Environmental Engineering Reference
In-Depth Information
Lake phytoplankton
N, 11%
Neither, 15%
A
P, 27%
62 studies
N+P, 47%
Wetland plants
N+K, 9%
K, 7%
N+P, 7%
N, 42%
B
45 studies
P, 36%
Stream periphyton
N, 13%
Neither, 25%
P, 18%
C
158 bioassays
N+P, 44%
FIGURE 16.6
Summary of nutrient bioassays reported in the literature indicating stimula-
tion of biomass of phytoplankton (A), wetland plants (B), and stream periphyton (C). Data in
A from Elser
et al.
(1990a), data in B from Verhoeven
et al.
(1996), and data in C compiled
from various sources. Percentage of the total cases is given after each type of fertilization.
equally available in environments (e.g., pulses of nutrients occur), and not
all organisms have the same competitive abilities. Models have been
proposed for multiple limiting factors (Verduin, 1988), but these have not
been well investigated. In contrast, the links between Leibig's law and phy-
toplankton diversity have been well investigated.
The Paradox of the Plankton and Nutrient Limitation
The
paradox of the plankton
was proposed by Hutchinson (1961). Al-
though it may be viewed as a “straw man” given what is currently known
about aquatic ecology, the paradox forms a useful starting point for dis-
cussion and perhaps forms the basis for the most common question asked
in aquatic ecology graduate qualifying exams in the past 30 years.
The paradox is based on applying Leibig's law and the
competitive ex-
clusion principle
(Hardin, 1960) to phytoplankton communities. Compet-
itive exclusion occurs because only one species can be the superior com-
petitor for a single limiting resource. In an environment in which several
species are competing for a single resource, the superior competitor even-
tually will drive the others to local extinction.
Hutchinson argued that because lakes are very well-mixed environments,
limiting nutrients are well mixed and equally available to the phytoplankton.
Given that most cells have similar requirements and are competing for the
Search WWH ::
Custom Search