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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. 1.

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slide4

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.

Hydrology (Biology vs. Engineering)

2

slide6

Hydrology

  • Spatial Variation

Discharge variation & velocity resistance,

impart spatial and thus habitat variation w/in streams

-What does channelization do to biodiversity?

  • Temporal Variation

Stream Types:

1. Perennial: Year-round discharge

2. Intermittent: Discharge most of the year

3. Ephemeral: Discharge during & after

rainfall/snowmelt

3

slide8

5

Seasonal Discharge Variation

Spring

Same Location

Fall

morphology definitions
Morphology: Definitions

WC = Wetted Channel

ACS = Active Channel

FP = Flood Plain

7

slide11

Morphology: Definitions

Channel Units: (must be greater than one active channel width)

Riffle: - Moderate gradient, turbulent water surface

- Areas of high velocity; Erosional

Pool: -Low gradient, little or no surface turbulence

-Areas of low velocity; Depositional

Riparian Zone: Transition zone between the aquatic

system and the adjacent land

8

slide15

Riffles and Pools

Direction of flow

Riffle

Pool

Water surface

Porous bedrock

Gravel

Fine sediments

Stream Reach = each riffle-pool sequence

(or other repeatable units)

9

slide16

Riffles and Pools

Elevation

Pool

Riffle

Pool

Riffle

Pool

Riffle

Pool

Downstream

a

Erosion

b

Erosion

Point bar

Thalweg,

fastest

velocity

Riffle

a’

b’

Point bar

Pool

Erosion

b’

b

a’

a

a’

a

Current rotation

at bend

Velocity contour,

cross sectional at crossover,

maximum in center

Velocity contour,

cross sectional at bend,

maximum to outside

10

slide18
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

slide22
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?

Hydrology: How to Measure Discharge

What factors might influence curve shape?

14

morpology hydrology discharge
Q = Discharge= Volume of water passing a point per unit time

Q=VA

How to measure: Q= v1a1+v2a2+………vnan

Morpology (&Hydrology): Discharge

W

*

*

ai

*

*

*

*

*

P

n portions; Set intervals (e.g. 1m); Mean depth

15

slide29

There are more small than large streams

This is just an example….

How could these relationships vary with different types of

watersheds?

17

stream changes with distance from source
Stream Changes with Distance From Source
  • decrease in current velocity
  • increase in temperature range
  • decrease in oxygen available

source

rock

headstream

boulders

height

above

outfall

gravel

middle course

sand

mature river

silt

(estuary)

outfall

Distance from source

18

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Discharge

A

Rain

Rainfall, Discharge

Undisturbed

B

Urbanized

Discharge

Time (h)

Effects of Watershed Alteration on

Surface Hydrology

Hydrographs

20

slide34

1930

1980

The Effect of Dams on Missouri River Discharge

22

slide41

Sediments

Fine Course Gravel,

Silt Sand Sand Pebbles

Erosion

Transportation

Sedimentation

Fall

Velocity

27

slide43
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.

Other: Oxygen

30

other oxygen1
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

slide46
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

slide47

Other: Light

First Light Filter: Riparian

Second “ “ : Water!

33

slide49

34

Abiotic-Biotic

Relationships

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