Farm Pond Management-Water Quality

The Aquatic Food Chain

Water Quality

Water Quality Parameters

Liming

Fertilization

Thermocline and Turnover

Additional Resources

The Aquatic Food Chain in Farm Ponds

 
The aquatic food chain is comprised of several different trophic levels: producers, primary, secondary, and tertiary consumers, and decomposers. 

Producers are the numerous species of floating and rooted aquatic plants that absorb sunlight, water, oxygen and soil minerals and includes microscopic, floating plant life known as phytoplankton.

Primary consumers are tiny, herbivorous organisms that feed on phytoplankton and other aquatic plants including insects, tadpoles, very small fish, snails, and microscopic animals known as zooplankton.

Secondary consumers are organisms that feed on primary consumers and include many species of fish, frogs and other amphibians, crayfish, turtles, and water snakes.

Tertiary consumers are organisms that feed on primary and secondary consumers and include large fish, humans, birds, and numerous small mammals.

Decomposers are bacteria, fungi, and insect and animal scavengers that release elemental nutrients by breaking down dead and decaying aquatic plants and organisms.

The following sections provide information on maintaining water quality in your farm pond, which has a direct effect on the aquatic food chain. A balanced food chain is critical to having a healthy pond.

 

The farm pond food chain

 
 

Water Quality

 
Maintaining good water quality in your farm pond is essential for a healthy fish population and the aquatic food chain as a whole. Water quality incorporates several important parameters including dissolved oxygen (DO), alkalinity, pH, turbidity (cloudiness), and fertility (nutrient levels). Unsuitable levels of any of these parameters can negatively affect the fish populations in your pond.

Water quality testing kits can be purchased online or at local retailers such as swimming pool supply companies and some hardware and department stores. Water quality test kits to determine pH, nitrogen levels, total alkalinity, and dissolved oxygen levels are a good start.

Performing routine water quality testing, at least once a week for newer ponds, can help alert you to changes in your pond’s chemistry. Due to fluctuating oxygen and pH levels throughout the day, water quality testing should occur at the same time of day for each test. Based on the results, it can be determined if corrective action is needed to maintain good water quality.  Ask your local biologist for help finding a simple water quality kit near you.
 
 
 

Water Quality Parameters

 
Dissolved oxygen (DO) - Adequate dissolved oxygen (DO) is essential to fish survival.  Fish prefer DO levels > 6 milligrams per liter (mg/l), and become stressed when concentrations fall below 3 mg/l.   Oxygen is produced during daylight hours by algae and plants during photosynthesis, and is continuously consumed by algae, plants, bacteria, and aquatic organisms (including fish) during respiration.  Therefore, oxygen levels are highest during the day (when more oxygen is being produced than consumed), and lowest at night just prior to sunrise (when oxygen is only being consumed).  Most ponds in Kentucky maintain suitable oxygen levels; however, oxygen can occasionally become depleted for a variety of reasons, including excess nutrients, algae or plant die-offs, and pond turnover.  When oxygen levels are very low (< 1 mg/l), stressed fish are lethargic and can be found “hanging” at the pond’s surface gulping air.  Emergency procedures, such as tilting a boat motor to spray water into the air, or agitating the pond’s surface with paddle wheels, etc. can help aerate the water and improve oxygen levels enough for fish survival.  Ponds with chronic, low oxygen problems or a history of fish kills may require aeration devices. 
 
pH - indicates whether the water is acidic (pH < 7), basic (pH > 7), or neutral (pH = 7).  Pond pH levels vary throughout the day due to photosynthesis and respiration.  Nighttime respiration increases CO2 concentrations, forming carbonic acid and causing pH to fall.  During the day, phytoplankton and other green plants absorb CO2 for photosynthesis, causing pH to rise.  Fish can tolerate a fairly wide range of pH levels, although 6.5 to 9 are considered most desirable for fish.  Values less than 4 or greater than 11 are usually lethal to fish.  Low pH levels often indicate inflow of acidic waters, most commonly from acid mine drainage from coal mining operations.  Conversely, high pH levels often indicate that the water is too fertile (too many nutrients) and /or lacks adequate alkalinity.  Liming can improve pH levels and prevent wide swings in pH levels.
 

 
 
Alkalinity - is the total concentration (as mg/l of CaCO3) of bases in the water, primarily bicarbonates, carbonates, and hydroxides.  Adequate alkalinity is important for pond productivity and water chemistry.  Ponds should have total alkalinities of at least 20 mg/l CaCO3, and desirable levels range from 75-200 mg/l.  If total alkalinity levels are less than 20 mg/l, then liming can be used to raise alkalinity levels.  Adequate alkalinity (>20 mg/l) is also important if starting a fertilization program.  Alkalinity can be easily determined by using a simple test kit available locally or on-line through major environmental retailers. The required kit should be able to test “Total Alkalinity”. 
  
Turbidity - refers to the clarity of the water.  Ideally, pond water should not be extremely clear or extremely turbid.  Extremely clear waters indicate inadequate nutrient levels in the pond (or nutrients being tied up in excessive submerged aquatic vegetation).  High turbidity (muddiness) can be the result of many factors, including chemical, environmental, and biological factors.
 
