Marsh Management Strategies: Introduction
Over 16,000 ha of productive coastal salt marshes and mangrove forests along the Indian River Lagoon have been impounded for mosquito control. Research during the past 10 years, has shown that impounding can have severe environmental impacts on the marshes and the adjoining estuary. Of particular concern are degradation of water quality, isolation of habitat needed by sport and commercially important fishery species during critical times in their life cycles, elimination of productive marsh vegetation, possible adverse impacts on estuarine seagrasses, and interruption of the free flow of nutrients and organisms between wetlands and the lagoon.
The same body of research, however, has been used to develop management techniques that mitigate many of these adverse effects while retaining the capability to control mosquitoes without having to use potentially harmful pesticides in these fragile areas. Some of these techniques, such as Rotational Impoundment Management (RIM), have been tested and used repeatedly in the lagoon, while others with equal potential for effecting different environmental benefits have been implemented only infrequently. The major reason for this is that there are no comprehensive, lagoon-wide management strategies that take into account the suitability of individual areas for different purposes and the types of management strategies being used in surrounding areas. Along with the research data available on which to base management decisions, a successful mechanism has been established to promote wise, multi-resource management of Florida's wetlands resources. This vehicle is the legislatively established (F.S. Chapter 388) Subcommittee on Managed Marshes (SOMM), an interagency committee with representatives from : (1) agencies responsible for wetlands resources, (2) institutions involved in wetlands and estuarine research, and (3) agencies responsible for mosquito control (Appendix A). This committee, first established in 1983, is regarded by many as one of the finest examples of interagency cooperation to achieve wide-based consensus on ecologically-sound wetlands management solutions.
For several years, SOMM has endorsed the concept of "block management". This concept involves the grouping of impoundments and marshes into geographically and ecologically meaningful "management areas", so that management decisions can be made in the context of the surrounding areas. The concept was applied by SOMM in developing plans for one such area along the lagoon, The Sebastian Inlet Management Area (SIMA), a region extending from CR 510 in Indian River County north to Hog Point, in Brevard County. The St. Johns River Water Management District, through their Surface Water Improvement and Management Program (SWIM) has funded the implementation of most parts of the management plan in cooperation with the Indian River and Brevard Co. Mosquito Control Districts.
However, without a comprehensive, lagoon-wide management strategy, the block management technique will not be widely applied because impoundment management continues to take place on an impoundment by impoundment basis. As a result, opportunities for improving environmental conditions in the lagoon may not always be recognized, particularly when it may be desirable to implement alternative management practices in an area (e.g., for wading or migratory birds, endangered species, wildlife management, stormwater retention, etc.) to achieve variety in management to foster diversity in food chain linkages.
This project continues development of Lagoon-wide management strategies by identifying and delineating all the appropriate management areas in the Indian River Lagoon, and by developing specific management strategies for these areas in a format that can be directly incorporated in present and future comprehensive planning efforts for the Indian River Lagoon.
The quarterly meetings of SOMM have provided the forum for discussion, fine-tuning, revising and generally supporting the resulting document. This process assures broad agency input into the resulting documents. In addition, presentations on this project have been made to a number of groups with special interest in the Indian River Lagoon (Appendix B) and their input has been solicited.
The approach to development of management strategies has been based upon the need to achieve a balanced overall strategy that takes into consideration past conditions and current status. The heavy human impacts already imposed upon the lagoon and its marshes makes it imperative that we consider current problems and solutions in terms of constraints placed upon our management capabilities by human activities.
Re-establishing physical linkages between marshes and the lagoon in impounded areas is considered the top priority in the overall lagoon strategy given the more specific overall goals of restoring tidal access to the marsh, promoting natural hydroperiods and detrital-based food webs, and restoring natural marsh vegetation. This is not always possible and/or practical, however, and other conflicting needs have not been ignored. Fortunately, the large number of impounded wetlands along the lagoon makes it possible to implement alternative management in some areas without compromising the overall goal of enhancing marsh-lagoon connection (but see below).
