1. The River Continuum Concept

2. Stream Classification
Goal: Generalization
2 general types of classification
Within streams (longitudinal)
Among streams
Longitudinal Classification
What Changes?
Size
Substrate
Temperature
Water chemistry
Organic matter
Biota!

3. Study from French Pyrenees river:
1. Spp common at high altitudes
2. Spp common across a wide range
3. Spp in springs and small streams at lower altitudes
….etc…
6. Large river spp
Fig. 4.18, Ward 1992
Altitude
Go over what spp #s are what…
Why wouldn’t the large river specialists (#6) extend up to higher altitudes? (there are no large rivers up there!)

4. Discrete transition zones
3 Longitudinal Views
Discrete transition zones
21a – alpine zone - meadows
21b – crystalline subalpine forest – Engelmann spruce and subalpine fir
21c (Light green) – crystalline mid-elevation forests – ponderosa pine
21d (very light green) – foothill shrublands – sagebrush, Gambel oak,
25l – front range fans – shortgrass and mixed grass prairie
21f – sedentary mid-elevation forests
25b – Rolling sand plains
25c (orange) – moderate relief plains
25d (yellow) – flat to rolling plains

5. 3 Longitudinal Views Continuum Continuum Ecotones
21a – alpine zone - meadows
21b – crystalline subalpine forest – Engelmann spruce and subalpine fir
21c (Light green) – crystalline mid-elevation forests – ponderosa pine
21d (very light green) – foothill shrublands – sagebrush, Gambel oak,
25l – front range fans – shortgrass and mixed grass prairie
21f – sedentary mid-elevation forests
25b – Rolling sand plains
25c (orange) – moderate relief plains
25d (yellow) – flat to rolling plains

6. Discrete transition zones
3 longitudinal views:
Discrete transition zones
Ecotones
Continuum
Zonation
Convenient, works in many drainages
Can account for discontinuities (e.g., foothill / plains transition)
Hard to generalize broadly
Ecotones: sort of like zones, but more realistic
Sometimes things change quickly (foothills/plains) along the longitudinal gradient; sometimes more gradual.
BUT: hard to generalize among lots of different types of streams using zonation schemes. Some attempts….

7. Zonation schemes Fish -- Huet (1949) 1) Physical characteristics
 Width/depth, gradient, temperature, substrate, etc.
2) Biotic zonation
Fish -- Huet (1949)
4 zones:
Trout
Grayling
Barbel
Bream
Huet (for example) – these schemes are not widely used; Huet uses cold, cool, warm water fish to delineate zones.

8. Zonation schemes 3) Combination of Physical and Biotic
Illies (1961) and Illies & Botsaneanu (1963), a “worldwide classification system”
Kryon = glacier brook (1-5°C)
Crenon = spring
*Rhithron = stream (annual range T < 20°C)
*Potamon = river (> 20°C)
Illies, et al – first to use a combination of physical and biological. “worldwide” part – supposed to even apply to tropical regions, but the temps adjusted slightly higher. Also: substrate size, flow characteristics, etc same for all regions.
Rhithron and potamon are the 2 major zones of rivers; other 2 are different types of headwaters.
Boundary corresponds to sharp faunal discontinuities (like mtn to plain).

9. Illies & Botsaneanu “worldwide classification system”
General Categories
Rhithron
O2 always high
High gradiant – flow is fast and turbulent
Coarse substrates – erosional
No plankton
Macroinverts are cold stenotherms (lotic forms)
cool-water, cold-water fish
Potamon
Warm stenotherms/eurytherms
Facultative rheophiles
crenon
rhithron
potamon
Fig. 4.19, Ward 1992
What are some macroinverts you’d expect to find in rhithral vs. potamal streams?
Rhith: heptageniidae, ephemerellidae, baetidae, other stuff you’d find in our mtn streams.
Potamal: several beetles and hemipterans expected to appear, burrowers, more diversity of Diptera: horseflies, mosquitoes, etc., Leptoceridae, Hydroptilidae, dragonflies…

10. The River Continuum Concept (RCC)
Idea of gradual clinal change works in many drainages
Hynes, H.B.N The stream and its valley. VIVL
Vannote et al River Continuum Concept. CJFAS
Textbook (Allan):
“Bold attempt to construct a single synthetic framework to describe the structure and function of lotic ecosystems from source to mouth.”
continuum idea: there is a constant gradual change along the longitudinal gradient of a river. RCC in particular suggests a continuous resource gradient from headwaters to sea, and that resource gradient is what structures the community.
So: taking the “worldwide applicabilty” a step farther.
What is “VIVL”?? A: Verhandlungen der Internationalen Vereinigung für Theoretische und Angewandte Limnologie

