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Source: Barnes and Mann (1991).

Source: Barnes and Mann (1991).

transport. The fish secretes mucus on the gills in response, and this reduces oxygen transport.

Dissolved organic carbon (DOC) in water absorbs ultraviolet (UV) light, which is harmful to algae. In the Experimental Lakes Area of Ontario, UV-B light normally penetrates 20 to 30 cm from the surface. When the lakes were experimentally acidified, the DOC precipitated and settled. UV-B penetration increased to almost 1.5 m.

Fish are most susceptible to low pH just after hatching. Aquatic invertebrates which provide food for fish at all stages may be affected. Lakes in Ontario and the eastern United States lose their lake trout population when their pH falls below 5.6 to 5.2. The eggs and tadpoles of frogs and toads are sensitive, but other amphibians, such as newts, are less so and may increase in abundance due to reduced competition. However, if the pH remains below 5, all animals and many plants will be eliminated. Some attached green algae and the acid-loving Sphagmum moss may flourish, sometimes maintaining primary productivity. Table 15.23 shows the impact of acidification on a variety of animal groups. Many of the lakes experienced total elimination of mollusks and leeches.

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