Human Impacts on the Biosphere Chapter 43

Eutrophication Human activities have increased the supply of nitrogen compounds available to primary producers, mostly through commercial fertilizers. Removal of vegetation removes nutrients from soil. Agricultural runoff results in excess nutrients in aquatic systems, causing oxygen depletion, then death of organisms. Lake Erie; Lake Washington

Acid Precipitation Burning of fossil fuels releases gases into the atmosphere which form acidic solutions when combined with water vapor. Sulfur oxides – sulfuric acid Nitrogen oxides – nitric acid Carbon dioxide – carbonic acid. pH decreases in lakes, rivers, etc, as well as soil, leaching nutrients, diminishing productivity, and harming organisms.

Toxins in the Environment Biological magnification – toxic substances become more concentrated higher up the food chain. Top-level consumers are most affected. Many toxins persist in the environment for long periods of time. DDT, mercury, PCBs (polychlorinated biphenyls).

Greenhouse Gases Naturally-occurring greenhouse gases include methane, carbon dioxide, and water vapor. Human activities produce more of these, plus nitrous oxides and CFCs. Intensification of greenhouse effect is referred to as “global warming” and may be contributing to climate change. Snow/ice melt, shifting plant/animal communities, extreme weather patterns.

Ozone Depletion Ozone (O3) in the stratosphere blocks most UV radiation from reaching the earth’s surface. Accumulation of CFCs has resulted in thinning of the ozone layer. Animation Montreal Protocol (1987) banned manufacture and use of CFCs. Some developing countries still use CFCs; CFCs persist in the atmosphere for decades.

Threats to Biodiversity Biological diversity includes species diversity, genetic diversity, and ecosystem diversity … all are resources for humans. #1 Habitat loss and fragmentation (managing protected areas) #2 Introduced species (control of transplanted species, restoration) #3 Overexploitation (establish population minimums, conservation) ALIENS!

New Species and Diseases Introduced species which are pathogens can have drastic effects on a population. Native species can have little natural immunity; acquired immunity and the evolution of resistance takes time. Dutch Elm Disease: Fungal (native to Asia) infection transmitted tree-to-tree or by bark beetles; hit the U.S. by 1930 from a shipment of logs from Europe. Small Pox: Virus probably from China; Europe, then Americas; ~30% mortality rate in Asia and Europe; 40 to 100% mortality for Native American tribes. Video