11. The River Continuum Concept (RCC)
Structure in this way:
1) What are assumptions of RCC?
2) What are predictions of RCC?
- HW, mid-reaches, large rivers
3) What are omissions of RCC?
-e.g., Networks Dynamics
First line is KEY; emphasize physical conditions and energy sources AND biotic adjustments. ALSO: that these are PREDICTABLE.
Recognizing functional groups was a big deal – because doing this instead of naming taxa meant that it really did have the potentially to be widely applicable!

12. The River Continuum Concept (RCC)
General Idea
Predictable changes in physical conditions and energy sources as you go from HW to mouth lead to biotic adjustments
What are the “predictable changes?”
wider, deeper, flatter, finer substrate
 Changes in canopy cover, energy sources, temperature, hydrologic regime
What are the “biotic adjustments?”
Biotic responses to available energy sources, temperature, physical environment
 downstream species replacements and change in functional groups
First line is KEY; emphasize physical conditions and energy sources AND biotic adjustments. ALSO: that these are PREDICTABLE.
Recognizing functional groups was a big deal – because doing this instead of naming taxa meant that it really did have the potentially to be widely applicable!

13. Assumptions of RCC Headwater Streams
1) heavily-canopied with deciduous vegetation
2) groundwater fed
3) coarse substrate
4) light-limited
5) nutrient-poor
6) undisturbed (by humans)
Initially developed for undisturbed streams in the deciduous forest ecosystems of eastern N. America. (“worldwide applicability?”)
(focus on HW streams because this is where a lot of the argument has been… get to that later…)
(but you can already imagine what some of the arguments might be…)

14. RCC Patterns/Predictions
Break the continuum into segments (zonation?)
1) Headwaters (Orders 1-3)
2) Mid-reaches (Orders 4-6)
3) Large Rivers (Orders 7-12)
*What are main assumptions/ predictions for each of these?
Energy sources + reasoning behind them; P/R ratios;
invertebrate responses.
“Zones” are easier to think about, even if there is a gradient between them!

15. First, just understand each of big categories
First, just understand each of big categories. Write down the row and col headings, then see if you can fill it in yourself.
These are just the main effects (e.g. “allochthonous” means that most production is that, but some could still be autochthonous – e.g. some plankton in large rivers).

16. Another RCC Diagram
this one is cool because it also shows the relative amounts of different food sources.
No matter what, allochthonous food sources are always important in streams, just to varying degrees.

17. Yet Another RCC Diagram
this one is cool because it also shows the relative amounts of different food sources.
No matter what, allochthonous food sources are always important in streams, just to varying degrees.

18. Exercise Graph the following (given RCC assumptions):
Physico-chemical Factors
Substrate Size
Bottom Light
Diel ΔT
Annual Δ T
Annual Δ Q
Environmental Heterogeneity
Energy Sources
CPOM/FPOM
Nutrient Levels
Nutrient Availability
(to 1° Producers)
P/R
Diversity (Richness)
Benthos
Fish
Algae
Macrophytes
Plankton
Class exercise – split into groups

19. bottom light
diel D T
substrate size 1 12 1 12 1 12
annual D Q
Environmental Heterogeneity
annual D T 1 12 1 12 1 12
CPOM / FPOM
Nutrient Levels
Nutrient Availability 1 12 1 12 1 12
P / R
Benthic Diversity
Fish Diversity
These are all presumed “mean states” – assumptions of RCC. In reality, there is a lot of scatter around these mean states, and sometimes these aren’t even really the patterns (think desert streams, alpine streams, NZ – no shredders, etc). 1 12 1 12 1 12
Algal Diversity
Macrophyte Diversity
Plankton 1 12 1 12 1 12
Stream Order
Stream Order
Stream Order

20. Criticisms of RCC Assumptions Tributary can 'reset’ continuum
Some streams have autochthonous headwaters
Tributary can 'reset’ continuum
Can import CPOM, coarse substrate, cooler water, etc.
Absence of shredders in some canopied headwaters
New Zealand streams are “different”?!
Downstream sources of FPOM (floodplains)
Historical alterations of rivers
 beavers
 floodplain disconnection
Allan book: “perhaps the generality of the RCC is a handicap when it is applied to a multitude of specific situations.”
Tribs resetting – sort of has been addressed in later interpretations of the RCC (and is in Allan figure!) – we’ll address this issue in a little while (a river “discontinuum”)
Floodplains – produce CPOM and FPOM as energy resources for large rivers. (some of these things you could easily incorporate into the RCC; others not so much)
Tribs, beavers, human impacts, landslides, etc, etc… is it a River “Discontinuum??”

