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Understanding Water Quality |
Surface water is never found in a pure state. Even the cleanest lake or pond will contain various concentrations
of dissolved gases, salts, minerals, metals and organic compounds. Most waters are teeming with microscopic plants,
animals and bacteria along with suspended sediments and organic matter. Water quality is determined by the collective
interaction of these chemical, physical and biological components. Some of the more important water quality parameters,
and their relation to the "health" of a lake or pond, are discussed below. Corrective measures for some problem situations
are also included.
Dissolved oxygen concentrations are an important gauge of existing water quality and the ability to support a well-balanced
aquatic animal and plant population. Through the natural mechanisms of aquatic plant photosynthesis and surface absorption,
oxygen is constantly being added to the water. At the same time, there is a continuous consumption of oxygen taking place
throughout the water column by fish, zooplankton (the microscopic animals upon which small fish feed), aquatic insects,
snails, crayfish and a diversity of other swimming and bottom-dwelling organisms. Competing for this same oxygen are
multitudes of bacteria which utilize oxygen in the decomposition of organic materials (dead plants and animals, fertilizer,
animal wastes, run-off water contaminants, septic seepage, etc.) entering or within the system. Aquatic plants may compound
the oxygen balance problem by using, instead of producing, oxygen. This occurs during the night, under extended cloudy
periods or beneath snow and ice cover.
As a result, variations in oxygen content occur from the surface to the bottom and also from day to night. In addition,
seasonal variations occur which affect chemical and biological cycles within the entire water body. When water temperatures
are equal throughout the water column in spring, surface and bottom waters will mix. This distributes dissolved oxygen
vertically and horizontally, virtually equalizing concentrations throughout the water. As the surface warms by the heat
of the sun, layering begins to develop. Cooler, denser water is trapped at the bottom while lighter, warmer water remains
near the surface. This temperature-based layering, known as thermal stratification, creates a natural barrier to vertical
mixing within the water column. Within or near the bottom sediments, dissolved oxygen concentrations may become depleted.
Meanwhile, surface water remains oxygenated through absorption and horizontal mixing by wind action. Fish and other
beneficial life forms are then restricted to this surface stratum.
The cooling of the surface water in fall will eventually break down this stratification. This again allows complete mixing
of surface and bottom waters and re-oxygenates the water column before the onset of winter. In areas where an ice cover forms,
absorption of oxygen from the atmosphere ends and virtually all mixing comes to a standstill. Under the ice, life becomes
totally dependent upon existing dissolved oxygen and that produced by surviving vegetation. If thick ice or snow cover shuts
off sunlight, plants will die or respire and become oxygen users instead of producers. When oxygen demand exceeds supply,
a winterkill of fish and animal life occurs.
Generally, a minimum of 5 mg/L dissolved oxygen is required to support warm water fish and 6-7 mg/L for cold water species.
Dissolved oxygen is also essential to the efficiency of the decay process on the bottom. If oxygen is depleted, microbe
populations switch from aerobic (with oxygen) to anaerobic (without oxygen). The by-products of anaerobic decomposition are
noxious, malodorous gases such as hydrogen sulfide ("rotten egg" odor) and methane. Due to inefficient breakdown of dead plant
and animal materials under these conditions, a black muck or sludge will form on lake and pond bottoms.
Aeration equipment can be installed to overcome oxygen deficiency problems. Benefits of proper aeration include:
- prevention of winter/summer fish kills
- fish habitat promotion/expansion
- elimination of noxious anaerobic gas build-up
- improved water quality
- reduction of certain nutrient problems due to oxygenated benthic (bottom) interactions
- increased decomposition of organic materials in an aerobic bottom layer
- complete de-stratification of the water column equalizing temperatures and oxygen concentrations throughout
the lake or pond.
Normally, this is only practical in ponds and small lakes. Aeration of large bodies of water can be difficult, and if the
installed system is not sized properly, increased nutrient cycling may occur.
Numerous types of systems are commercially available including:
- compressed air systems (systems pump air from shore through tubing to diffusers on the bottom)
- bottom and floating horizontal aerators (force water movement horizontally)
- floating vertical aerators and fountains (pumps water vertically into air).
