Lotic vs. Lentic Systems

1
Lotic vs. Lentic Systems
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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 lt3 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