to survive disturbances (floods, hurricanes) than an ecosystem with low biodiversity.

Causes of diminished biodiversity: Habitat destruction Humans are directly involved in altering many habitats (convert natural areas into farms, subdivisions, industrial centers, marinas). reduction of nesting & overwintering habitats led to decline of migratory songbirds (warblers, flycatchers)

Introduction of nonnative (exotic) species Introduced exotic species may displace native species. brown tree snake in Guam zebra mussels in the Great Lakes Hydrilla verticillata in Florida rabbits in Australia western corn rootworm in Yugoslavia

Humans have begun process of trying to correct past mistakes. Enacting environmental legislation Clean Air & Clean Water Acts Endangered Species Act (1973) Implementing restoration projects (Everglades & Aral Sea plans) Creating refuges for native species Slowing human population growth

Overall goal – To protect resources for the future, while maintaining a reasonable standard of living for all people.