also loosen metals, releasing them from the soil into surface and groundwater where they can affect plant growth and aquatic life (Tennesen 1997)." Air pollutants can weaken trees extremely by starving and poisoning them, and burning their leaves. Once the trees have been weakened, all they need are some harsh weather conditions to finish them off.Another study conducted on the affects of ozone on plants found that brittle leaves on some plants may be caused by ozone damage. The study tested the affects of ozone on major U.S. crops such as soybeans, green beans, barley and wheat. All crops showed the same brittle characteristics after exposed to common ozone levels. This may explain the estimated $5 billion annually in reduced yields for farmers (Bock 1988).Another common organism that has been extremely affected by air pollution is lichen. Lichens are weather-hardy and widely distributed life forms that grow on rocks, stumps, shingles, and tree branches (Bennett 1996). A common misunderstanding of lichen is that they are a single organism, but they are actually formed of two separate organisms that depend on one another for survival (a fungus and an alga). "Because they lack a cuticle or skin, they are exposed directly to the atmosphere and, along with nutrients and water, they soak up lead, sulfur, zinc, cadmium, and an array of other chemical and heavy metal air pollutants (Bennett 1996)." Due to the lichens sensitivity to air pollution, they are used as indicator organisms for air pollution levels. Lichens have been proven to accurately show levels of pollution even in remote and seemingly pristine environments. Although lichens have come in handy as indicator organisms, some species are at risk of becoming endangered or extinct. "Chronic exposure over long periods of time could result in the loss of species well beyond the dozen lichen deserts now identified in North America (Bennett 1996)."Air pollution has negatively affected so...
