Download Benthic Algae and Macrophytes

Benthic Algae and
Macrophytes
Benthic habitats
Epilithic - rock substrates
Epiphytic - plants
Epipelic - mud and silt
Epipsammic - sand
Epizooic - animals
Benthic Algae
Benthic algae are the dominant primary
producers in many shallow lakes and
streams
Distributions of benthic algae in lakes
are regulated by the penetration of light
Phytoplankton
Planktonic algae settle to the sediments and
resting stages may accumulate in sediments
Though the phytoplankton community may
receive some inoculum from the benthic
zone, algae from the benthos are not required
for the phytoplankton
All species of phytoplankton that are found in
a lake during the year may be found at any
time in the phytoplankton (though they may
be very rare at times)
Benthic Primary Production
In many lakes, benthic algae may
contribute a major portion of the primary
production in the lake and may even
provide the majority of the primary
production
Vascular Macrophytes
Emergent macrophytes
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Occur on submersed sediments to a water
depth of approximately 1.5 m
All produce aerial reproductive organs
Examples: Typha, Scirpus
Vascular Macrophytes
Floating-leaved macrophytes
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Occur at depths ranging from approximately 0.5 m
to 3 m
Possess both submersed and floating leaves
" Morphology of these different leaves may also be
different
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Reproductive organs may be both floating and
aerial
Examples: Nuphar, Potomogeton
Vascular Macrophytes
Submersed macrophytes
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The submersed macrophytes include many
vascular macrophytes as well as mosses and
charophytes
The submersed vascular macrophytes occur only
to a depth of approximately 10 m (one
atmosphere)
" Macroscopic algae and mosses may occur much deeper
as long as light intensities are sufficient to support
photosynthesis (mosses are restricted by the availability
of free CO2)
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Reproductive organs may be submersed, floating,
or aerial
Vascular Macrophytes
Free-floating macrophytes
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May be large to minute
Examples: Lemna, Azolla, Hydrocharis
Annual Growth Patterns
Maximum biomasses of aquatic macrophytes
generally occur in late summer
Germination occurs in the spring
Exponential growth phase occurs in spring
and early summer
Macrophytes begin to self-shade in summer
During the period of maximum biomass, the
reproductive phase occurs
After reproduction in late summer, the
macrophytes senesce and die
Patterns of Primary Production
In nutrient-poor lakes, attached algae
and phytoplankton dominate the low
levels of primary productivity
As fertility increases, primary
productivity by submersed macrophytes
and attached algae become dominant
Patterns of Primary Production
As fertility increases further, shading by
phytoplankton, attached algae, and the
macrophytes themselves cause a
dramatic reduction in the contribution of
submersed macrophytes to the primary
productivity
Patterns of Primary Production
Primary productivity is dominated by
attached algae and phytoplankton
The relative amounts of primary
productivity by the attached algae
decreases because of the decline in
submersed macrophytes but the
contribution is still significant
Patterns of Primary Production
With increasing fertility and decline of
submersed macrophytes, relative contribution
of the emergent macrophytes increases
In extremely fertile lakes, contribution of
phytoplankton decreases because of selfshading
In shallow lakes, emergent macrophytes and
attached algae on them provide most of the
primary production