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Freshwater
Water that contains relatively little
dissolved salt
Freshwater ecosystems include:
Standing waters of lakes and ponds
moving waters of rivers and streams
areas where land and water come together
known as the wetlands
Plant and animal life found in a
freshwater ecosystem depends on
the depth of the water
how fast the water moves
the amount of mineral nutrients, sunlight, and
oxygen.
A pond or lake ecosystem is structured
according to how much light is available
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–The shallow-water area near the shores of
lakes and ponds where sunlight reaches the
bottom is called the littoral zone
It is a nutrient rich area
farther out from the shore:
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open waters that get enough sunlight for
photosynthesis is dominated by phytoplankton
(tiny plants) and zooplankton (tiny animals)
areas that are too deep for photosynthesis to
occur: dead plants and animals drift down from
above and are decomposed by bacteria, and a few
fish adapted for cooler, darker water also live
there.
Benthic zone – The body of water which is
inhabited by decomposers, insect larvae, and
clams.
Eutropic lakes
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a lake with a large amount of plant nutrients
As the amount of plants and algae grows:
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the number of bacteria feeding on the decaying organisms
also grow.
These bacteria use up the oxygen dissolved in the lake’s
water.
eventually, the diversity of species declines
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Lakes naturally become eurtophic over a
long period of time
However, the process of eutrophication can
be accelerated by runoff from sewage,
fertilizers, and animal wastes.
PLANT AND ANIMAL
ADAPTATIONS
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Along the shore:
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cattails
reeds
they are rooted in the bottom mud. their upper
leaves and stems emerge above the water
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in deeper water
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pond lilies – a floating plant
waterbettles trap air in the hairs under their
bodies because they cannot get air directly from
the water.
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dark lake bottom:
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catfish – whiskers help catfish sense food
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adaptations to temperature:
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lake trout need cold water
bass prefer warmer waters
regions where lakes partially freeze in winter,
amphibians burrow into the littoral mud.
WETLANDS
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– areas of land that are covered with water
for at least part of the year.
2 types of freshwater wetlands and 1
type of saltwater wetland
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marshes – land covered with water; contain nonwoody plants
swamps – land covered with water; contain
woody plants or shrubs
estuaries (we will talk about later)
functions of wetlands:
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fish use the wetlands for feeding and spawning
they provide a home for native and migratory wildlife,
including endangered and threatened species
wetland vegetation traps carbon that would otherwise be
released as carbon dioxide (which is harmful to the
atmosphere
remove pollutants from the water,
control flooding by absorbing extra water when rivers
overflow,
produce many commercially important products
such as cranberries, blueberries, and peat moss.
Marshes
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plants include reeds, rushes and cattails
they are rooted in the bottom sediments,
but their leave are above water.
The benthic zone is rich, containing plants
and numerous decomposers and
scavengers.
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waterfowl: grebes and ducks have beaks
adapted for eating marsh vegetation.
herons have spear like beaks that is used to
grasp small fish and frogs.
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marshes attract nesting birds such as
blackbirds
marshes are characterized by its salinity
and organisms are adapted to live within
the ecosystem’s range of salinity
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Brackish marshes have slightly saline water
tidal marshes – contain saltier water
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the everglades in Florida is the largest
freshwater marsh in the united states
swamps
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occur on flat, poorly drained land, often
near streams
they are dominated by shrubs or watertolerant trees such as red maple, cedar,
oak, or cypress
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mangrove swamps occur in warm climates
near the ocean, so their water is saline
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ideal habitat for many amphibians such as
green frogs and salamanders and birds
such as wood ducks that nest in hollow
swamp trees.
threats to wetlands
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used to be considered wastelands… they
were drained and cleared for farms or
development.
their importance is now recognized:
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purifiers of wastewater and absorbers of
otherwise hazardous flood waters
the federal government and most states
now prohibit destruction of some wetlands
RIVERS
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most originate from snowmelt in mountains
at its headwaters it is usually cold and highly
oxygenated, running swiftly through shallow
riverbeds
rivers then broaden, become warmer, lose
oxygen, and flow more slowly.
runoff provides rivers with nutrients, which settle
to the bottom as sediment. therefore the
surrounding land affects the growth and health of
organisms in rivers.
plant and animal adaptations
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near the headwaters,
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mosses have root like structures called rhizoids
that they use to anchor themselves to rocks.
mayfly nymphs use hooks on their legs to cling to
any stable surface
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frogs use the suction cups on their toes to
maintain stability
trout and minnows thrive in the cold, oxygen-rich
headwater
trout have streamlined bodies that present less
resistance to the strong current and they’re
powerful swimmers.
further downstream
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Catfish and carp prefer the warmer, calmer
waters. carp are adapted to gliding over the river
bottom but not to swimming against the current.
water crowfoot set roots down into the sediment
fig 4-45: shows how the arrowhead plant’s leaf
shape varies according to the strength of a river’s
current.
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In fast waters the leaves are submerged
In slower waters the leaves are floating
In calm waters the leaves are aerial
Threats To Rivers:
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Industries use river water in manufacturing
processes and as a receptacle for waste.
People use rivers to “take away” their sewage and
garbage.
pesticides and other poisons coat riverbeds with
toxic sediments
Dam building alters river flow and may destroy
fish habitat.