Farm Pond Management-Water Quality

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.

 

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.

 

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.

 

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.