21. Legacy / Importance of RCC
Enduring Insights:
1) Stream organisms "predictably" structured along longitudinal resource gradients, reflecting changes in
energy inputs
temperature
2) Downstream communities depend on upstream processes
Scales of application
The very big differences (e.g., Headwaters vs. Mouth) are usually observable (e.g., CPOM vs. FPOM, shredders vs. collectors)
But differences among sites along the continuum are often obscure due to local variation
RCC difficult to “test” in meaningful ways
Main value, and limitation
A conceptual framework for viewing whole river basins, with a focus on linear, upstream-downstream linkages
RCC is a theory about the “mean state” of the system along the longitudinal profile, NOT the variance
In main value, limitations: “linear” part limits, also does not recognize the variance around mean state.

22. How to account for local controls (variance) within continuum?
1) Process Domain Concept
Montgomery, D.R Process Domains and the River Continuum Concept. J. Am. Water Res. Assoc. 35:
 Geomorphology controls disturbance regime which controls ecological organization
A couple of other ideas have come out more recently to help explain some of the local variation interrupting the continuum.
Also: recognizing that hydrologic disturbance regime may be very important and override predictions of the RCC (ie, maybe predictions are met only when streams are very stable!)

23. Process Domain Concept
Developed for montane streams
Prediction: Aquatic communities in same “domain”
(e.g., A and B) more similar than those in same stream size but different domains (e.g., A and C)
Some evidence supporting, but not well tested. A B C
The figure: different “process domains” are determined by altitude, stream size, geology, slope of the terrain, other geomorphic considerations. These dictate the disturbance types and regimes, which in turn determine the composition of the biota.
With disturbance having an overriding influence, the energy sources don’t matter as much, nor do the functional feeding groups of the inverts. Other important traits would come into play instead (like having the ability to attach to the substrate in a flood, or things like that).

24. How to account for local controls (variance) within continuum?
2) Network Dynamics Hypothesis (Benda et al., BioScience 2004)
River network is a population of tributaries and their confluences.
Tributaries interrupt river “continuum”
inputs of water, sediment and organic material at tributary junctions – varies in time depending on disturbance in the trib’s watershed
Degree of “interruption” depends on size of tributary relative to mainstem, which in turn depends on network geometry.
Temporal variation in disturbances cause confluence effects to wax and wane over time.
Shape of network, coupled with watershed disturbance regime, influence habitat heterogeneity and therefore will also influence biological organization.
Tribs interrupt continuum in a variety of ways…
Disturbance in trib’s watershed – related to above.

25. Effects of disturbance in a trib watershed on mainstem
expanded floodplain
lower channel gradient, meandering upstream; steeper gradient downstream
deposition of woody debris and sediment
overall increase in habitat heterogeneity
Explain picture first, all parts.
An alluvial fan enlarged following a fire triggers tributary junction effects in the North Fork Boise River (320 km2 drainage area). Junction effects include expanded floodplains, and increased channel meandering and side channels upstream of the fan (from Benda et al

26. Network Dynamics Hypothesis
Degree of heterogeneity is determined by size of disturbance (and also size of trib relative to mainstem).
Closely-spaced confluences also yield bigger effects.

27. Network Dynamics Hypothesis
Size of tributaries influences confluence effects (bigger in relation to mainstem = bigger effect).
Therefore, the basin shape is important in predicting the overall influence of confluence effects in the whole system.
Look at shapes with respect to how many tribs are first-order. If most are first-order, there won’t be as many confluence effects.
In the “real” examples, the bottom one has mostly first-order tribs, big ones are rare, and the important ones are pretty far apart.

28. Network Dynamics Hypothesis
Comparisons of predictions
a. RCC
b. Network dynamics included
Branching networks are more like reality than a single, linear river!
The b graphs aren’t don’t exactly have worldwide applicability, but if you know something about the network structure and where large tribs come in, then you can apply the hypothesis to make a general prediction about your own system.
Conclusion: accounting for tributary influences may help explain longitudinal deviations from the “central tendencies” predicted by a linear continuum hypothesis.