Some of the ways in which water pollution affects plants may be fairly obvious. An increase in numbers or a dramatic swelling of a population can be relatively easy to detect. Other ways in which plants may be affected can be more subtle. Of, course besides known or observed effects there may well be those that are as yet unstudied and unknown.
Eutrophication is a term ecologists use to describe an increase in nutrients in an aquatic community like a pond or a lake or a wetland. An increase in nutrient levels, or eutrophication, is a natural process that occurs over time in many aquatic ecosystems. When there’s an unnatural source of nutrients entering an aquatic ecosystem, though, something ecologists call accelerated eutrophication can occur. An example of this would be farm runoff or other sources of fertilizer flowing into a pond and essentially fertilizing it. The effect on plant life in the pond is an increase in plant growth stimulated by excess nutrients. This can result in what otherwise would be more or less open water being choked by an extreme overgrowth of vegetation.
Plants whose excessive growth is stimulated by water pollution in the form of extra nutrients eventually die. And because plants are living, growing and dying in increased numbers—or increased biomass—the result is a buildup of dead plant material. Then microbes, including bacteria, decompose the dead vegetation and in the process use oxygen. This is another process that occurs in an unpolluted body of water. But where pollution is increasing the nutrient level and the excess plant growth—and the decomposition is also excessive—in turn microbial consumption of oxygen is also increased. This further results in reduced oxygen levels in the water, a condition called “hypoxia.” The low oxygen levels can adversely affect all manner of organisms, including plants, in the biological community of a pond or other body of water.
In addition to giving off oxygen through photosynthesis, green plants need oxygen in their surrounding environment for their own metabolism. So the reduced oxygen levels traced back to the water pollution can affect plants as well as many other organisms detrimentally.
Besides unnatural and increased growth from eutrophication, plants can accumulate a whole range of toxic loads in their tissues. Whether or not this manifests itself as obvious effects on the plants directly, there can still be an impact. Biomagnification—the accumulation of contaminants working their way up the food chain—is a real and insidious threat. A class of compounds known as endocrine disruptors is implicated in detrimental physiological effects on fish and amphibians, among other organisms. Just what effect this has on the plants themselves is a matter for continuing study.
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