ABSTRACT: Late in 1991 the Rhode Island Department of Environmental Management's Division of Fish and Wildlife, the Rhode Island Department of Transportation, and the U.S. Army Corps of Engineers initiated a salt marsh restoration project at the Galilee Bird Sanctuary in Narragansett, Rhode Island. The project was designed to restore effective tidal circulation to 25 hectares of former salt marsh which has received little or no tidal flow since 1956, when the Galilee Escape Route was built across the northern part of the marsh. In October 1997, the Sanctuary was reopened to full tidal flow. Introduction of salt water to the Sanctuary on a regular basis has the potential to significantly increase mosquito populations in the vicinity. Since the overall objective of the restoration project is to enhance the quality of this wetland and develop public support for such efforts, increased mosquito production could create a major public relations problem. Open Marsh Water Management (OMWM) has been initiated to reduce this threat. An estimate of breeding potential and likely species of concern have been identified. A phased approach to the problem has been designed and much of Phase 1(which calls for a network of ditches that allows for good tidal circulation in the marsh, precluding the production of mosquito breeding habitat) has been implemented. Upon completion of this Phase, the project will be closely monitored for effectiveness, and any future mosquito breeding will be addressed in a Phase 2 design. Limitations to the effectiveness of the Phase 1 design center around the accuracy of projected salt meadow-upland interfaces.
In 1956 a four- lane highway, known as the Galilee Escape Route, was constructed from Point Judith Road to the Port of Galilee (Myshrall and Golet 1996); (Figure 1). The purpose was to provide residents of Galilee and Great Island with a safe path to the mainland during hurricanes. The east-west highway traversed a 51-ha salt marsh, greatly reducing tidal flow to the southern three quarters (37-ha) of the estuarine system. The southern portion which was acquired by the State in 1956 and which is managed by the Department of Environmental Management's Division of Fish and Wildlife, is known as the Galilee Bird Sanctuary. In addition to this alteration, the western portion of the marsh had been subjected to deposition of dredged materials associated with construction and maintenance of the breachway and port at Galilee. The impacts of these activities and the resulting freshwater impoundment, caused serious degradation of the Sanctuary as a provider of habitat for shorebirds, migratory waterfowl, fish and shellfish. Most of the salt marsh vegetation was replaced by woody thickets and an extensive stand of the common reed (Phragmites australis).
In 1991 a memorandum of agreement (MOA) was set forth by the RI Department of Transportation (RIDOT) and the RI Division of Fish and Wildlife (RIDFW) to undertake restoration efforts at the Sanctuary. RIDOT became involved as a result of mitigation requirements associated with construction of the Jamestown-Verrazano Bridge project (Applied Bio-systems 1991). The MOA called for RIDOT to develop engineering designs to restore full tidal circulation to the area south of the Escape Route while RIDFW was charged with the collection of baseline ecological data for the Sanctuary. In turn, RIDFW contracted the University of Rhode Island's Department of Natural Resources Science, under the supervision of Dr. Frank Golet, to undertake the ecological studies (Myshrall and Golet 1996).
The Galilee salt marsh restoration was declared a 'Coastal America' project by the President's Council on Environmental Quality in early 1992 and informational workshops and hearings commenced in early 1993.By 1994, a host of Federal, State, and local agencies had agreed to participate in the restoration project. These included the United States Army Corps of Engineers(COE) New England Division, the U.S. Fish and Wildlife Service (FWS), U.S. Environmental Protection Agency, Town of Narragansett, Ducks Unlimited, and the National Fish and Wildlife Foundation.
The COE undertook an environmental assessment to determine the best alternative for the restoration design (U.S. Army Corps of Engineers. 1995 ). The study determined that dredged material in the northwest portion of the Sanctuary marsh should be removed and a pre-existing channel in the same vicinity should be reconstructed. Upon completion this area would be connected to tidal flow on the northern side of the Escape Route by means of two 1.8-m x 3.0-m box culverts equipped with self regulating tidegates. Similarly, at the northeastern corner of the marsh, two small, ineffective 75-cm culverts were to be replaced with two more 1.8-m x 3.0-m box culverts, also equipped with self- regulating tide gates. The self- regulating tide-gates were designed to close during abnormally high tides. During most of the lunar cycle, the restoration area would be subject to daily tidal inundation. It was hoped that, in time, this area would revert to a condition similar in productivity and appearance to the marsh found north of the Escape Route.
