Lec 11: Stream Ecology- Abiotic Features

• Lentic-Lotic Comparisons -Major influences & processes

• Hydrology, Morphology, & Discharge

• Human Alterations & Sediments

• Chemistry & Other Physical Features

1

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.

2

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

3

Global Distribution of Permanent and Intermittent Streams

4

Seasonal Discharge Variation

Same Location

Spring

Fall

5

Seasonal Discharge Variation

76

Morphology: Definitions

7

WC = Wetted Channel

ACS = Active Channel

FP = Flood Plain

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)

8

Direction of flow

PoolRiffle

Fine sedimentsGravel

Porous bedrock

Water surface

Riffles and Pools

Stream Reach = each riffle-pool sequence(or other repeatable units)

9

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

10

• 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

11

AD P

W

Morphology: Open-Channel Hydraulics

12

• 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

13

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?

14

What factors might influence curve shape?

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

15

* ******

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

)

• Classification systems: Stream order

16

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

17

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

18

Effects of Watershed Alteration on Surface Hydrology

19

Rai

nfal

l, D

isch

arge

A Discharge

Rain

Time (h)

Dis

char

ge

B UndisturbedUrbanized

Effects of Watershed Alteration onSurface Hydrology

20

Hydrographs

21

22

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

Sediments

23

Sediments

24

Embedded Substrate

25

Sediments

26

Sediments

27

Fine Course Gravel,Silt Sand Sand Pebbles

SedimentationTransportation

Erosion

Fall Velocity

Sediments 28

• 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

29

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.

30

• 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

31

• 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

Other: Light

First Light Filter: RiparianSecond “ “ : Water!

33

Jordan River – above inflow into Sea of Galilee

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Abiotic-Biotic Relationships