II.A.5 CYCLIC MANAGEMENT

Cyclic impoundment management involves the rotation of several different management techniques in different cells of an impoundment or in groups of impoundments. The rotation may be seasonal, or different techniques may be applied during succeeding years. Objectives may include wildlife enhancement (primarily waterfowl), runoff filtration, saltmarsh vegetation enhancement, and mosquito control.

The most common strategy involves a 3-year rotational cycle. Impoundments are prepared for one year before the rotation starts. The preparatory phase can include saltwater flooding of cells, burning of vegetation, and drawdown to eliminate weedy vegetation such as cattail. Those cells not in active cyclic impoundment management are usually maintained under RIM.

The first active year, a cell is flooded by June and flooding continues with closed culverts through December, at which time the culverts are open. The second year the cell is flooded with Indian River Lagoon water in November and then drawn down in February; therefore there is no flooding for mosquito control during the summer of that year. Some restriction to marsh-estuary water flow may be imposed during this period for salinity or overdraining control. The third year, after the culverts are opened in February, the cell follows standard RIM.

Other cells in the group begin the same cycle in sequence one year behind. The whole process can then be repeated every three years.

Advantages:

1) A great deal of variety can be introduced in a modest area. 2) Complementary strategies can be implemented in neighboring impoundment groups. 3) Management can be adjusted to optimize seasonal utilization of the area. 4) Some strategies that may be beneficial, but which need not be implemented continuously (e.g. drawdowns for sediment oxidation) can be incorporated into the regular management schedule without precluding use of other strategies at other times. 5) If proper salinities can be maintained the area will be attractive to waterfowl, and provide waterfowl food. 6) The impoundment is unsuitable for mosquito and sandfly production during 2 out of 3 years.

Disadvantages:

1) May be labor intensive and expensive to implement.

2) If not carefully designed, may result in fragmented management of areas too small to produce maximum benefits.

3) Access to the marsh by aquatic organisms is limited during 2 out of 3 years.

4) The impoundment is suitable for mosquito and sandfly production during 1 out of 3 years.

CYCLIC MANAGEMENT SCHEMATIC

II.A.6 OPEN MARSH WATER MANAGEMENT (IMPOUNDED)

This mosquito control method reduces immature mosquito production by establishing more regular hydroperiods that are less conducive to mosquito oviposition, and by enhancing water exchange and circulation to allow recruitment and maintenance of larvivorous fish populations. It utilizes ponds, ditches and canals connected to tidal sources.

In areas with a heavy concentration of mosquito-producing depressions, ponds are constructed so as to eliminate the depressions. The ponds serveas 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. Ditchesare 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. Technique is often used in impounded marshes to allow the marshes to remain open for longer periods of time, often throughout the whole year.

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 endangered Atlantic salt marsh snake along the edges of ditches.

3) May allow breaching of dikes in some impoundments, or maintaining culverts open for longer periods of time in others.

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 of 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.A.7 CONTINUOUS BLEED

This type of management is generally accomplished by pumping enough water into the managed system so that its water level is higher than the surrounding estuary. This allows for a constant flow of water out of the managed area (through bottom water release culverts or over flapgate risers) into the estuary. Many modifications of this technique can be done. For example, water levels could be kept at a level that would allow for high tides to augment the input from the pumps. This modification would allow tidal water to enter the marsh at selected tidegates giving the manager much flexibility in determining inflow and outflow points. Because tides tend to be variable, this technique can be combined with tidal trapping allowing the manager to use the pumps when tides are low and natural tides when tides are high. Like many other management schemes, this method can be combined with other techniques for increase management versatility.

Advantages:

1) Creates a flow through system, giving the manager a choice of options on the amount of water released and the location of release points.

2) Can easily vent water from top or bottom by using various tidegate configurations.

3) Tends to improve water quality by continually circulating water in the system.

4) May compensate for the absence of natural tidal flushing which is found in many natural systems.

5) Allows for great versatility in management.

Disadvantages:

1) Running pumps for long periods of time is expensive.

2) Pump failure may cause large fish mortalities because of sudden decrease in water quality.

3) May cause the managed system to depart too much from the type of system which would normally be found in a marsh/swamp environment (are we creating an aquarium?).