FERTILIZING LAKES & PONDS DURING SUMMER: AVOIDING POTENTIAL PROBLEMS
Of course you know that a good fertilization program begins in the spring. If you have waited until now to fertilize, you are not only late but you may be creating some potential problems for the proper management of your lake. Most lakes if left unmanaged during the spring will remain clear, promoting the growth of undesirable plants or pond weeds. Adding fertilizer at this stage will simply fuel the growth of these noxious plants, creating a real management problem. We will show you how to avoid other potential problems that may occur during the summer, but first let’s review some of the basics of fertilization.
Fisheries biologists and good lake managers view lake fertilization not as a single act but a planned program that begins during the spring when surface water temperatures stabilize in the mid-sixties and continues into the fall. A proper fertilization program is the single-most cost-effective management tool available to the lake owner. An efficient fertilization program can more than triple the food production for a lake, greatly improving the growth and health of your fish. Increasing the fertility of your lake increases the basis of the food chain, usually measured as single-cell planktonic algae. The abundance of this type of algae in your lake is called a “bloom” and is often measured by how far below the surface you can see a white object.
Water quality can significantly influence the efficiency of a fertilization program and the majority of lakes throughout the southeastern United States would benefit from the addition of agricultural limestone. Notable exceptions are those lake constructed in “black belt” soils or areas of extensive limestone watersheds. A simple test can determine the alkalinity of your water and predict if your lake will benefit from the addition of agricultural limestone. Alkalinity is measured in parts per million (ppm) and if the value is below 20 ppm your fertilization program will benefit from the addition of agricultural limestone being spread evenly over the lake bottom. Although pH is a water quality parameter recognized by most lake owners, it is not a reliable predictor of the need for liming.
There are numerous types of fertilizers that have been used over the years to fertilize lakes. Each type has a preferred method of application. Granular fertilizers are among those that have been used since the late 1940s to increase lake fertility. 20-20-05, commonly known as “farm pond fertilizer,” has been recommended by County Extension Agents and State Wildlife and Fisheries personnel since the early 1950s. It still works like it did a half century ago, but it needs to be placed on a platform beneath the water at a rate of 50 pounds per surface acre. Liquid fertilizers, such as the 10-34-0 clear poly N, has been used successfully to fertilize lakes. It needs to be applied by mixing with water at a rate of 1 gallon per surface are. It is a heavy liquid, weighing 12 pounds per gallon, can be messy and difficult to transport in 5-gallon containers. There are new water-soluble concentrates that require from 5 to 7 pounds per surface acre to apply and do not have to be mixed with water. The best of these, in our experience, is Perfect Pond Plus,12-48-08, which is a complete fertilizer containing micro-nutrients. It dissolves immediately into the upper two feet of the water column and in lakes less than 5 acres, can be broadcast from one location. It is effective and easy to apply.
There are numerous precautions that should be taken during summer fertilization. Mid-July through mid-September is the peak of oxygen related fish kills, and you do not want to create an unsafe environment through over-fertilization. Many lake owners will pencil a certain day each month for fertilization, regardless of how their “bloom” looks. It is best to fertilize based on visibility or “bloom” rather than a certain day of the month. Measure the bloom with a secchi disc or a piece of white plastic on the end of a stick. During the heat of the summer, if the visibility is less than 24 inches, wait until the lake begins to clear before fertilizing again.
Each lake is different and may respond differently to fertilization during the heat of the summer. If your lake develops a heavy bloom following a normal fertilization application, try reducing by half the amount of fertilizer you apply. You do not want to create a bloom that is 16 inches or less. Heavy blooms are a recipe for oxygen-related fish kills during the heat of the summer. Over fertilization may also induce the development of toxic blue-green algae that looks like a bluish-green paint scum floating on the surface of your lake. Wind currents will often push this scum along a bank or cove, developing a very thick layer of alga that has a distinct pungent odor. Blue-green blooms emit a chemical that can be toxic to fish.
Heavy plankton blooms produce an abundance of oxygen during hot sunny days, but these tiny one-celled plants also use oxygen during the night and have an extremely high demand for oxygen during nighttime respiration. A few days of cloudy weather, which limits the sunlight (energy) required for photosynthesis, can result in excessive nighttime oxygen demand. During low oxygen events, fish are often seen on the surface during the early morning gasping for air. Typically a fish kill ensues, with the largest fish dying first. Depending on the severity of the oxygen depletion, you may experience a complete kill or a partial kill with only adult fish dying.
Often when plankton begin to die, the oxygen demand immediately increases as these single-cell plants rapidly decay. This compounds the problem for your fish. As the plankters die, a change in pond color usually occurs. Your pond was a heavy green color one day and suddenly changes to a clear brown or even a milky color the next, a sign of a plankton die-off.
Don’t be your lake’s worst enemy by failing to observe the condition of your lake during the summer. Do not over fertilize and create conditions that increase the probability of summer fish kills. Consult with a qualified fisheries biologist about an aeration system for your lake or even managing your lake to prevent problems. Many reputable lake management companies, such as American Sport Fish, provide these service.
By Barry Smith