lec 11: stream ecology- abiotic features
DESCRIPTION
Lec 11: Stream Ecology- Abiotic Features. Lentic-Lotic Comparisons -Major influences & processes Hydrology, Morphology, & Discharge Human Alterations & Sediments Chemistry & Other Physical Features. 1. - PowerPoint PPT PresentationTRANSCRIPT
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Lec 11: Stream Ecology- Abiotic Features
• Lentic-Lotic Comparisons -Major influences & processes
• Hydrology, Morphology, & Discharge
• Human Alterations & Sediments
• Chemistry & Other Physical Features
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Hydrology (Biology vs. Engineering)
• Engineers study water as a commodity which can be stored, moved, or controlled as needed.
• Stream ecologists study water as a dynamic medium, home to communities of organisms.
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Discharge variation & velocity resistance, impart spatial and thus habitat variation w/in streams
-What does channelization do to biodiversity?
Stream Types:1. Perennial: Year-round discharge2. Intermittent: Discharge most of the year3. Ephemeral: Discharge during & after
rainfall/snowmelt
Hydrology
• Spatial Variation
• Temporal Variation
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Global Distribution of Permanent and Intermittent Streams
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Seasonal Discharge Variation
Same Location
Spring
Fall
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Seasonal Discharge Variation
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Morphology: Definitions
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WC = Wetted Channel
ACS = Active Channel
FP = Flood Plain
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Riparian Zone: Transition zone between the aquaticsystem and the adjacent land
Morphology: Definitions
Riffle: - Moderate gradient, turbulent water surface - Areas of high velocity; Erosional
Pool: -Low gradient, little or no surface turbulence-Areas of low velocity; Depositional
Channel Units: (must be greater than one active channel width)
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Direction of flow
PoolRiffle
Fine sedimentsGravel
Porous bedrock
Water surface
Riffles and Pools
Stream Reach = each riffle-pool sequence(or other repeatable units)
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Ele
vatio
n
Downstream
Pool Pool Pool PoolRiffle Riffle Riffle
Thalweg,fastest velocity
Point bar
Point bar
Erosion
Erosion
Velocity contour,cross sectional at crossover,maximum in center
Velocity contour,cross sectional at bend,maximum to outside
Current rotationat bend
a
a’
aa’ a’ ab
b
b’
b’Ero
sionPool
Riffle
Riffles and Pools
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• A - Cross sectional area• W - Top width = distance from the water’s edge on
one bank to the water’s edge on the other bank• P - Wetted Perimeter = distance along stream bed
and banks where they contact water– R: Hydraulic Radius = the ratio of cross-sectional area to
the wetted perimeter: R=A/P– D: Hydraulic Depth = the ratio of cross-sectional area to
top width: D=A/W
• Graphic on next frame
Morphology: Open-Channel Hydraulics
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AD P
W
Morphology: Open-Channel Hydraulics
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• Water Dynamics• The following 3 terms are often misused
interchangeably – Flow (bad) can mean discharge or velocity
– Velocity is distance per unit time (m/s)
– Discharge is a measure of volume per unit time (ft3/s)
Hydrology
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Hydrology: How to Measure Discharge
• Velocities are typically measured at a standard depth
• Mean Velocity is calculated for each vertical measure. Cross-sectional Velocities are summed and divided by N to get a mean stream velocity. – Is mean or variation
important for biota?
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What factors might influence curve shape?
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Morpology (&Hydrology): Discharge
• Q = Discharge= Volume of water passing a point per unit time– Q=VA
• How to measure:Q= v1a1+v2a2+………vnan
n portions; Set intervals (e.g. 1m); Mean depth
ai
P
W
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* ******
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x
Size particle Index Observed ProductCategory size (mm) score (tally marks)
(A) (B) (AxB)Boulder >256 5 5 25Cobble 64-256 4 19 76Pebble 16-64 3 4 12Gravel 2-16 2 0 0Sand and silt <2 1 4 4Total 32 117Note: cobble very small 3.6563 AVG
Q = 0.97615 m3/s
x
Substrate Composition: The classification of mineral substrates by particle
Sediment Composition
0
5
10
15
20
Boulder Cobble Pebble Gravel Sand and silt
Particle Size
Pro
du
ct
0
5
10
15
20
25
024681012
Cumulative river width (m)
Wat
er d
epth
(cm
)
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• Classification systems: Stream order
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10-2
10-1
100
101
Leng
th (
km)
A
A
102
103
104
105
106
Num
ber
B
0 1 2 3 4 5 6 7
Stream order
102
103
104
Tot
al le
ngth
(km
)
C
This is just an example….
How could these relationships vary with different types of watersheds?
There are more small than large streams
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Stream Changes with Distance From Source
source
headstream
middle course
mature river
(estuary)
outfall
Distance from source
heightaboveoutfall
• decrease in current velocity• increase in temperature range• decrease in oxygen available
rock
silt
boulders
gravel
sand
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Effects of Watershed Alteration on Surface Hydrology
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Rai
nfal
l, D
isch
arge
A Discharge
Rain
Time (h)
Dis
char
ge
B UndisturbedUrbanized
Effects of Watershed Alteration onSurface Hydrology
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Hydrographs
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The Effect of Dams on Missouri River Discharge
1930 1945 1960 1975 199010000
100000
1000000
Dis
cha
rge
(m
3 d-1
)
A
A
1/1/19304/2/1930
7/2/193010/1/1930
12/31/19300
200000
400000
600000
800000
B
1/1/19804/1/1980
7/1/19809/30/1980
12/31/1980
Date
0
200000
400000
600000
800000
C
1930
1980
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Sediments
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Sediments
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Embedded Substrate
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Sediments
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Sediments
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Fine Course Gravel,Silt Sand Sand Pebbles
SedimentationTransportation
Erosion
Fall Velocity
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Sediments 28
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• Temperature varies more than high volume lentic systems
• Canopies of forested areas keep waters cooler than they would be in open areas.
• Prairie streams are almost always hotter than their neighboring forested counterparts.
Other: Temperature
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Other: Oxygen
• Oxygen is rarely a limiting factor for biota in streams: – Turbulence and air friction usually facilitate enough
diffusion to keep the oxygen at or near saturation.– Heavily vegetated streams can reap oxygen from
photosynthesis– Oxygen can become reduced in:
• Very slow rivers• Rivers with high organic contents (microbial
respiration) tropical streams or rain forests.
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• Unnatural addition of organic pollutants especially feces from humans or livestock increases the “Biological Oxygen Demand” BOD which is a measure of microbial respiration (How to measure?)
• Civil engineers and hydrologists use BOD frequently as a measure of organic pollution and to determine if the native biota are in danger of experiencing hypoxic conditions
• The removal of canopies on traditionally cold water streams has reduced the oxygen concentrations and had adverse affects on cold-water, oxyphilic fish like trout.
Other: Oxygen
BOD
Oxygen, Light, & Heat
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• Riparian vegetation & canopies reduce solar radiation -Influences on temperature and lower oxygen
• Turbidity: Reduce PAR for primary producers,visual predators & predator-prey dynamics
Other: Light
• Turbidity (scattering of light) is affected by – substrate type– bank erodability– overland runoff– land practices in the catchment basin– velocity– soil types– uniformity of stream channel and stream bed
• roughness allows for breaks to settle suspended solids 32
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Other: Light
First Light Filter: RiparianSecond “ “ : Water!
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Jordan River – above inflow into Sea of Galilee
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Abiotic-Biotic Relationships