Accelerated aquatic plant growth: too much, too fast

The growth and reproduction of aquatic plants is stimulated by eutrophication, a natural process which, over geological time, turns a lake into a bog and eventually into land. But today, in many places, this process is tremendously accelerated by high concentrations of phosphorus and nitrogen (from fertilizer, for example) which enrich the water with nutrients, causing the aquatic plants to bloom. As the plant growth explodes, it chokes off the oxygen supply normally shared with other organisms living in the water. When the plants die, their decomposition uses up even more oxygen. As a result, fish suffocate and die, and bacterial activity decreases.

Yet if phosphorus and nitrogen inputs are reduced or stopped, the system can recover by itself. In the late 1960s, Lake Erie experienced such an extreme case of eutrophication that fish were dying and the decomposing algae, washed up on bathing beaches, had to be removed with bulldozers.

The phosphorus (phosphate) in laundry detergents washed into the lake was the main culprit. A law was passed to reduce the substance, and in 1972 laundry detergent phosphate contents were cut by approximately 90%. Lake Erie has since made a remarkable recovery.

Water Pollution Menu  Previous  Next