Sources of Nutrient Loading in Ponds
Landscape debris can be a major problem in small ponds. This comes from many sources; mowers , blowers and weedeaters throwing the debris into the pond can be a major contributor. Branches and leaves falling or being trimmed along the pond edge are another source. Fertilizer can enter the pond either while being applied or through runoff. Be very careful when fertilizing around the lake edge and try to control runoff after fertilizer is applied to the adjacent areas.
Street drains can carry a wide variety of material into the pond. If you have streets draining into your lakes, they should be kept free of trash and debris and every effort should be made to keep foreign material off the streets and out of the drains. We have seen an endless number of possibilities of what people have put down street drains; oil, paint, carpet cleaning tanks, cleaning supplies, swimming pools and spa cleaning chemicals, and endless amounts of dirt and mud from street cleaning and hosing off the street near construction sites and other work areas.
Once you find any of these intrusions you should do as much as possible to correct the problem. Even small changes can do a lot for your water quality.
It is becoming more common for golf courses and other pond owners to use recycled water for filling ponds and irrigating turf. In many instances the local regulations make it mandatory that these large water users make effluent water a part of their water program. This recycled or effluent water is less expensive and recycling helps conserve a precious resource, fresh water. While the recycling of water is important and beneficial to all of us, incoming water from treatment plants is also very high in nutrients and salts. Excess nitrogen and phosphorus are commonly found in effluent water. This water is also often treated with chlorine at the source. Chlorine has no part in a natural pond maintenance program. You should consider that while the chlorine will dissipate from the pond water fairly quickly it also will leave a variety of salts that would not have been present without the effluent water. Awareness that effluent water is nutrient-enriched water will help in determining the proper management approach. It is very helpful to mix the effluent water and fresh water at the source. If your fill water only contains 50% effluent you will be much better off than with 100% effluent. Effluent ponds can be managed with the same approach as fresh ponds, the effluent water just intensifies some of the concerns and your maintenance decisions and treatment amounts will need to be adjusted accordingly. A microbial approach is the best way to address the excess nutrients, although your treatment amounts may go up to compensate for the extra nutrients.. Good circulation and aeration becomes even more important.
Another major source of nutrient loading is from waterfowl excrement. Waterfowl, including ducks, are the most common visitors to urban waterways. Ducks all appear much the same, but there is an underlying struggle taking place between wild duck species and more domestic waterfowl. The Mallard is the most widespread duck species throughout the Northern Hemisphere. There are thirty or more duck types derived from the Mallard that have the ability to interbreed and produce fertile offspring, further exerting a negative impact on the wild population. The Mallard is very adaptable and is found near large marshes, small rivers and bays, city and golf course ponds. Most of its natural diet is vegetable matter. It will feed in shallow water, on dry ground and will graze. While other species of ducks will migrate through and will forage in the pond, the mallard is very easily domesticated, often taking up permanent residence on ponds.
Bird populations are often artificially supported by augmented feeding, commonly seen when parents bring their children along to feed the ducks and enjoy a wildlife experience. The result is a quickly established high-density bird population. Avian diseases can also spread rapidly in this situation, and are ruthless once unleashed within the waterfowl population, causing ducks to die in large numbers, which can distress the visitors who consider these birds their pets. Salmonella and viral infections that originate in the local duck population are also an often underestimated risk to people trying to enjoy the park or golf course where these fowl live. Waterfowl is one of the primary carriers of the Avian Flu that is becoming a serious worldwide health issue.
Despite the problems waterfowl may cause, they are a valuable natural resource; they are a source of recreation for hunters and bird lovers alike. It is important to remember that ducks, geese, as well as other migratory birds, are protected by the Migratory Bird Treaty Act of 1918. Destroying waterfowl is not an acceptable solution to the problem. The answer lies in managing waterfowl populations in order to prevent damage. You should do your best to keep waterfowl populations to a minimum and strongly discourage artificial feeding. Even with strenuous effort to control waterfowl, they will often reach excessive levels on golf courses and public ponds. If you do not want to, or cannot rid your pond of waterfowl, then the extra nutrient load should be considered when deciding on a treatment approach.
