This talk is part of the Fountain Fundamentals Conference, July 10-11, 2013, Kansas City, MO.
Aquatic Plants for Water Quality Maintenance in Water features and Fountains
Mary Willeford-Bair : The National Park Service is responsible for the management of a variety of constructed water features across the nation. The National Park Service is held to a high standard of environmental stewardship. We’re required to preserve natural and cultural features for future generations to enjoy.
Managing water features is a monumental task. National Mall and Memorial Parks has more water features than any other park service unit. Fountain management plans include standard operating procedures that are specific for each water feature and include water treatment options. This can vary from mechanical, chemical, biological, and abiotic treatments. Light plus food equals algae. This food in the water could be there through your water filling source. The municipal water supply in DC changed from chlorine to chloramine water treatment in 2000. The resulting leaching of lead from pipes made the use of orthophosphate necessary in 2004. Since then there have been increased algae problems and fountain stainings. Also the city water is not treated for algae until there are complaints of musty smells from the water. By that time our pools have been inoculated with algae because water fowl can truly be water foul and their droppings can provide a very good nutrient source for which algae can feed upon.
Many of the water features at the National Mall have recirculating systems but not all of them and even those with recirculating systems may not have adequate filtration. The water will go through filters but the question is what kind of filters is being used. Is it a sand filter or a bead filter? This will determine the size of particulates that are able to be filtered out and the biggest question of all is, is it in good working condition. A clean fountain may not necessarily mean that it is totally free from debris but rather it is aesthetically acceptable in appearance. The primary goal is to maintain water clarity.
There may be more than one treatment option that can be used to obtain the desired results and one of these could be the addition of plants. While decomposers in the water can breakdown leaves and other debris found in the water column, the plants are then effective at filtering out the nutrients that this decomposition provides. However, bear in mind that not all water features will be appropriate for the addition of plants. Many times this will be determined by the cultural resource specialist.
Many of the historic sites within the National Park Service have been well documented. Cultural landscape inventories are very comprehensive and they include information about the intent of the area when it comes to the aesthetics and also the land use. For example, when it comes to the Lincoln Reflecting Pool, the expectation is that the water surface would remain smooth and reflective and that would preclude the use of plants in this particular water body. And many of our memorials have a very formal feeling to them and would not lend themselves to the addition of vegetation.
Aquatic plants can occur in different portions of the pools. Some of them are beneath the surface or are submerged aquatic vegetation. Others may be floating on the surface. Emergent vegetation has its roots in the water but the upper portion of the plant is above the surface. Care must be taken when selecting aquatic plants as there are many species that can become a nuisance when introduced into the natural environment. Examples of these are water hyacinth, hydrilla, yellow iris, and curly pond weed.
The creation of planting plans requires consultation with a landscape architect in conjunction with the cultural resource specialist. Plantings are based on the scale of the water body. For example, Constitution Gardens Lake holds over six million gallons of water, which means quite a bit of plant material is needed to maintain water clarity. The lake is a kidney-shaped shallow cement pond with a depth along the edge of only 17 inches and a maximum depth of 54 inches located in two depressions and along a narrow band just south of the 56 Signers Island. Constitution Gardens Lake provides a natural setting in the heart of Washington, DC. This lake is stocked with fish for catch and release fishing. Algae can be both submerged and floating. In the morning many times the filamentous algae lies along the bottom of the lake. As photosynthesis occurs, oxygen bubbles are formed and the mats rise to the surface. You might be surprised to learn that not all algae is bad. This pond scum can be very good fish habitat providing shelter for fish and the invertebrates that they feed on. It also provides shade, which is very important at this particular lake that lacks tree cover along the edges.
Algae can be beneficial however, too much algae can become very unsightly. Also, if all of it dies at once, it could lead to oxygen depletion in your pool and also the development of blue green algae which is actually not an algae but a sign of bacteria. This would give our pool a pea green appearance and a foul smell. Algae can be mechanically removed and what this does in essence is also remove the nutrients that it has collected to grow. Another way to remove excess algae is to apply a chemical such as hydrogen peroxide. This product is OMRI approved as organic and what it does is bleach the chlorophyll out of the algae causing it to die. However if you have quite a bit of algae in the pool, you would still need to mechanically remove it so you do not get a harmful algal bloom. This hydrogen peroxide product is nontoxic to wildlife. It will also not harm vascular plants however; keep in mind that your plantings may be subject to being destroyed by animals such as fish that are looking for a spawning ground or perhaps a nesting area. It is strongly recommended that fish not be added to ornamental pools. The exception to this might be a very small pool that has a very efficient filtration system, otherwise your water will become very murky and the fish moving around will continue to stir up sediment.