Fertility/Nutrients - Most farm ponds naturally have adequate nutrient (e.g. nitrogen, phosphorus) levels to support a healthy phytoplankton population, which is the basis of the pond’s food chain. Ponds with low nutrient levels can be limited in phytoplankton production and are typically very clear. Ponds with high, unsuitable nutrient levels can have water quality issues such as low dissolved oxygen levels, high pH, low water clarity, and excessive nuisance aquatic vegetation. These issues can cause increased fish stress and/or mortality. If high nutrient levels are observed in your farm pond, there are several methods to limit nutrient levels such as utilizing a good, correctly sized filtration system, adding nitrogen consuming bacteria to your pond, and removal of organic debris such as dead leaves, grass clippings, and dead fish or insects. Ponds with very clear water can benefit from a fertilization program. Adequate nutrient levels typically result in water clarity between 1.5 and 2 feet.
 
 
Table 1. Desired range and potential remedies for water quality issues.
Parameter​Desired Range​Remedy/Action of not in desired range​
pH​​6.5 - 9.0​Add lime if pH < 6.5; limit nutrients if pH > 9.0
​Total Alkalinity​75 - 200 mg/l​Add lime if alkalinity < 20 mg/l
​Dissolved Oxygen​6.0 - 9.0 mg/l​Aerate if D.O. < 4.0 mg/l; extremely high values likely the result of algal bloom or excessive vegetation
Water Clarity​​1-1/2 - 2 feet​Extremely clear water indicates low nutrients or nutrients tied up in plant biomass.  Fertilize if clarity increases beyond 2 feet.  Low clarity may be the result of suspended solids (muddiness) or too much fertility (plankton bloom).
 
 

Liming

 
 
Benefits of Liming - Liming can improve the productivity of your pond, raise pH and alkalinity levels, prevent wide daily pH fluctuations, and enhance the effect of fertilizers.  Ponds that are acidic (pH<7) and have low alkalinity (<20 mg/l) in particular will benefit from liming. 
 
Liming procedures -   To find out how much lime to apply, get a soil test done at a farm supply store or your county extension office. You want the lime application rate that would be used for an alfalfa field.  Total alkalinity of a water sample can also be tested at some of the District Fisheries Offices, contact your local office to find out if they can assist.
 
Apply agricultural lime at the prescribed rate during the winter or early spring months. You can have the truck dump the lime in the pond drainage and let rain wash it in or you can apply it to the pond yourself. Applications may not need to be done every year afterward. Test your pond alkalinity annually or every other year and lime as necessary.   
 
Check the lime requirements of the soil in a newly constructed pond and make applications on pond bottom before impoundment.  See the links in the Additional Resources section for more information on liming.
 
 

Fertilization

 
Fertilization and the aquatic food web - If your pond has an insufficient drainage and you can see 3 feet deep or more into the water throughout the summer, then you probably should fertilize. Fertilizing can reduce problem aquatic plant growth and improve fish growth by producing more plankton, which are microscopic plants and animals.  Plankton actually clouds the water to shade out plants, but it also provides food for young fish. One caveat to fertilizing is that once you initiate a program, you will need to fertilize every year. Fertilization increases the carrying capacity of the pond. Ending a fertilization program will leave a pond with more fish biomass than it can support, resulting in stunted, skinny fish or a fish kill.
 
Fertilizing specifics - Pond fertilization should be done at two-week intervals. Begin when water temperatures reach 60 degrees, usually around the middle of April, and continue until around June 15 (depending on weather and water temperature). The easiest and most efficient fertilization method is with a liquid (9-18-9, 7-14-7, or similar formula) applied at the rate of one gallon per acre. Dilute with pond water during application. Apply one gallon per acre of fertilizer, wait two weeks and follow up with another application. After two additional weeks, follow up with a third application.  After the third dose you should regularly monitor water clarity using a secchi disk. If clarity reaches two feet or more, make an additional application. Typically, all fertilization needs to cease around June 15. See the links in the Additional Resources section for more information on fertilization.
 
Do not fertilize if:
 
• The pond is not fished heavily.
• The pond water is muddy.
• The pond is infested with undesirable fish species,
• The pond is infested with aquatic plants.
• Pond water continually runs out of the spillway or water control structure.
• You are feeding fish commercial feed.
• Fish populations are out of balance.
 
 

Thermocline and Turnover

 
During the summer most ponds have adequate oxygen levels in only the upper 6 to 10 feet of water. The colder, deeper water is essentially devoid of oxygen.  The upper, warmer layer of water remains separated from the colder water because of a difference in density between the two. Cold water is heavier than warm water and, therefore, remains associated with the bottom. The thin layer where these two areas meet is called the thermocline.
 
During the summer, your pond or lake will stratify into three layers: the upper layer is warmer and contains adequate oxygen; the bottom layer is colder and has very little oxygen; and the middle layer is the transition zone between the upper and bottom layers.

As fall approaches, the upper water layer cools down and the density difference between the upper and lower water layers is reduced. A cold rain or strong wind can result in a sudden mixing (turnover) of the two layers. If the deeper layer is relatively large as compared to the upper layer, then it is possible that a fish kill could result. This problem can be avoided by not building the pond too deep (see pond construction), or by installing an aeration system. Even with precautions, most ponds will eventually experience some type of fish kill or turnover.
 
 

Additional Resources: