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Impoundment Management

ji-impoundmentsThe District manages 4500 acres of coastal mangrove swamps and salt marshes to abate mosquitoes by minimizing available exposed mud for egg-laying during the summer.  During the 1950s and early 1960s, IRMCD impounded approximately 2600 acres of the nearly 4500 acres of coastal marshes in Indian River County, by constructing low earthen dikes around the high marshes. The District uses an ecosystem management approach for saltmarsh mosquito control, following adaptive strategies based on biological and chemical research.

The impoundments are connected to the lagoon by culverts which are open to natural tides most of the year to allow for free exchange of water, nutrients, and organisms.  During the summer season, these areas are kept flooded during the summer season to minimize the amount of exposed mud available for mosquito egg-laying.  Stationary electric or portable diesel pumps are used to add enough lagoon water to the marshes until the marsh is covered with a minimum of a few inches of water. This prevents the saltmarsh mosquitoes (Aedes taeniorhynchus and Aedes sollicitans) from laying their eggs and the production cycle is stopped. This technique is known as Rotational Impoundment Management (RIM).  The ecosystem management protocols result in multi-species benefits, especially to fish and wading birds, and is an example of insect control by a resource management method that does not require pesticides.

IRMCD works cooperatively with several agencies responsible for fish and wildlife resources (e.g., U.S. Fish and Wildlife Service, St. Johns River Water Management District, Florida Department of Environmental Protection) to manage these impoundments for both mosquito control and natural resource interests. Ongoing dike and water control structure maintenance is accomplished largely by District Staff.

Approximately 1800 acres of the salt marshes in Indian River County are not impounded.  Mosquito production can be very high in these areas and must be controlled by larviciding.  A crop-duster type aircraft is utilized to apply granular larvicides, an insect growth regulator, or bacterium, to areas where ground treatments are not feasible.