Aquatic Ecosystems
Aquatic Ecosystems
 The major kinds of aquatic environments are streams
and rivers, lakes, wetlands, estuaries, and oceans.
 Each of these can be subdivided further with respect
to many factors.
Aquatic Ecosystems
 In aquatic ecosystems, depth, water temperature,
flow rate, and oxygen and nutrient concentrations
are the dominant physical factor
 Many of the producers in many aquatic ecosystems
are single-celled algae
 Aquatic ecosystems have been classified by salinity,
water movement, and depth
Flowing Water: Streams and Rivers
 All aquatic ecosystems interact with the terrestrial
biomes that surround them
 Streams receive runoff, groundwater, and organic
matter from the surrounding land
 A variety of organisms live their lives in both aquatic
and terrestrial environments
Flowing Water: Streams and Rivers
 Could you name some other interactions between
aquatic ecosystems and terrestrial biomes?
 Frogs and salamanders, for example, have aquatic
larval stages and terrestrial adult stages
 Some terrestrial animals feed on organisms that grow
in streams and lakes
 Many organisms with aquatic larval stages, such as
mosquitoes, feed on terrestrial organisms
Flowing Water: Streams and Rivers
 Stream and river systems are referred to as lotic
systems
 Flowing water erodes
 Rivers and streams are created by erosion
 Most streams and rivers are older than lakes –
although they move around more
Flowing Water: Streams and Rivers
 Streams form wherever
precipitation exceeds
evaporation
 Streams grow with distance
as they join together with
rivers
Flowing Water: Streams and Rivers
 River continuum conceptecosystems are more complex and
more productive downstream
because water flows more slowly
and becomes warmer and richer in
nutrients.
Flowing Water: Streams and Rivers
 Riffle areas are where
water runs rapidly over a
rocky substratum
 Water is well oxygenated
in riffles
Flowing Water: Streams and Rivers
 Pools are deeper
stretches of more slowly
moving waters
 Pools tend to
accumulate silt and
organic matter
Flowing Water: Streams and Rivers
Are these two areas productive or unproductive?
Both areas tend to be unproductive because the nutrients needed for
life are washed away in riffles, whereas the oxygen and sunlight
needed for life are lacking in pools.
Flowing Water: Streams and Rivers
 Streams lack the richness and
diversity of life
 Toward the headwaters of
rivers, the productivity of algae
and other photosynthetic
organisms tend to be low
 Riparian zones are transitional
areas between the aquatic
system and adjacent land
 Riparian zones are influenced by
seasonal flooding and elevated
water tables
Flowing Water: Streams and Rivers
 Much of the food web of
headwater ecosystems
depends on leaves and
other organic matter
 Organic material that
enters the aquatic
ecosystem the outside is
termed allochthonous
Flowing Water: Streams and Rivers
 The larger the river , the more its
organic material is autochtonous,
originating where it is found
Flowing Water: Streams and Rivers
 As you move
downstream, rivers
become wider, slower
moving, more nutrient
laden, and more
exposed to sunlight
 Nutrients and sunlight
support growth of algae
and plants
Flowing Water: Streams and Rivers
 Lotic systems are sensitive to any modification of
their water flow
 Rates of flow, water temperature, and sediment
patterns are all altered
 Could you name one major modification?
Flowing Water: Streams and Rivers
 Dams are built for flood control, to provide water for
irrigation, or to generate electricity
 Water behind dams becomes warmer, and bottom
habitats become choked with silt, destroying habitat
for fish and other aquatic organisms
 Using dams for flood control changes the seasonal
cycles of flooding
 Dams disrupt the natural movement of aquatic
organisms
Standing Water: Lakes and Ponds
 Referred to as lentic systems, distinguished by non-flowing waters
 Range in size from small, temporary rainwater to lakes that
are about a mile in depth
 Example: Lake Baikal,
in Russia, contains about
1/5th of all the fresh
water at the surface of the
earth.
