Ecosystem processes and the river continuum concept
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Ecosystem Processes and the River Continuum Concept . Unit 1: Module 4, Lecture 5. Objectives. Students will be able to: classify sources of organic matter. diagram the flow of instream organic matter. factors that influence the storage of organic matter in streams.

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Ecosystem Processes and the River Continuum Concept

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Ecosystem Processes and the River Continuum Concept

Unit 1: Module 4, Lecture 5


Students will be able to:

  • classify sources of organic matter.

  • diagram the flow of instream organic matter.

  • factors that influence the storage of organic matter in streams.

  • explain the river continuum concept

  • compare and contrast low order, mid-order, and high order streams. .../SCRfig2-33web.jpg

General organic matter pathway manual/6doing.htm veg/brfredmaple.html swm10.html

Sources of organic matter

  • Autochthonous – instream

  • Allochthonous – out of stream

Dissolved organic matter

Soluble organic compounds that leach from leaves, roots, decaying organisms, and other sources

Largest pool of organic matter in streams

Particulate organic matter

Coarse particulate organic matter

Woody material & leaves > 1 mm

Fine particulate organic matter

Leaf fragments, invertebrate feces, and organic precipitates < 1 mm

Types of organic matter

This figure depicts the routes carbon follows as it is processed within a stream.

Microbes, macro-invertebrates, fish, and other organisms all play roles in the physical and chemical processing of organic matter.

Instream organic matter processing

The River Continuum - sti/pratt/energy.html

A caddisfly of the family Limnephilidae

Macroinvertebrate functional roles in organic matter processing

  • Shredders

    • Dominant food

      • Vascular macrophyte tissue

      • Coarse particulate organic material (CPOM)

      • Wood

  • Feeding mechanisms

    • Herbivores - Chew and mine live macrophytes

    • Detritivores - Chew on CPOM

  • Representatives

    • Scathophagidae (dung flies)

    • Tipulidae (crane flies)

  • A blackfly of the family Simulidae

    A caddisfly of the family Hydroptilidae

    Macroinvertebrate functional roles

    • Collectors

      • Dominant food

        • Decompose fine particulate organic matter (FPOM)

    • Feeding mechanisms

      • Filterers - Detritivores

      • Gatherers - Detritivores

  • Representatives

    • Filterers

      • Hydropsychidae

      • Simulidae (black flies)

  • Gatherers

    • Elmidae (riffle beetles)

    • Chironomini

    • Baetis

    • Ephemerella

    • Hexagenia

  • A dipteran of the family Thaumaleidae

    Macroinvertebrate functional roles

    • Scrapers

      • Dominant food

        • Periphyton (attached algae)

        • Material associated with periphyton

    • Feeding mechanisms

      • Graze and scrape mineral and organic surfaces

  • Representatives

    • Helicopsychidae

    • Psephenidae (water pennies)

    • Thaumaleidae (solitary midges)

    • Glossosoma

    • Heptagenia

  • A stonefly of the family Perlidae

    A “true bug” of the family Notonectidae

    Macroinvertebrate functional roles

    • Predators

      • Dominant food

        • Living animal tissue

    • Feeding mechanisms

      • Engulfers - Attack prey and ingest whole animals

      • Piercers - Pierce tissues, suck fluids

  • Representatives

    • Engulfers

      • Anisoptera (dragonflies)

      • Acroneuria

      • Corydalus (hellgrammites)

  • Piercers

    • Veliidae (water striders)

    • Corixidae (water boatmen)

    • Tabanidae (deerflies & horseflies)

  • Low concentrations in winter and fall

    High concentrations in summer

    Seasonal variation in particulate organic carbon

    Photos by g. merrick

    Organic matter that enters streams may be (percent estimates are approximate and variable):

    Stored within the stream bank or channel (25%)

    Exported downstream (50%)

    Metabolized and respired as carbon dioxide by organisms (25%)

    Photo – g. merrick

    Fate of organic matter

    Storage of organic matter

    • Factors that are likely to increase retention time are debris dams, beaver dams, floodplains, and geomorphological features of the stream or river that impede flow.

    Net primary production versus litter fall

    Bear Brook in New Hampshire is the site of a famous organic matter budget study (Likens, 1973).

    In the this small, forested headwater stream it was found that greater than 99% of the carbon input to Bear Brook came from allochthonous sources (POM slightly greater than DOM).

    Close to 65% of this input was exported downstream from the 1700 meter long study site.

    Input of DOM exceeded exports

    Due to leaf fall more POM was exported than entered the site

    Bear Brook, New Hampshire

    The River Continuum Concept

    Low order streams

    Shaded headwater streams

    Coarse particulate matter (CPOM) provides resource base for consumer community

    Stream order and the RCC

    Mid-order streams

    Energy inputs change as stream broadens

    Shading and contribution of CPOM decreases

    Sunlight supports significant periphyton production

    Upstream processing of CPOM results in input of fine particulate matter (FPOM)

    Stream order and the RCC

    Stream order and the RCC

    • High order streams

      • As streams widen even more and flows drop, macrophytes become more abundant

      • In the largest rivers, macrophytes are limited to the river margins because mid-channel conditions are typically too turbid

      • Bottom substrate becomes smaller

    Figure 12.1

    Carbon fluxes in a stream ecosystem

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