Ecosystem Processes and the River Continuum Concept

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Ecosystem Processes and the River Continuum
Concept

• Unit 1 Module 4, Lecture 5

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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.
• explain the river continuum concept
• compare and contrast low order, mid-order, and
  high order streams.

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General organic matter pathway
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Sources of organic matter

• Autochthonous instream
• Allochthonous out of stream

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Types of organic matter

• 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 gt 1 mm
• Fine particulate organic matter
• Leaf fragments, invertebrate feces, and organic
  precipitates lt 1 mm

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Instream organic matter processing

• 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.

The River Continuum - www.oaa.pdx.edu/CAE/Programs
/ sti/pratt/energy.html
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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)

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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

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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

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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)

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Seasonal variation in particulate organic carbon

• Low concentrations in winter and fall

• High concentrations in summer

Photos by g. merrick
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Fate of organic matter

• 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)

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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.

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Net primary production versus litter fall
Stream Autotochthonous Allochthonous
Bear Brook, NH 0.6 g C/m2/year 251 g C/m2/year
Silver Springs, FL 981 g C/m2/year 54 g C/m2/year
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Bear Brook, New Hampshire

• 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

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The River Continuum Concept
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Stream order and the RCC

• Low order streams
• Shaded headwater streams
• Coarse particulate matter (CPOM) provides
  resource base for consumer community

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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)

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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

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Carbon fluxes in a stream ecosystem