1. Lotic vs. Lentic Systems

2. Comparisons Surface area - 1/18th that of lakes
Age - most stream channels ancient compared to most lakes
Flow - the most influence on making stream environments different than lakes

3. Flow Produces structure of river, bed, influences biota
Currents vary seasonally, longitudinally, vertically

4. Flow Generally <3 m/sec (up to 8 m/sec)
Maximal during greatest runoff (wetter season)

5. Flow Current speed decreases as depth increases
Decrease from mid-channel to edges (frictional forces between water, substrate - produce boundary layer)

6. Flow
Average velocity at 0.6 depth for shallow streams (or average of readings at 0.2 and 0.8 depth in deeper streams or rivers)

7. Flow Velocity generally decreases from headwaters to mouth
Headwaters - erosional - larger substrates
Near mouth - depositional - smaller substrates

8. Flow General pattern not always present
Velocity may be constant, or may increase

9. Alternating Habitats Riffles and pools Faster currents in riffles
Regular spacing - riffles 5-7 stream widths apart

10. Water Temperatures More rapid changes than in lentic waters
Daily cycles up to 6º C in summer
Average temperatures tend to increase downstream

11. Water Temperatures Little stratification because of flows
Warmer temps alter viscosity
Faster flow
Carry less silt
Reduces boundary layer

12. Water Temperatures
Winter - entire stream declines to 0º C before ice forms
Ice formation at any layer
Frazil or anchor ice

13. Light Penetration Less in moving vs. standing waters
Increased turbidity
Increased shading by riparian vegetation

14. Chemistry Dependent on drainage basin
General inverse relation between discharge and concentrations of dissolved materials

15. Chemistry Little zonation of dissolved materials or gasses
Turbulent flow, gasses at saturation for temp., pressure
Significant changes by activities of living organisms

16. Biota Phytoplankton in streams relatively meager Few planktonic forms
Mostly benthic forms

17. Biota In larger streams, plankton always present
Planktonic diatoms dominate
Selective elimination of other types?

18. Biota
Most primary production in small streams from periphyton growing on bottom
Unusually productive because of nutrient delivery

19. Biota Zooplankton numerous only in larger systems
Dominated by rotifers
Few crustacean zooplankters

20. Biota Benthic invertebrates diverse (especially insects)
Substrate is major controlling factor

21. Biota Soft substrate types found in both flowing, standing waters
Hard substrate types often unique
Adaptations to cope with flowing water (flattening, hooks, suckers, secretions, ballast)

22. Biota Longitudinal rather than depth zonation
Changes in response to temp., current, food availability

23. Biota Fish exhibit distinct habitat, longitudinal differences
Those in pools or downstream zones also found in lakes

24. Biota
Those in headwaters adapted for life in moving water