« NOTE: This is the second post in a series devoted to what you can do to reduce the duration of the next harmful algal bloom. »
As we endure a terrible red tide outbreak on our coast, coupled with blue-green algae clogging inland waters, I hear many people ask what they can do to prevent the next algal bloom. Number two on that list is:
Stormwater is the biggest contributor to water pollution in Florida and wet detention ponds are the most common method for stormwater management (Rushton et al. 1997). You may call them lakes, but the technical term for these surface water bodies is wet detention ponds. The purpose of wet detention ponds is to detain stormwater temporarily in order to protect the surrounding infrastructure from floods and enhance the quality of stormwater flowing downstream.
There are more than 6,000 ponds in Sarasota County. Of these, more than 4000 are classified as wet detention ponds. These 4,000-plus water bodies temporarily store water before releasing it downstream by canals, ditches, and pipes to federal- and state-regulated waters. It is worth noting here that all the creeks and bayous that drain into the bays of Sarasota County have too much pollution to meet water quality standards (Figure 1). So let’s start cleaning up our waters by first looking toward ourselves (see the first blog post in this series called “We All Contribute to Nitrogen Pollution“) and then turning to our neighborhood “lakes.”
Our stormwater ponds are not in ecological balance
Residents and stormwater managers are taking notice of our wet detention ponds (herein stormwater ponds) because they are showing signs of being off balance. Three of the most common symptoms of unbalanced ponds are:
- the loss of land associated with pond erosion,
- frequent algal blooms, and
- the loss of once abundant wildlife.
Over the past several decades, pond management has often been reduced to monthly chemical applications to kill undesirable aquatic plants and algae living in and around the ponds. This heavy reliance on pesticides to manage stormwater ponds led professionals to ask: are we poisoning our ponds and subsequently our downstream waters in order to enhance our view?
The intent of wet detention ponds
Stormwater ponds are designed to store water during the dry season, and filter water during the wet season (June 1 to September 30). The goal of stormwater ponds is to reduce downstream water pollutants by 80%. However, this is not assessed or monitored.
The history of stormwater ponds
Stormwater ponds in the southwest Florida landscape can be seen in the earliest aerial imagery from the late 1940s. Stormwater ponds were designed to mimic wetlands that once covered more than half of the state and naturally cleaned the water and provided habitat for Florida wildlife. Stormwater management in Florida became mandated by law on February 1, 1982 under Chapter 62-25 F.A.C. This Florida state statute outlines regulations of stormwater discharge and delineates the design, maintenance, exemption, and construction of stormwater discharge facilities.
The statute makes clear that “(e)ffective stormwater management is essential to reduce existing nonpoint source pollution and protect surface water resources from stormwater pollution for existing and new land uses.” In fact, stormwater management is intended to replicate the pre-construction water flow of the site, and to protect against erosion, remove pollutants, regulate salinity, and to provide “cost effective water quality and water quantity solutions”.
Turning pits that were created from the need to elevate developments into stormwater ponds quickly became the easiest and cheapest way to comply with state law. Unfortunately, the increased number of impaired waterbodies in Florida is evidence that these systems are not functioning as intended and that somewhere along the way there has been a breakdown between conception, design, implementation, and long-term management.
Sarasota County stormwater pond guidelines
In Sarasota County, there are 6,272 ponds (and counting), and 4,666 of these are wet detention ponds, meaning that they store water temporarily and are connected to federal and state regulated waters by canals, ditches, and pipes. Sarasota County has multiple guidelines for contractors to follow when designing and installing wet detention ponds.
The County requires “ponds for any project that either singularly, or cumulatively when constructed in phases, includes a stormwater detention pond or pond system greater than or equal to one (1) acre necessary for purposes of treatment” to have littoral zones that cover at least 30 percent of the surface area (Environmental Technical Manual). Littoral zone plantings must consist of three native herbaceous plants, and one of the species cannot represent more than 50 percent of the vegetation cover.
It also prohibits the release of exotic fish (i.e. grass carp, tilapia) in ponds that have littoral zones (Sarasota County, 1997). Littoral zones should be 65 percent covered by native vegetation with less than 15 percent coverage by invasive species. If invasive species cover exceeds 15 percent of the littoral zone, and hinder the ability for native plants to establish, then the plants must be manually removed (Sarasota County, 1997).
Thirty-six years after the state enacted into law management of stormwater ponds, these ponds are showing their age. Extension agents are often called about stormwater pond problems, which range from algae blooms, no plants, dead plants, exotic plant removal, littoral and bank plant design, and how to slow down, stop, and combat bank erosion. Site visits give Extension Agents a unique perspective of stormwater ponds and their evident mismanagement.
Mismanagement is observed when littoral zones are cleared of plants, nuisance fishes have become detrimental to the integrity of the pond, bank erosion is so severe that trees have fallen and water threatens the integrity of homes and condos, and water is either crystal clear with a blue hue or completely covered in various forms of algae. During these visits homeowners have reported instances of individuals and past homeowner association board members intentionally removing required littoral vegetation from the pond in effort to enhance their view and ward off unwanted wildlife such as mice, snakes and alligators. These practices are against the professional judgment of experts.
Locally, the shear lack of plants in and around stormwater ponds illustrates the fact that little attention has been paid by residents to their permits and to the scientific evidence that supports the use of vegetation to balance the chemical, physical, and biological inputs to these stormwater management systems.
What you can do
In order to enhance your neighborhood ponds or lakes you must first start with the permitted design. Was a littoral zone required as part of your pond permits? Are your littoral zones meeting County standards?
Next, use a holistic approach to pond management that includes reducing your inputs and building up your pond’s natural defenses (Figure 2). Reduce your fertilizer use, keep lawn clippings and tree debris (especially acorns and leaves) out of your stormwater pipes and ponds. Build up your pond’s natural food web, which will provide natural checks and balances for erosion, invasive fish, and nutrient management, and in turn reduce algal blooms. Restore or enhance your pond’s littoral zone with native wetland plants.
Finally, create a low-maintenance buffer around the perimeter of your pond to secure the bank and allow for some additional removal of nutrients and other non-point source pollution before entering the pond.
For a pond assessment and more information, contact me at the Extension office (941-861-9818) or Mollie Holland of Sarasota County’s Neighborhood Environmental Stewardship Team (941-861-5000).
- Stormwater Systems in Your Neighborhood: Maintaining, Landscaping, and Improving Stormwater Ponds
- Florida-Friendly Plants for Stormwater Pond Shorelines
- Stormwater Ponds: A citizens guide to their purpose and management
- Living on the Waters Edge: A homeowner’s guide to low-maintenance landscaping along stormwater ponds
- Creating Wildlife Habitat with Native Florida Freshwater Plants
- Watershed Education and Training: Ponds, Lakes and Neighborhoods (WETPLAN)
- Pond Watchers: Local Efforts for Clean Ponds link to Cleaner Water in SWFL