Quiz 7 Flashcards
(35 cards)
What are the 8 topics in this lecture?
Turbidity Colour Conductivity Transparency pH Alkalinity Hardness Oxidation-reduction
What is turbidity? (4)
It is an optical characteristic of water
It is the measure of relative clarity of a liquid
It is the expression of the amount of light scattered by material in the water when a light is shined through a water sample
The higher the intensity of scattered light, the higher the turbidity
What materials cause water to be turbid? (7)
Clay
Silt
Finely divided inorganic and organic matter
Algae
Soluble coloured organic compounds (eg.tannins)
Plankton and other microscopic organisms
What is turbidity measured with? (3)
Nephelometer - which measures light scattered at a 90 degree angle
Unit of measurement is the nephelometric turbidity unit (NTU)
Sometimes use a spectrophotometer which measures transmitted light
What general impacts arise from turbidity? (3)
High concentrations of particulate matter affect light penetration and productivity, recreational values, and habitat quality
Can also cause lakes to fill in faster
In streams, increased sedimentation and siltation can occur, which can result in harm to habitat areas and other aquatic life
What are some deleterious effects of sediment? (4)
Turbidity/sedimentation can cause reduced intra- and inter-gravel water flow meaning that the spaces between spawning gravels that used to shelter alevin, juvenile fish, and other aquatic organisms is filled in
Can cause impairment for the health of fish and other aquatic organisms through the clogging and abrasion of gills and smothering of eggs and juveniles
Can reduce water clarity and visibility which impairs the ability of aquatic life to find food, mate, and escape predators
Elimination of critical food items such as insects and aquatic invertebrates through smothering, loss of habitat, death etc.
Turbidity rule for potable water (3)
Average daily source water turbidity levels measured at equal intervals (min of every 4 hours), immediately after a disinfectant is applied, needs to be around 1.0 NTU, but cannot exceed 5 NTU for more than 2 days in a year
This is because particles can shelter contaminants like metals and bacteria
So turbidity is an indicator of potential pollution
What is water colour? (6)
Colour is an optical characteristic of water
Is dependent on two things: dissolved (eg. tannins) and suspended (eg.sediment) components
Transparent water with low accumulated dissolved materials appears blue
Dissolved tannins from organic matter can produce a yellow or brown colour
Algae can cause red or green water
Soil runoff produces yellow, red, brown, or grey colours
What causes blueness in water? (2)
Water is not colourless but has a slightly blue tint because observed colour in water is greater for shorter wavelength than longer ones
This is caused by scattering of light upwards after passing through the water to various depths and undergoing the selective absorption of other colours (red, orange, yellow etc.)
How do we measure colour in water? (3)
Measured by a comparison to a standard solution of potassium chloroplatinate in Nessler Tubes
Sometimes use a spectrophotometer which can measure transmitted light at a specific wavelength
Units are in Pt units
What is conductivity? (4)
Also known as specific conductance
It is a measure of the waters capacity to conduct an electric current
Unit of measurement is uS/cm where the S is for Siemens
Influenced by water temperature
How does water temperature affect conductivity? (2)
Conductance (uS/cm increases 2-3% for every degree C increase in temperature
Limnologists always report 18C standard temperature when reporting conductance for convenience
Rule of thumb for conductance (2)
Estimation of total concentration of dissolved ionic matter in water is roughly related to conductivity so can use:
TDS (total dissolved solids) can be estimated by multiplying specific conductance by 0.5 to 1 (usually 0.65) but depends on if you have soft water, hard water, or inorganic nutrients
What is transparency and how is it measured? (4)
Can be measured using a Secchi Disk in a lake in situ
Transparency (like colour) can be due to dissolved and suspended components
Using a standard weighted disk of 20cm with 4 black and white quadrants lower until lose sight of disk
Mark line in 10cm increments (depth measured in either m or cm)
Rule of thumb for Secchi Disk measurements
2 x Secchi depth = depth of 1% light transmission (the depth of the euphotic zone)
Correct Secchi procedure (6)
Measurements should be done by the same person
Ideally with polarized sunglasses
On the shady side of the boat
At the same time of day (between 10am and 2pm because of angle of light)
Either with or without a viewing chamber
Be consistent!
What is pH? (5)
pH is a measure of how acidic or basic water is
True definition is that pH is a measure of the relative amount of free hydrogen and hydroxyl ions in the water
It is a good indicator of chemical change because chemical ions will change pH
pH is the negative log of the hydrogen ion concentration
Water that has more free hydrogen ions is more acidic H+
What is Kw? (4)
Kw is the ionization constant of pure water
K = [H+][OH-]/H2O Kw = [H+][OH-]
At 25C, Kw = [H+][OH-] = [10-7][10-7]=10-14
But when an acid is added, it upsets this balance and increases H+ ions
Eg. [H+] = 10-1, then [OH-] = 10-13
[H+][OH-] can never be 0
pH and logarithms (2)
pH is reported in logarithmic units so each unit represents a 10-fold change in the acidity or basicness of the water
eg. Water wth a pH of 5 is 10X more acidic than water having a pH of 6
pH and pollution (2)
Pollution can severely change a water’s pH, in turn harming animals and plants living in the water
Eg. acid rain caused by coal fired plants or
water from abandoned copper mine with pH of 2 would kill anything in its way (Tsolum River)
What is alkalinity? (4)
Alkalinity refers to the capacity of water to neutralize an acid
It is really an expression of buffering capacity
Therefore, the question is how much acid (H+ ions) can you add before the pH changes?
This is usually buffered by carbonate-bicarbonate ions in natural systems (HCO3-, CO3-2, and OH-)
What is “Total Alkalinity”? (3)
Refers to the 3 buffering ions in natural systems
HCO3-
CO3-2
OH-
Each combine in a different way with H+ ions to buffer the acid
Carbon dioxide and acidity (6)
When carbon dioxide enters water, some of the dissolved carbon dioxide hydrates and becomes carbonic acid
CO2 + H2O <=> H2CO3
This carbonic acid then dissociates forming bicarbonate and a free hydrogen ion
H2CO3 <=> HCO3- + H+
Bicarbonate further dissociates to carbonate and a free hydrogen ion
HCO3- <=> CO3-2 + H+
These reactions are always in a state of flux, creating H+ ions in the water
Carbon dioxide can also be created in water through respiration which decreases pH
CO2 + H2O => H2CO3 => CO3 + 2H+
CO2 is also removed by photosynthesis, which decreases H+ and increases pH
Where does natural water alkalinity come from? (4)
Determined by the soil and bedrock through which it passes
Main sources for natural alkalinity are in rocks containing bicarbonate, carbonate, and hydroxide compounds
Borates, silicates, and phosphates may also contribute to alkalinity
Limestone has high carbonates so areas with limestone have high alkalinity (eg. Okanagan)
