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Exercise 22
LITTORAL MACROFLORA
Distribution and Biomass of Vegetation
The qualitative distribution of the macro vegetation may be analyzed by careful
sampling within quadrats. Sampling sites can be selected from either a stratified
random design or along a transect (see discussions in Exercise 11 and Appendix 2). The
calculation of relative abundance (percent) of species within a given area is helpful in
interpreting data obtained by intensive quantitative measurements of biomass.
Although many marsh and aquatic plants can be identified to species from their
vegetative characteristics, reproductive parts are frequently needed for positive
identification [cr., Muenscher (1944), Fassett (1957), Mason (1957), Prescott (1969),
Correll and Correll (1972) and Godfrey and Wooten (1979, 1981)].
As much as 90% of the biomass of aquatic plants can occur below ground. While the
average percentage of biomass production below the sediments is higher among
emergent macrophytes than in submersed plants, in all cases it is essential to sample
biomass from both above and below ground in any quantitative study. Among annual
plants which reproduce by seed, the biomass persisting from one year to the next is
negligible. Because most aquatic plants are perennial, the above-ground biomass dies
and enters the detrital pool annually; part of the below-ground biomass dies, but much
of it remains alive and perenniates new shoots for several years (up to 15 yr in certain
water lilies). Analysis of growth, then, is complicated in that the quantity of roots
/rhizomes often constitutes the cumulative result of several years growth. Estimations
of annual turnover rates of root material are possible but require rather elaborate
experimental techniques.
The determination of the below-ground biomass of macrophytes requires care
because it is difficult to differentiate which parts are living and which are dead. Often
when the below-ground materials are separated, the color of the roots is a rough
indicator of which are alive (lighter color, more firm in texture) and which are dead
(darker browns, black; softer). Tetrazolium dyes, some of which become red when
they react with respiratory products, can be helpful in determining viability.
Since the below-ground biomass is usually very dense, it is impractical to estimate
this biomass from whole quadrats (e.g., 0.25 m 2 ) used to determine above-ground
biomass. Therefore, replicate sediment cores including the below-ground biomass often
are taken within the quadrats. The material from these cores then is washed with a
vigorous stream of water over a straining sieve to catch any fragments. The living
components are separated from the dead.
The dry weight of the biomass is determined after drying the material for 24 h at
105°C or by freeze-drying. Representative samples then are homogenized, and
subsamples are combusted for at least 4 h at 550°C to remove organic matter from ash
materials. Dry weight less ash weight yields ash-free dry (organic) weight. The average
amount of carbon in the organic matter of aquatic macrophytes has been found to be
46.5 % of ash-free dry weight (Westlake, 1965).
Productivity of Macrophytes
The primary productivity of macrophytes is most commonly evaluated by changes in
biomass. In an annual plant, the initial biomass of seeds is negligible, and biomass
changes follow a typical sigmoid growth curve (Fig. 22.1). Gross productivity decreases
with time and becomes negative as respiration continues to increase with greater
Exercise 22
LITTORAL MACROFLORA
Distribution and Biomass of Vegetation
The qualitative distribution of the macro vegetation may be analyzed by careful
sampling within quadrats. Sampling sites can be selected from either a stratified
random design or along a transect (see discussions in Exercise 11 and Appendix 2). The
calculation of relative abundance (percent) of species within a given area is helpful in
interpreting data obtained by intensive quantitative measurements of biomass.
Although many marsh and aquatic plants can be identified to species from their
vegetative characteristics, reproductive parts are frequently needed for positive
identification [cr., Muenscher (1944), Fassett (1957), Mason (1957), Prescott (1969),
Correll and Correll (1972) and Godfrey and Wooten (1979, 1981)].
As much as 90% of the biomass of aquatic plants can occur below ground. While the
average percentage of biomass production below the sediments is higher among
emergent macrophytes than in submersed plants, in all cases it is essential to sample
biomass from both above and below ground in any quantitative study. Among annual
plants which reproduce by seed, the biomass persisting from one year to the next is
negligible. Because most aquatic plants are perennial, the above-ground biomass dies
and enters the detrital pool annually; part of the below-ground biomass dies, but much
of it remains alive and perenniates new shoots for several years (up to 15 yr in certain
water lilies). Analysis of growth, then, is complicated in that the quantity of roots
/rhizomes often constitutes the cumulative result of several years growth. Estimations
of annual turnover rates of root material are possible but require rather elaborate
experimental techniques.
The determination of the below-ground biomass of macrophytes requires care
because it is difficult to differentiate which parts are living and which are dead. Often
when the below-ground materials are separated, the color of the roots is a rough
indicator of which are alive (lighter color, more firm in texture) and which are dead
(darker browns, black; softer). Tetrazolium dyes, some of which become red when
they react with respiratory products, can be helpful in determining viability.
Since the below-ground biomass is usually very dense, it is impractical to estimate
this biomass from whole quadrats (e.g., 0.25 m 2 ) used to determine above-ground
biomass. Therefore, replicate sediment cores including the below-ground biomass often
are taken within the quadrats. The material from these cores then is washed with a
vigorous stream of water over a straining sieve to catch any fragments. The living
components are separated from the dead.
The dry weight of the biomass is determined after drying the material for 24 h at
105°C or by freeze-drying. Representative samples then are homogenized, and
subsamples are combusted for at least 4 h at 550°C to remove organic matter from ash
materials. Dry weight less ash weight yields ash-free dry (organic) weight. The average
amount of carbon in the organic matter of aquatic macrophytes has been found to be
46.5 % of ash-free dry weight (Westlake, 1965).
Productivity of Macrophytes
The primary productivity of macrophytes is most commonly evaluated by changes in
biomass. In an annual plant, the initial biomass of seeds is negligible, and biomass
changes follow a typical sigmoid growth curve (Fig. 22.1). Gross productivity decreases
with time and becomes negative as respiration continues to increase with greater