This water often carries sediment from surrounding areas as well as nutrients from fertilizer, animal waste, or failing septic systems. As a result, phytoplankton can bloom to great densities and cause oxygen depletion in the water, or filamentous algae can grow which covers the pond with dense mats during the summer months.
Controlling aquatic weeds can be frustrating. Design features to help minimize aquatic weed problems include steeply sloping sides that drop to depths of three to four feet rapidly and buffer strips that trap nutrients to prevent them from entering the water. In addition, nuisance aquatic plants can be controlled by mechanical, biological, or chemical methods.
Another management challenge in development storm water ponds is minimizing waterfowl use of them. While Canada geese and ducks are beautiful to look at, they frequently bring aquatic plant species into ponds on their feet and feathers. They also create nutrient problems from their waste material, which is deposited in and around the pond.
To maintain optimum nutrient and pollutant capture potential, stormwater ponds must maintain their capacity for holding water. Ponds that are not managed properly will experience reduced life and increased maintenance costs. For example, ponds that fill in with undesirable vegetation, such as Phragmites or cattails, or support a large resident goose population, will experience excessive organic matter accumulation and reduced pond function and water quality. Removing this accumulated material becomes very costly and may require special sludge disposal permits. Newer ponds are designed with a two-stage pond system. The smaller forebay or primary pond receives runoff first, followed by the larger, main stormwater pond. The forebay is designed to capture the bulk of sediments before water enters the main pond, which can prolong the life of the main stormwater pond. As the reduction of storage capacity approaches 50 percent, roughly every 5 to 7 years, sediment should be removed from the forebay, which is designed for easy access of equipment.
A pond is a small aquatic ecosystem. A variety of natural and interrelated biological and chemical processes help maintain a healthy environment for a diverse population of animals and plants. Each species plays a specific role.
Although stormwater ponds are designed to trap sediments and nutrients from the adjacent watershed, a pond’s natural processes can only accommodate a specific amount of nutrient load. Overfertilization of lawns, or an excessive waterfowl population for example, can easily overload the ability of the plants and beneficial microbes to process nutrients. Nutrient overloading can impact many aspects of water quality, including dissolved oxygen, ammonia, pH and hydrogen sulfide.
Following recommended turf grass management practices, using organic sources and low phosphorus fertilizers will help reduce excessive nutrient loading of ponds. Additionally, using beneficial plant species along shoreline or in floating settings will help take up nutrients and reduce incidence of problem vegetation and water quality issues. See Choosing Plant Species (below) for a detailed information about plants useful for stormwater ponds.
Aquatic plants are the foundation of a healthy ecosystem. They provide shade and cover for fish (especially fry), food and cover for birds and animals, and a home for aquatic and non-aquatic inhabitants such as frogs, toads, tadpoles, salamanders, and insects (like water beetles, dragon and damselflies, butterflies, bees, and spiders). Many aquatic plants are well equipped to compete for nutrients in the pond environment. When nutrient levels are high and plants are absent, algae and toxins proliferate, contributing to poor water quality.
A good supply of native plants with favorable traits should be the goal when planning a stormwater pond. Plantings in rafts can improve nutrient uptake by increasing root exposure to the surrounding water body. Some plants provide bold flowers and foliage for increased aesthetic value. Non-flowering foliage plants should not be overlooked, however, simply because they don’t produce colorful flowers. Some of the most dramatic landscapes are founded on foliage texture, color, form and shape. Large bodies of water are often viewed from a distance, and the gentle nuances that occur from a light breeze can be as captivating as flowers.
To limit sediment runoff and reduce weed seed germination, same-plant species should be grouped together to help provide dense growth. Many species of wildlife prefer dense cover for nesting and as a food source, and dense plantings can be pleasing to the eye.
For detailed information about aquatic plants that can be used in ponds, click here.
Sustainable turfgrass management helps reduce nutrient runoff from lawns to stormwater ponds. Many homeowners hold certain misconceptions about turfgrass maintenance. Adapting few simple management techniques will yield healthier lawns and stormwater ponds.
Both turfgrass and ornamental plants are only as healthy as the soil they grow in. Regular soil testing is imperative. A soil test can provide information on levels of phosphorus, potassium, magnesium, pH, soil texture, organic matter, and recommendations for fertilizer applications.
Improved soil quality can lead to better air and water flow, resulting in a deeper root system, reduced erosion, and an overall healthier lawn and landscape. Unproductive soil, such as clay or sand, is one of the most difficult challenges faced by homeowners. Adding organic matter is the best way to improve soil structure by slowly releasing nutrients to the roots and increasing microbial activity.
Proper mowing and irrigation can reduce weeds and stress on turfgrass. Cutting turfgrass lower that what is recommended for the species or mowing infrequently is one of the major causes of decline in most lawns. Slow and deep watering to 4 to 6 inches in the early morning hours will yield maximum irrigation benefits.
Use herbicides only as needed. Herbicides should not be applied to drought-stressed or dormant lawns.