|Langston University Aquaculture|
Urban Pond Management
By Kenneth Williams
Many housing developments now have a pond as the central focus of the neighborhood. These ponds are often landscaped and include walking trails and picnic sites. The ponds are also used for fishing and sometimes swimming and may be open to small boats. Single family housing and associated streets cover most of the pond watershed.
Most of these ponds soon become choked with algae and rooted aquatic plants. Fish kills due to low dissolved oxygen soon follow. Fishing quality declines due to stocking inappropriate fish. The pond becomes a neighborhood eyesore and the local home owners association is charged with finding solutions to pond problems. This article will explore ways to maintain healthy urban ponds and rejuvenate ponds that are in decline.
Most problems in urban ponds are caused by poor water quality, improper maintenance or age, but by far the most common problem is poor water quality. The pond may receive runoff from yards, gardens and streets in the sub-division. Runoff water can contain a variety fertilizers, pesticides and herbicides. It may also contain oil washed from streets, tire rubber dust, antifreeze, paint and other household chemicals that make their way from home to the pond. There is the possibility of sewage pollution In neighborhoods with septic systems.
Urban pond remediation begins with the water shed and the practices of each member of the community. Community members must be made aware of pond problems and why they occur. Residents also must be willing to work together to improve conditions in the pond and watershed. Most recommendations discussed are easily implemented and require only awareness and minor changes in most home owners lawn and garden maintenance practices.
Problem - Fertilizers
Fertilizer is the most common cause of urban pond problems. Fertilizer consists of various combinations of the plant nutrients, nitrogen, phosphorous and potassium. It often is used to excess in home yards and gardens. During heavy rainfalls the nutrients are washed from the yards, collect in the streets and run into the pond. Small amounts of excess nutrient running from each yard combine to create a large amount of fertilizer entering the pond.
Fertilizer in the pond provides nutrients for luxuriant growth of rooted aquatic plants, floating mats of algae (pond scum or "moss") and can cause heavy phytoplankton blooms creating very green water. Ponds can be almost completely covered in vegetation during the summer. At this point fishing becomes difficult. Abundant vegetation slows water circulation which reduces available oxygen in lower layers of the pond. Decayed plant material accumulates on the pond bottom and requires oxygen to breakdown. Algal blooms expand and die. As they decay they place further demands on the available oxygen in the pond. Soon, a combination of weather factors and the oxygen demand of decaying plants and phytoplankton cause a reduction in dissolved oxygen levels sufficient to kill many or most of the fish in the pond. (See fact sheet "Water Quality In Sport Fish Ponds" for an explanation of the dissolved oxygen cycle and its consequences in fish ponds.)
The neighborhood community must be informed and work together to solve excess nutrient problems caused by home fertilizer use. Many people feel the need to maintain a lush, green yard and at the same time want a beautiful community pond. Both these desires can be achieved with some compromise and planning. Begin by reducing the amount of fertilizer spread on the lawn. Have yard soil tested and only apply an amount of fertilizer that is recommended from the soil tests. Contact your county extension or Natural Resource Conservation Service office for information on soil testing. Tests show that many yards contain several times the required amounts of many plant nutrients. Nitrogen is often the only type of fertilizer the lawn may need. Most soils in lawns have excess amounts of phosphorous. Excess phosphorous is a major problem in nutrient polluted ponds. Know the fertilizer formulation that you use. There are 3 numbers written on each fertilizer bag. For example: 10-20-5. This formulation number means that there is 10% nitrogen, 20% phosphorous and 5% potassium in the formulation. Use a formulation that contains 0 in the last 2 numbers , 10-0-0 or 20-0-0.
Mulching lawn mowers also reduce the amount of fertilizer needed for lawns. Mulched grass stays in the lawn and decays, releasing nutrients bound in the plant material. When grass is bagged, nutrients are removed from the lawn and exported to the land fill thus requiring more fertilizer applications to maintain lawn quality.