Of primary consideration are the energy efficiency and the rate by which oxygen is distributed throughout the water column.
Vertical water pumping systems, while decorative, are costly to run and are slow to disperse oxygen in larger bodies of water.
Compressed air systems provide an effective, cost-efficient and flexible means of adding oxygen while moving and mixing the
water. Horizontal aerators have similar energy requirements to those of vertical aerators, but have the ability to mix water
in shallow stagnant areas where other systems may be ineffective.
Sizing and placement of equipment may vary with the size, depth and configuration of a body of water. In addition, timing of
installation must be considered to avoid too rapid of a change in conditions. Therefore, it is recommended that lake and pond
owners contact the manufacturer or a consultant prior to installation.
It should be noted that aeration is not in itself effective in controlling aquatic weed and algae growth. The only benefits in
this regard may be a shift in species from noxious blue-green algae to green algae, and oxygenated benthic interactions may prevent
certain nutrients key to aquatic growth from re-entering the water column. Note that any nutrient reduction may not be sufficient
to eliminate aquatic growth problems and will not prevent nutrient recycling through rooted aquatic plants.
Water fertility is determined by the amount of dissolved nutrients (mainly nitrates and phosphates) available within a body of water.
The productivity or degree of vegetation growth is directly related to water fertility. Lakes and ponds with high nutrient levels are
called eutrophic and the process of nutrient enrichment is called eutrophication. At any point in time, nitrogen and phosphorous might
be found within bottom sediments as a component of plant and animal tissue or dissolved within the water. Seasonal variations are common,
as these nutrients are recycled within the aquatic environment from one form to another.
Controlling outside sources of nutrients plus reducing those already within a lake or pond is a long-term idealistic approach towards
eliminating the main cause of overabundant plants. Attempts at doing this have been met with mixed success. Limiting nutrient input from
sources within the watershed can range from making a few simple alterations around a pond to redesigning sewage systems and agricultural
lands along drainage systems entering a lake.
Microbial bio-augmentation techniques can be utilized to try to establish an additional aquatic food web component to limit nutrients
available for aquatic plant growth. By limiting soluble phosphorus and nitrogen, the amount of algal growth may decrease and a shift of
species may occur. In addition, the reduction of soft organic sediment that may occur would limit the nutrient sink utilized by rooted
vegetation. Success using this method has been seen by applicators, but only in conjunction with proper management of the surrounding
watershed and proper aeration (discussed under dissolved oxygen).
Technology is available for reducing or inactivating dissolved phosphate through the addition of 100 to 160 pounds of aluminum sulfate (alum)
or 40 to 120 pounds of ferric sulfate per acre-foot. These chemicals precipitate or are lost from solution, taking available phosphates
with them. The amount required is dependent upon the existing concentration of phosphorous and the pH of the water. Actual dosages are
best determined by laboratory analysis. Overdosing could result in drastic pH change and a loss of fish life. Professional assistance is encouraged.
Removing nutrients from the water column will have a particular effect upon reducing algae and free-floating plant growth. A more limited
effect will be seen on rooted plants since they can derive nutrients from the sediment. As an additional benefit, alum and ferric sulfate
will act as water clarifiers by removing particulate materials suspended in the water column.
Turbidity refers to a measure of the relative clarity of water. Turbidity or muddy water is often caused by suspended silt or clay particles,
which diffuse or scatter light. As a result, light does not penetrate through the water column and the water appears unclear. This should not
be confused with discolored water, which sometimes results from dissolved materials such as organic acids from leaf litter.
Erosion of soil along shorelines or within the watershed is a primary contributor to excessive turbidity. Poor construction or farming practices is
often to blame. Wind and wave action or the disruption of bottom sediments by carp and bullheads can create or contribute to the problem.
High turbidity will reduce light penetration and retard bottom plant growth. It may also have the negative impacts of irritating fish gills and
impairing spawning and predation success. Turbid water is typically poor for game fish production and undesirable from an aesthetic and recreational
standpoint.
