Clean Water: Your Management Signature
Sparkling, fresh and clean, water can be a beautiful aesthetic asset as well as a necessary component for healthy turfgrass irrigation. Water features add a luster to the environment that can transform any landscape into an inviting oasis. Too often, we see ponds or lakes which have become management nightmares, diminishing their aesthetic as well as functional value. Many times these problems could have been avoided. Knowledge of the dynamics which affect water quality make it possible for contractors to effect solutions which will make water features less problematic and easier to manage.
A thorough understanding of the factors which impact water quality will aid in the design and management of water features. Aquatic weeds, algae, sludge build-up, odors, and poor clarity are the most common problems. Not surprisingly, these problems are often inter-related.
Mother Nature has supplied us with an effective water clean-up tool, aerobic digestion. Aerobic bacteria will metabolize organic nutrients in the water, making them unavailable for vegetation. When a pond is in balance, there are sufficient levels of oxygen in the water to allow the bacteria to respire and digest these nutrients. When nutrient influx outstrips the bacteria’s metabolic rate, the lake is thrown out of balance. The bacteria cannot keep pace with nutrient loading, and nutrient levels explode. We commonly see algae bloom as the result.
Nutrients come from several sources: bottom sludge, dead organic material, incoming water, and in the leaching of fertilizers. Surprisingly enough, the greatest source of nutrients in a lake is often found in the bottom sediment and dead organic matter. Algae typically has a two-week life cycle. When the algae dies, it sinks to the lake bottom, forming an “aquatic compost pile.” Thus, over the course of the years, the amount of available nutrients in the water feature grows at increasing rates.
Incoming water from treatment plants, called effluent water, is also very high in nutrients and salts. Excess nitrogen and phosphorus are commonly found in effluent water. Foaming is an indicator of high phosphorus levels. An awareness that these are nutrient-enriched waters will help in determining the proper management approach.
The third source of nutrients is from the leaching of fertilizers. Research indicates that two to four percent of fertilizers applied near a lake can leach into the water. Phosphorus has been identified as the greatest single contributor to aquatic weeds and algae growth.
Orthophosphorus or dissolved organic phosphorus has been identified as the number-one limiting factor in aquatic vegetative growth. Levels greater than 0.05 mg per liter are considered high, and we see nuisance populations of algae and aquatic weeds when phosphorus exceeds 0.1 mg per liter.
Another factor which impacts water quality is temperature. Cooler water temperatures help inhibit aquatic weed and algae growth. Temperature also affects the water’s capability to hold dissolved oxygen. Cool waters can hold up to forty percent more oxygen than warm waters, and we know the important role that oxygen plays in supporting the natural clean up mechanism, aerobic digestion.
Light also plays a part in the aquatic ecosystem. In shallow bodies of water, sunlight penetrates to the water bottom. These shallow areas are typically warmer, which can accelerate plant growth. Green plants will only photosynthesize/ grow in the presence of sunlight. The area of the lake in which the sun penetrates is called the photozone. Hence, depth plays a role in water quality management.
Nutrients, temperature, depth, light, bacteria, oxygen, and run-off all play an inter-related role in the water quality of every lake. Let’s look at some management practices we can employ to promote higher water quality, more attractive and functional lakes and, in turn, happier customers.
When considering lake management practices, it is important to keep in mind proactive and reactive, or preventative and fixative, strategies. Preventative strategies tend to deal with the causes of problems while fixative strategies deal with the symptoms. Since many of the visible symptoms of poor water quality take a long time to develop, it is advisable to always develop a proactive, preventative program. Most of the proactive approaches are biological tools which have a positive impact on the environment. Let’s look at the proactive, preventative solutions first.
Nutrients need to be addressed in two ways: limiting nutrient run-off into the water feature, and supporting aerobic digestion which limits the available nutrients in the water feature itself.
By limiting nutrients from reaching the water, we lower the nutrients available for plant growth. By using topological relief, such as a berm, we limit the leaching of nutrients into the water. The more dramatic the berm, the fewer nutrients reach the water. Even a slight topographical relief will help. Creating a “no fertilizer” zone from 15 to 30 feet around the lake’s perimeter can help limit nutrient run-off into the water.
Dr. Bob Blackburn of Auburn University, in Alabama, pioneered a process more than a decade ago which he calls “Aquascaping.” By planting desirable, rooted aquatic plants in the littoral or shoreline zone, such as cattails or rushes, we can “buffer” the nutrients which reach the open water, or lininetic zone. These shoreline plants absorb the nutrients before they reach the open water. Dr. Blackburn calls this practice “the lake manager’s first line of defense.” While this may not give the look you desire in every water feature, it is effective.
