Chapter 20 The Earths Ecosystems
Section 3 Freshwater Ecosystems
What You Will Learn
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Describe the 3 lake zones
describe the wetland ecosystems
explain how a lake or pond can become a forest
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Describe the characteristics (biotic and abiotic) of aquatic communities
give examples of adaptations organisms have which make them suited to life in their ecosystem
Recognize that changes in environmental conditions can affect the survival of both individuals and
entire species
Streams and Rivers (clear flowing water)
two water sources (called headwaters)
 melting snow
 springs
Water flow
 streams grow larger and merge to become rivers
o each stream is called tributary of that river
 rivers flow to lower altitudes
o may end in a delta opens to ocean or seas (very silty, low diversity and productivity)
o may end in an estuary which opens to ocean (high diversity, high productivity)
Abiotic factors
 major one is how quickly the water flows
 temperatures vary by season and latitude, but will be very cool
Biotic factors
 food webs cross into surrounding land biome
 Plants will line the edges, other producers attach to rocks
 animals may live in mud or use suction disks to keep from being washed away
 fish will live in the open deepest water where the current slows or may find sections of still
water, may also migrate up and down the river
Ponds and lakes:
Standing or still freshwater(less than 1% salt)
isolated, so limited species diversity
temperature varies by depth and season
ponds are smaller and shallower, lakes are larger and deeper
Divided into zones, conditions are different
 Littoral zone
o top most zone, near shore
o warm and shallow water
o diverse community
 algae and lots of plants(cattails, rushes, water lilies,
 snails, insects, clams, worms, frogs, salamanders, turtles, fish and snakes
 Limnetic zone (open-water zone)
o llighted area near surface
o dominated by plankton and freshwater fish(bass, lake trout)
 Profundal zone (deep-water zone)
o colder and denser water
o little light (no autotrophs)
o animals may be detritivores(carp, catfish, worms, crustaceans, fungi, and bacteria)
Wetland Ecosystems:
most are freshwater
standing water that supports aquatic plants
plant species adapted to very moist and humid conditions (hydrophytes)
important in flood control and help to add water to underground aquifers
abiotic factors dependant on climate
high diversity and productivity
Two types:
 Marshes
o treeless wetland dominated by grasses
o depth of water varies (can be just squishy soil)
o shallow areas near shores of other freshwater ecosystems
o biotic
 plants-grasses, reeds, bulrushes, wild rice
 muskrats, turtles, frogs, and birds
 Swamps
o dominated by trees and vines
o low-lying areas beside slow-moving rivers
o flooded part of the year
o Biotic factors
 plants: willows, bald cypresses, oaks, vines, orchids, water lilies
 biotic: many fish, snakes, reptiles and esp. birds.
Succession of a Lake, Pond:
 rivers and streams carry sediment or silt to the standing body of water
 these settle to the bottom
 decaying organisms sink to bottom
 decomposing bacteria feeds on the decaying matter using up all the oxygen
 other heterotrophs die for lack of oxygen
 over time the area is filled with sediment, shallow areas first
 other plants begin growing on this filled in area
 as the depth becomes more shallow, it becomes a wetland or marsh
 if sedimentation continues it can fill in completely and become a forest