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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Stream ecologists study water as a dynamic medium, home to communities of organisms.Hydrology (Biology vs. Engineering)
Discharge variation & velocity resistance,
impart spatial and thus habitat variation w/in streams
-What does channelization do to biodiversity?
1. Perennial: Year-round discharge
2. Intermittent: Discharge most of the year
3. Ephemeral: Discharge during & after
Seasonal Discharge Variation
WC = Wetted Channel
ACS = Active Channel
FP = Flood Plain
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
Direction of flow
Stream Reach = each riffle-pool sequence
(or other repeatable units)
cross sectional at crossover,
maximum in center
cross sectional at bend,
maximum to outside
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
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)
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?
How to measure: Q= v1a1+v2a2+………vnanMorpology (&Hydrology): Discharge
n portions; Set intervals (e.g. 1m); Mean depth
This is just an example….
How could these relationships vary with different types of
Distance from source
Effects of Watershed Alteration on
The Effect of Dams on Missouri River Discharge
Fine Course Gravel,
Silt Sand Sand Pebbles
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.
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
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
Oxygen, Light, & Heat
Turbidity: Reduce PAR for primary producers, visual predators & predator-prey dynamics
First Light Filter: Riparian
Second “ “ : Water!