Objectives:
Learn the many habitats a stream provides:
microhabitats
macrohabitats
Learn the characteristics and function of Riparian Areas
The Many Habitats a Stream Provides
Even a small mountain stream provides an astonishing number of different places
for animals to live, or habitats. The casual visitor would not see more than water
and rocks, yet the stream is filled with unseen creatures. Where do they all live?
http://www.bae.ncsu.edu/programs/extension/wqg/srp/rc101.html
Stream Habitat
Physical habitat in stream varies throughout the year.
Seasonal changes in streamflow, sediment deposition, aquatic vegetation and
riparian vegetation affect the physical conditions within a channel.
Aquatic and terrestrial life is adapted to seasonal variability and relocates or
weathers the elements.
Key factors affecting the quality and diversity of physical habitat:
Gradient: steepness, any change in gradient by man-made structures or
alterations will change stream power, current velocities, water depth, sediment
and woody debris transport
Sinuosity: meandering streams greater diversity, strait streams fewer habitats
Water velocity: many species adapted to fast or slow speed.
Substrate: all natural materials
Cover: any place or situation that provides aquatic animals with a place to rest,
hide congregate or feed includes: water depth, substrate, boulders, logs, stumps,
rootwads, undercut banks, aquatic and riparian vegetation
Stream Habitat
Rocks provide several different habitats. There is the side that faces upriver: animals
that are very good at clinging to rock will do well here. The side that faces downriver
provides a certain degree of shelter from current, while still allowing an animal to hunt
for food. The top of a rock, if it is contacting air in some places, will be a good place for
animals that can't breathe underwater and need to surface now and then. Underneath
the rock is a very popular place for animals who don't want to be eaten!
Microhabitat
describes very local habitats as the small spaces that are chosen by each organism. Some
creatures make their own microhabitats. Many (but not all) caddisflies build cases about
themselves. Other animals dig holes in banks or in the mud on the bottom.
Fallen logs and branches (Large Woody Debris, or LWD), provide a place for some animals to
burrow into and surfaces for others to attach themselves, as they might to a rock.
They also create areas where small detritus such as leaf litter can pile up underwater. These
piles of leaf litter are excellent shelter for many creatures, including hellgrammites (large,
fiercely predaceous larvae of dobsonflies).
Besides providing microhabitats, fallen logs, branches, rootwads, and even rocks perform the
valuable service of clogging streams. A well-obstructed stream is a healthy one. Streams
clogged with natural debris form countless small pools, waterfalls, and other features that
provide habitat, as well as hiding places for young fish.
There is other debris, leaf litter, and algae floating downstream, and animals cling to this or
burrow into it, as well as eat it. Parasites make their host their habitat.
http://www.bae.ncsu.edu/programs/extension/wqg/srp/rc101.html
Cross-Section of a Stream
Surface
http://chamisa.freeshell.org/habitat.htm
Skaters, insects that walk on water, may be found on the surface of a
stream. They are light, and their feet are small and spread far apart, making
it possible for them to avoid breaking the water's surface tension. Whirligig
beetles may also be found. They are heavy and small, so they should sink-but their fast whirling motion keeps them afloat. A whirligig beetle can dive
by trapping an air bubble under its abdomen and sinking with it. The air
bubble functions as a diving lung.
Other forms of life that may be found on the surface are the leaves of
macrophytes , algae, frogs, ducks, otters, muskrats, minks, and beavers.
The surface also provides abundant food for fishes. Insects come to the
stream's surface to drink or reproduce and may be caught. Bugs fall from
overhanging branches, or get blown in by wind. And even the organic
material like leaves that fall on the stream's surface will wind up hosting life.
Because there is food on the surface, topminnows, killifish, and
mosquitofish may be found there, waiting for a meal. Many other fishes
come to the surface momentarily, to grab quick breaths of air or a snack.
The surface is where the stream breathes (exchanges gases with the
atmosphere, including nitrogen, oxygen, carbon dioxide, and carbon
monoxide).
Cross-Section of a Stream
Water-column
http://chamisa.freeshell.org/habitat.htm
Water-column
Microscopic rotifers, protozoa, and bacteria may often be
found drifting downstream in the water-column.
Some plants have roots in the stream-bottom and leaves on
the surface. These plants have their stems in the watercolumn. Some plants that are tall and grass-like may have
leaves that grow up into the water-column. Trees often have
roots in the water-column that have been uncovered by
stream erosion. These stems, leaves, and roots are habitats
for microscopic organisms and algae (making a fuzzy coating
called aufwuchs), snails, flatworms, and insects.
Many fishes have specialized to stay in the water-column,
eating algae, macroinvertebrates, and detritus or lurking and
waiting for a meal to show up on the surface.
