Transparency is the
measurement of water clarity. How clear the water is at your site will depend on
the amount of soil particles suspended in the water and on the amount of algae
or other growth at your site. Transparency may change seasonally with changes in
growth rates, in response to precipitation runoff, or for other reasons. The
clarity of your water determines how much light can penetrate. Since plants
require light, transparency becomes an important measurement in determining
productivity of your water site.
In the field you would
measure transparency in one of two ways; with a Secchi disk in deep, still
waters or with a turbidity tube if your site has shallow or running water. For
the lab practice station, we will use the turbidity tube.
Water temperature is the
temperature of a body of water such as a stream, river, pond, lake, well, or
drainage ditch as it appears in nature. Water bodies can vary greatly in
temperature, according to latitude, altitude, time of day, season, depth of
water, and many other variables. Water temperature is important because it plays
a key role in chemical, biological and physical interactions within a body of
water. For example, high temperatures may be an indicator of increased plant
production. The temperature of the water determines what aquatic plants and
animals may be present since all species have their natural limits of tolerance
to upper and lower temperatures. Water temperature can therefore help us to
understand what may be happening within the water body without directly
measuring hundreds of different things within the body of water.
All living things depend on
oxygen to survive. In a water environment molecules of oxygen gas dissolve in
the water. This is called dissolved oxygen (DO). In air, 20 out of every 100
molecules are oxygen. In water, only 1-5 molecules out of every million
molecules are oxygen. This is why dissolved oxygen is measured in parts per
million (ppm). Different species of aquatic organisms require different amounts
of oxygen, but generally aquatic organisms require at least 6 ppm for normal
growth and development.
Water temperature and
altitude influence how much oxygen water can hold; i.e., the
"equilibrium" value. In general, warmer water cannot hold as much
oxygen as colder water. Similarly, at higher altitudes water cannot hold as much
oxygen as waters at lower altitudes. Look for these patterns in the Temperature
and Altitude Tables in the DO protocol. This is why we use a distilled water
standard in the protocol and correct for temperature and altitude.
The actual amount of DO in a
water may be higher or lower than the equilibrium value. Bacteria in the water
consume oxygen as they digest decaying plant or animal materials. This can lower
the DO levels of the water. In contrast, algae in lakes produce oxygen during
photosynthesis which can sometimes result in higher DO levels in summer.
pH is an indicator of the
acid content of water. The pH scale ranges from 1 (acid) to 14 (alkaline or
basic) with 7 as neutral. The scale is logarithmic so a change of one pH unit
means a tenfold change in acid or alkaline concentration. For instance, a change
from 7 to 6 represents a solution 10 times more acidic; a change from 7 to 5 is
100 times more acidic, and so on. The lower the pH the more acidic the water.
The pH of a water body has a strong influence on what can live in it. Immature
forms of salamanders, frogs, and other aquatic life are particularly sensitive
to low pH.
Alkalinity is a measure of
the ability of a body of water to resist changes in pH when acids are added.
Acid additions generally come from rain or snow, although soil sources may also
be important in some areas. Alkalinity is generated when water dissolves rocks
such as calcite and limestone. The alkalinity of natural waters protects fish
and other aquatic organisms from sudden changes in pH.
Nitrogen is one of the three
major nutrients needed by plants. Most plants cannot use nitrogen in its
molecular form (N2). In aquatic ecosystems blue-green algae are able
to convert N2 into ammonia (NH3) and nitrate (NO3-)
which can then be used by plants. Animals eat these plants to obtain nitrogen
that they need to form proteins. When the plants and animals die, protein
molecules are broken down by bacteria into ammonia. Other bacteria then oxidize
the ammonia into nitrites (NO2-) and nitrates (NO3-).
Under suboxic conditions nitrates can then be transformed by other
bacteria into ammonia (NH3), beginning the nitrogen cycle again.
Typically nitrogen levels in
natural waters are low (below 1 ppm nitrate nitrogen). Nitrogen released by
decomposing animal excretions, dead plants, and animals is rapidly consumed by
plants. In water bodies with high nitrogen levels eutrophication can occur.
Nitrogen levels can become elevated from natural or human-related activities.
Ducks and geese contribute heavily to nitrogen in the water where they are
found. Man-made sources of nitrogen include sewage dumped into rivers,
fertilizer washed into streams or leached into groundwater, and runoff from
feedlots and barnyards.
Nitrate levels are measured
in milligrams per liter nitrate nitrogen.
Phosphate
Background
Phosphates in some amount are
necessary in all living things. Phosphates are found in various minerals.
Calcium phosphate is found in shells, bones, and teeth. Plants must have
phosphate to grow properly. This is why farmers and gardeners add fertilizers
that contain phosphate to the soil. We use soaps and detergents for washing
clothes, dishes, floors, and ourselves. Soaps, detergents, and other cleaners
often contain phosphates.
Phosphates are powerful cleaners. Too much phosphate in water is usually the
result of human activity. Plants absorb some of the phosphate in fertilizer put
on farms and lawns. Any unused phosphates may be carried to a stream, creek,
pond, or river by runoff.