Environmental Engineering Reference
In-Depth Information
16 Lake Production, Succession,
and Eutrophication
16.1
PRIMARY AND SECONDARY PRODUCTIVITY
16.1.1
p rIMary p roductIon
16.1.1.1 Introduction
Primary production refers to the rate at which new plant biomass is synthesized from inorganic
materials and energy. This production forms the base of the food chain, supporting all other lake
organisms. Since no transfer of energy is 100% eficient, the biomass that can be supported of
organisms that feed on the primary producers must be less than the biomass of the organisms on
which they feed. So, biomass or biomass productivity must decrease as one moves further up the
food chain, often depicted graphically as an ecological pyramid. Or, in a quote usually attributed
to G. Tyler Miller Jr., an American chemist: “Three hundred trout are needed to support one man
for a year. The trout, in turn, must consume 90,000 frogs, that must consume 27 million grasshop-
pers that live off of 1,000 tons of grass.” So, suficient biomass is required to support a healthy
food chain. On the other hand, excess primary productivity can also lead to problems (see e.g.,
Figure 16.1).
Primary production is controlled by a combination of physical (e.g., residence time, temperature,
and light), chemical (e.g., nutrients), and biological (e.g., grazing) conditions. Primary production
can be represented by Equation 16.1 (Stumm and Morgan 1996; Chapra et al. 2007; assuming for
this example that ammonia is used as a substrate):
P
R
+
2
+
14H
106CO HHPO
+
16
+
+
106
HO CHONP O
+
106
+
(16.1)
2
4
4
2
106
263
110
16 1
2
where P refers to production and R to respiration. So, while plants may produce biomass in the presence
of light, they also respire. The result produces diel variations in oxygen and carbon dioxide concentrations.
Gross primary productivity refers to the overall production of organic carbon, while net primary
production refers to the difference between gross production and respiration. This may be based
on individual plants, communities, or ecosystems. For example, an ecosystem's (or community) net
productivity would be the difference between gross primary production (GPP) and respiration by all
organisms: both autotrophs and heterotrophs.
Primary production (expressed as net or gross) refers to the rate of production of plant bio-
mass, as opposed to the quantity of that biomass, or the standing crop. Although the two are
related, they are different. The standing crop is a measure of the biomass at a point in time, but
tells nothing about how long it took to attain that biomass or the factors that affected it. For
example, there are many terrestrial ecosystems (e.g., some tropical forests) with high biomass,
but with low rates of productivity. Conversely, in lake systems, the biomass of planktonic algae
may be exceeded 100 times by annual production, so that the standing crop does not relect
annual production (Cole 1979).
In lakes, biomass or the standing crop is often directly related to the trophic state of lakes and the
stage in the succession of lakes. For example, the widely used trophic state index (TSI) developed
 
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