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Physical Factors Important to Stream Biota

Physical Factors Important to Stream Biota. Four Major Physical Variables in Stream Ecosystems. Current (velocity) Substrate Light Temperature. Four Major Physical Variables in Stream Ecosystems. Current (velocity) Substrate Light Temperature.

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Physical Factors Important to Stream Biota

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  1. Physical Factors Important to Stream Biota

  2. Four Major Physical Variables in Stream Ecosystems • Current (velocity) • Substrate • Light • Temperature

  3. Four Major Physical Variables in Stream Ecosystems • Current (velocity) • Substrate • Light • Temperature

  4. Hydraulic conditions in a stream viewed from different scales Source: Hauer & Lamberti (1996)

  5. Current Effects • Size of particles in substrate (sorting) • Pollutant transport • Improves physiological richness of water • Improved oxygen • Brings nutrients and food to organisms e.g. Oedogonium kinzii • Takes up P32 10x faster @ V=18 cm/sec than in still water • Rate of uptake > up to V=40 cm/sec

  6. Current Effects • Force exerted on biota causes change in morphological characteristics • Hydrodynamic form • Dorso-ventral flattening • Attachment devices • Long tails • Dorsal eyes

  7. Caddisfly case shape and weight varies depending upon current velocity (Delgado and Carbonell, 1997) Typical northern case maker

  8. Maximum velocity of current at which some invertebrate species remain fixed

  9. Relationships between current velocity and sediment particle size

  10. Habitat conditions What can live there? Substrate diversity Chemical composition Sand : little adsorptive capacity Silt : high capacity to hold pollutants Substrate Classification

  11. A variety of substrate sizes provides ‘homes’ for many different benthic organisms.

  12. A ‘good’ stream has a variety of these different substrate sizes

  13. Streams with silty substrates have limited benthic habitat opportunities

  14. Substrate counts document the type and diversity of substrates available to benthic organisms

  15. Larger substrate particles are preferred as habitat • Greater substrate stability • Collect more organic debris • o.m. < 1mm = food • o.m. > 1mm = substrate

  16. Macroinvertebrates can be classified by the substrate they prefer • Lithophilous – stony substrate • Psammophilous – sand • Phytophilous – aquatic plants • Xylophilous – wood • Woody debris more common in headwaters • Can be most impt. substrate in lowland rivers • e.g., Satilla River, GA • Woody debris 40 genera 5825 mg/m2 (biomass) • Sand 20 genera 94 mg/m2 • Mud 17 genera 592 mg/m2

  17. Abundance and species diversity of aquatic insects in five habitats in Quebec Source: Allan, 1995

  18. Substrate Embeddedness low high http://el.erdc.usace.army.mil/elpubs/pdf/sr36.pdf http://www.epa.gov/owow/monitoring/volunteer/stream/vms42.html

  19. Light • Limited by: • Geology (shading bluffs) • Streamside vegetation • Trees can completely shade small streams • Large rivers are shaded little by streambank trees • Primary production within streams is not as important as it is in lakes. Allochthonous energy sources more important in streams.

  20. A closed canopy filters out most of the available sunlight.

  21. Light (and 1o productivity) varies seasonally in canopied streams Chl. Maximized prior to leaf out and after leaf fall Chl. Production mirrors light availability Data source: MA river

  22. Temperature • Direct solar radiation is the most important heat source in lakes and large rivers. • In small, shaded streams air or ground temperature is more important. • Temperature regulates: • Biotic metabolisms • Chemical reaction rates

  23. Biotic mechanisms regulated by temperature • Feeding and duration of digestion • Development time of larva and pupa • Cellular activity can only occur between two limits: the minimum and maximum thresholds Max. activity Activity Curve Activity Upper threshold Temperature

  24. Temperature affects survival times

  25. O2 consumption in macroinvertebrates increases with temperature

  26. O2 consumption in fish also increases with temperature

  27. Not all biota react to temperatures the same

  28. Spatial Temperature Change • Backwater areas >>temperature than channel • Provides opportunities for biota needing >temperatures O2 consumption Temperature

  29. Temporal Temperature Change • Diel • Low T in headwaters (buffered by springs) • High T in mid-order streams • Low T in higher orders (tempered by large volume) T Headwaters Mid-Order High Order

  30. Temporal Temperature Change • Seasonal • Acts as cue to development • e.g., larva pupa • Synchronizes life cycles • e.g., mayfly emergence

  31. Temperature varies daily in streams

  32. Temperature also affects viscosity CONSEQUENCES • Silt sinks twice as fast at 23o as it does at 0oC • Warm water carries less silt than colder water

  33. Effects of Ice Cover • Surface ice – little biological significance • Can insulate water from further heat loss • Underwater ice may also form • Forms during clear, cold nights at air temperatures of -15.6 to -23 0C • Anchor Ice: forms in shallow water (50cm) • Usually only a few centimeters thick • Begins forming on upstream side of riffle stones & spreads downstream

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