Construction commenced during the fall of 1996 and the dredged material removal and culvert installation specified under a $1,844,650 contract issued to C. Pezza & Sons by the COE were completed by September of 1997.
Since the Galilee Bird Sanctuary was now to be subject to daily tidal inundation, the potential for high populations of salt marsh mosquito species now existed. To offset the devastating impact these mosquitoes could have, both as a public health nuisance and public relations problem, a program of Open Marsh Water Management(OMWM) was commenced during the early fall of 1997.
This report describes the planned OMWM program, the rationale
behind the phased approach being undertaken, and the methods employed
to design and construct the installed system. Before detailing
these topics, however, it is important to discuss the biology
of the mosquito species to be controlled and the basic principles
of OMWM.
There are three species of mosquitoes that are most likely to breed in a salt marsh environment like the restoration site at Galilee; they are Aedes sollicitans, A. cantator, and A. taeniorhynchus. All are perfectly adapted to a life cycle within the marsh. Aedes mosquitoes lay their eggs individually on dried surfaces that are subject to flooding. Breeding habitats may take the form of drawn down woodland pools; deep tire ruts; artificial containers (such as cans or tires); and, in the case of salt marshes, shallow pans or depressions in the high marsh. In all cases, the larvae only hatch after the deposition site has been covered with water. Sufficient water must remain in the breeding depression for the larvae to undergo four instar stages, and a pupa stage before complete metamorphosis into an adult. Normally, during summer months, this entire process takes 4-7 days.
In salt marshes, the salt meadow zone (designated by stands of
Spartina patens, Distichilis spicata and Juncus gerardii) is infrequently
inundated and provides larval habitat for mosquitoes but poor
habitat for predaceous fish. Breeding depressions often flood
as a result of rainfall, and in these instances predators are
most definitely excluded. Such breeding sites thus have the potential
for producing large swarms of A. sollicitans, A. cantator, and
A. taeniorhynchus.
Aedes sollicitans
The larvae of this species occur mostly in coastal salt marshes, although they have also been found in brackish water swamps in many of the inland states, particularly in oil fields (Carpenter and Lacasse 1955). The adults are strong flyers and often migrate in large numbers to human population centers many miles inland from their breeding sites. They are occasionally found up to 100 miles from their birthplace. The females are persistent biters and attack any time of day or night. The species has been implicated as a vector of Eastern Equine Encephalitis in the Eastern Seaboard states. Its distribution covers 36 states and 4 provinces of Canada (Darsie and Ward 1981).
Aedes cantator
The larvae are found in coastal marshes including both fresh and
salt water, but fresher water seems to be preferred. Freshwater
pools formed by rain and drainage from the uplands are preferable;
larval production is always much heavier in areas of the marsh
adjacent to the upland (Carpenter and Lacasse 1955). Aedes cantator
tends to be the dominant species during the spring and early fall,
with lesser numbers during the summer months. They are essentially
evening biters, although they will bite during the day if their
resting areas are invaded. The adult is also capable of extended
flights from larval habitats. Its geographical distribution includes
13 eastern states and 6 Canadian provinces (Darsie and Ward 1981).
Aedes taeniorhynchus
Rhode Island is at the northernmost limit of the geographical distribution of this species. Its habitat requirements and activity are very similar to those of Aedes sollicitans, but it will likely be of little importance at the Galilee Sanctuary since it has rarely been observed in large numbers in Rhode Island.
During the Great Depression, the Civilian Conservation Corps and the Works Progress Administration grid-ditched an estimated 90% of New England coastal marshes (Bourne and Cottam 1950). The ditch system was designed to remove surface water and lower the water table in the marsh. This was purportedly done in the name of mosquito control, yet, in many instances even marshes where mosquitoes did not breed were ditched. The effectiveness of this ditching and its impact on marsh processes has been a matter of great debate (Buchsbaum 1994). Major issues appear to be the reduction in waterfowl, which resulted from the lack of standing water and the introduction of high marsh shrubs into pristine stands of marsh grasses, which resulted from improper disposal of spoils during ditching.
In response to the concerns expressed over grid-ditching, a new
method referred to as Open Marsh Water Management (OMWM) was developed
in the mid-Atlantic states (particularly New Jersey) during the
l950's (Ferrigno et al. 1975). OMWM calls for the selective use
of tidal and non-tidal systems that effectively control mosquitoes
while retaining water on the marsh surface. The surface water
consists of reservoirs and canals in mosquito breeding areas that
allow for control of mosquitoes by predatory fish. Sumps are designed
within these reservoirs to allow for fish survival during neap
tides. This design is much more selective than the generalized
grid-ditching of the 1930's. Issues of spoil disposal have been addressed with the development of specially designed equipment with rotary heads that spread spoils thinly over the marsh surface.
