Ch Human Impact on the Environment

Of all animals, humans have the greatest impact on communities worldwide. Ex: logging, clearing for housing, mining, farming, reduction of species diversity In this unit we will look at several environmental problems: # 1 - Introduced Species:- humans move a species from its native location to a new geographic region. Either accidental or intentional. They gain a foothold, prey on native organisms, outcompete native species. Ex:kudzu (top left) zebra mussels (bottom left), fungus that causes Dutch Elm disease, European starlings, purple loosestrife, fire ants in Texas. Cost economy over $130 billion in damage and control efforts

# 2 Eutrophication - overfertilization of lakes, due to sewage outflow, agricultural fertilizers,and pesticides, which stimulate heavy algal growth,and explosions of bacteria that can eventually suffocate all aerobic life including fish. #3 Deforestation -the amount of nutrients leaving an intact forest ecosystem is controlled mainly by plants: no trees = loss of nutrients. #4 Toxic chemicals - Ex: mercury, DDT, PCBs, & an insecticide called pyrethroids to kill mosquitoes. They get stored in fat tissue and magnify up the food chain = biological magnification. (see left) DDT was banned in 1971 in U.S.

#5 Global Warming - there has been a marked increase in atmospheric CO 2 concentrations during last 150 years. Due to burning of fossil fuels and wood/deforestation. Warming of 2 degrees C could cause melting of polar ice caps, raise sea level, coastal cities would be underwater, alter precipitation affecting agriculture. #6 Ozone Layer Depletion - due to use of chlorofluorocarbons, used in refridgeration and in aerosol cans. Ozone layer protects us from UV radiation. Consequences - increase incidence of skin cancer, cataracts, damage crops and phytoplankton many nations ended production of CFC’s at least by year 2010.