Salt marshes of the Indian River Lagoon, Florida (USA) were once p.'olif]c producers of mosquitoes. Mosquitoes lay their eggs on the infrequently-flooded high marsh surface when the soil surface is exposed. The eggs hatch when the high marsh is flooded by the inflequent high tides or summer rains. To control mosquito production, most of the salt marshes (over 16,200 ha) were impounded by the early 1970s. Flooding, usually by pumping water from the Lagoon, effectively controlled mosquitoes.However, impounding had a profoundly negative impact on the wetland plant, fish, and invertebrate communities. Isolation fiom the Lagoon cut off aquatic access by transient estuarine species that used the wetlands for feeding or as nursery area. In one study, the number of fish species dropped fl'om 16 to 5 alter impounding Wetland vegetation within some impoundments was totally eliminated: other impoundments developed into freshwater systems.When tidal exchange is restored through hydrologic connection, usually by culverts installed through the perimeter dike, recovery to more natural conditions is often rapid. In one impoundment where wetland vegetation was totally eliminated, recovery of salt-tolerant plants began ahnost immediately. In another, cover of salt-tolerant plants increased 1,056% in less than 3 years. Fisheries species that benefitted the most were snook, ladyfish, and striped intlllet. Over 1,500 juvenile snook were captured in a single 3-hr flood-tide culvert trap as they attempted to migrate into an impoundment. The zooplankton community rapidly returned to the more typical marsh-Lagoon community. Water quality and sediment sulfides returned to typical marsh values. Overall, reconnection enhances natural productivity and diversity, although water quality in the perimeter ditch, an artifact of dike construction, remains problematic.Earlier experiments demonstrated that flooding only during the summer mosquito breeding season provided as effective mosquito control as year-round flooding. In standard management, the impoundment is flooded in summer, then left open to the Lagoon through culverts the rest of" the year. Culverts are typically opened when the thll sea level rise first floods the high marsh. Impoundment reconnection is being implemented by a multi-agency partnership. The total reconnected area is expected to reach 9,454 ha by the end of 1998, representing 60% of the impounded wetlands in the entire IRk system. One stumbling block is private ownership of many of the remaining isolated impoundments.-" Uni\ersity of Florida, IFAS. Journal Series No. R-05201. ; Itarbor Branch Contribution Number II52. 94 VOLUSIA t IR ~Mkk Merritt r Island ! i. BR Impounded Wetlands in the Indian River Lagoon 9 Impoundments _ land Water KILOMETERS 0 6.43 12.8

No abstract

A recent study by Middleton et al. (2008; Mar Ecol Prog Ser 371:117-129) characterizing mangrove swamps impounded for mosquito control in Florida has a number of problems that weaken some of the resulting conclusions. We examine some of these issues, which we divide into (1) errors of fact, (2) methodological problems, (3) unwarranted conclusions. Errors of fact include incorrect historical assertions, incorrect site descriptions, and inaccurate statements on the general effects of impoundments. Methodological problems include inadequate sampling for the stated purpose, in particular using results of one-time sampling of very small marsh areas to characterize entire marshes and groups of marshes; defining inadequate controls; use of heterogeneous experimental treatment groups, including highly atypical and unrepresentative sites within experimental treatments; selective sampling; and others. Unwarranted conclusions include the characterization and comparison of marshes and management strategies based upon unrepresentative sampling, and the attribution of differences in habitat function as a result of management strategy without any experimental evidence to suggest such an effect. We make suggestions for mitigating some of these issues.

No abstract