STREAM ECOSYSTEMS

What is a stream?

• A flowing body of water confined within a bed and banks

• Does a stream really end at the edge of the water?

Dynamic Nature of Streams

• Streams are constantly changing:– Upstream water flows downstream– Amount of water fluctuates– Stream bed changes over time

• Anything that affects a watershed will eventually impact the stream

Important Aspects of aStream Ecosystem

• Stream morphology

• Parts of the stream

• Substrate

• Riparian buffer zone

• Biological communities

• Physical & chemical properties of water

Stream Morphology

• Size and shape of the stream

• Described by the:– Longitudinal slope– Dimensions of cross

section– Meander pattern

Parts of the Stream

• Riffle – section where water is more shallow and the flow is turbulent

Parts of the Stream• Run/Glide – section with smooth flow

Parts of the Stream• Pool – section where water is deeper

with a slower flow

Substrate

• Composition of the stream bottom is very important

• Provides important habitat for aquatic life

• Organisms show preferences for various substrates

• The higher the substrate diversity, the more habitats available

Types of Substrate

• Inorganic substrate:Bedrock > Boulder > Cobble > Gravel >

Pebble > Sand > Silt > Hardpan

• Organic substrate:Detritus

Muck

Large Woody Debris

• Refers to all wood located within the stream bed

• Key aspect of a healthy stream:

– Provides important habitat (esp. for fish)– Impacts flow, creating pools– Stabilize banks & minimize erosion

• In general, it should not be removed from a stream

Leaf Packs

• Accumulation of leaves in a stream

• Provide input of energy– Organic molecules leach out, creating a

nutrient rich “tea”– Biological communities colonize leaves – Smaller pieces of processed leaves

provide nutrients downstream

What is a riparian buffer zone?

• Area of vegetation along the banks of a river or stream

• “Green Zone”

• Can be forest, wetlands, etc.

Importance of Riparian Buffer Zones

• Slow down the movement of water, minimizing flooding & erosion

• Stabilize banks, reducing streambank erosion

• Act as filters, reducing non-point source pollution

Importance of Riparian Buffer Zones

• Provide important habitat to terrestrial & aquatic species

• Canopy provides shade to help regulate water temperature

• Leaves of trees are an important food source for many macroinvertebrates

Impacts on Riparian Buffer Zones

• Over half in US have been destroyed

• Most have been degraded or removed due to agriculture or development

Biological Communitiesof Streams

• Many streams rely on input of riparian vegetation as base of food web

• In-stream producers may include:– Algae (periphyton & phytoplankton)

– Aquatic plants

• Consumers include a variety of fish and macroinvertebrates

What are aquatic macroinvertebrates?

• Invertebrates that live in an aquatic ecosystem and are visible with the naked eye

• Also referred to as benthos

• EPA – Benthic Macroinvertebrates in our Waters

Aquatic Invertebrate Life CycleComplete Metamorphosis

Incomplete Metamorphosis

Identifying Aquatic Macroinvertebrates

• Key to Macroinvert. Life in the River

• Key to the Orders of Benthic Insects

• Aquatic Macroinvertebrate Key

• EEK! – Water Critter Key

Functional Feeding Groups of Aquatic Macroinvertebrates

• Macroinverts. can also be classified based on their role in an ecosystem– Shredders– Grazers/Scrapers– Collectors (filterers, miners & browsers)– Piercers– Predators

Fish Communities in Streams

• Types of fish vary based on :– stream temp., flow, dissolved oxygen– types of aquatic invertebrates present or

other food sources

• Primary Headwater Habitat Stream Organisms in Ohio

• Fish Identification & Life Histories• Fishes of Ohio’s State Scenic Rivers

Biological Communitiesof Streams

• Decomposers have a very important role!– Fungi and bacteria break down leaves – Consumer that feed on the leaves get

nutrition from the decomposers– Decomposers also break down dead

organisms, recycling the nutrients

The River Continuum Concept

• Holistic view of a river as a gradient

• Parts of a river are linked by flow

• First proposed by Vannote and others in 1980

• What happens upstream affects what happens downstream

• Links between land & aquatic communities are strongest in headwaters

• Predictable changes occur in the physical, chemical, and biological aspects of the river

The River Continuum Concept

Stream Order

• Measure of the relative size of a stream

• Stream order increases when two streams of the same order join

Upper Reaches

• 1st, 2nd, and 3rd order streams

• Narrow & shaded by riparian canopy

• Low & consistent temp.

• Dissolved oxygen conc. high

• Coarse substrate

• Swift current

Upper Reaches

• Biological Communities:– Low diversity– Primary producers are rare– Food chain relies on organic input from

trees in riparian zone– Macroinvertebrates are mostly shredders

(feed on leaves & debris) & collectors– Fish adapted to cool, swift water feed

primarily on insects

Middle Reaches

• Stream orders 3 – 6

• Wider stream channel

• Temperature is variable

• Dissolved oxygen conc. varies

• Smaller substrate

• Current not as fast

Middle Reaches

• Biological Communities:

– High diversity

– Primary producers (mostly periphyton) are dominant source of energy

– Macroinvertebrates are mostly grazers & collectors

– Higher diversity of fish that feed on other fish, insects, and periphyton

Lower Reaches• 6th order streams and above

• Wide stream channel

• Fine substrate

• Light penetration is limited due to higher levels of plankton & suspended solids

• Higher temperatures

• Slow current (but a much larger volume)

Lower Reaches• Biological Communities:

– Low diversity

– Food chain supported by phytoplankton & organic matter from upstream

– Macroinvertebrates are primarily collectors

– Fish adapted to warmer water with slower current

– More bottom feeders

Credits

• Thanks once again to Professor Kimberly Royal at Tri-C East for the Power Point presentation materials.

• Course: “Promoting Watershed Stewardship” for Environmental Science Educators