Transcript Streams

Hydrological Cycle
Streams
 Stream = water flowing downhill in a defined
channel. (River = large stream; Creek & Brook =
small streams)
Lotic system = flowing (fresh)water system;
Riparian system = of/around river/stream;
Fluvial = river/stream ; Rheos/Rrheic = stream
Quantifying Stream Flow
 Gradient = meters of drop per kilometer
of stream
High gradient = fast
Low gradient = slow
 Discharge = the amount of water carried
by a stream (often varies seasonally and with
precipitation) Usually measured as m3 per second at
a given point of the stream.
Streams
 Basin/Drainage/Catchment =
area drained
by a stream.
 Headwaters = small source streams that
originate from springs (groundwater) or
runoff from the basin.
 Mouth = terminus of a stream at another
body of water.
 Floodplain = level area along a stream that
is “frequently” flooded.
 Riparian Zone = area where vegetation is
influenced by the stream.
Mississippi Basin
“Typical” Stream
“Typical” Stream Profile
headwaters / source
mouth
highlands stream
-high gradient
-low discharge
-low turbidity
lowlands stream
-low gradient
-high discharge
-high turbidity
Stream Order
 often streams begin at a
spring (ground-water
becomes surface water).
 Stream Order = pattern
of stream branching.
1st Order Stream = headwater streams.
2nd Order Stream = streams formed by
uniting of 1st order streams.
Etc.
 Usually lower order = high gradient, cool,
low turbidity, few species, small discharge,
more variable flows over time.
Stream Order
“Typical” Stream Section
 Flood Plain = area around a higher order
stream covered by water during floods.
 Channel = area where a stream usually flows.
 Main Channel (thalweg?) = deepest part.
 Levee = raised area on either side of a
stream channel.
Channel
Main Channel
Streams, Runoff, & Groundwater
 More surface runoff → greater discharge
 Stream at groundwater level → more
continuous discharge
(won’t “go dry”; if channel
above groundwater, then may “go dry”)
 If stream higher than groundwater and
channel, then may “re-charge” groundwater
(especially if lower flow).
groundwater
Channel & Flow
 Water flows faster further away from the
substrate which causes turbulence.
 More irregular channels slow flow more
than regular channels.
 Straighter channel sustains higher flow.
Meanders/Bends
 Channel composition determines erosion
 Channels of evenly erodable material...
still form regular meanders/bends.
deposition
Cutbanks & Bars
erosion
deposition
Meandering Channel
Meanders/Bends
Oxbow Lakes
 Oxbow lake =
Portion of a bend cut
off from the main flow of the stream.
Braided Channels
 Braided Channel =
multiple
channels in a large (high order)
stream separated by islands/bars.
Pools, Riffles, & Runs
 Pool =
relatively deep portion with
slower water flow (lower dO2)
 Riffle = relatively shallow portion
with faster water flow where the
water ripples or breaks on the
substrate (higher dO2)
 Run = relatively deep portion with
faster water flow.
Pools & Riffles
Substrate & Cover
 Substrate usually composed of larger
elements the lower the order.
 Cover = the percent of the sky above
the stream that is shielded by
vegetation. % cover usually higher the
lower the order.
Drift
 (Stream) Drift = normally benthic organisms
in the water column moving downstream.
Allows re-positioning and/or benthic predator
avoidance (but makes vulnerable to large
predators). - Always one way.
Drought and Floods
 Effects usually most dramatic on low and
mid- order streams.
 Drought – problem = too little water;
surface flow may be very low or absent
drought refugia - isolated pools often
connected by subsurface flow or
connected higher order stream
 Floods – problem = scouring flow;
surface flow in channel very rapid
flood refugia – inundated floodplain or
water behind large structure (i.e., boulders) or
connected higher order stream
In-Stream Primary Production
 Very high flow, intermittent stream flow, and
high turbidity reduce (or eliminate) in-stream
photosynthesis.
 In clear streams, periphyton (microphytes) &
macrophytes may be able to undergo instream photosynthesis).
 Phytoplankton (& zooplankton) only rarely
present in very high order streams (consistent
low flow but… high turbidity).
 Marginal emergent vegetation and riparian
zone vegetation can undergo significant
production, especially in higher order
streams.
Allochthonous Inputs
 In most streams most nutrients come from
surrounding terrestrial environments (dead parts
of organisms, such as leaves, or dissolved molecules)
Allochthonous material = organic matter
from a different habitat;
CPOM – coarse particulate organic matter
FPOM – fine particulate organic matter
DOM – dissolved organic matter
 Detritivores (animals that eat detritus) and
decomposers (bacteria & fungi that decompose dead
organisms) are very important in most streams.
 Flow washes detritus downstream, more FPOM
and less CPOM in higher order streams.
Low Order Stream
Food Web
runoff or
groundwater entry
leaf
litter
periphyton
conditioning
(microbial colonization)
bacteria
coarse particulate
& fungi organic matter (CPOM)
grazing grazing
fishes
insects &
crustaceans
shredding
dissolved organic
compounds (DOC)
fine particulate
organic matter (FPOM)
insects &
crustaceans
collecting
“predatory”
fishes
predatory
insects &
crustaceans
insects, crust.,
nematodes, &
annelids
bacteria
& fungi
N. Amer. Stream Insect Shredders
crane fly larva
caddis fly
larvae
N. Amer. Stream Insect Collectors
blackfly
larva
caddisfly
net
chironomid,
midge larva
baetid,
mayfly
larva
N. Amer. Stream Insect Grazers
stone fly
larva
glossosomatid,
caddis fly larva
heptageniid, mayfly larva
N. Amer. Stream Insect Predators
rhyacophilid, caddis fly larva
(non-case building)
damselfly
larva
Hellgrammite,
Dobson fly larva
N. Amer. Decapod Crustaceans
 When crayfishes, crabs, and/or shrimps are
present, they often have significant
ecological effects as feeding generalists
(acting as shredders, collectors, grazers, AND
predators).
Low Order Stream Fishes
High Order Stream Fishes
Colorado River Fishes
Differences in Tropical Streams
 Bacterial and fungal decomposition of
allochthonous material is more rapid.
 Allochthonous inputs are often (but not
always) less seasonal.
 Fewer aquatic insects. Fishes (and in some
places decapod crustaceans) serve as the major
shredders, collectors, and grazers.
Human Impacts: Runoff/Erosion
 Increased nutrient inputs via agricultural
fertilizers – favors algal periphyton and
bacteria (can result in anoxia)
 Increased turbidity due to erosion – less instream photosynthesis
Human Impacts: Channelization
 Channelization and elimination of flood plains
– reduces groundwater recharge, increases
water velocity in flood and severity of floods
when levees breached
Human Impacts: Impoundments
 Formation of Lakes via damming of rivers.
 Greatly changes conditions, especially
downstream. (e.g., hypolimnetic release)