LaMotte Water & Soil pH - Manual (Page 5)

pH & WA TER
The pH of water is a concern to many people. Many factors contribute to
the pH of water, including the quantity of plant and animal life, the rocks
and other minerals the water is exposed to, and the pH of incoming
substances.
Plant and animal life in the water are constantly undergoing chemical and
biological processes which alter the water’s pH. Two of these processes are
respiration and photosynthesis. When plants and animals respire, or
breathe, carbon dioxide is released. The carbon dioxide reacts with the
water to form carbonic acid, which lowers the pH. Simultaneously, plants
are undergoing photosynthesis, a process which removes carbon dioxide
from the water before it is transformed into carbonic acid, raising the pH
of the water. Since plants need light to photosynthesize, photosynthesis
only occurs during daylight hours, but respiration occurs throughout the
day and night, so the pH of water tends to be higher during the day.
The pH is also dependent on the minerals in the water. As water passes
over and through rocks, minerals from the rocks dissolve into the water.
Some minerals, such as calcium, occur in a form which raises the pH,
while others lower the pH.
Natural waters normally have a pH between 5.0 and 8.0. When the pH is
out of this range, it may be an indication of pollution, and further testing
is necessary. Chemicals and other pollutants intentionally or
unintentionally added to the water can alter the pH.
One pollutant that can cause water to be acidic is acid rain. Acid rain,
defined as rain, snow or other precipitation with a pH of less that 5.6, is
formed from air pollutants, particularly sulfur dioxide and nitrogen oxides,
which are released as gases into the atmosphere. Power plants, smelters,
automobiles, and volcanic activity are all contributors to acid rain. In the
atmosphere, the gases combine with moisture to form sulfuric acid and
nitric acid solutions, which return to the Earth as acid rain.
pH testing is also important in water used for industrial or domestic
purposes. Acidic water can corrode metal pipes, while alkaline water can
leave deposits known as scale, potentially clogging pipes and ruining
equipment.
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