Bolivar was one of our first water features that used plants as a filtration system. Unfortunately, fish were added to this pool and they bred rampantly uncontrolled. The water constantly looked dark because of their churning up sediment from the bottom. Many of the fish had reached quite a large size and the sheer numbers found in this small water body was staggering. Clean up of the pool was quite a task. There was anywhere from six to twelve inches of muck that covered the bottom.
Much to the surprise of even our cultural resource specialist, we found that the bottom of the pool was done in a beautiful blue tile. In order to protect the tile, the native plants that were going to be placed into the pool were to be planted in boxes that were raised up above the surface. The cinder blocks were even set on plywood boards so that they would not scratch the bottom of the pool because you do not want plants to get a hold in the bottom of your water feature. The plant roots will try to get in between the stones, will compromise the grout, if you have a cement bottom and there’s any cracks, the plants can grow into those cracks and enlarge them, eventually compromising the structural integrity of your water feature. Adjustments can be made to the height of the planters within your water feature. Attention to the water levels is critical for the success of emergent plants. For example, blue flag iris like to keep their feet wet constantly however, they do not like to be inundated by more than six inches of water on a constant basis. Combining plants that have the same requirements for water depth in a single planter will allow you greater success. Even if the plants are properly situated for the water level, many times you will have animals such as ducks. To prevent destruction of your vegetation you can install barriers such as low fencing that will keep birds such as ducks from nesting. These can be removed after the plants have filled in.
With planning, the plantings within a water feature can take on a very pleasing appearance and this can be done with native plants. With the assistance of a landscape architect, we were able to design a very aesthetically pleasing pool that is able to have the water quality maintained simply by virtue of the plants filtering it. The process of getting the native plants introduced took a little over a year because we were unable to remove all of the other planters in there immediately because if we had removed those plants, we would have lost their filtering capability and the young plants did not have the root systems yet developed to be able to provide the type of nutrient uptake that was needed to keep the water clear.
The regional office building pool now is totally devoid of exotic plants. All of the species there now are native. There are submerged aquatic vegetation that consists of raccoons tail, on the far end we have native water lilies and in the planters, blue flag iris that blooms very proficiently in the spring. Duckweed is a very small plant that can be naturally introduced into your pool. In large quantities this tiny plant can give the appearance of a film covering the entire surface but you usually do not need to worry about this. As the name implies, ducks love to eat it and it will soon be gone from your pool. Native plants can provide excellent water filtration in order to maintain clarity within your pools. If you require further information, feel free to contact Catherine Dewey, Walter Zachritz, or Mary Willeford-Bair.
Aquatic Plants for Water Quality Maintenance in Water Features and Fountains by Mary Willeford-Bair, Catherine Dewey, and Walter Zachritz
The National Park service is responsible for the management of a variety of constructed water features across the Service. Constructed water features are the built features and elements that use water for aesthetic or utilitarian functions in a landscape. Examples of features associated with constructed water features include fountains and ornamental pools, canals, cascades, pools, and reservoirs. These features vary by water source used, climate, location, discharge requirements, discharge location, water treatment options and practices, plant or animal communities, general operation, flow schemes, and a host of other attributes. The materials used for these features range from masonry and tile to various metals such as bronze, stainless steel, or iron, and are often combinations of these. Some features consist of concrete basins, synthetic-lined pools, tiles, or unlined ponds. Many of these features are strictly visual or provide auditory aesthetics and function with little or no biological activity. Other features support artificial but complex ecosystems that are functional components of the landscape. This special category of water feature that relies on aquatic plant growth coupled with microbial processes to maintain water quality is the focus of this presentation. The effects of water quality on the materials of the water feature will be examined.
Aquatic plants with their diverse speciation, prolific growth rates and hardiness in many climate zones are excellent for application in many areas of water quality improvement. They can be integral to the water feature form or they can be separate treatment units through which water is circulated. Aquatic plants can be floating, submerged, or emergent. The plants and associated roots provide a media for the growth of a wide range of beneficial bacterial and other micro-organisms that, along with the plant growth and uptake, contribute to the treatment process. Care must be taken when selecting aquatic plants as there are many species that can become a nuisance when introduced into the local environment. The spread of water hyacinth beginning in the early part of the last century from Africa to South America to North America is a good example of the spread of an invasive species that has become a major nuisance. Native species can provide many of the same attributes that exotics species have without the risk of an unwanted introduction.