Lotic vs Lentic Systems Comparisons Surface area 118

Lotic vs. Lentic Systems

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

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

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

Flow Ø Current speed decreases as depth increases Ø Decrease from midchannel to edges (frictional forces between water, substrate - produce boundary layer)

Flow Ø 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)

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

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

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

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

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

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

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

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

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

Biota Ø Phytoplankton in streams relatively meager Ø Few planktonic forms Ø Mostly benthic forms

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

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

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

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

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

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

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

Biota Ø Those in headwaters adapted for life in moving water