Several issues remain important and must be considered when attempting to evaluate management alternatives for an area:
One problem that often arises when trying to implement best management practices in some wetlands is private ownership. In some areas, land owners have not been amenable to work in their property for fear of losing mitigation potential of closed impoundments. In other areas, mosquito control officials are hesitant to pursue re-connection or other management changes because agreements that allow mosquito management in these areas are verbal and non-binding on the owners. To solve these problems, public acquisition of impoundments is being actively pursued by a multi-agency group including the St. Johns River and South Florida Water Management Districts, the counties involved, and the Nature Conservancy.
Not all agencies share identical priorities and often compromises are necessary to reconcile conflicting mandates with best management practices. For example, The U.S. Fish and Wildlife Service manages the Merritt Island and the Pelican Island National Wildlife Refuges to provide habitat for migratory waterfowl, wading and shore birds. This often requires that impoundments be closed during periods not required by mosquito control. However, all agencies involved are actively cooperating to implement ecologically sound compromises that maximizes tidal connection while satisfying the mandates of the USFWS and mosquito control agencies.
Perhaps the most difficult management issue is implementation of alternative management practices at a site when these conflict with the overall goal of marsh lagoon re- connection. Examples of these include temporarily closing an impoundment with heavy bird utilization in the fall to enhance feeding opportunities for the birds, or maintaining an impoundment closed year round because it receives heavy runoff or treated water. Research has demonstrated environmental benefits of marsh- lagoon connection, but research to date does not address the acreage or proportion of marshes that need to be connected to achieve maximum benefits lagoon-wide, nor regionally. Alternative management practices also have documented and perceived benefits, but given our state of knowledge, the trade-offs are difficult to estimate.
One school of thought proposes that the prudent approach is to implement such management only under exceptional circumstances, because marsh lagoon connection results in more natural conditions and many benefits have been documented. On the other hand, some suggest that given the extreme impacts to the lagoon caused by human activities, we should take advantage of the water management capabilities provided by mosquito impoundments to try to mitigate some of the known adverse impacts, and we should introduce variety in management to address some of the unknowns. Other factors complicating the issue include questions on how realistic and desirable it is to attempt to restore conditions to those existing in the Lagoon 100 years ago, and on how much marsh-lagoon exchange actually took place before man's impact (many natural marshes have fronting berms that effectively isolate them from the estuary, at least during parts of the year). Some consider that implementation of management strategies for the benefit of specific groups of species (such as wading or migratory birds) is inappropriate because of limited benefits, while others argue that benefits to the particular target group are never isolated but are always accompanied by ancillary benefits.
In this document, we have proposed alternative management mostly in the wildlife refuges, but there are also a few exceptions in other areas that we have tried to justify when proposed. The fact that management data for surrounding areas is now available has simplified the process somewhat, and although there may be some disagreement on a few of the areas, there is overall accord on the proposed strategies.
Numerous people have contributed to this project. We would specially like to thank David Mook and Jody Rosier, who wrote important sections of this document. We also thank the members of SOMM for the many hours of discussion that considerably improved the final product. Personnel from Volusia, Brevard, Indian River, St. Lucie and Martin Co. Mosquito Control, from the Merritt Island National Wildlife Refuge, and from the St. Johns River Water Management District were extremely helpful in providing information and comments. In particular, we would like to thank Paul Haydt, Scott Taylor, Pete O'Bryan, Jim David, Blake Faulkner, and Harvey Hill for their help with the project. Finally, we thank the members of the special interest groups listed in Appendix B for their input. This project was partially funded by the Coastal Zone Management Program (NOAA, Cooperative Agreement Award No. NA370Z0427), administered by the Florida Department of Community Affairs, and by the Indian River Lagoon National Estuary Program via St. Johns River Water Management District contract number 95W208.