II.A.8 MERRITT ISLAND NATIONAL WILDLIFE REFUGE MANAGEMENT STRATEGY (MIS)

This technique is a special case of a cyclical management strategy, specially suited for the Merritt Island National Wildlife Refuge goals and mandates. It encompasses four different strategies that alternate as needs and conditions dictate as follows:

• Open all year.
• Open fall, winter, spring and closed and flooded in summer with pumping or passive water capture and retention.
• Open spring, flooded summer, fall and winter for waterfowl habitat and mosquito control.
• Open spring and summer, flooded fall and winter for waterfowl.

The Refuge strives to maintain impoundments open as much as possible and to alternate management so that nearby impoundments are not all managed the same at any particular time. In some cases, impoundments are left open for several years to help oxidize sediments and consolidate the substrate, or are closed for 1 to 2 years (with periodic flushing) to control exotic vegetation.

Advantage:

This technique gives the MINWR the needed flexibility to manage the impoundments to satisfy their mandate of providing habitat and food for migratory birds and waterfowl while maintaining as much marsh-lagoon connection as possible both in a geographical and temporal sense.

Disadvantage:

Some impoundments remain closed longer than necessary for mosquito control.

II.A.9 OTHER

A variety of other techniques may be utilized, alone or in combination to attain specific management objectives. These techniques may represent a temporary change in management (e.g. leaving an impoundment open during a specified period of time to oxidize the sediments and then resuming normal management), or they may be permanent management strategies (e.g. stormwater retention). Some (e.g. exotic removal, prescribed burns) may be applied in conjunction with other strategies.

Many variations on the standard management options can be envisioned; some possibilities include: (1) prescribed burning, (2) stormwater processing, (3) overflooding, (4) scheduled exotic removal, (5) wastewater retention, and many others. Specific techniques will vary depending upon the objectives and the structure of the impoundment(s) in question.

II.B.1 OPEN MARSH WATER MANAGEMENT (UNIMPOUNDED)

In areas with a heavy concentration of mosquito-producing depressions, ponds are constructed so as to eliminate the depressions. The ponds serve as reservoirs for predatory fish during low water periods, and as water sources for nearby areas. Radial ditches may extend from the ponds to eliminate breeding in areas near the ponds. Ditches are also used to eliminate scattered breeding depressions and to interconnect the ponds, and deeper ditches are used to connect the system with a tidal source. Ditches are often silled at their connection to the lagoon to prevent over drainage of the high marsh during low tide periods.

Detailed standards and protocols for OMWM have been produced for New Jersey (Bruder 1980; Proc. N.J. Mosq. Control. Assoc. 67:72-76), Maryland (Lesser 1982; Proc. N.J. Mosq. Control. Assoc. 70:29-34), and Delaware (Meredith et al. 1985; Wetlands 5:119-133), and various modifications of OMWM have been devised for dealing with slight tidal ranges and unpredictable tidal events (closed systems, ditch sills, etc.). In Florida, the method has been modified to suit the Indian River's low tidal amplitudes. The use of both open and closed systems, variations in the placement and height of silled connectors, and the use of graded, meandering ditches, are used to accomplish specific management needs.

Because of the small tidal amplitude in the Indian River Lagoon, and other limitations imposed by vegetation structure and equipment, opportunities for OMWM may be restricted along the lagoon. However, the technique may offer significant benefits in specific cases, or when used in combination with other techniques to achieve primary or secondary management goals.

Advantages:

1) Reduces pesticide use.

2) May increase suitable habitat for the Atlantic salt marsh snake along the edges of ditches.

3) In open systems, a connection can be maintained year round between the marsh and the estuary. Usually results in improved water quality and more stable water levels.

4) Minimal system maintenance can be expected for up to ten years.

5) Provides a passive management system that requires little personnel for operation.

6) Increases edge habitat.

7) Variations in techniques provide flexibility for different situations and/or objectives.

Disadvantages:

1) Works best in areas with high tidal energy.

2) Limited applicability in areas dominated by mangroves because the necessary modifications would be difficult to construct.

3) Marsh hydrology changes, with lowering of water table a distinct possibility.

4) May require maintenance and, possibly, continued modification as conditions in the marsh change. Periodic inspections are needed to keep track of changing marsh conditions.

5) May foster the spread of mangroves into salterns and herbaceous halophyte areas and invasion of salterns by herbaceous halophytes.

6) Depends partially upon weather and tidal events, which may cause control failures in part of the marsh. Larval inspections are still necessary.

II.B.2 DITCHED

This category includes marshes that were ditched in the past (particularly during the 1940s and 1950s) in attempts to control mosquitoes; It does not include ditches constructed as part of OMWM systems or shallow ditches that may be used to complement RIM. The usual strategy was to construct an evenly-spaced grid system of deep ditches that would drain the marsh and often lowered water tables. This approach was not successful because considerable breeding still occurred between the ditches. Furthermore, spoil deposition in the marsh interfered with sheet flow and provided sites for invasion by exotic species and upland plants.

Many of these ditches have fully or partially closed with time, particularly at the marsh-estuary edge. Although new ditch systems of this type are not likely to be constructed, maintenance of old ditches may be advisable in some cases as some of the ditches may promote water circulation and may be used as part of other management strategies. Partially closed ditches are often heavy mosquito producers, and may require maintenance to prevent mosquito production and water stagnation. Finally, spoil piles or berms created by this technique often block water movement and may have to be removed.

Advantages:

In some marshes where the deep ditches have remained functional, mosquito breeding has been reduced, thus reducing the need to use pesticides for mosquito control.

Disadvantages:

1) Frequently not effective for long term mosquito control.

2) Spoil piles created by the deep ditching interfere with sheet flow, block circulation, and promote invasion by exotics and upland plants.

3) Often lowers marsh water table.

4) Has made traversing some marshes virtually impossible, thereby hindering inspections for larval mosquitoes.

5) Ditch banks can be suitable habitats for sandflies.

II.B.3 OTHER

As with impounded marshes, a variety of other techniques may be utilized, alone or in combination to attain specific management objectives. These techniques may represent a temporary change in management or they may be permanent management strategies. Some (e.g. exotic removal, prescribed burns) may be applied in conjunction with other strategies.

Many variations on the standard management options can be envisioned. Specific techniques will vary depending upon the objectives and the structure of the marshes in question.