Lotic vs. Lentic Systems

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

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

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

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

Biota Those in headwaters adapted for life in moving water