 |  Environmental Science: A Global Concern, 7/e William P. Cunningham,
University of Minnesota
Mary Ann Cunningham,
Vassar College
Barbara Woodworth Saigo,
St. Cloud State University
Biomes, Landscapes, Restoration, and Management
BE ALERT FOR: Changing Oxygen Quantities in Aquatic Systems
Temperature, light, and oxygen are important abiotic factors in ecosystems, including aquatic ones. They are distributed particularly unevenly in aquatic systems, however. All three of these factors are typically present in surface-to-bottom gradients, producing a prominent layering or stratification effect. Because of these differences, the composition of the plant and animal community can be significantly different in shallow waters than in deeper waters or at the bottom. These conditions often grade toward less light, cooler temperatures, and less available dissolved oxygen with increasing depth.
Complicating things for consumers in aquatic systems even more is the fact that oxygen levels undergo significant seasonal changes. This is particularly true in temperate lakes where deeper waters can become devoid of oxygen at certain times of the year. More of this story will be taken up in a later chapter.
BE ALERT FOR: Mending Ecosystems
Mitigating damage to an ecosystem means performing actions to reduce the adverse impacts of an action or to replace an ecosystem. As your text says, the ideal form of mitigation would be to avoid doing the damage in the first place. Failing that, the remaining options are to try to repair the damage or to provide a substitute.
The problem is that substituting one area for another that has been destroyed or creating an artificial ecosystem typically cannot truly replace the ecosystem processes present in the original community. Ecologists are fearful that the effort to protect natural ecosystems could easily be undermined by the attitude that it’s all right to destroy natural ecosystems because we can always create new ones to replace them.
One way around the problem would be to use replacement or substitute ecosystems only to address past acts of ecosystem destruction. By not doing it for actions to be taken in the future, society could avoid the risk of legitimizing further ecosystem destruction.
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2003 McGraw-Hill Higher Education