Have you ever wondered where leaves blown into drainage ditches, storm drains or ponds end up? Landscaping activities run off, draining pools and street cleaning can contribute a great deal to the nutrient levels in your pond. Many ponds, either intentionally or through poor design, can act as retention basins for the street and landscape areas near them. Virtually anything that touches the ground can make its way into storm drains and landscape drainage systems and flow directly into ponds. Leaves, grass clippings and fertilizers can be carried into ponds increase the load of decomposing organic matter in the environment. The accumulation of debris results in an increased BOD (Biological Oxygen Demand), decreasing in the level of oxygen available to aquatic organisms, and moving the pond toward eutrophication. Other pollution like cleaning chemicals, paint, oil and dirt can also enter the pond in this manner.
Watershed Analysis is a helpful tool for identifying nutrient loading concerns but this field of study can get very complex. Excess nutrients speed the aging process of ponds and lakes and add to weed and algae problems. This analysis does not need to be overly complicated to be helpful in identifying most of the major problem areas where nutrients are entering the pond. Often, simple changes in design or management can significantly improve water quality.
Watershed analysis is defined as ecosystem analysis at the watershed scale. A watershed analysis is performed to determine the ecological stability of a watershed. Every watershed is different, so every watershed analysis should have a different focus. Many watershed analysis reports contain carefully written narratives, comprehensive tables, and electronically-generated maps, all on familiar subjects: soil, vegetation/landscaping, wildlife, fish habitat, roads, sediment, and so on. The subjects may be grouped under different headings, such as "issues" or "conditions," but they remain the same basic concerns found with any small pond.
A complete watershed analysis can be very time consuming and expensive and might not be necessary. Simply checking the pond for obvious problems can identify most of the sources of extra nutrients entering your pond. This is a composite list of some of the things you might find with an observant eye.
When a pond is filled and fed completely with recycled water it is possible for the pH and alkalinity to get too high for bacteria to survive. When this happens you lose your last possibility of making this pond into a pleasant balanced aquatic environment. What you have left is a retention pond for smelly, nutrient rich, turbid, recycled water. The best choice is to avoid using recycled water in your ponds or to dilute the effluent with fresh water at the source to keep the impact to a minimum.
Coots are another species that can become a real problem. American Coots are noted for many qualities, some considerably less redeeming than others. Conspicuous, noisy, and aggressively territorial, they have a repertoire of about fourteen displays or actions to communicate among themselves. Coots are opportunistic feeders. In addition to hunting for themselves, they will also take leftovers from other species such as Mallards. They pirate plants, brought to the surface by diving ducks, such as Canvasbacks. Young coots are opportunistic as well. Groups of up to five juveniles may pirate aquatic vegetation from the bills of ducks and geese. Coots are among the least graceful of marsh birds. Commonly called "splatterers", they scramble across the surface of the water with wings flapping not only to confront intruders but also to become airborne. Coots bob their heads while walking. While foraging on insects, they bob quickly; while eating greens, they bob slowly. Appearing somewhat like aquatic pigeons, coots also bob their heads while swimming.
Both Mallards and coots will feed on landscape vegetation as well as turf and they can do a great deal of damage. Waterfowl excrement contains heavy amounts of both nitrogen and phosphorous. We have mentioned before that your pond can be effected by as low as .05 ppm of phosphates and 5 ppm of nitrates. The duck population needed to achieve this is amazingly small. About four ducks per surface acre will add the needed nitrates, and less than 1 duck per surface acre can add more phosphates than your pond can handle. The amounts of nutrient entering your pond will vary with several factors, including where the birds are feeding and the food source.
There is a standardized set of tests used to evaluate these risks in public waterways called the Water Quality Index. The Water Quality Index is used to evaluate aquatic systems and includes collection of 9 tests developed in 1970 by the National Sanitation Foundation. The index encompasses comparisons of different rivers and lakes, at different locations, over extended periods of time. The WQI is determined by obtaining data related to nine different water quality indicators:
1. Dissolved Oxygen
2. Fecal coliform
3. pH
4. 5 day Biochemical Oxygen Demand
5. Temperature
6. Total phosphates
7. Total nitrates
8. Turbidity
9. Total solids
Bioaugmentation is the most practical way to address a situation of heavy nutrient loading. The microbes will help keep nutrient levels in line, even with a consistent load being added from outside sources.
Consistent addition of beneficial bacteria, coupled with good aeration of the water, will help prevent harmful bacteria from developing in the pond that can be dangerous to waterfowl, wild and domestic animals and humans coming in contact with the water.
