Typical organisms
in aquatic environments (oceans, estuaries, salt marshes, lakes,
ponds, rivers and springs) include:
phototrophs
oxygenic phototrophs - cyanobacteria
(Nostoc, Anabaena, Oscillatoria,
Synechocystis), algae (Cholrella,
Chlamydomonas) and diatoms prevail in aerobic
areas (especially in surface layers of water); these are
generally the primary producers (determine biological activity
of ecosystem)
phytoplankton - float in the photic zone (top 300
meters of water); neusonic organisms are those that float at
the water-atmosphere interface
benthic algae - attached to bottom or "sides" of
aquatic basins
anoxygenic phototrophic bacteria prevail in
anaerobic areas, especially in deeper regions or on the bottom
of freshwater or marine environments
phototrophs - e.g., Green Sulfur Bacteria such as
Chlorobium, Purple Sulfur Bacteria such as
Chromatium
photoheterotrophs - e.g., Purple NonSulfur Bacteria such
as Rhodospirillum, Rhodopseudomonas,
Rhodomicrobium
chemotrophs - mostly
found in water to a depth of 1000 meters
protozoa - e.g. such as Paramecium,
Didinium, Dinoflagellates
Productivity in various
aquatic environments
oceans
productivity of open ocean areas is generally very low
because inorganic nutrient levels needed for phytoplankton
growth are low (exceptions are in areas where currents or winds
cause upwelling of water, which brings nutrients to the
surface)
productivity of inshore ocean areas is generally high
because nutrient levels are high due to enrichment from rivers,
etc.
lakes - productivity generally
high-to-very high, depending upon nutrient concentrations
rivers - high productivity due to
good aeration (water flow mixes) and organic matter supply
Disruption of aquatic
environments
eutrophication - nutrient
enrichment (especially P and N) stimulates growth of plants, algae
and bacteria, frequently upsetting the "normal" balance of
organisms
cyanobacteria grow faster than algae at higher
temperatures (30-35C)
cyanobacteria grow faster than algae at higher pH
(8.5-9.5)
carbon dioxide is used at high rates during
photosynthesis
cyanobacteria thus select for themselves by raising
the pH of the water
cyanobacteria produce hydroxamates, which bind iron,
thus restricting its supply for other organisms (including
algae)
excess of organics causes organotrophs to dominate the
aquatic habitat - this also increases the rate of oxygen
consumption, leading to oxygen depletion in extreme cases
at low organic compound levels, algal growth predominates,
thus replenishing oxygen; this eventually selects against them,
because they can't grow at higher oxygen levels
thermal
stratification - development of temperature gradients; get
"turnover" due to changes in heating and specific gravity in
spring and fall
epilimnion - warmer, upper layer of water
hypolimnion - cooler, lower layer of water
thermocline - zone of rapid temperature decrease
between epilimnion and hypolimnion
oxygen stratification
nutrient-poor (oligotrophic) water is generally aerobic
throughout, even though significant photosynthetic oxygen
production generally occurs near the surface of most bodies of
water (depends upon clarity of the water and which phototrophs
are present)
nutrient-rich (especially eutrophic) water in temperate
regions is frequently aerobic near the air/water interface and
anaerobic near the bottom during the summer, but "turns over"
during the winter, reaerating the deeper water
during summer the sun heats the surface layer
(epilimnion) so it becomes warmer and less dense than the
colder, more dense bottom layer (hypolimnion); the two
layers are separated by a transitional thermocline region,
in which the temperature and density of the water changes
rapidly with increasing depth
during winter the surface layer becomes colder and more
dense than the bottom layer, so it sinks, mixing with the
deeper water and reaerating the bottom layer
