Nutrient loading from lawn fertilizer runoff is a major factor in promoting algae growth in urban ponds. It is ironic that the commercial products that make your lawn so lush and green are the same products that make your pond green and smelly. Fertilizer (phosphorus and nitrogen) fuels the out-of-control growth of algae and aquatic plants. Without nutrients, these pests are unable to grow and flourish. Phosphorus is the limiting nutrient in aquatic environments and is the fundamental base of the entire ecosystem. Due to large scale stormwater runoff, it is impossible to completely prevent nutrient influx in urban ponds, however, there are some things you can do to reduce it. While algaecides/herbicides address the symptom of the problem, taking some of the steps below can help address the cause of the problem.
Landscape Fertilizer is a Pond’s Worst Enemy
We have seen it a million times…..someone running a fertilizer spreader directly adjacent to a community pond. If mechanical spreaders are used, it is important to keep fertilizer pellets away from the water’s edge. We recommend keeping a “buffer zone” of at least 25 feet between the pond’s edge with all fertilizer applications. Even a light rainfall can wash a significant amount of nutrients into the pond and cause severe algae blooms overnight. It is also important to bag your grass clippings and fallen leaves rather than blow them into the pond.
A Single Goose Can Cause Nearly 500 Pounds of Algae Each Year!
Nutrient loading by waterfowl is another major concern. A single goose can contribute upwards of 1 pound of phosphorus to your pond each year. That is enough phosphorus to generate 300-500 pounds of wet algae over the growing season. Not only do waterfowl add excess nutrients to the water, but they muddy up water and litter walk paths and fountains with feces. It is highly recommended to avoid feeding waterfowl and other wildlife in urban areas. In fact, many local municipalities have adopted ordinances to restrict feeding in public spaces.
Well Water Can Be a Problem
A major source of nutrients often goes unnoticed. We have found that the level of phosphorus in area groundwater is increasing every year due to urban sprawl and over-landscaping practices. Land historically used for agriculture is also a contributor to this nutrient seepage. In fact, we have tested several local well sources that now have phosphorus concentrations that are 20 times higher than the EPA standard for “polluted” surface waters. This means if your pond uses a well as a filling source, then you are at an extremely high risk of frequent and severe algae blooms. In some cases, no amount of pond management will be enough to keep the pond aesthetically pleasing at all times.
How Are Excess Nutrients Addressed?
There are various commercial products available that bind nutrients and render them unavailable to algae. These products are used in highly fertile (eutrophic) waters to restore water quality. In severe cases, we may recommend the use of these products on your pond. Keep in mind that nutrient binders will need to be applied periodically to offset future stormwater influx. Ponds that are regularly filled with groundwater will require several applications per year.
When used under the right conditions, supplementing with beneficial pond microbes can be effective at nutrient reduction. Microbes work by consuming excess nutrients, thereby reducing the fuel that algae need to grow. Therefore, the frequency and severity of algae blooms should decline depending on the source of nutrients. Through experience, we have found that microbe treatments work best in small, highly oxygenated ponds. Recirculating systems with little or no water exchange respond most effectively to bacteria treatments. Besides aeration, water quality variables (most notably pH and alkalinity) also determine microbe effectiveness. Since algaecides work quickly, the expectations are often that microbes will be an immediate fix. However, all biological controls work naturally. You should allow a minimum of 6 weeks to notice visual improvements in water quality. Not that organic, microbial treatments will have no effect on rooted aquatic weeds.
The guidelines below should be followed to minimize nutrient pollution in community ponds:
- Halt the use of landscape fertilizer around the pond and on slopes that drain toward the pond
- Bag all grass clippings in the community
- Do not mow or weed-eat all the way to the pond edge
- Preserve native, aquatic plants in moderation. The pond is NOT a swimming pool!
- Do not feed waterfowl or other wildlife in the community
- Clean up after pets