Transcript Lecture 2: Physical Properties of Water

Lecture 3: Fluid/Physical
Properties of Waters (Part 2)
Dr. Robert Vega
MARI-5421
September 6, 2006
Lecture 3

Continue with physical properties of
water:
salinity
electrical conductance
turbidity
color
total gas pressure
Physical Variables: salinity (S)






Often considered a chemical attribute of water.
Salinity: the measure of the concentration of
dissolved ions in water (ppt, mg/L).
Practical Salinity Units (psu)
Major ions: Na+ and ClSubstantial ions: Mg2+, Ca2+, K2+, SO4=, and
bicarbonates HCO3Salinity sum total of geological and hydrological
conditions in region.
Major and Minor Ions
From Sumich, page 22
Physical Variables: Salinity




Freshwater surface waters in arid regions
have higher salinity, changes rapidly with
rainfall.
Marine seawater salinity: 35 ppt +/- 2 ppt.
Brackishwater: highly variable salinity due
to tidal and run-off effects.
Heavy rainfall in ocean often creates
freshwater lens effect.
Physical Variables: Salinity (S)




“Chlorinity” is not the same as salinity.
Chlorinity: the total weight of chlorine,
bromine and iodine contained in 1 kg of
seawater after all of the bromine and
iodine have been replaced by chlorine.
estimation: S = 0.3 +1.805 [Cl-]
Make sure the chloride reading is in g/L or
ppt Cl-
Physical Variables:
Salinity
How to measure salinity:
 chlorinity
 glass hydrometer
 conductivity meter
 refractometer
 mutiparameter water quality meter
 Other methods?
Salinity and Physiology




Many aquaculture species have the ability
to modify blood/hemolymph cellular
osmotic pressure to achieve homeostasis.
If not, physiological stress results.
Osmoregulation: maintenance of cellular
pressure relative to an external medium via
transport of salts and other low molecular
weight compounds (e.g., amino acids).
Very energy-expensive activity.
Physical Variables: Salinity
Euryhaline: having an osmoregulatory
capacity and ability to tolerate
varying levels of salinity.
 Stenohaline: limited tolerance
 Most freshwater fish have a blood
osmotic pressure of 7 g/L.
 If external salinity increases above
this, growth is reduced, < 2 g/L is
recommended.

Physical Variables: Salinity




Osmoregulation involves passing a solvent
through a membrane.
The solvent (e.g., water) always passes
from a more dilute solution to a more
concentrated one.
Membranes are continuously “bombarded”
on both sides by solute and solvent.
More molecules of solvent will strike the
membrane surface on the concentrated
side than on the dilute side.
Physical Variables: Salinity




There is a net movement of water then from
the dilute side to the concentrated solution
(REM: we are talking about solvent).
This phenomenon is known as passive
diffusion.
This situation can be reversed by adding
pressure to the concentrated side.
This pressure is known as osmotic pressure,
the process of adding pressure is know as
osmoregulation.
Physical Variables: Salinity



For fish and crustaceans, the body fluids
are one solution, the surrounding pond
water is the other solution.
Freshwater species have body fluids more
concentrated in ions than the surrounding
water (hypersaline or hypertonic).
Saltwater species are just the opposite:
hyposaline or hypotonic.
Physical Variables: salinity





Osmoregulation of fw species involves the
uptake of ions from the environment and
restriction of ion loss.
fw species excrete water to keep [ion]
high.
sw species do the opposite (excrete salts).
Not only are salts used as osmoregulators,
so are amino acids (low mw: gly, ala, pro)
from blood/hemolymph proteins.
These amino acids also impart more flavor.
Isosmotic to Hypoosmotic
Sea cucumbers are osmoconformers
Osmoregulation: swfw
Chinook salmon are osmoregulators
Physical Variables: Salinity
Upper Salinity
Tolerance Range
Species
(mg/L)
Trout
20
Grass carp
10-14
Tilapia aurea
10
Red hybrid tilapia
17
Litopenaeus vannamei
25-30
Litopenaeus stylirostris
45-50
Physical Variables: Salinity
Although several marine crustacea
are euryhaline, they cannot
accommodate quick changes in
salinity.
 They must be gradually acclimated.
 Rate should not typically exceed 1 or
2 ppt per hour.
 Discuss experience red drum
Sciaenops ocellatus (lake stockings).

Physical Variables:
Electrical Conductance






Electrical Conductance: the measurement
of of the dissolved mineral content
(salinity) of water.
Changes in direct proportion to salinity.
Water ionizes slowly and, thus, is a poor
conductor of electricity.
Unit of measurement: microohm/cm
Range: 20 - 1,500, much higher for sw.
Can be used to estimate salinity or TDS.
Physical Variables: Turbidity





Turbidity: measurement of
light penetration in water.
Produced by dissolved and
suspended substances (clay,
humics, silt, plankton,
colored compounds).
Typically measured with
secchi disk or turbidometer.
More dense = higher
turbidity.
Some forms are more
desirable than others.
Physical Variables: Turbidity




Clay turbidity of over 30 cm typically
retards phytoplankton blooms in
freshwater.
Fine particles can increase respiratory
rate, smother fish eggs, clog filtration
equipment.
Fish appear to be more sensitive to
suspended solids than clay turbidity.
Upper tolerance level: around 80 mg/L vs
20,000 mg/L for clay turbidity
Physical Variables: Color






The reaction of incident light with
impurities in the water.
Why are natural bodies of water blue?
Humics (organic acids) = tea color, not
directly harmful to aquaculture species.
Phytoplankton: red, green, yellow, brown
Often used as a management tool.
Can be qualified by spectrophotometer
(where is the absorbance peak?).
Color: scattering/reflection
Color: absoption/penetration
Physical Variables:
Total Gas Pressure





Total Gas Pressure (TGP): the sum of the
partial pressures of all gases dissolved in
water.
Barometric Pressure (BP): weight of the
atmosphere imparted on water surface.
equillibrium: TGP = BP
When TGP > BP, gas goes from water to
atm.
When BP > TGP, gas goes from atm to
water.
Physical Variables:
Total Gas Pressure




%TGP = (BP + P) x 100/BP.
Obviously, if % TGP is over 100%,
conditions are supersaturated.
Many discharge and site selection
criteria are based upon > 50% partial
pressure for oxygen.
Remember, TGP is not an indication of
how “good” or “bad” the water is, you
must look at individual gases,
composition of TGP.
Physical Variables: Total Gas
Pressure (implications)





Supersaturation is an unstable condition,
which can result in gas bubble trauma.
Chronic % TGP of over 105% undesirable.
Long-term exposure in catfish of 110%
causes gas bubble trauma (Tucker and
Robinson, 1990).
Bubbles are formed when gas comes out
of solution.
Embolisms, restriction of flow in blood
vessels.
Physical Variables: Total Gas
Pressure (GB trauma)
Gas Bubble Trauma is affected by
submersion depth.
 Greater depth = hydrostatic
pressure = gases remaining in solution.
 At 21oC,
P is reduced by 67 mm Hg
for every meter of submersion.
 Implications of tank culture?
 Implications for recirculating
systems?

So, the Physical Properties of Water
discussed today:
 Salinity
 Electrical Conductance
 Turbidity
 Color
 Total Gas Pressure
Next time, Chemical Properties
of Water