EXERCISE 10
Composition and Biomass
of Phytoplankton
The structure of photosynthetic populations in variations in spatial and temporal distribution.
aquatic ecosystems is dynamic and constantly Changes in species composition and biomass
changing in species composition and biomass may affect photosynthetic rates, assimilation
distribution. An understanding of community efficiencies, rates of nutrient utilization, grazing
structure is dependent on an ability to dif- rates, and so on.
ferentiate between true population changes and
SAMPLING
Phytoplankton in the open water of a lake or stream often is sampled by means of
water bottles such as the Van Dorn model (Fig. 7.1). These samplers are lowered
open to specific depths and then are closed by means of a weight messenger that is
dropped along the cable to trip the closing mechanism. Since a number of analyses
may be done on the same water sample, it is important that the surfaces of the
sampling device in contact with the water sample be chemically inert.
A Van Dorn or similar sampler may be too large to use in very shallow habitats
or in specialized situations where acute micro stratification of phytoplankton
populations is of interest. Horizontally held Van Dorn samplers frequently cause
major water distribance by creating turbulence. Small pumps driven by
battery-powered motors or simple hand-pump vacuum siphoning systems can be
effective with minimal disturbance at shallow depths. Sampling of phytoplankton
populations near the sediments may require coring devices (see Exercise 12), from
which samples can be removed carefully from the overlying water.
The manner in which sampling is done should conform to the objectives of the
studies. Analyses of species composition and biomass of algal populations are
time-consuming. Ecologically useful evaluations of species composition and biomass
may be made more effectively by less precise analyses of replicated samples from the
same place rather than by very precise analyses of a single sample.
Tubular or integrating water samplers [e.g., Schroder, (1969) and Straskraba and
lavornicky (1973)] permit the collection of water from the surface to some preselected
depth for a composite plankton sample. Such integrated samples may give more
139
Composition and Biomass
of Phytoplankton
The structure of photosynthetic populations in variations in spatial and temporal distribution.
aquatic ecosystems is dynamic and constantly Changes in species composition and biomass
changing in species composition and biomass may affect photosynthetic rates, assimilation
distribution. An understanding of community efficiencies, rates of nutrient utilization, grazing
structure is dependent on an ability to dif- rates, and so on.
ferentiate between true population changes and
SAMPLING
Phytoplankton in the open water of a lake or stream often is sampled by means of
water bottles such as the Van Dorn model (Fig. 7.1). These samplers are lowered
open to specific depths and then are closed by means of a weight messenger that is
dropped along the cable to trip the closing mechanism. Since a number of analyses
may be done on the same water sample, it is important that the surfaces of the
sampling device in contact with the water sample be chemically inert.
A Van Dorn or similar sampler may be too large to use in very shallow habitats
or in specialized situations where acute micro stratification of phytoplankton
populations is of interest. Horizontally held Van Dorn samplers frequently cause
major water distribance by creating turbulence. Small pumps driven by
battery-powered motors or simple hand-pump vacuum siphoning systems can be
effective with minimal disturbance at shallow depths. Sampling of phytoplankton
populations near the sediments may require coring devices (see Exercise 12), from
which samples can be removed carefully from the overlying water.
The manner in which sampling is done should conform to the objectives of the
studies. Analyses of species composition and biomass of algal populations are
time-consuming. Ecologically useful evaluations of species composition and biomass
may be made more effectively by less precise analyses of replicated samples from the
same place rather than by very precise analyses of a single sample.
Tubular or integrating water samplers [e.g., Schroder, (1969) and Straskraba and
lavornicky (1973)] permit the collection of water from the surface to some preselected
depth for a composite plankton sample. Such integrated samples may give more
139