There are other fishes that have specialized to eat smaller
fishes who spend their time in the water-column.
Kingfishers are birds that dive into the water to catch these
fishes.
Cross-Section of a Stream
Benthic
The stream bed is called the benthic zone. Many
organisms live here on the substrate (mud, sand, rock,
and organic debris). Coating the substrate may be
found diatoms, aufwuchs, and fungi. Diatoms are
responsible for the yellow or brown coloring of rocks,
and for the slimy feel of rocks when you first pull them
out of a stream. Aufwuchs is a term describing the
fuzzy green coating of algae, protozoa, diatoms,
bacteria, and fungi that you may find on submerged
logs and branches which help break down wood and
leaves.
http://chamisa.freeshell.org/habitat.htm
Cladophora, long strands of green algae, attach
themselves to rocks, and a number of macrophytes
(stream plants) grow from sand and mud, growing
their own coatings of aufwuchs.
Clinging to and eating from all these slimy, edible
surfaces are larvae and nymphs of all sorts of insects,
water mites (Hydracarina), snails, clams, worms,
leeches, and flatworms.
Cross-Section of a Stream
Benthic
http://chamisa.freeshell.org/habitat.htm
Also spending their time in the benthic zone and
feasting on these many small creatures and algae are
crayfish, salamanders, and bottom fish (including
sturgeons, suckers, sculpins, and many minnows like
daces and chubs).
Large fishes must hide if they are to hunt other
fishes. They need to be in dark places so they can't
be seen. They then dart out at high speed to grab
unsuspecting passersby. They choose places like
underwater ledges, logdams, and pools.
The benthic zone is a popular place for many fish to
spawn, Salmon and trout create nests out of gravel,
sculpins attach eggs to the undersides of rocks, and
catfish nest in holes in the banks.
Insects and mammals found in the water-column are
often on their way between the surface and the
bottom.
Terrestrial insects and organic material from the
land are in the process of sinking or being stirred up
by currents or a passing animal. (This is called
detritus)
Cross-Section of a Stream
Hyporheic
http://chamisa.freeshell.org/habitat.htm
The hyporheic zone is the rock and sand beneath the stream
bottom. How deep it goes depends on whether it is a gravelly
stream or a silty and muddy one. A stream that is mostly silt
and mud will not allow for much of a hyporheic zone.
Organisms that are found on the stream bottom may also be
found beneath it. Most of them live within the top 50 cm or
so.
There is a constant supply of fresh water, oxygen, and food
flowing through the hyporheic zone.
During drought, organisms that can live in the hyporheic zone
may be able to survive temporary stream-drying. The
hyporheic zone also offers refuge from extreme temperature
changes (heat and freezing). Very small insect larvae and
nymphs often begin their lives here, to keep from getting
swept away by strong currents.
Female salmon built large nests of gravel and bury their
fertilized eggs in the hyporheic zone, keeping them safe from
predators and assuring that they will have plenty of oxygen
and nutrients
Stream Corridor Longitudinal Profile
Stream Corridor Restoration: Principles, Processes, and Practices. 1998. Federal Interagency Stream Restoration Working Group.
Cascade, Falls, Pool, Run, Riffle
Channel and floodplain characteristics change as
rivers travel from headwaters to mouth
http://www.bae.ncsu.edu/programs/extension/wqg/srp/rc101.html
http://www.citizenscientists.ca/Channel_Morphology_and_Site_Features.html
http://www.rvca.ca/watershed/aquatic_habit
at/SAR_fish_habitat_mapping.html
Riffles, pools, and cascades
• Riffles and pools alternate in somewhat predictable
patterns
www.aquatic.uoguelph.ca/rivers/chphys.htm
CASCADE
When water flows over larger rocks and
boulders, it becomes a cascade. Cascades are
rough places to live. But there is a lot of life in
cascades because of the high oxygen levels.
To live in cascades, animals need ways to stick
themselves to rocks. Many diatoms do this
very well. Some true fly larvae use pads to
stick themselves to rocks. Caddisflies may built
dome-shaped cases that are glued to rocks.
Mayflies are built in ways that allow them to
stick to rocks almost like suction cups.
There are few fishes that can live in cascades,
but the dace—with its remarkable shape that
allows the water to force it against the bottom.
Trout and young salmon may be found
traveling down cascades, and adult trout and
salmon may be found traveling up cascades,
on their way to spawn.
Falls
A brutal environment. The water is highly
oxygenated. Diatoms are able to cling to vertical
services quite well. Any animal that wants to live
in a falls is going to have to be able to perform
the same feat, water is moving fast.