Time fertilizer applications. Check the weather forecast before applying fertilizer, insecticides or herbicides. Do not apply these chemicals when rain is in the forecast. Heavy rains can wash fertilizer and other lawn chemicals out of the yard and eventually into the pond. This is costly because the fertilizer application does not produce the intended effect and it degrades the pond. It is best to apply fertilizer and then lightly water the nutrients into the soil.
Consider alternative landscape materials. Lawns can be converted totally or partially into low cost, low maintenance perennial gardens. Shrubs and perennial ground covers require less trimming, no mowing and little or no fertilizer. This has become a preferred option for many home owners with little time to spend on lawn care.
Save water and money by using efficient irrigation systems on the lawn. Over watering washes nutrients out of the soil that are usually replaced by adding more fertilizer. Turn off automatic systems when rain is forecast. Make sure water goes on the lawn and not into the street. Only water when it is actually needed.
For those who like automatic sprinkler systems, irrigation is now available that will measure soil moisture, humidity, temperature and cloud cover to computer micro manage each irrigation point. These systems can save 25% or more of water normally used for lawn watering.
Each home owner choosing to adopt one or more of the above practices can greatly reduce the amount of fertilizer entering the pond.
Pond Management Solutions
Other methods may be needed to supplement neighborhood lawn management practices. Often, heavy rooted aquatic plant growth or excessive phytoplankton blooms occurs because excess nutrients continue to enter the pond or have accumulated there. Also large areas of the pond may be too shallow allowing for excessive light penetration and subsequent growth of extensive plant beds.
Over time, ponds fill with sediment, leaves and decayed vegetation until large areas of the pond are very shallow, less than 3 feet deep. These ponds are difficult to manage because much of the surface area is covered in dense aquatic vegetation. Pond vegetation management tools can be used with some effect but many of these ponds must be drained and rebuilt before they can regain aesthetic and productive qualities. Rebuilding the pond can be less expensive than trying to manage weed problems wit herbicides, dyes or other techniques.
cattails often expand to nuisance proportions in a short time especially in ponds with large areas of shallow water. Cattails can be killed with herbicides such as Rodeo, Reward or weedtrine-D. Other control methods also are effective including: deepening edges of the pond. A backhoe can effectively do this in many ponds while removing cattails at the same time. Cutting. Cattails require several cuttings before they are eradicated. Cut cattails in early summer before seed heads develop for best control. Also, reduce the amount of nutrients entering the pond.
A combination of good lawn, garden and pond management practices is usually necessary to manage the nutrient load received by many urban ponds.
Grass carp can be an effective control of soft, rooted aquatic vegetation. They do not control algae, cattails, or other relatively tough, emergent plants. Stock grass carp at least 8-10 inches in length in ponds with an existing largemouth bass population. Stocker fingerlings (8-10 inches) can reach a weight of 5-7 lb in a growing season, 15-20 lb after 3 years provided an adequate food supply exists.
Grass carp can control vegetation in sportfish ponds when stocked at 5 to 10 fish per water surface acre or 15 fish per vegetated acre. This rate gives good vegetation control in about three years after stocking fish. Little control may be noticed the first year, however, holes will begin to open in plant beds during the second year. It is usually best to remove vegetation slowly to prevent total aquatic plant eradication in sportfish ponds. If quicker vegetation control is required, increase stocking densities to as much as 25 fish per acre . Grass carp can be combined with herbicide use for quick and lasting aquatic vegetation control.
Grass carp, like many other species of fish are attracted to, and will follow a current of water. A spillway screen must be constructed to keep the fish in the pond while water is running across the spillway. (See fact sheet titled "Emergency Spillway Screen Construction".)
Dyes can be used in ponds to shade out rooted vegetation and reduce algal blooms. Cost is about $40/acre/month. Dye may only be needed during the warm months, May through August.
Dyes give the water a pleasing though perhaps unnatural blue-green color that reduces light penetration and helps prevent weed growth. It can be useful to use dyes in conjunction with grass carp.
