Lake Production, Succession, and Eutrophication - Hydro-Environmental Analysis: Freshwater Environments - page 457

TABLE 16.2
Selected Common Characteristics of Oligotrophic and Eutrophic Lakes

Characteristic Oligotrophic Eutrophic

Bathymetry Steep shoreline, bottom Shallow, moderate to low bottom slope

Nutrient and organic matter enrichment Low High

Phytoplankton growth Little High

Macrophyte growth Low Extensive

Plant biomass Low High

Productivity Low High

Sedimentation accumulation Low High

Light penetration (e.g., Secchi depth) Deep Shallow

Oxygen content High throughout water column Low to none in hypolimnion

Fisheries Usually cold water, may be two layer Warmwater isheries

He then went on to make some rather disparaging remarks about the farmer, “whose farm abutted
on this sky water, whose shores he has ruthlessly laid bare,”… “who never saw it, who never bathed
in it, who never loved it, who never protected it, who never spoke a good word for it, nor thanked
God that He had made it.”
Thoreau's ponds illustrate many of the characteristics of, and controversies associated with, the
trophic status of lakes. For example, are “lakes of crystal glass” the most desirable? To a poet per-
haps, but to a isherman? Also, what impact does man have on that trophic status, as did Thoreau's
farmer? The topic of cultural eutrophication is discussed later, but irst more comparisons of the
characteristics of the trophic status of lakes.
Oligotrophic lakes, as with Thoreau's description of Walden Pond in 1854, can be thought of as
crystal-clear waterbodies with typically rocky shores and steep shorelines. These lakes typically
have low-nutrient concentrations and low productivity, so they remain clear. Since productivity is
low, there is little decay, so the hypolimnion remains oxic. For example, extremely deep oligotro-
phic lakes, such as Lake Superior and Lake Tahoe, have hypolimnia that remain completely satu-
rated with oxygen the entire year.
Eutrophic lakes, in contrast, are often relatively shallow, with larger contributing watersheds and
higher nutrient loads and productivity. Often associated with higher productivity and solids loads,
the light penetration is much reduced. Seasonal variations are greater and, due to the seasonally
higher productivity and lower light penetration, the hypolimnion of many eutrophic lakes is void of
oxygen for much of the year.
There are exceptions to each of the aforementioned trophic classiications, so that, for example,
an anoxic hypolimnion does not necessarily indicate eutrophy. Some of the more common charac-
teristics of oligotrophic and eutrophic lakes are summarized in Table 16.2. Mesotrophic lakes are
intermediate between these two. One of the primary differences between the trophic statuses of
lakes, as discussed in the following section, is due to their productivity and biomass.

16.3 EUTROPHICATION

16.3.1 e utropHIcatIon p aradIGM
The term eutrophication has been commonly used to characterize the natural process of the aging
of lakes, or the successional changes in a lake's trophic status. The trophic state, as described by
Naumann, refers to the amount of plant biomass in a body of water (Carlson and Simpson 1996) or
plant productivity. Eutrophication is then taken as the natural progression of lakes from those with
low plant biomass (or low productivity or both), Naumann's oligotrophic lakes, to those with high