Black-fly larvae are found in large numbers in
falls because of their ability to stay attached to
surfaces, and they like a lot of oxygen. They have
two little filtering appendages on their heads that
allow them to gather microscopic nutrients from
the water. The faster that water flows, the better-because their filters will fill up faster.
Some caddisflies ( Hydropsychidae) that build
shelters and fishing nets out of silk. They can
build their shelters quite close to the bottom of a
falls and stay out of harm's way, while still pulling
in a good catch.
During spawning season, trouts and salmons
leap up and over falls to get upstream.
Pools
Regions of slower water current characterized by the deposition
of finer sediments
Deepest reaches of stream. A low flows pools have low to
moderate velocities and little surface turbulence except near
obstructions
Pools provide darkness and slow movement of water. Their
oxygen levels are often low. During droughts, pools are
sometimes the only parts of a stream that stay wet. The
stream's water suddenly slows down, dropping its load of silt
and organic materials.
The layer of silt and organic materials at the bottom of a pool is
an environment that is friendly to plants and animals which
can't tolerate higher water velocities. Aquatic earthworms and
midges bury themselves in the silt. Diving beetles find pools
pleasant places to live.
Fish such as trouts, salmons, and catfishes, are common
residents of pools. They need the darkness and depth in order
to be able to hide from their prey. When a small fish swims by,
they can quickly lunge at it. Pools often contain large pieces of
wood and ledges that help big fish hide.
Surface-feeding fish like killifish, topminnows, and
mosquitofish like pools because it is much easier to float near
the surface and grab prey where water currents are minimal.
Importance of Pools
• Refuge for fish during
low flow, drought
periods
• Rest stop and food area
for fish
• Predator refuge for
young fish
www.aces.edu/.../streams/.../AL%20Biological%20Stream%20Functions,...
Run and Glides
Deeper and slower than riffles and shallower and
swifter then pools
Swift to moderate velocities and minor turbulence.
Long, smooth-flowing stretches of fast water. are
called runs. The surface may seem smooth, or it may
have whirls of turbulence--but there is no froth or
spray.
Runs are not good places for plants.
Most of the big fish that we associate with streams
and rivers can be found in runs, including gar,
sturgeons, paddlefish, bass, sunfish, salmon,
catfish, suckers, and trout. Naturally they have to eat
something, and indeed there are many smaller
animals here as well, creeping along the bottom,
swimming in schools, and hiding in piles of woody
debris. These include the same kind of aquatic
invertebrates you might find in a riffle as well as
minnows, juvenile fish, suckers, and crayfish.
www.aces.edu/.../streams/.../AL%20Biological%20Stream%20Functions,...
Riffle
Shallow , swift, highly productive areas that provide
habitat and help add oxygen to the water through
aeration. Shallowest, steepest and often swift and
most turbulent habitat . Substrate generally
bedrock, gravel, cobbles, boulders. Characterized by
rapid flow carrying small particles in suspension,
coarse sediments on stream bed, and removal of
finer sediments
www.aces.edu/.../streams/.../AL%20Biological%20Stream%20Functions,...‎
Riffles are a rich part of any stream. Because the
water is not deep, there is plenty of sunshine,
encouraging a rich growth of diatoms on rocks and
organic debris. Large, predatory fishes are too big to
travel across them. Current velocities are lower than
in cascades and runs.
Cladophora--long filaments of green algae--attach
themselves to rocks and wave downstream.
Caddisflies, mayflies, and stoneflies are all
abundant. There are many true flies that enjoy
riffles, as well. Snails, clams, and water mites are
common.
Fishes live in riffles, too. They are small, and their
hydrodynamic shapes and stiff fins keep them from
getting washed away. Daces, chubs, and sculpins
are common residents of riffles.
Importance of Riffles
• Areas of oxygenation
• Highly diverse
substrate and habitat
• Diverse
macroinvertebrate
population
www.aces.edu/.../streams/.../AL%20Biological%20Stream%20Functions,...‎
Others Habitats include:
side channel-which is a small area where water has left and
then returned to the stream, running parallel to the stream.
backwater-much like a side channel but with the upstream
end blocked off, creating stagnant water
embayment- which you might say is almost like a backwater,
but not nearly so extreme or cut off, the water is still actively
running
plunge an area where water runs off a submerged obstacle
and creates a deep, though flowing, area on the other side of it
(and still technically part of the run).
River Architecture
Changes downstream
Slope
Bed material size
Streamflow
Channel width
Channel depth
Flow velocity
www.usda.gov/stream-restoration
Downstream trends of a stream are generally classified
into three longitudinal zones:
headwater, middle reach, and lower reach
Material stored in floodplains
Relative influence of vegetation on
channel and floodplain form
Dynamic relationships between discharge and physical
feature of a stream channel as you move downstream.
