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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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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


Hydrology moved, or controlled as needed.

  • 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


Global distribution of permanent and intermittent streams
Global Distribution of moved, or controlled as needed.Permanent and Intermittent Streams

4


5 moved, or controlled as needed.

Seasonal Discharge Variation

Spring

Same Location

Fall


Seasonal Discharge Variation moved, or controlled as needed.

7

6


Morphology definitions
Morphology: Definitions moved, or controlled as needed.

WC = Wetted Channel

ACS = Active Channel

FP = Flood Plain

7


Morphology: Definitions moved, or controlled as needed.

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


Riffles and Pools moved, or controlled as needed.

Direction of flow

Riffle

Pool

Water surface

Porous bedrock

Gravel

Fine sediments

Stream Reach = each riffle-pool sequence

(or other repeatable units)

9


Riffles and Pools moved, or controlled as needed.

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


A moved, or controlled as needed. - 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


Morphology: Open-Channel Hydraulics moved, or controlled as needed.

W

A

D

P

12


Water Dynamics moved, or controlled as needed.

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 moved, or controlled as needed.

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 moved, or controlled as needed. = 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


Classification systems: moved, or controlled as needed.Stream order

16


There are more small than large streams moved, or controlled as needed.

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 moved, or controlled as needed.

  • 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


Effects of Watershed Alteration on moved, or controlled as needed.

Surface Hydrology

19


Discharge moved, or controlled as needed.

A

Rain

Rainfall, Discharge

Undisturbed

B

Urbanized

Discharge

Time (h)

Effects of Watershed Alteration on

Surface Hydrology

Hydrographs

20


21 moved, or controlled as needed.


1930 moved, or controlled as needed.

1980

The Effect of Dams on Missouri River Discharge

22


Sediments moved, or controlled as needed.

23


Sediments moved, or controlled as needed.

24


Embedded moved, or controlled as needed. Substrate

25


Sediments moved, or controlled as needed.

26


Sediments moved, or controlled as needed.

Fine Course Gravel,

Silt Sand Sand Pebbles

Erosion

Transportation

Sedimentation

Fall

Velocity

27


Sediments moved, or controlled as needed.

28


Temperature varies more than high volume lentic systems moved, or controlled as needed.

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: moved, or controlled as needed.

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


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 -Influences on temperature and lower oxygen

First Light Filter: Riparian

Second “ “ : Water!

33


Jordan River – above inflow into Sea of Galilee -Influences on temperature and lower oxygen


34 -Influences on temperature and lower oxygen

Abiotic-Biotic

Relationships


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