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Stream Ecology (NR 280)

Stream Ecology (NR 280). Chapter 1 – Introduction to Fluvial Systems Basic Concepts. Stream Order – Strahler Number Arthur Strahler (1957) after Robert Horton (1945). Source: http://www.krisweb.com/stream/stream_order_kris.htm. River continuum concept.

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Stream Ecology (NR 280)

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  1. Stream Ecology (NR 280) Chapter 1 – Introduction to Fluvial Systems Basic Concepts

  2. Stream Order – Strahler NumberArthur Strahler (1957) after Robert Horton (1945) Source: http://www.krisweb.com/stream/stream_order_kris.htm

  3. River continuum concept • Vannote et al. (1980) Canadian Journal of Fisheries and Aquatic Sciences • Rivers as gradients: An array of physical, chemical and biological characteristics change continually and gradually with distance downstream Figure from the original paper

  4. RCCForcing Factors • Slope decline • Discharge increase Note: Hypothesized decrease in velocity is not true

  5. How might these landscape factors affect “master” environmental variables like light and temperature?

  6. Longitudinal Trend in Temperature (and Light) • Tends to decrease with elevation drop and canopy spreading • Daily range in temperature is most extreme in middle reaches- canopy is open and depth is shallow

  7. Light and Temperature Strongly Control Primary production • Primary Production (P): the product of photosynthesis • Respiration (R): the product of energy generation • What happens to biomass if P<R? P>R? P=R? • In the Vannote et al. where might P:R be greatest? Lowest?

  8. Is primary production the primary source of “fuel” for stream ecosystems? • Detritus – biomass that was once alive and is now dead. Potential food. • Autochthonous production – produced within the stream (i.e. primary production) • Allochthonous production – produced in the terrestrial environment and transported to streams • Note: All three of these terms were borrowed from Geology!

  9. Energy sources for the stream foodweb • Detritus is continually carried downstream and processed along the way • CPOM becomes FPOM • FPOM becomes finer and more recalcitrant • The stream is a detritus processing factory

  10. Logical consequences of the RCC • What benthic macroinvertebrates eat determines how they are ordered along the longitudinal profile (functional groups) • Shredders: low-order streams • Grazers: middle order • Filter Feeders: middle order?? • Collectors: high-order • Predators: evenly distributed • Fish respond to physical habitat and to food resources.

  11. Linkages between physical habitat, food resources, and biotic diversity

  12. Challenges to the RCC • RCC assumes a forested watershed • Bulk of stream studies in such systems • Many streams run through prairie, agricultural areas, deserts, tundra or alpine regions • Tree leaf input minimal • No canopy • Here autotrophs may peak at low order, P>R throughout

  13. Challenges to the RCC • The amount of streamside vegetation is assumed to remain constant • In fact riparian vegetation is discontinuous • Streams pass through areas of logging, agriculture, villages… • Canopy opens and closes; CPOM input varies • CPOM input is season dependent and so is stream shading and solar input

  14. Challenges to the RCC • Dams disrupt the continuum • Reservoirs alter temperature, sediment, and flow regimes, altering productivity and diversity. • The Serial Discontinuity Concept (Ward and Stanford 1983) • Each impoundment sets back the river continuum to a new starting point

  15. Challenges to the RCC • Assumption that autotrophs are light limited may not always be true • If nutrients are limiting, productivity will not increase in middle reaches no matter how much the canopy opens • Assumption that food resources or physical factors control animal populations can be wrong • They may be controlled by predators

  16. Challenges tothe RCC • Assumption that all (or most) FPOM is produced upstream and carried downstream could be wrong • Doesn’t take into account inputs from backwaters, marshes and the floodplain • The Flood-pulse Concept (Junk et al. 1989) presents an alternative (tropics) • The most important hydrological feature of large rivers is the annual flood pulse, which extends the river out onto its floodplain • Biotic communities have adapted to this pulse and use it to exploit the floodplain environment

  17. Which concept is right? • In environmental sciences a theory that is uniformly “right” for all places is an anomaly. (Doesn’t exist?) • Elements of each of these theories has merit in some systems. • The RCC spawned decades of productive research on streams and rivers that has contributed substantially to our knowledge of stream ecosystems.

  18. Opportunities for future research • Lateral organic matter and nutrient exchange • Hyporheic processes • The effects of nutrient spiraling • Processing of DOM and DOC • Impacts of high flow events • Minimum flow thresholds (“river needs”) • Climate change impacts • Research on large rivers in general • Research on urban or highly developed rivers

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