Trophic State and Eutrophication - Freshwater Ecology: Concepts and Environmental Applications - page 364

6. bans on phosphorus-containing detergents and treatment methods such
as chemical precipitation and denitrification to remove nutrients from
wastewater.
6. Management of eutrophication in lakes includes oxygenation of the
hypolimnion, addition of chemicals to precipitate phosphorus, and
chemicals that kill algae.
7. Case studies of eutrophication demonstrate that controlling sources of
nutrients and improving water management, rather than treating the
symptoms of eutrophication, are the best way to avoid problems
associated with excessive nutrients. In lakes, correcting eutrophication
problems is much more difficult after the lake has become excessively
productive and O 2 disappears from the hypolimnion.
8. Wetlands can also become eutrophic. Wetlands have been used for
tertiary treatment of sewage because of their ability to retain
nutrients. The Everglades have been harmed by eutrophication
through mismanagement of the drainage basin.

QUESTIONS FOR THOUGHT

1. Why is a common classification system
for trophic state useful for aquatic
scientists, even if it is mainly a way to
classify a continuous gradient of habitat
type?
2. Why is the notion of a slow, constant
movement toward a more eutrophic
state in natural systems probably naive?
3. Why does a lake manager need to be
aware of the variance associated with
loading equations when making
management recommendations?
4. Why might some ecoregions have lakes
that naturally have blooms of
heterocystous cyanobacteria?
5. Why would addition of Fe 3 to remove
PO 4 3 from the epilimnion cause only
temporary relief from eutrophication
when the hypolimnion is anoxic?
6. Why is the relationship between total P
and planktonic chlorophyll in lakes
stronger (less variable) than the
relationship between total P in streams
and benthic chlorophyll?
7. Why might eutrophication of wetlands
make insectivorous plants, such as sun
dew and Venus flytrap, less competitive?
8. Some people have treated eutrophication
problems in lakes by diluting them with
river flow. What conditions are
necessary for this solution to work?

ations in hydrology (Newman et al., 1998) and
increases in agricultural runoff (Doren et al.,
1996). Increases in agricultural activities have
been related to almost a threefold increase in
input rates of phosphorus compared to histori-
cal levels (Davis, 1994). A major increase in sug-
arcane production in the area was fueled by the
crisis in relations between the United States
and Cuba in the 1950s and 1960s (Harwell, 1998).
Controlling phosphorus inputs from up-
stream agriculture will be difficult. Control will
require advanced water treatment of agricul-
tural runoff, purchase of sugar farming opera-
tions, curtailing fertilization, or some combina-
tion of these measures. To further complicate
eutrophication management, conversion of
mercury deposited from the atmosphere to
more readily bioconcentrated toxic forms
(methylmercury) by microbes occurs at lower
rates under more eutrophic conditions, leading
to less contamination of fishes (Gilmour et al.,
1998). Thus, eutrophication may lead to fewer
fish consumption advisories.
Despite the best efforts to preserve the Ever-
glades, they are severely threatened. They may
retain long-term biotic integrity only if a series
of steps are taken to control nutrient inputs,
provide a natural hydrologic regime, and con-
trol atmospheric inputs of mercury.