Figure 22.1. Generalized growth and
metabolic patterns for a typical annual
aquatic macrophute. - - = Biomass;
- -.. - - - = current gross productivity;
----- = current net productivity; - - =
current respiration rate; ...... = death losses. [From Wetzel, (1983a) after Westlake
(1965).J
0::
o
I
I~
o a::
(J
o SPR ING
The Littoral Zone
293
SELF-SHAOING
TI M E ~
SEASONAL MAXIMU M
BIOMASS
FLOWE RING '
ORIBUND
FRUITI NG
DVING
SUMMER
biomass. Maximum biomass, the maximum cumulative net production, is reached
when the current daily net productivity becomes zero. This type of annual growth is
characteristic of many plants in which the number ofperenniating organs decreases to a
mlmmum.
When much of the plant survives by means of below-ground tissue to the next
growing season, the annual net production may be estimated from the difference
between the final and initial biomass. Many aquatic plants lose a portion of the biomass
produced during the growing season, e.g., sloughing oflower leaves as the main apical
tissue grows. This complication requires that the rate of turnover of foliage be
evaluated [cf. Westlake (1965), Mathews and Westlake (1969), Dickerman and Wetzel
(1985), and Dickerman et a1. (1986)].
LITTORAL ALGAE
In comparison with the quantity of knowledge about phytoplankton, little is known of
the physiology or ecology of algae attached to substrata, loosely aggregated in the
littoral areas of lakes, or in shallow zones of streams. The littoral zones contain a
substantial number of microhabitats associated with surfaces of submersed macrophytes, with particulate detritus, and with the sediments. Moreover, these habitats are
changing constantly, e.g., as the larger plants grow, as sediments are redistributed, and
so on. As a result, attached algae are distibuted heterogeneously and are exposed to
more variable environmental conditions than are planktonic algae.
Because of the heterogeneity in distribution and growth of attached algae,
approaches to quantitative analyses have included placing artificial substrata (plates of
glass, blocks of styrofoam, and other materials) of defined surface area in the littoral
zone. These substrata are left for a period of several weeks for colonization by the
microflora [cr., reviews by Sladeckova (1962), Wetzel (1964), and Wetzel (1 983b)]. The
attached algae then are removed and analyzed quantitatively for biomass by
enumeration, pigment analyses, or other parameters (cf., Exercise 10). By the
incubation of colonized substrata in chambers, the oxygen difference and 14C-uptake
methods have been used to estimate rates of primary productivity [e.g., Allen (1971)].
metabolic patterns for a typical annual
aquatic macrophute. - - = Biomass;
- -.. - - - = current gross productivity;
----- = current net productivity; - - =
current respiration rate; ...... = death losses. [From Wetzel, (1983a) after Westlake
(1965).J
0::
o
I
I~
o a::
(J
o SPR ING
The Littoral Zone
293
SELF-SHAOING
TI M E ~
SEASONAL MAXIMU M
BIOMASS
FLOWE RING '
ORIBUND
FRUITI NG
DVING
SUMMER
biomass. Maximum biomass, the maximum cumulative net production, is reached
when the current daily net productivity becomes zero. This type of annual growth is
characteristic of many plants in which the number ofperenniating organs decreases to a
mlmmum.
When much of the plant survives by means of below-ground tissue to the next
growing season, the annual net production may be estimated from the difference
between the final and initial biomass. Many aquatic plants lose a portion of the biomass
produced during the growing season, e.g., sloughing oflower leaves as the main apical
tissue grows. This complication requires that the rate of turnover of foliage be
evaluated [cf. Westlake (1965), Mathews and Westlake (1969), Dickerman and Wetzel
(1985), and Dickerman et a1. (1986)].
LITTORAL ALGAE
In comparison with the quantity of knowledge about phytoplankton, little is known of
the physiology or ecology of algae attached to substrata, loosely aggregated in the
littoral areas of lakes, or in shallow zones of streams. The littoral zones contain a
substantial number of microhabitats associated with surfaces of submersed macrophytes, with particulate detritus, and with the sediments. Moreover, these habitats are
changing constantly, e.g., as the larger plants grow, as sediments are redistributed, and
so on. As a result, attached algae are distibuted heterogeneously and are exposed to
more variable environmental conditions than are planktonic algae.
Because of the heterogeneity in distribution and growth of attached algae,
approaches to quantitative analyses have included placing artificial substrata (plates of
glass, blocks of styrofoam, and other materials) of defined surface area in the littoral
zone. These substrata are left for a period of several weeks for colonization by the
microflora [cr., reviews by Sladeckova (1962), Wetzel (1964), and Wetzel (1 983b)]. The
attached algae then are removed and analyzed quantitatively for biomass by
enumeration, pigment analyses, or other parameters (cf., Exercise 10). By the
incubation of colonized substrata in chambers, the oxygen difference and 14C-uptake
methods have been used to estimate rates of primary productivity [e.g., Allen (1971)].