Standing Water: Lakes and Ponds
 Many lakes and ponds are
formed by the
retreat of glaciers
 Glaciers leave
behind gouged-out
basins and blocks
of ice buried in
glacial deposits
 Example: The
Great Lakes of North
America formed in glacial
basins
Standing Water: Lakes and Ponds
 Lakes are also formed in
geologically active regions
 Vertical shifting of blocks of
the earth’s crust creates
basins w/in water
accumulates
Standing Water: Lakes and Ponds
 Oxbow lakes are broad bends of the former river cut
off by shifts in the main channel
Standing Water: Lakes and Ponds
 Lakes are subdivided into several ecological zones,
each of which has distinct physical conditions
 Littoral zone
 Limnetic zone
 Benthic Zone
Standing Water: Lakes and Ponds
Littoral zone is the shallow zone
around the edge of a lake or pond w/in which one finds rooted
vegetation Limnetic zone is the open water
where producers are floating singlecelled algae, phytoplankton.
Standing Water: Lakes and Ponds
 The sediments at the bottoms of lakes and
ponds make up the benthic zone
 The benthic zone provides habitat for
burrowing animals and microorganisms
Standing Water: Lakes and Ponds
 Are lakes and ponds
permanent?
 Most temporary ponds can dry out each year
 Most small temperate lakes that formed when glaciers
retreated will gradually refill in w/ sediment until there is no
open water
 What will happen to the
former aquatic ecosystem?
 The formerly aquatic ecosystem will slowly change into a
terrestrial ecosystem, first a wet meadow and later the natural
terrestrial biome of the region
Wetlands
 Areas of land
consisting of soil that
is saturated w/ water
and supports
vegetation specifically
adapted to such
conditions
Wetlands
 What are some examples of wetlands?
 Swamps, marshes, and bogs
 Salt marshes and mangrove wetlands associated w/ marine
envrionments
Wetlands
 Most of the plants can tolerate low oxygen
concentrations in the soil. Many are specialized for
anoxic conditions and grow nowhere else
 Wetlands provide important habitat for a wide variety
of animals
 Wetlands protect coastal areas from the ravages of
hurricanes and other storms
 Wetland sediments immobilize potentially toxic or
polluting substances dissolved in water
Estuaries
 Estuaries are found at the
mouths of rivers
 Are unique because of their
mix of fresh and salt water
 Are abundantly supplied w/
nutrients and sediments
carried downstream by
rivers
 Estuaries tend to be areas
of sediment deposition
 Supports high biological
productivity
Marine Aquatic Systems
 Oceans cover the largest portion of the earth
 Variation in marine environments comes from
differences in temperature, salinity, depth, currents,
substrata, and tides
 What does depth influence?
 Depth influences light and pressure.
Marine Aquatic Systems
 The littoral zone (also called
the intertidal zone) extends between the highest and
lowest tidal water levels
 Exposed periodically to air
 Ecological conditions w/in
the littoral zone change
rapidly as the tide flows
in or out
Marine Aquatic Systems
 The neritic zone extends to
depths of about 200m, which
correspond to the edge of
the continental shelf
 Region of high productivity
 The sunlit surface layers
of water are close enough
to the nutrients in the
sediments below that
strong waves can move
them to the surface
Marine Aquatic Systems
 The oceanic zone is beyond the neritic zone where
the seafloor drops rapidly to great depths
 In the oceanic zone, nutrients are sparse and
production is strictly limited
 The seafloor beneath the oceanic zone is the benthic
zone.
Marine Aquatic Systems
 Both the neritic and oceanic
zones are subdivided vertically
into a photic zone
 In the photic zone, there is
sufficient light for
photosynthesis
Marine Aquatic Systems
 Organisms in the aphotic zone depend mostly on organic material
raining down from above
Marine Aquatic Sytems
 What other ecosystem could be compared to the
open ocean?
 What other ecosystem could be compared to the
tropical rainforest?
Marine Aquatic Sytems
 Coral reefs are like tropical rainforests, both in the
richness of their biological production and the
diversity of their inhabitants
 Reef-building corals are found in shallow waters of
warm oceans
 Coral reefs usually surround volcanic islands, where
they are fed by nutrients eroding from the rich
volcanic soil and by the deep water currents forced
upward by the profile of the island
Marine Aquatic Sytems
 Coral reefs are doubly productive
because photosynthetic algae w/in
their tissues generate carbon
energy that fuels the coral’s rates
of growth