A more indepth look at pH (taken from our newsletter,
back to the list of parameters
What is pH?
pH is a relative measure of alkalinity and acidity, its an expression
of the number of free hydrogen atoms present. Its measured on
a scale of 1 to 14, with 7 indicating neutral neither acid nor
base; lower numbers show increasing acidity, whereas higher numbers
indicate more alkaline waters. The pH scale is logarithmic and goes
from 0 to 14. For each whole number increase (for example 1 to 2) the
hydrogen ion concentration decreases tenfold and the water becomes less
acidic. Therefore, small differences in numbers can be significant:
a pH of 4 is a thousand times more acidic than a pH of 6.
Why is it important?
Most species of life have a specific pH range in which they can survive.
A wide variety of aquatic animals prefer a range of 6.5-8.0 pH. If pH
is altered beyond an organisms normal range it will suffer and
soon die off. Many pollutants push pH readings toward the extremes of
the scale. A change of more than two points on the scale can kill many
species of fish. At the extreme ends of the pH scale (2 or 13), physical
damage to fish gills, fins, and exoskeleton occurs. Changes in pH can
also alter the concentra-tions of other toxic substances in the water.
For example, a decrease in pH below
6 may increase the amount of mercury soluble in water.
How do we measure pH?
There are several methods for measuring pH. The one we use at Stream
Team is a pH meter. When placed in water, an electrical force produced
between the internal solution and the water can be measured. This force
is a measure of pH.
What factors affect pH?
Pure water has a pH of 7.0, so what gives our rivers and creeks different
pH readings? pH can change due to external inputs, both manmade and
A change in tree type, for example: conifer needles are acidic
and maple leaves are basic
A change in stream bottom material, for example: gravel, silt,
and bedrock all have different pH levels
A large change in temperature can affect pH: in fresh water,
increasing temperatures decreases pH
A large change in algae growth can affect pH: when algae use
CO2, pH increases
Acid rain or acid mine drainage can decrease pH
What are expected pH levels?
All liquids around us have an expected pH level. Examples of alkaline
substances are blood (7.5), seawater (9.3), and household ammonia (11.4).
Examples of acidic substances are urine (6.0), oranges (4.5), Coca Cola
Classic (2.5) and the contents of your stomach (2.0). In fresh water,
like our Stream Team sites, we want to see levels between 6.5 and 8.5.
This range is healthy for most organisms that live in fresh water.
Stream Team pH results
Good news! In both Ventura and Goleta
Stream Teams, we nearly always find pH levels within the healthy range
(6.5 to 8.5). Out of 528 records, we have only exceeded this range 15
times. All of these exceedances were on the high end (over 8.5) and
the highest number recorded was 9.0. The sites that most commonly exceeded
the 8.5 limit were Ventura Site
2 (Stanley Drain) and Goleta Site AT3
(Atascadero at Puente); both of these sites exceeded the limit 4 times.
See the results posted on page 4 of our Jan