1. Ecosystem Processes and the River Continuum Concept
Unit 1: Module 4, Lecture 5
The Effect of Current on Organisms
Photo: Glenn Merrick

2. 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.

3. General organic matter pathway
geography.uoregon.edu/ .../SCRfig2-33web.jpg
The path energy follows through consumers in a food web and the flux of organic matter through an ecosystem are closely related topics.

4. Sources of organic matter
Autochthonous – instream
Allochthonous – out of stream
/streamwatch/ swm10.html
manual/6doing.htm
veg/brfredmaple.html
Autochthonous organic matter – produced within the stream
- diatoms; algae; submerged, floating, and emergent macrophytes
Allochthonous organic matter – produced outside of the stream and imported into the channel.
- includes, but is not limited to leaves, woody debris, dissolved organic compounds, dead organisms

5. 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 > 1 mm
Fine particulate organic matter
Leaf fragments, invertebrate feces, and organic precipitates < 1 mm
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 and their fragments > 1 mm in diameter
Fine Particulate Organic Matter
Leaf fragments, invertebrate feces, and organic precipitates < 1 mm in diameter

6. 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.
Following the fate of organic matter introduced into a stream from its source, through transport, storage, and respiration allows the development of a general understanding of ecosystem function and, possibly, efficiency if organic matter components are quantified.
The River Continuum - sti/pratt/energy.html

7. 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 caddisfly of the family Limnephilidae
The River Continuum

8. 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 blackfly of the family Simulidae
A caddisfly of the family Hydroptilidae
The River Continuum

9. 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 dipteran of the family Thaumaleidae
The River Continuum

10. 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)
A stonefly of the family Perlidae
A “true bug” of the family Notonectidae
The River Continuum

11. Seasonal variation in particulate organic carbon
Low concentrations in winter and fall
High concentrations in summer
Particulate organic carbon varies primarily by seasonal changes in biological processes and by discharge. In general:
POC is high in summer at low flows
POC is low in winter and at high flows
Photos by g. merrick

12. Fate of organic matter Stored within the stream bank or channel (25%)
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
Organic matter that enters streams may be (percent estimates are approximate and variable):
1) stored within the stream bank or channel (25%)
2) exported downstream (50%)
3) metabolized and respired as carbon dioxide by organisms (25%)

13. 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.
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.

14. 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
Net primary production is far greater in open compared to closed canopy streams, but the relative contribution of energy by primary production and litter fall to an ecosystem’s energy is also influenced by climate and nutrient availability.
Data from selected from Table 12.5 in Allan, J.D., 1995
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15. 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
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

16. The River Continuum Concept
The River Continuum Concept is an attempt to describe the function of lotic ecosystems from their source to their mouth and explain the variation among sites that result from differences in their terrestrial setting. These differences are manifested in structural and functional differences among stream reaches that can be tied to stream order. Differences between low, middle, and high order streams show up primarily in terms of
- geomorphology
- energy pathways
- diversity and relative abundance of functional groups
The differences are a result in changes in percent canopy cover, gradient, substrate type, temperature, and other factors that necessarily change the stream’s physical nature as it increases in size in its path downstream.

17. Stream order and the RCC
Low order streams
Shaded headwater streams
Coarse particulate matter (CPOM) provides resource base for consumer community

18. 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)
Photo by G. Merrick

19. 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

20. Carbon fluxes in a stream ecosystem
Figure 12.1
Processing of organic matter in streams, whether autotochthonous or allochthonous, is largely carried out by macroinvertebrates and microbes. Carbon not assimilated is exported and carbon that is respired is exported or evolved back to the atmosphere.
Figure 12.1 Simplified model of principal carbon fluxes in a stream ecosystem. Solid lines indicate dominant pathways of transport or metabolism of organic matter in a woodland stream. R-circle denotes mineralization of organic carbon to carbon dioxide respiration. (Modified from Wetzel, 1983)