BESC 320 – Water and Bioenvironmental Science
(Lecture 3 – 27 January 2016)
“Your education really is the job of a lifetime and it commences now.” David Foster Wallace
How do we study without a text*?
 Lecture notes point to concepts.
 Rely on your notes to know what detail to learn—outsource
learning material (e.g. Wiki’s etc.).
 Pay attention to my cues (“you need to know this”; “understand
this in concept”)
 Even my tangents if they have information content (not just
stories about Lynn Margulis).
 External content is important—that is why I provide links in the
notes to any external content I use—so you can review the
material outside of class.
 Example questions:
o e.g. from a tangent: What is “planetary physiology”?
a. dynamics of vulcanism on Earth
b. atmospheric exchanges with space
c. connected cycles acting on a planetary scale
d. use of satellites to monitor planetary conditions
e. telepathy
o conventional question: What % of Earth’s water is fresh?
a. 97%
b. 30%
c. 5%
d. 3 %
e. 0.01%
o What holds water together all dense and viscous?
(see Wiki on hydrogen bonds)
Other Unique Properties of Water


Clouds are white (increase albedo of planet)
As for most substances, water becomes more dense as temperatures
drop. Except as temperature drops below 4 °C water grows less dense and
solidifies at 0 °C.
 Water has high molar heat capacity allowing it to adsorb and emit
relatively large amounts of heat without a change in temperature
 Water has large latent heats of evaporation and freezing as a result of
hydrogen bonds, with the result that phase changes of water are an
important heat-transport vehicle
 Strong cohesion (surface tension) & adhesion (wetting), the balance of
which makes for capillarity
water
(dyed)
mercury
What are
some
important consequences you can
think of regarding water’s high
cohesion and adhesion?
More fun with the properties of water: cohesion, adhesion, capillary action and
surface tension:
http://science.jrank.org/pages/1182/Capillary-Action.html
(Note the video at the bottom begins slow but gets good)
Ponder:
Why does rain fall in drops? Why not cubes?
How does the former answer relate, abstractly, to this:
Why do water droplets run together?
How do trees hoist water to their limbs hundreds of
feet above ground?
How do sweating, panting and swamp coolers work to cool?
Water physical sciences II (geology)
Water,
liquid and
solid,
covers
more than
70% of
world’s
surface




More than 370 billion billion gallons
97% salt—oceans
3% fresh—mostly (70%) ice, much groundwater (29%), 1% surface
do the math: 0.00003 of the world’s water is “easy”
Table of volumes—with the residence time—relates to potential sustainability of
use
Precipitation—the greatest part of residence and refreshment times
Of course the local view has been
even more ugly, recently:
Hydrologic Cycle
Be able to describe key components:
 Evaporates or transpires from land, water, organisms
 Condensation (dew or cloud formation)
 Precipitation (rain, snow)
 Storage (water bodies, groundwater, glaciers)
 Infiltration (movement of water into soil)
 Percolation (movement of water through soil to zone of saturation)
 Runoff (movement of water into rivers and water bodies)
Solar energy drives the hydrologic cycle.
Key concept: solar energy ultimately drives nearly everything, with water as the
planet’s life’s blood.
Dynamics at the Earth’s surface contained in watersheds
The nexus of river forks point the
direction of flow (e.g. also
indicates the landscape gradient).
See example topography at right.
Note that things happening in one
part of the watershed influence
everything downstream (and
often, below ground).
The gradient also creates
ecological diversity.
Stream order—literally, the order
in which streams occur from high
to low gradient. Headwaters are
1st order, and the larger rivers that go to sea are typically 4th order or higher.
Practice this on the map or on Google Earth.
Low order streams—small size, rapid gradient change, fast flow, clear & clean
(oligotrophic) water, carries few but large parent materials. High order streams are
opposite the descriptors given for high order streams.
Oligotrophic—few (but diverse) organisms feeding off limited nutrients in the
water.
Eutrophic—a true feast for many (but undiverse) organisms feeding off abundant
nutrients in the water.
Mesotrophic—intermediate state between the ends of the gradient defined above
Stream geomorphology
Gradient, pathway, architecture of flowing water. Sinuous paths are typical for
high order streams. Floodplain is part of stream structure.
Imagine a
straight
channel
of water,
1m
deep, 10
m wide,
going
straight
to
Houston. Think about what volume of water that channel holds. Now imagine a
highly sinuous path with the same depth and width. How does that volume of
water compare?
Thus a major function of natural, reticulate, sinusoidal riverways is storage of
water. When that storage capacity is exceeded, floodplains generally contain the
remainder.
A floodplain is the natural basin in a watershed that floods during times of
seasonally high precipitation. Plants are highly adapted to flooding regime.
Presence of floodplain prevents flooding elsewhere, such as major cities.
vs.
Channelization (local flood
control, “pass the buck”)
 Straightening stream paths, often accompanied by concrete guides
 Pushes water quickly downstream, away from the control zone (where the
water becomes the problem of others)
Development on bank, or other unfortunate locations on floodplain has the same
effect, by removal of infiltration. (Local e.g.—Bryan Target)
“They paved paradise, put up a
lot” —Janis Joplin
What did they do with the trees?
parking
Fast flow creates erosion, in channels but also on banks, especially on outer bank.
This process tends to cut into the land so much the stream path becomes
increasingly meandering. Some meanders are so acute the stream can come back
and intersect itself, at which time the meander gets cut off to form an oxbow lake.
Outer bank (bank on the outside of a turn) are heavily erroded and often highly
alluvial just downstream.
Alluvial refers to deposition of materials by flowing water. Alluvium would be the
noun describing the actual material deposited.
nice animation: meander and oxbow hydromorph (YouTube)
We discussed the importance of rivers for holding water. That trait is an example
of an ecosystem services. The term is self explanatory.
Discussion:
What are some other ecosystem services provided by rivers?
What are some of the consequences of using these services?