Chemical Parameters for Water Study
pH
pH = potential of Hydrogen
pH is a measure of the dissolved hydrogen ion concentration [H+] in water. It is found by
determining the negative log of the hydrogen ion concentration.
pH = -log [H+]
Its counterpart is pOH which is a measure of the dissolved hydroxide ion concentration [OH-]
in water. It is found by determining the negative log of the hydrogen ion concentration.
pOH = -log [OH-]
Pure water ionizes to form equal amounts of hydrogen and hydroxide ions:
HOH
H+ + OH –
The concentration of each ion in a solution of pure water is 1 X 10 -7 M (moles per liter).
Since the log of this number is -7, the pH is 7 and the pOH is also 7. Pure water has a neutral
pH because the concentration of hydrogen and hydroxide ions are equal.
This leads to the pH scale (and its counterpart pOH scale) with 7 in the middle. A
concentration of 10-6 is more concentrated than 10-7. 10-5 is more concentrated than 10-6 and
so on.
Concentration
High
Concentration
pOH Concentration
100 M
0
14
10-14 M
10-1M
1
13
10-13M
10-2 M
2
12
10-12 M
10-3M
3
11
10-11M
10-4 M
4
10
10-10 M
10-5M
5
9
10-9M
-6
10 M
6
8
10-8 M
10-7M
7
7
-8
8
6
9
5
10
4
10 M
-9
10 M
10-10 M
10-11M
10-12M
10-13M
Low Concentration
pH
10-14 M
11
12
3
2
Low Concentration
10-7M
10-6 M
10-5M
10-4 M
10-3M
10-2M
10-1M
13
1
100M
14
0
High
Concentration
pH Ranges and Aquatic Life
pH
Acidic 0 _________________________7________________________________14 Basic
Bacteria
1_________________________________________________13
Aquatic Plants
Carp, Suckers, Catfish,
some invertebrates
6.5 ______________________________13
6_________________________________13
Bass, Crappie
6.5 _____________9
Snails, Mussels
Amphibians
7 __________9
5 ___________________9
Most others
6.5 ____ 7.5
http://www.adopt-a-stream.org/parameters.php
Rain is naturally acidic (pH 5.0 – 6.0) due to the absorption of carbon dioxide in the
atmosphere. Usually a lowered pH (more acidic) has greater affect on aquatic organisms.
Toxicity of many compounds increases at lower pH and the solubility of metals (aluminum,
copper) also increases at lower pH. Both have a direct effect on the viability of aquatic
organisms.
Sources
Earth Force Water Quality Standards
http://www.eeweek.org/assets/files/Water%20Quality%20Testing/Water%20Quality%20Parameters.pdf
US EPA – Acid Rain
http://www.epa.gov/acidrain/effects/surface_water.html
Dissolved Oxygen
Oxygen (O2) is an essential element for most living things. The air that we breathe is about
20% oxygen (the rest being mostly nitrogen gas). Out of 100 molecules of air, 20 of them
will be oxygen – or 20 parts per hundred (pph).
Gases dissolve in water at very low concentrations and are affected by changes in
temperature (and pressure). Leave an open soda out overnight and it goes flat. The increase
in temperature has caused most of the dissolved carbon dioxide to escape. Cooler
temperatures mean higher concentrations of dissolved gases.
The concentration of dissolved gasses is measured in parts per million (ppm or
milligrams/Liter), not parts per hundred. In most streams, dissolved oxygen is not a problem
due to the mixing of the water with air in riffle zones and readings of 8 to 12 ppm are
common. In pools the level might be lower and in cut-off oxbows near the stream, the level
of dissolved oxygen may approach zero. Various levels of dissolved oxygen are needed for
different organisms. Most game fish, for example, need higher levels than bottom dwelling
fish such as catfish.
In aquatic systems the amount of dissolved O2 is also dependent on time of day, season,
shade or sun conditions (all related to temperature differences), aquatic plant activity
(production of oxygen gas but usually found in lakes and ponds), decomposition of organic
material (aerobic decomposition uses up oxygen), stream velocity and other factors.
Conductivity
Conductivity is a measure of the dissolved ions in solution. Water is a good solvent and most
metal salts will dissolve to some degree in water. If salts dissolve, ions form in solution as
illustrated below:
CaCl2
Ca+2 +
2 Cl-1
Metal salts are found in nature in the form of rocks (limestone is calcium carbonate, gypsum
is calcium sulfate) and soil constituents, both of which can leach into the water. Additional
salts come from fertilizers, road salts, wells and industrial sites to name a few.
Not all rocks will dissolve in water, however. Sandstones of Eastern Kentucky are made
mostly of silicon dioxide which is insoluble. There are regional differences in conductivity
around the state.
Pure water will have a conductivity of zero. Ocean water will be in the thousands. The
conductivity test indicates the presence of dissolved salts in the water but it does not identify
the salts.
Alkalinity
Related to pH is the alkalinity of a system. Alkalinity refers to the ability of a system to
resist changes in pH. For freshwater systems, this usually means that the concentration of
carbonate ions in water is relatively high (other ions also contribute to alkalinity –
specifically the hydroxide ion – OH- , and the hydrogen carbonate ion – HCO3-1). The
carbonate ions are present in nature in the form of calcium carbonate or magnesium
carbonate, both of which are found in carbonate rocks – i.e. limestone, dolomite, marble.
Calcium carbonate is slightly soluble in water, especially if the water is acidic – i.e. from
rain.
CaCO3
Ca +2 + CO3-2
In water, the carbonate ion (CO3-2) is able to bind with excess hydrogen ions (additional
acid) to keep them from increasing the concentration of hydrogen ions and decreasing the
pH.
