The Princeton Guide to Ecology

By Simon A. Levin | Go to book overview

VII.5
Managing Nutrient Mobilization
and Eutrophication
D. W. Schindler
OUTLINE
1. History of the term
2. The role of thermal stratification
3. Natural and cultural eutrophication
4. Ratios and sources of key nutrients
5. Whole-lake experiments and their role in eutrophication control policy
6. Nonpoint sources of nutrients
7. The trophic cascade
8. Internal recycling of phosphorus
9. Eutrophication in flowing waters
10. Eutrophication and the quality of drinking water
11. Eutrophication of estuaries

Increasing the inputs of the nutrients phosphorus and nitrogen to freshwater bodies and estuaries causes increased growth of nuisance algae, termed eutrophication. In lakes, eutrophication can be prevented by controlling inputs of phosphorus. In estuaries, there is still controversy over whether nitrogen, phosphorus, or both must be controlled.


GLOSSARY

epilimnion. The uniformly warm upper layer of a lake when it is thermally stratified in summer.

eutrophic. Eutrophic lakes are richly supplied with plant nutrients and support heavy plant growths.

eutrophication. The complex sequence of changes initiated by the enrichment of natural waters with plant nutrients.

hypolimnion. The uniformly cool and deep layer of a lake when it is thermally stratified in summer.

mesotrophic. Mesotrophic lakes are intermediate in characteristics between oligotrophic and eutrophic lakes. They are moderately well supplied with plant nutrients and support moderate plant growth.

oligotrophic. Oligotrophic lakes are poorly supplied with plant nutrients and support little plant growth.

thermocline. Thermal or temperature gradient in a thermally stratified lake in summer. Occupies the zone between the epilimnion and hypolimnion.

Eutrophication is the word used by scientists to describe the result of overfertilization of lakes with nutrients. The first symptom noticeable to casual observers is that the fertilized lakes turn green with plant growth. Paradoxically, we value the increased growth of plants that follows fertilization on land but abhor similar effects in our waters.


1. HISTORY OF THE TERM

Eutrophication is derived from the German word eutrophe, which means “nutrient-rich.” The two nutrients that are responsible for increasing growth of algae and other aquatic plants are nitrogen and phosphorus. Eutrophic lakes typically have dense algal blooms. They can also have dense beds of rooted aquatic plants if the lakes have shallow areas with mud or sand bottoms.

The term eutrophication was coined by the German wetland scientist C. A. Weber in 1907 to refer to the rich wetlands in areas of Europe that received nutrient runoff from surrounding lands. The term was first applied to lakes by Einar Naumann roughly a decade later. The term oligotrophic (nutrient poor) was applied to nutrient-poor lakes, which generally have clear water and deep waters that contain high concentrations of oxygen. Lakes that are between these two extremes are generally termed mesotrophic. All three categories of lakes can undergo eutrophication if nutrient concentrations are increased. Recently, extremely eutrophic lakes have been termed hypereutrophic.

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