Trophic State and Eutrophication - Freshwater Ecology: Concepts and Environmental Applications - page 341

value of property on a lake can decrease with eutrophication. Algal blooms
are not aesthetically pleasing; they look bad and smell worse. The proba-
bility of objectionable algal blooms increases with greater cultural eu-
trophication (Hart et al., 1999). Taste and odor problems become more
acute as lakes become more eutrophic (Fig. 17.4). Both planktonic and at-
tached cyanobacteria contribute to taste and odor problems (Sugiura et al.,
1998). These problems related to eutrophication are difficult to solve with
standard water purification methods, leading to greatly increased costs for
supplying potable water (Wnorowski, 1992). To make matters worse, al-
gal blooms may be toxic; cyanobacteria and dinoflagellates produce neu-
rotoxins and hepatotoxins (see Sidebar 8.2). Toxin production may be
stimulated by phosphorus pollution (Jacoby et al., 2000)
Fish kills related to anoxic events are common symptoms of eutroph-
ication (see Sidebar 11.2). With a series of cloudy days or under an ice
cover in a eutrophic lake, fish may die. Cold-water fisheries can be estab-
lished in deep lakes with cool hypolimnia. If the hypolimnion is anoxic,
heat-intolerant fish have no refuge from high temperatures in the epi-
limnion. High pH associated with algal
blooms can also cause fish kills (Kann and
Smith, 1999). Finally, eutrophication can
lead to decreases in species richness and di-
versity of algae, which may have negative
consequences for the food web (Proulx
et al., 1996).

Sidebar 17.1.
Lago Di Monterosi: Anthropogenic
Eutrophication, BC

In the 1960s, G. E. Hutchinson assembled a
group of scientists to study the history of the
Italian Lago Di Monterosi (Hutchinson, 1970;
Hutchinson and Cowgill, 1970). The scientists
included paleontologists who worked on sedi-
ment cores from the lake, historians, a geolo-
gist, and limnologists. The group members
were from Italy, the United States, and Britain.
Lago Di Monterosi was formed by a volcanic
blast about 35,000 years ago. It has remained
shallower than 10 m since that time, and it ap-
proached a depth of 1 m during a very dry pe-
riod about 10,000 years ago. Analyses of pollen
and preserved remains of aquatic plants, ani-
mals and microalgae suggest that the lake re-
mained moderately productive until about 2000
years ago. During approximately the first 30,300
years, the lake slowly evolved into a shallow-
oligotrophic lake, became slightly acidic, and
contained some Sphagnum, indicating peat bog
formation, at least along parts of the shores.
Historical records and archeological re-
mains suggest that the Roman Empire built the
Via Cassia by 171 BC . The paved road was prob-
ably built to improve rapid transit from Rome to
the strategically important Tuscany. The road
passed through the edge of the lake water-

NATURAL AND CULTURAL PROCESSES
OF EUTROPHICATION

The idea that over thousands of years a
natural developmental ontogeny of lakes oc-
curs from deep and oligotrophic to shallow
and eutrophic, a wetland, and then a terres-
trial meadow has been present in the eco-
logical literature for decades. The filling of
lakes with sediments is a natural process be-
cause lakes are depressions in the watershed
that collect sediments over time. This idea
of a succession of lake types is applicable to
many small to medium lakes but must be
viewed with caution, especially in regard to
very deep lakes.
Large tectonic lake basins are generally
oligotrophic and likely will remain so for
the majority of their histories in the absence
of human intervention. For example, Lake
Baikal is millions of years old and about 1.5
km deep with up to 7 km of sediment (Fig.
6.6). The time period, if and when the Baikal
basin fills and becomes a shallow productive