Placing stones at the water’s edge helps prevent erosion, shoreline weed growth and, to some degree, muskrat burrowing. This technique, called rip rap, consists of placing fist to head-size rocks along the shoreline. Another effective method of minimizing the littoral zone shallows is the use of railroad ties to build retaining walls at the lake edge. Both are aesthetically pleasing and functional.
Depth and water temperature make the littoral zone the most difficult area in the water feature to control or manage. When sunlight penetrates to the bottom, the water can become very warm, and nutrient levels are usually very high. Typically this is where aquatic weed and algae problems develop. The goal should be to limit this shallow shoreline area.
Lining the pond’s bottom can be an effective tool in many situations; to help eliminate bottom rooted weeds, to improve clarity when the soil is a light clay which is easily mixed into suspension, and in sandy soils when the earth will not hold water.
Aeration, fountains, and waterfalls are all common tools for the lake manager. All add oxygen and mixing to varying degrees. By adding oxygen, we support the process of aerobic digestion, lowering the nutrients available for algae and weed growth while helping to retard the growth of, or even reduce the sludge bed. The water in a lake should be turned over four to seven times a day. Dissolved oxygen rates should be in the three to five ppm or mgL range. While waterfalls and certain types of fountains are helpful, they do not have sufficient mixing and aeration capabilities to be used as a stand alone tool. Supplemental aeration must be used.
There are three types of aeration systems: surface spray, horizontal aspirators, and bottom diffusers. Each has a set of strengths and weaknesses which need to be considered. Surface spray aerators are the best choice when the basin is less than four meters or twelve feet in depth, and irregularly shaped. Testing indicates that the better units add more than 2 lbs (lkg) of oxygen per horsepower per hour to the water and 2mg of oxygen at depths over 3 meters (10 feet.) The surface spray can be shaped like a fountain. Check for oxygen transfer rates and pumping rates when selecting a system.
Horizontal aspirators have a directional flow. They are the best choice for long narrow bodies of water or canals.
Bottom-diffused aeration is extremely effective in water 15 ft (5m) deep or deeper. As the bubbles rise to the surface, they transfer into the water column and circulate. As the bubbles rise at roughly 1 ft (30cm) per second, depth becomes critical. These types of systems require 5m (15 ft) in depth to operate at peak efficiencies.
Ozone is a relatively new approach to lake water quality management. While double or triple the costs of aeration systems, it provides benefits in severe water quality management situations.
Lake dyes are a chemical preventative solution. Available in powder or liquid form, lake dyes prevent the sun’s ultraviolet light from penetrating the water. Aquatic plants can’t photosynthesize without ultraviolet light. Dyes are a good tool to use when you have bottom-rooted weed or benthic algae problems.
Bioaugmentation is relatively new in the management of golf course lakes. Aerobic bacteria are added to the lake, which compete with the algae for nutrients.
Bioaugmentation should only be considered in ponds with a neutral pH. A pH higher than nine will kill the bacteria. Temperature is also an important factor. In cooler waters, the metabolic rate of the bacteria slows, making it an ineffective alternative. The pond or lake must also have adequate levels of dissolved oxygen to support the increased demand for oxygen the bacteria will create.
Grass carp are an effective method for providing an ongoing solution for rooted weed problems. These fish are relatively inexpensive and require no upkeep or labor once they are in the water. They have short intestinal tracts for animals that eat vegetation.
These proactive, preventative measures are best taken before a problem occurs. The old saying “An ounce of prevention is worth a pound of cure” is especially true in the lake management field. Let’s take a look at some of the fixative, reactive tools we can employ once lakes are in a crisis stage.
The quickest way to rid a lake of nuisance algae and weeds is to use an algaecide or herbicide. The North American Lake Manage-ment Society reports that chemical weed control was introduced in the 1940s, when arsenic was added to lakes to manage weed problems. Today’s products are safer. Many are copper-based. They are available in liquid form to kill floating plant life and in granular form to kill rooted plant life. Dosage usually increases with the alkalinity of the water. It is extremely important to know the surface area and volumes of your lakes when figuring dose levels.
Chemicals may be applied by hand or through spray apparatus. It is extremely important to use products which have approval from both local and national regulatory agencies. Chemicals may be quite costly, and permits or licenses may be required to apply these products. There are lake management firms which can supply more expertise on a local basis. For many years, chemicals were used as a stand-alone management program. While they are valuable lake management tools, they are best considered a fixative as opposed to an ongoing management tool.
By taking a proactive approach to water quality management, you can help insure that your ponds and lakes have cleaner waters, and the aesthetic appeal you desire. All water features have a life cycle; as they gradually fill in with sludge and nutrients, the aging process accelerates. By remembering the factors which impact water quality (nutrients, temperature, light, and depth) you can make use of the proper management rationale and tools to create lakes and ponds which are functional, beautiful and have a long life. Integrated lake management, or combining several practices, can help ensure your lakes never reach crisis levels. Clean water — it can be your management signature.