Download Location and Climate

7th Grade Science
Ecology
Freshwater Ecosystems
Facts and Information
Description
Streams and Rivers
With three-fourths of the Earth being covered with
water, it is not surprising that many organisms make
their homes there. Water ecosystems can be either
salty (marine) or fresh. Freshwater ecosystems
include lakes, ponds, streams
and rivers. Abiotic factors such
as sunlight, temperature, oxygen
and salt content affect all water
ecosystems.
Streams and rivers are freshwater ecosystems with
moving water. These
waters can either
move fast or slow.
Fast-moving water
has a higher amount of
oxygen then slow-moving water. Organisms that
live here need the additional oxygen to survive.
Most plants are not adapted to survive the moving
water, so they grow mainly on the banks of the river
or stream. Primary consumers that live in the
moving waters of the river rely on leaves and seeds
that fall in there for food. Animals of
the
moving-water
ecosystems
include:
large-mouth bass,
perch, fathead minnows,
crayfish, leeches, trout and
many species of insects
Sunlight is especially important.
Plants need energy from the
sun in order to carry out their
food-making process called
photosynthesis. Since water
absorbs sunlight, photosynthesis
only occurs at the surface. For this
reason, most of the plants in water ecosystem food
chains are algae.
Ponds and Lakes
Freshwater ecosystems can have either still water or
moving water. Ecosystems with still water are
called ponds and lakes. Lakes are
larger and deeper than ponds.
Many ponds are small and shallow
enough to allow sunlight all the
way through to the bottom. These
ponds have plant life all the way to
the bottom. Many plants such as
cattails, reeds, and other grasses
grow along the edge of the lake
where their roots can reach the soil. Animals that
live in lakes and ponds must be adapted to the still
water. In addition, the animal life changes,
depending on where in the lake you are! Along the
shore you would find animals such as frogs, snails
and insects. In the open water, animals such as
sunfish feed on the algae floating
on the surface. At the bottom of
the lake, animals such as catfish
scavenge for bits of food left over
from predators’ meals.
SBISD
As the fast-moving streams and rivers flow toward
the ocean, they eventually join other flowing water
ecosystems. As these moving waters join, the speed
of the flow slows down. More soil circulates
throughout the water and this slower water allows
more plants and animals to make their homes here.
Spring 2009