Ponds that habitually have dense phytoplankton blooms and fish kills can benefit from pond aeration devices. Regenerative, rotary vane or diaphragm pumps are most efficient for this application; although fountain aerators are very popular. Aeration systems destratify ponds by circulating water from the pond bottom to the surface. With adequate aeration, dissolved oxygen will be distributed throughout the water column, allowing organic material opportunity to decompose rather than accumulate on the bottom.
Destratification prevents anoxic water from accumulating and causing fish kills. Fountain aerators are not as efficient as other types at circulating water. They do provide an oxygenated haven of water for fish in the event of low dissolved oxygen conditions. However, on hot sunny days, evaporative loss to the atmosphere from fountain aerators can be very high. For detailed information on aeration pumps for ponds refer to the Langston University fact sheet titled "Simple Aeration Systems For Recreational Fish Ponds".
Herbicides can be used to kill aquatic vegetation but it is not a permanent solution. Plants can quickly regrow. Dead plants decay and provide nutrients for more luxuriant growth. When herbicides and algicides are used to control aquatic vegetation measures also should be introduced to control nutrient input into the pond. If not, the problem will persist and likely become worse.
Treat no more than 1/4 of the pond with herbicide at any one time. Large quantities of dead and decaying plant material can use all available dissolved oxygen in the water and cause a fish die-off. Most herbicides are not toxic to fish.
Use an herbicide appropriate to weed species present. If unsure of aquatic plant identification, consult a fisheries professional or county extension.
Pesticides can occasional cause fish kills in urban ponds but, this is not as large a problem as excessive fertilizer use. Closely follow label directions when applying herbicides and insecticides. Insecticides and fungicides can be very toxic. Insecticides formulated for ticks have caused fish kills. Do not apply insecticides on your lawn or garden or around the pond before rains.
Trees around the pond provide beauty and shade that encourage community use of the pond. They should be planted along walking trails and in back yards. Trees should not be planted on the pond dam. Roots from trees on dams can cause channels that will produce leaks and even failure of the dam. Annually remove any trees that begin to grow on the dam. Do not remove large established trees. Removing large trees will kill roots and hasten leakage problems.
Erosion from roads or other drainage areas must be repaired and prevented. A well maintained vegetative cover is the best solution to bank erosion. Stone can be used along eroding banks although cost can be prohibitive. Wind generated waves can cause severe erosion on leeward banks in exposed ponds. Rip rap is the best solution for this problem. Line the erosion prone bank with 3 inch or larger stone 2-3 feet below the water line.
It is important to prevent residents and friends from haphazardly stocking fish into the pond. Get the advice of a fisheries professional and follow a management plan. Fish species to avoid in most ponds include: Crappie, green sunfish, bullhead catfish, flathead catfish, and common carp. For more information on fish management refer to our fact sheets titled:"Sportfish Management And Evaluation" and "Challenges To Managing Sportfish Ponds".
Geese are currently the most common nuisance waterfowl. A few geese are always welcome on the pond but numbers can swell to the hundreds. Geese graze on grass surrounding the pond. Their droppings are unsightly and also increase the amount of nutrients entering the pond. Contact the State Department Of Wildlife Conservation for information on trapping programs and control methods.
Snakes can be a problem in some urban pond environments. Most common water snakes are nonpoisonous but they can bite if provoked. The cottonmouth is an exception. However, it is not likely to be found west of a north/south line through Okmulgee Oklahoma and along the Red River. The copperhead is closely related to the cottonmouth and can be found along the shoreline of some ponds, particularly in brushy areas.
The best way to manage snake populations is to mow pond banks and clear dense vegetation from shorelines. Also, remove fallen logs, trash and other debris that can provide shade or resting places for the snakes.
Turtles are often perceived to be pond problems. This is usually not true. Our most common pond turtle is the red-eared slider. This turtle feeds mainly on aquatic vegetation and dead organisms. It will try to feed on fish hung on stringers but does not often feed on fish swimming in the pond. Snapping turtles do eat fish but only a few each year. Their populations in ponds are usually small and they have little impact on fish populations. For more information on turtles and turtle traps refer to the fact sheet titled "Turtles And Turtle Traps".
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