Zoology · Ch 13 — Environmental Issues
Eutrophication
Eutrophication
When run-off from land carrying nutrients reaches water bodies such as lakes, it results in dense growth of plant life -- a phenomenon called eutrophication. This is, in one sense, a completely natural process: lakes age naturally, and this ageing is itself accompanied by gradual nutrient enrichment of the water. A young lake begins in the oligotrophic stage, where the water is cold and clear and supports relatively little biological life. Over time, streams draining into the lake introduce nutrients such as nitrates and phosphates, which encourage the growth of aquatic organisms; aquatic plants and animal life then grow more rapidly, and organic remains begin to accumulate on the lake bottom, marking the mesotrophic stage. Left undisturbed, this natural ageing process would take place over very long geological timescales. The problem is that pollutants from human (anthropogenic) activity -- effluents from industries and homes -- can radically accelerate this ageing process; when human activity is the driver rather than natural ageing alone, the phenomenon is specifically termed cultural or accelerated eutrophication. Excess nutrients stimulate explosive growth of algae and water hyacinth, which can clog canals, rivers, and lakes, displac …
What this figure shows. A diagram titled 'Stages of Eutrophication' depicting a lake's progression through the stages of nutrient enrichment described in the text. An early panel shows the oligotrophic stage: a lake with cold, clear, relatively empty-looking water and minimal visible plant growth, representing a nutrient-poor, low-productivity state. A later panel shows the mesotrophic stage: the same lake with visibly denser aquatic plant growth near its margins, more turbid water, and organic material beginning to settle and accumulate on the lake bottom, reflecting the effect of nutrients such as nitrates and phosphates draining in from surrounding streams. The progression from one panel to the next visually captures the section's central point that eutrophication is a gradual, sequential ageing process moving a water body from a clear, low-nutrient state toward an increasingly nutrient-rich a …