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Freshwater Biomes
Salinity: is the abiotic factor that most influences aquatic life zones
Other important abiotic factors in aquatic biomes:
• Amount of dissolved salts (chemistry) in a sample of water
• Depth of water
• Flow rate and amount of dissolved oxygen in water
Two types of Aquatic Life Zones
Salt water, aka marine
 Estuaries
 Coastlines
 Coral reefs
 Coastal marshes
 Mangrove swamps
 Oceans
Freshwater
 Lakes
 Ponds
 Streams
 Rivers
 Inland wetlands
Salinity
• Measured in parts per thousand (ppt)
• Ocean is approximately 30 ppt
• Freshwater is approximately 0.5 ppt
Salt Water Testing - Salt water is denser than freshwater;
Objects have more buoyancy in salt water than in freshwater
Depth
The primary factor in depth and distance from shore is sunlight; different plants can live
with different amounts of light. Bodies of water are divided into depth zones
Photic Zone: The top layer of water that receives enough light for photosynthesis to occur
In ocean – up to 200 m deep
Dependent on water clarity
Aphotic Zone: Sunlight never reaches this depth (chemotrophs)
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Only occurs in the oceans and very deep
lakes
Benthic Zone: The floor of a body of water. In
shallow water, light reaches this zone; In deep
water, light may not reach it
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

Littoral Zone: warmest since it is
shallow and can absorb more of the
Sun’s heat
Limnetic Zone: near-surface open
water surrounded by the littoral zone
o well-lighted (like the littoral zone) and is dominated by plankton, both
phytoplankton and zooplankton
Profundal Zone:
o Near the bottom of lakes and ponds
o Plankton have short life spans—when they die, they fall into the deepwater part of the lake/pond
o much colder and denser than the other two
o little light penetrates all the way through the limnetic zone into the
profundal zone
o animals are decomposers
Freshwater Ecosystems are divided into two types based on water flow:


Standing-water (also called Lentic) – Lakes, Ponds, Wetlands, Marshes,
Swamps, and Bogs. Water generally NOT moving.
Flowing-water (also called Lotic) – have a constant water flow (LO rhymes
with flow)
Standing
 Lakes
 Ponds
 Inland wetlands
Flowing
 Lakes
 Ponds
 Inland wetlands
 Streams
 Rivers
Organisms: Producers and Consumers
Different levels of the water offer different habitats due to light, temperature, DO.
Plankton: organisms that drift in the water and about the size of dust in freshwater
• Phytoplankton carry out photosynthesis
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•
Zooplankton: include microscopic animals and protists that do not
photosynthesize. protist are mostly unicellular like Amoebas (Protozoa) and Algae.
Decomposers: benthic organisms are often scavengers; especially in deep lakes and
ponds They feed up on (decompose) organic debris floating down from above.
Flowing Water Ecosystems
Streams: All above ground bodies of flowing freshwater. The following terms are
included in this category: Rivers, Streams, Creeks, Brooks
Aquifer: freshwater flowing underground
Organisms: Are adapted to a rate of water’s movement (flowing-water). Methods of
adaptation include:
 Insect larvae with hooks
 Suckers for rock anchoring
 Breeding cycles - Salmon that live in the ocean but spawn in freshwater streams
Stream flow
 Sediments: small particles that settle to the bottom of a body of water.
 Sedimentation and erosion: change the course of streams over time
TOWARDS THE HEADWATERS OR SOURCE (Where river
starts)
 Faster flow (steeper), more dissolved oxygen
 Colder (sun hasn’t shone on water as much)
Riffles,
 Clearer water (less accumulated sediment)
TOWARDS THE MOUTH OF RIVER (WHERE IT
ENDS)
 Slower flow (less steep incline), more plants
 Warmer (more time for sunlight to head)
 Cloudier (more accumulated sediment)
 More phytoplankton at base of food chain (more
nutrients from sediments), so more food for
consumers.
Runs, and Pools
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NEED TO KNOW RIFFLES, RUNS, and POOLS! See above diagram for descriptions.
Floodplains
 Flat land along the sides of streams and is usually found in the lower course of a
river
 Tend to have fertile soils
 Good for growing crops
 The floodplain is covered with water when a river floods. Alluvium is a type of mud
(very fertile) which is left behind when the flood waters go.
 As rivers meander (twist and turn), the banks erode in some areas and the
sediments fall out of suspension in others. This process affects the
meandering/winding of a stream.
Human Impact on Freshwater Systems
 Nutrient pollution from agricultural waste, fertilizers, and human sewage can impact
systems
 Dams, diversions, canals
 Destroys habitats by reducing water flow
 Flood control levees, dikes
 Alter and destroy habitat
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 Cities and farmlands
 Add pollutants and excess nutrients
 Draining inland wetlands to grow crops or covering with asphalt and buildings