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The River Continuum Concept (or not?)

Stream Classification   Goal: Generalization

  2 general types of classification   __________ streams (longitudinal)   __________ streams (e.g., hydrologic regime

classification)

  Longitudinal Classification   What Changes?

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  Zonation (1 & 2 above)   Convenient, works in many drainages   Can account for discontinuities (e.g.,

foothill / plains transition)   Hard to generalize broadly

  Continuum maybe more general?

_______ transition zones

_________ __________

Zonation schemes 1) _________ characteristics

Width/depth, gradient, temperature, substrate, etc.

2) ___________ zonation   Fish -- Huet (1949)

  4 zones:   Trout

 Grayling

 Barbel

 Bream

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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

 *___________ = stream (annual T range <20°C)

 *___________ = river (> 20°C)

Illies & Botsaneanu “worldwide classification system”

  General Categories   Rhithron

  O2 always high   High gradient – 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   Some plankton

crenon

rhithron

potamon

Fig. 4.19, Ward 1992 “über classification”

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The River Continuum Concept (RCC)

  Vannote et al. (1980)

  Continuum   Idea of gradual change works in many drainages

  Textbook (Allan textbook, 1995):   “Bold attempt to construct a single synthetic framework to

describe the structure and function of lotic ecosystems from source to mouth.”

  Textbook (Allan & Castillo textbook, 2007):   “… proven to be a resilient encapsulation of the relative roles

played by different basal resources along an idealized river systems. Furthermore, the longitudinal distribution of functional feeding groups often, although not invariably, can be shown to be at least approximately in accord with expectations.”

The River Continuum Concept (RCC)

 General Idea   “_____________________” in physical conditions and

energy sources as you go from headwaters to mouth lead to biotic ______________

  What are the “predictable changes?”   ___________________________________   Changes in canopy cover, energy sources,

temperature, hydrologic regime   What are the “biotic adjustments?”

  Biotic responses to available _____________, __________, physical _______________

  downstream species replacements and change in functional ______________ groups

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Assumptions of RCC   Headwater Streams

1) heavily-canopied with __________ vegetation 2) ______________ fed 3) coarse substrate 4) ___________________ 5) nutrient-poor 6) undisturbed (by humans)

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 the main predictions for each of these size domains?

www.oxbowriver.com/

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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

1 12

1 12

1 12

1 12 1 12 1 12

1 12

1 12

1 12 1 12

1 12

1 12

substrate size bottom light diel Δ T

annual Δ T annual Δ Q Environmental Heterogeneity

CPOM / FPOM Nutrient Levels Nutrient Availability

P / R Benthic Diversity Fish Diversity

1 12 1 12 1 12 Stream Order Stream Order Stream Order

Algal Diversity Macrophyte Diversity Plankton

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Evidence for RCC predictions? Grubaugh et al. (1996) – Fig. 14.4 from text

Criticisms of RCC   Assumptions

  Some streams have substantial ___________________ headwaters

  Some streams lack _______________ sources

  _______________ can 'reset’ continuum   Can import CPOM, coarse substrate, cooler water, etc.

  Absence of ______________ in some canopied headwaters due to zoogeography (e.g., islands)

  Downstream sources of _____________ (floodplains)

  Historical alterations of large rivers create artifacts beavers

floodplain disconnection

Allan book: “Perhaps the generality of the RCC is a handicap when it is applied to a multitude of specific situations.”

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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

  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

How to account for variation within continuum?

tributary

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How to account for variation within continuum?

1)  Transition zones in Continuum   Process Domain Concept

Montgomery, D.R. 1999. Process Domains and the River Continuum Concept. J. Am. Water Res. Assoc. 35:397-410

2)  Tributary interruptions of Continuum  Link Discontinuity Concept

Rice, S.P., M.T. Greenwood, and C.B. Joyce. 2001. Tributaries, sediment sources, and the longitudinal organisation of macroinvertebrate fauna along river systems. Can. J. Fish. Aquatic. Sci. 58:824-840.

 Network Dynamics Hypothesis Benda, L., N.L. Poff, D. Miller, T. Dunne, G. Reeves, G. Pess, and M.

Pollock. 2004. The network dynamics hypothesis: how channel networks structure riverine habitats. BioScience 54:413-427.

A

B

C

  Developed for higher gradient, montane streams

  Prediction: Aquatic communities will be similar in same “domain” even if stream size varies somewhat

For example: compare A and B (same domain) versus A and C (same stream size but different domains)

  Some evidence supporting, but not well tested.

Process Domain Concept Geomorphology controls disturbance regime which controls ecological organization

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Tributaries: Link Discontinuity Concept

  Tributary _____________ are sites along a main channel where, because of the introduction of water and (or) _________, the water volume, bed sediment character, and water quality of the mainstream can change abruptly.

  Hypothesis: “The arrangement of tributaries and related features is an important control on the longitudinal organisation of macroinvertebrate benthos at moderate spatial scales.”

4 Lateral sediment sources (LSSs) are marked by arrows and delineate links in the Pine study reach

(Rice et al. 2001)

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Some step-like changes in physical-chemical variables at tributary junctions.

D50

Distance downstream (km)

Some “re-setting” of benthic inverts below tributary junctions.

  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 ______________________________ cause confluence effects to wax and wane over time.

  Shape of network, coupled with watershed disturbance regime, influence habitat __________________ and therefore will also influence ecological _______________.

Tributaries: Network Dynamics Hypothesis

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  Effects of disturbance (sediment inputs) in a tributary watershed on mainstem river   ____________ floodplain   lower upstream channel

_________, meandering upstream; steeper gradient downstream

  deposition of woody debris and sediment

  overall increase in habitat ___________________

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. 2004.

  Degree of heterogeneity is determined by size of sediment input (and also size of tributary relative to mainstem).

  Closely-spaced confluences also yield bigger effects.

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  Therefore, the basin shape is important in predicting the overall influence of confluence effects in the whole system.

  Size of tributaries influences confluence effects (bigger in relation to mainstem bigger effect).

Comparisons of predictions

Conclusion: accounting for tributary influences may help explain longitudinal deviations from the “central tendencies” predicted by a linear continuum hypothesis.

River Continuum

Network Dynamics