Global Effects of Ozone Depletion
Ozone depletion in the earth’s atmosphere is under constant scrutiny by the American press and people. Perhaps the concern is warranted; the ozone layer protects life on earth by absorbing 97-99% of the damaging ultraviolet radiation from the sun (U.S. Environmental Protection Agency, 2006). Over the past twenty years, the stratospheric ozone has decreased approximately 3% per decade. Possible concerns have been raised about loss of polar caps, DNA damage, increased human health risks, and environmental process disturbance. Emerging research has helped clarify effects of global ozone depletion. Three areas that have received recent scientific attention include UV effects upon macroalgae, decomposition, and nitrogen fixation.
Ozone is depleted both by natural and industrial sources. One natural source of depletion is volatile organohalogens, which are produced by marine macroalgae (Laturnus, et. al., 2004). Scientists are not sure why macroalgae produce organohalogens, but many believe it is due to stress. UV radiation is a known source of plant stress. If this is the case, then plants would likely produce more organohalogens if exposed to increased UV radiation. To test this hypothesis, a group of Swedish scientists applied increased levels of radiation to five marine macroalgal species. After four hours, the levels of organohalogens produced by the macroalgae were measured. The scientists found that “exposure to ultraviolet radiation rendered a significant increase in the concentration of four or more of the volatile organohalogens for each of the studied macroalgal species” (Laturnus, et. al., 2004).
Although the findings appear quite disturbing initially, the increases in chloroform and methyl iodine are relatively minor. Macroalgae (natural sources) account for less than .2% of the global input of chloroform and methyl iodine (Laturnus, et. al., 2004). However, approximately 90% of chloroform comes from natural sources. Therefore, if increased UV radiation has a similar effect on other natural chloroform-emitting sources, the increase in organohalogens could be much more significant. If such an increase were significant, it would create a vicious circle – increased UV radiation causes stress to living organisms; increased stress causes a higher production of organohalogens; organohalogens breakdown stratospheric ozone; lower levels of ozone increase earth’s surface radiation.
Increased surface radiation has also been linked indirectly to increased decomposition time. Barley that has been exposed to increased levels of UV-B radiation has been shown to have increased levels of lignin (a binding agent) and cellulose (Pancotto, et. al., 2005). Microbes are unable to breakdown lignin and cellulose as quickly as soluble carbohydrates. As a result, decomposition takes longer. Scientists speculated that barley litter exposed to higher levels of UV radiation would decompose...