CO3-2
+ H+1
HCO3-1
This ability to absorb excess acid in a system is called buffering. (Aspirin is often buffered
because it is an acid and can cause excess acid in the stomach. Antacids such as Tums and
Rolaids contain calcium carbonate to reduce excess stomach acid – buffers). Streams and
lakes in Kentucky are usually well buffered and low pH is not a problem. There are regional
differences due to the underlying geology of the region.
Alkalinity is measured in parts per million (ppm) of calcium carbonate. Levels from 20 –
200 ppm are common in streams. In central Kentucky readings in the range of 100 – 200
ppm show relatively high alkalinity and buffering capacity.
Alkalinity represents buffering capacity mainly due to carbonate, hydrogen carbonate and
hydroxide ions in solution.
On another note:
The presence of carbonate rocks also increases the Hardness of water. Hardness is due to the
calcium ions (Ca +2) and magnesium ions (Mg +2) in the water. Hard water increases the
residue left behind as water evaporates – the “scale” on your shower head or teapot.
Chloride
Chlorides are salts resulting from the combination of the gas chlorine with a metal. Some
common chlorides include sodium chloride (NaCl) and magnesium chloride (MgCl2).
Chlorine alone as Cl2 is highly toxic and it is often used as a disinfectant. In combination
with a metal such as sodium it becomes essential for life. Small amounts of chlorides are
required for normal cell functions in plant and animal life. Chloride is the main extracellular
anion in animals, including humans. It is a highly mobile ion that easily crosses cell
membranes and is involved in maintaining proper osmotic pressure, water balance, and acidbase balance in animal tissues. Recent studies indicate that the chloride ion also plays an
active role in renal function, neurophysiology, and nutrition.
Chlorides may get into surface water from several sources including: rocks containing
chlorides; agricultural runoff; wastewater from industries; oil well wastes; effluent
wastewater from wastewater treatment plants, and road salting.
Chlorides can contaminate fresh water streams and lakes. Fish and aquatic communities
cannot survive in high levels of chlorides. The table below shows the effects of chlorides on
fish:
Chloride Above These Levels Can Be Toxic
Short Exposure (ppm)
2540
6570
6740
8000
8390
Long Term Exposure (ppm)
400
430
900
800
850
Species
Snails
Fathead minnow
Rainbow trout
Channel catfish
Carp
Public Drinking Water Standards require chloride levels not to exceed 250 ppm. Criteria for
protection of aquatic life require levels of less than 600 ppm for chronic (long-term) exposure
and 1200 ppm for short-term exposure.
Although chloride is an essential element for maintaining normal physiological functions in
all aquatic organisms, elevated or fluctuating concentrations of this substance can be
detrimental. More specifically, exposure to elevated levels of chloride in water can disrupt
osmoregulation in aquatic organisms leading to impaired survival, growth, and/or
reproduction. Because excess chloride is most frequently actively excreted from animal
tissues via the kidneys or equivalent renal organs to achieve osmoregulatory balance, the
bioaccumulation potential of chloride is low. Several factors such as dissolved oxygen
concentration, temperature, exposure time and the presence of other contaminants influence
chloride toxicity.
Sources:
EPA – British Columbia
http://www.env.gov.bc.ca/wat/wq/BCguidelines/chloride/chloride.html
River Assessment Monitoring Project
http://kywater.org/ww/ramp/default.htm
http://kywater.org/ww/ramp/rmcl.htm
http://kywater.org/ww/ramp/rmtests.htm
Turbidity
Turbidity is a measure of the relative clarity of water, and is based upon the number of
suspended particles present, and the resulting level of light transmission through the liquid.
Water with no suspended particles, such as distilled water, has a turbidity of zero, high level
of light transmission, and is, simply put, easy to see through. As the number of suspended
particles in the water increases, the greater the turbidity, the lower the level of light
transmission, and the harder it becomes to see through the water.
There is a natural level of turbidity found in watersheds, with particulate inputs from natural
erosion, organic decay, and algae. In urban areas, however, levels of turbidity are often
unnaturally high due to sediment from runoff, storm water, waste discharge, algal growth,
and the disturbance of ground sediments from storm events. High levels of turbidity are
associated with lower water quality.
Some of the direct and indirect impacts of increased water turbidity include:
 Increased water temperature and reduced oxygen levels (high turbidity water holds
more heat)
 Photosynthesis levels decrease as light cannot be transmitted to lower levels of the
water column
o Inhibited growth of submerged aquatic plants that can no longer receive light
and consequent effects on the species that are dependent upon these primary
producers
 Increase in levels of suspended particles in the water can clog gills, smother bottom
dwelling organisms, and reduce available habitat for aquatic life.
 Suspended particles can protect bacteria from ultraviolet (UV) sterilization of water
Turbidity is thus used as an important indicator of water quality. Several different methods
and units are used to measure turbidity. The units that you will most commonly use, and that
are used in your Water Test Kits, are Jackson Turbidity Units (JTUs). A JTU is inversely
related to the length of a column of water needed to completely obscure light viewed through
it. In other words, the longer the column of water needed to completely obscure the light, the
lower the turbidity, and the lower the number of JTUs. The higher the turbidity for the water,
the higher the JTU value, and the lower the quality of water. EPA standards for drinking
water are around 5 JTU or less.
One of most widely used methods to test turbidity,
especially in deeper lake or ocean waters, is with a Secchi
Disk. The black and white Secchi disk of standardized
size is lowered into the water until it reaches the depth at
which you are just unable to see it. This depth is your
Secchi measurement. Classifications for water quality are
sometimes given in Secchi Depth Measurements.
Source: http://www.optek.com/images/Secchi_disk.jpg