Microbial bio-augmentation methods may be able to reduce suspended organic solids by the microorganisms breaking down the material into gases and/or bio-mass.
Proper aeration (discussed under dissolved oxygen) and proper watershed management practices (see Preventative Maintenance Check List, page 105) should be in place.
This method will not have affect on inorganic suspended solids such as clay.
Application of flocculants such as ferric sulfate or alum (discussed under water fertility) or use of agricultural lime or gypsum at 1,000 pounds per
surface acre will help clear water. It is best to add these materials gradually to avoid rapid environmental changes. Some experimentation or consultation
with professional help is also recommended. Turbidity will be a recurring problem unless the source of the sedimentation is corrected.
Alkalinity and pH are important measures of the "chemical balance" within water. The types of aquatic life present are in part governed by these two parameters.
Alkalinity is a measure of buffering capacity or the ability to tolerate the addition of acids or bases without appreciable change in pH (a measure of the
water's relative acidity). Water's relative acidity (its pH) is based upon a logarithmic scale of 0 to 14 with 7 considered neutral, measurements less than 7 are
acidic and measurements above 7 are alkaline.
Generally, pH and alkalinity are dictated by the chemical make-up of bottom sediments, surrounding soil and water entering the system through run-off or rainfall.
The interrelationships between carbon dioxide, bicarbonates and carbonates (a process too complex to explain here) determine pH and alkalinity. Suffice it to say
that waters in limestone regions or where minerals are easily dissolved will contain carbonates and bicarbonates. These are typically termed hard water areas and
will be alkaline. Lowland bog areas, mountain lakes or those located in bedrock areas will contain free carbon dioxide. These are referred to as soft water areas
and waters will be near neutral to acidic.
Most freshwater life prefers a pH range between 6.5 and 9.0. Different organisms have varying tolerances. Relatively rapid changes in pH can occur in soft water
and are typically low in production of aquatic life. At the other end of the spectrum, higher alkalinities are associated with increased productivity. Algal blooms
can serve to raise pH by utilizing the free carbon dioxide being absorbed from the air.
Raising or lowering pH in a body of water is done on rare occasions. Some acid lakes affected by acid rain have had their pH raised through the addition of lime.
This is a temporary solution and may require maintenance applications. Newly dug ponds are occasionally limed to establish a higher potential for fish production.
These management techniques are not recommended unless under the guidance of an expert.
Coliform bacteria are important indicators of contamination from animal and human wastes. Determining their presence is particularly important in waters used for
swimming, domestic use or drinking. High levels of these bacteria raise concern over the potential existence of pathogenic (disease-type) bacteria and viruses.
Since they are short-lived organisms, their presence indicates recent contamination.
State and federal guidelines have been established that determine what levels are considered safe for body contact, drinking or domestic use. Water samples must
be collected in sterilized bottles and tests should be run by a certified laboratory. Multiple tests are done at varying frequencies to crosscheck results.
Frequent occurrence of high levels may require closing of swimming areas and the need to correct septic or sewage discharge sources.
Pollutants and contaminants from industry, agriculture and other sources can adversely affect water quality. Input can be airborne, contained in surface run-off
and groundwater, or found within direct discharges. Examples which have received recent attention include PCB's (polychlorinated biphenyls), dioxins, heavy metals
(mercury, arsenic, lead, etc.), hydrocarbons and pesticides.
Some pollutants can be detrimental to aquatic life and may even pose human health hazards. They can accumulate within bottom sediments or may be recycled within
the food chain. A build-up can occur within the flesh and tissues of gamefish, making them unfit for human consumption. Other contaminants will be directly
toxic to the organism itself or cause poor growth and reproduction.
The watershed and direct, in-flowing water (rivers, ditches, pipes, etc.) must be examined closely for potential sources of contamination. Use of agricultural
pesticides and fertilizers on surrounding land must be done with care. Herbicides, not specifically labeled for aquatic use sites, should never
be introduced for weed control in a lake or pond. If specific contaminants are suspected within the water or sediments, sophisticated testing with highly sensitive equipment
at a reputable laboratory is advised.
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