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Chapter 3

BIOL 3450 Chapter Notes - Chapter 3: Protozoa, Phytoplankton, River Source

Course Code
BIOL 3450
Beren Robinson

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BIOL 350 Ch.3 notes
2000 km^3 of water contained in river channels and discharge 41,000 km3 into
most rivers are perennial aka flowing year round
nature of river is determined by catchment
geology, topography and hydrological activity determine the physical form of the
channel and nature of the substratum while water chemistry is determined by
terrestrial environment from which water originates from
The abiotic environment
defining feature is continual downstream movement
not uniform movement
flow patterns are determined by the volume of water and velocity = discharge +
its channel morphology
velocity varies across river channel
at the interface of the solid substratum and the moving water, friction creates a
viscous sublayer called the boundary layer
velocity is lowest adjacent to the bed and to increase with depth
horizontal profile show velocity varies across the channel in response to depth,
channel topography and presence of obstacles
some areas of rapid flow called the thalweg, a narrow channel in the main body of
water in which flow is greatest surrounded by areas of lower flow
common feature is that flow varies according to short and long term
weather/climate patterns
baseflow is maintained by constant export from water storage areas such as
upland wetlands or groundwater
if river runs above water table, lose water to groundwater and will dry up
intermittent rivers flow during seasons where they are below the water table
ephemeral are always above and are fed by surface inputs
frequent and short lived peaks in discharge are common in headwaters not so
much in large rivers they show seasonal changes in discharge
River channel form
size of channel varies by discharge
rivers mostly flow at somewhat less than full channel capacity
channel size/ capacity is determined by occasional high flow events rather than
occasional high discharge causes most rivers to overflow
in lower reaches, channel may not be as clearly defined ie a floodplain and
constantly changes form and may become braided

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Whole channel features
low order has regular alteration between riffles and pools
riffles= shallow, high gradient stretches, high velocity water over substratum of
cobbles or boulders which break off and cause turbulence
pools= deep, low gradient, slow flowing and fine substratum
glides can occur between the two where water flows rapidly but smoothly as the
substratum does not break the surface
this sequence tends to occur where bed substratum is coarse and gradient is
when channel is steep the stream will create a pool –step sequence where water
falls over large boulders into deeply scoured pools also happens with fallen trees
low flow, riffles and steps have high velocity
as discharge increases, flow increases in pools more rapidly than in riffle until
flood conditions can be similar in both features
coarse sediment is much less susceptible to scouring
even at low flow scouring occurs outside of meander bends and immediately
downstream of water flows
Partial channel features
in the riffle- pool sequence gravel bars, undercut banks and slow flowing
banks on the inside of meanders are associated with the riffle pool sequence
or with the sinuosity of the rive channel
clumps of of aquatic veg, trailing bankside vegetation, fallen trees, roots and
gravel bars are indicative of dynamic river channel that is constantly eroding
and depositing sediment
River zonation
longitudinal trends can be identified along a river system, can be divided into 3
zones: headwater (erosion) zone, middle-order or sediment transfer zone and the
lowland or sediment deposition zone
can be defined in terms of water supply and sediment
erosion zone: major source of water and sediment; as channels slope is relatively
steep, deposition of sediment, is localized or ephemeral; substratum is large
( cobbles and boulders) and may erode to bedrock discharge is variable and
responsive to local precipitation; steep slope and coarse substratum can produce
turbulent flow
sediment transfer zone: river gradient is reduced, so water and sediment are
transported with little net loss or gain; erosion=deposition
sediment deposition zone: low gradient, stable and predictable discharge, site of
sediment load deposit as it approaches the sea and develops a delta or estuary,
most of the water is derived from upstream
river structure can be modified by local geology
River classification

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classification by purely biological parameters ie a species isn’t very helpful bc the
species may be restricted in areas they occurs
use stream ordering system
river water percolates into the sediments creating a fluvial groundwater which
flows in a downstream direction (slow)
inputs are low in upstream, can be the source of the river in the spring
further downstream, will enter the river if the water table is high and will be
responsible for continual flow in low precip
found in the sediment transfer or deposition zone, a flat valley bottom constructed
of loose or consolidated alluvial sediment deposited when the river floods or
shifts it channels
geomorpholically, it’s the area flooded with predictable ( not regular) frequency
ecologically, restricted to the zone that has regular, seasonal flooding
diff in flooding for low and high order stream
Changes in water quality
rain water is relatively pure but picks up solute and suspended matter as it flows
over the ground, once they enter the river they pretty much stay there, becoming
further concentrated by inputs and by evaporations
gradual increase in solutes and suspended particles as river proceeds from source
to mouth
fluctuations in impurities result from a high discharge, which resuspends sediment
from the bed and if causes flooding with input from the floodplains
with excess rain, excess water from the catchment passes rapidly through the
channel with a pulse of sediment, detritus and solutes ex) acid rain
passes so quickly it cant be neutralized, leaves the water
Ecological effects of the abiotic environment
effects of water flow are dependent on the organisms size and structure , its
activity and its position in the water column
current carries animals living in the water column downstream as a result pelagic
species tend to poorly developed in rivers
benthos is the dominant ecological group in rivers
Adaptation to microhabitats
most benthic species can swim weekly or if at all and endeavor to remain on the
epibenthos have adopted morpholically with hooks, suckers, claws and
behaviourial strategies like orienting the body parallel to the direction of flow to
reduce the surface area impacted by the current
boundary layer is so thin its normally very small org that are unaffected by current
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