Why do we monitor water temperature?
Water temperature affects physical, biological, and chemical
aspects of lake dynamics. High water temperatures stress aquatic ecosystems
by reducing the ability of water to hold essential dissolved gasses
like oxygen. The rate of decomposition, nutrient recycling, lake stratification,
and dissolved oxygen concentration are all affected by the temperature.
When a lake "mixes," cold water from the bottom of a lake
(hypolimnium) is brought to the surface (epilimnion), while warm water
is mixed downward, resulting in little temperature variation from
top to bottom in the lake. Mixing allows dissolved oxygen to be introduced
into the hypolimnium. When a lake stratifies, distinct temperature
layers are formed, and the mixing of the water is restricted. The
epilimnion (about the first 30 feet) warms the entire summer and continuously
mixes, while the hypolimnion does not mix or get any warmer all summer.
Shallow lakes (those less than 20 feet deep) usually will not stratify,
and will continuously mix from top to bottom.
Why do we measure Dissolved
Oxygen?
A good level of dissolved oxygen is essential for aquatic
life. Dissolved oxygen analysis measures the amount of gaseous oxygen
(O2) dissolved in an aqueous solution. Oxygen gets into water by diffusion
from the surrounding air, by aeration (rapid movement), and as a by-product
of photosynthesis. Oxygen is a necessary element to all forms of life.
As dissolved oxygen levels in water drop below 5.0 mg/l, aquatic life
is put under stress. Oxygen levels that remain below 1-2 mg/l for
a few hours can result in large fish kills.
What is pH and why do we monitor
it?
A vital determinant of a waterbody's health is its pH, which is a
measure of the acidic or basic (alkaline) nature of a solution. The
concentration of the hydrogen ion [H+] activity in a solution determines
the pH. Fish and other organisms require a pH range of 6.5 to 9.0
in order to be viable.
What are "nutrients"
and how do they affect the aquatic ecosystem?
In Oklahoma surface waters, Ammonia nitrogen, Nitrate
nitrogen, and phosphorus are the chemical compounds most commonly
referred to as "nutrients." These nutrients contribute to
the growth of aquatic plants and algae. Excessive nutrient levels
can cause plant and algal overgrowth, which can have a profound negative
effect on the physical, chemical, and biological characteristics of
a lake or stream. This process is known as eutrophication. Microscopic
floating plants (algae) multiply rapidly when fertilized by phosphorus,
and when the algae die, they decompose and the resulting bacteria
cause all the dissolved oxygen to be removed from the water. Lower
oxygen levels make it difficult for other aquatic organisms (fish
and macro-invertebrates) to survive.
What is Cultural Eutrophication?
Cultural eutrophication occurs when humans cause an increase
in the level of nutrients that are deposited into a lake. Cultural eutrophication
can produce an anaerobic condition where oxygen in the water is completely
depleted. This usually occurs near the bottom and produces gases like
hydrogen sulfide, which causes a "rotten egg" smell. Cultural
eutrophication causes a shift in aquatic life to a fewer number of species.
These are replaced by other species that can tolerate low dissolved
oxygen levels such as carp, midge larvae, and sewage worms (Tubifex).
The effects of cultural eutrophication can be controlled by: reducing
the use of lawn fertilizers (particularly inorganic forms) that drain
into waterways, better farming practices, preserving natural vegetation
near shorelines, preserving wetlands to absorb nutrients and maintaining
water levels, treating storm sewer wastes, requiring particular industries
to pre-treat wastes before sending them to a wastewater treatment plant.
What is turbidity and how is
it measured?
Turbidity is a measurement of materials suspended in the water (such
as algae or sediment) and is often an indirect indicator of the overall
quality of the lake water. There are several methods in measuring
turbidity, such as a turbidity tube, Secchi disc, or a turbidimeter.
OWW volunteers use both the Secchi disc and the turbidimeter methods
to determine turbidity. The OWRB uses a turbidimeter.
What is Chlorophyll and why do
we monitor it?
Chlorophyll is the pigment found in all green plants that is responsible
for their color. During photosynthesis, chlorophyll absorbs sunlight
that is used as the energy source to convert carbon dioxide and water
to oxygen and sugars. Chlorophyll data is collected because the green
pigment is found in algae and can be used to estimate how much phytoplankton
(floating algae) there is in the lake.
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