Access digital copies of guides and regulations publications from the Nebraska Game and Parks Commission.
Issue link: http://digital.outdoornebraska.gov/i/605475
68 • Nebraska Game and Parks Commission reach a critically low point, only aeration or the addition of fresh aerated water can prevent a fish kill. Summerkill Summer fish kills can result in the total or partial die-off of a pond's fish community. This type of fish kill is most common in small, shallow, heavily vegetated ponds containing a large amount of decomposing organic material. Summerkills can occur when certain environmental conditions cause a substantial decline in dissolved oxygen levels. Excessive vegetative growth, especially algae, in a pond can lead to a fish kill. Sunny conditions result in a long period of plant photosynthesis that produces high dissolved oxygen levels during late afternoon; however, during the night, oxygen is used for respiration by plants, fish, insects, and other organisms, and organic decomposition. If the oxygen produced during the daytime is insufficient to carry all pond life through the night, a fish kill will result. As long as the weather is sunny, oxygen production is usually adequate. However, several consecutive calm, cloudy days can result in vegetation dying (especially algae) and decomposing, reducing the pond's dissolved oxygen levels to the point that fish may not survive the night. These conditions are confounded during the summer when air and water temperatures are greater than 80 degrees and calm conditions prevail. A summerkill usually results in larger fish dying first, with minimal, if any, effect on other aquatic animal life, such as aquatic insects, frogs, and turtles. Ponds can become stratified during the summer, particularly those protected from the wind. Water density varies according to temperature, with the colder, denser water occurring at the bottom. The surface water normally has sufficient dissolved oxygen, while the denser bottom water may contain little or no oxygen because it is depleted by bacterial decomposition of organic matter. This is especially true in ponds with excessive vegetation. The differences in water densities keeps the pond water from mixing. But, a rapid inflow of cool surface runoff from a summer thunderstorm, combined with strong winds and waves, can result in mixing the surface water with the oxygen deficient bottom water. During this thermal turnover, or inversion, a fish kill can result. Lightning strikes can also cause a fish kill in the immediate impact area. Winterkill Winter fish kills result when oxygen levels fall too low to support fish under the ice. Since ice acts as a seal and prevents the absorption of oxygen directly from the atmosphere, oxygen produced by plant photosynthesis is crucial. Clear, thick or even cloudy ice typically allows The most obvious sign of an oxygen problem is fish gasping or gulping at the surface, particularly in the early morning hours. Dying and Decaying Plants Winterkill Winterkill Oxygen Depleted Snow Ice Excessive Growth of Submersed Vegetation Summerkill Summerkill Excessive Growth of Algae Oxygen Is Being Depleted Cloudy Days