IN summary, from a physical perspective, this explains
why rivers are ever-changing, dynamic forces on the
landscape.
NC stream restoration institute, river course natural stream processes, fact sheet 1
Riparian areas are the "green zones" which lie between stream channels
and uplands. They are the link between aquatic environments and
terrestrial ecosystems and are associated with running water systems such
as rivers, streams, and drainageways which contain a defined channel and
floodplain. Beaver ponds, seeps, springs, and wet meadows on the
floodplain of, or associated with, a stream or river are part of the riparian
area. Riparian areas may also include the fringes of land around ponds,
lakes, and certain other bodies of water. It is the presence of water during
all or a significant part of the growing season that makes riparian areas so
different from the uplands that surround them.
Characteristics of Riparian Areas
• “Green Zone” – link between aquatic and
terrestrial
– Water
– Landform
– Soil
– Vegetation
NC stream restoration institute, river course natural stream processes, fact sheet 1
Riparian Areas
,..
www.aces.edu/.../streams/.../AL%20Biological%20Stream%20Functions
• More dynamic than uplands.
Plant communities may be
.
especially susceptible to rapid change, but soil and water conditions may
change dramatically as well, often in relatively short periods. These
changes might include:
– Flooding (either temporary or more long term)
– Deposition of sediment(on streambanks and across floodplains)
– Accumulation of organic matter
– Dewatering
– Changes in location of channel
Functions of Riparian Areas
Healthy riparian areas provide several important functions which not
only enhance ecological health but have economic and social benefits
as well. These functions include:
1.
2.
3.
4.
5.
6.
water storage
flow energy dissipation
water quality
sediment trapping
bank building and maintenance
primary biotic production
Riparian Areas: Store and Release Water
• Soil – acts like sponge to
retain water
– Reduces flooding
– Extends time that surface
water is available
www.aces.edu/.../streams/.../AL%20Biological%20Stream%20Functions
This can significantly reduce downstream flooding. As stored water slowly seeps out of
the "sponge," it either percolates downward to recharge underground aquifers or
moves back into the stream channel, thus extending the availability of surface water in
the watershed later into the year.
Riparian Zones: Dissipate Energy of Flowing Water
Slows water
– Vegetation
– Woody debris
– Large boulders
– Cobbles
www.aces.edu/.../streams/.../AL%20Biological%20Stream%20Functions
As the water is slowed down, it loses some of its erosive force. This
reduces the amount of sediment coming into the channel from the
floodplain or the streambanks.
Riparian Zones: Provide Water Quality
• Natural pollution control
Trap sediments
(nutrients, pesticides,
toxic metals, bacteria)
www.aces.edu/.../streams/.../AL%20Biological%20Stream%20Functions
Sediments may themselves be pollutants if present in excessive amounts.
Riparian areas can prevent sediments from entering the channel from
adjacent uplands.
Riparian areas act as filter strips which can reduce nitrogen, phosphorus, and
organic solids in the water by as much as 60 to 90 percent. Some riparian
plants can absorb certain contaminants.
Riparian zones: Trap sediments
• Trap sediments – development of new streambanks and bars
Trapping of sediments may lead to the
development of new streambanks and bars. These
become the locations for new vegetation
communities, which further enhance soil stability.
Trapping of sediment and slowing of water velocity
are particularly important during spring runoff and
after major summer rainfall. How much sediment
is retained is also important because excessive
sediment loads reduce habitat quality for aquatic
life (including fish) and disrupt the normal flow of
water.
www.aces.edu/.../streams/.../AL%20Biological%20Stream%20Functions,...
Riparian Zones: Protect soil and water
• Shields soil and water from:
– Wind
– Sunlight
– Rain drop impacts
www.aces.edu/.../streams/.../AL%20Biological%20Stream%20Functions
This reduces erosion due to wind and the impact of rainfall as well as reducing
evaporation. Vegetation also provides shade, which reduces soil and water temperatures
and improves aquatic habitat. Dense vegetation may limit soil compaction through the
presence of healthy root systems. Thick shrub communities limit accessibility of domestic
livestock and wild ungulates, although they may also reduce understory densities.
Riparian Zones: Provide wildlife habitat
• Water, food, cover
and travel routes
– Birds
– Mammals
– Insects
– Fish
www.aces.edu/.../streams/.../AL%20Biological%20Stream%20Functions
http://www.mfwwc.org/PDFs/Riparian%20Vegetation.pdf
http://www.mfwwc.org/PDFs/Riparian%20Vegetation.pdf
http://www.mfwwc.org/PDFs/Riparian%20Vegetation.pdf
http://www.mfwwc.org/PDFs/Riparian%20Vegetation.pdf
http://www.mfwwc.org/PDFs/Riparian%20Vegetation.pdf