As well as enhancing waterfowl habitat, OMWM has been extremely effective in its stated purpose, showing reductions of from 75% to 99% in mosquito populations (Hruby et al. 1985). In addition to fish control of larval populations, the constant standing water eliminates the bare substrates needed for egg-laying and reduces larval populations.
In time, the Galilee project will incorporate many aspects of
OMWM, although to achieve this, a multi-phased approach must be
implemented.
Mosquito surveillance
Prior to any restoration work being undertaken at the site, I surveyed the entire project area for mosquito breeding habitat. I visited the site on numerous occasions during the spring and summer of 1996. Larval inspections were made throughout both north and south of the Escape Route. Inspections were made using a standard larval "dipper." I collected specimens of larvae from the various breeding habitats and verified species identification from the resulting emergent adults.
Development of OMWM Plans
The entire Galilee Bird Sanctuary shows evidence of an old Depression-era grid-ditch system. This finding further supported the concerns of breeding potential. Since those attempts to manage mosquito populations in the 1930's, however, sea level has risen about 10-15cm (Golet, personal communication). Thus breeding sites after restoration might be located in different locations from earlier sites. Reconstruction of the old ditches would not, in itself, appear to be a viable mosquito control method. Somehow, a determination had to be made as to where the greatest potential for breeding would be after restoration. After that, an appropriate plan could be developed.
As part of the University of Rhode Island's baseline ecological
studies, extensive elevation data were collected for the entire
Sanctuary (Myshrall and Golet 1996). In predicting post-restoration
plant communities, the rise in sea level was expected to be of
great significance. Not only was a reversal to salt marsh predicted
but much of the Sanctuary would also be wetter than it had been
prior to Escape Route construction. A high proportion of the marsh
was predicted to support Spartina alterniflora. Salt meadow would
also be present, but at higher elevations than in the 1950's.
Using the elevation data for the Sanctuary and an understanding
of elevation ranges of the various salt marsh plant species north
of the Escape Route, Myshrall and Golet (1996) created a predicted
vegetation map for the Sanctuary for the post-restoration period.
The map depicts low marsh, high marsh, and the anticipated salt
meadow-Phragmites australis interface. This interface was deemed
to be most critical as a site for mosquito breeding.
Restoration Mosquito Populations
North of the Escape Route, A. sollicitans larvae were found breeding in two small pans near the road. Adults were also much in evidence. South of the road, in the Galilee Bird Sanctuary, two distinct areas were revealed. An old causeway, believed to have been constructed by farmers in the distant past, diagonally bisects the Sanctuary (Figure 2). Areas north and east of the causeway (Zones D and E) support salt marsh and brackish marsh that were maintained by flow from the twin 75-cm culverts. These brackish to saltwater conditions supported the production of A. cantator in several locations and, although not observed, A. sollicitans was also considered likely.
Over the past 40 years, areas to the south and west of the causeway (Figure 2, Zones B and C) have reverted to a completely freshwater regime. Salinity
measurements taken in this area rarely exceeded 0 ppt (Myshrall
and Golet 1996), and tall robust stands of P. australis dominated
the area. Standing water was abundant, but repeated attempts to
detect breeding had revealed very little. At two locations, an
isolated larva was found. In both instances they proved to be
of a freshwater Culex complex. Very few adults were detected and
I concluded that the entire area was therefore low in mosquito
productivity. However, because this area was to be subjected to
a tidal regime after restoration, there was serious concern over
possible future salt water mosquito production.
OMWM Design
Using the predicted habitats map (Myshrall and Golet1996), I designed an initial system of tidal channels (Phase 1). A detailed design map accompanies this report, and completed portions of Phase 1 are depicted in Figure 3. The system had several objectives: 1.) To ensure tidal circulation throughout the Sanctuary while minimizing the amount of ditches constructed; 2.) To bring tidal water to the newly predicted upland edge wherever possible; and 3.) to use existing ditches. Ditches were designed to be 61 cm deep and 61 cm or 122cm wide depending upon the anticipated volume of tidal flow. Channels were dug at least 60 m apart; this distance was considered sufficient to remove water from the marsh surface quickly enough to prevent significant breeding through the main body of the marsh.
Care was taken to ensure that new ditches were located in areas
previously believed to be breeding sites ( as indicated by existing
ditches). Where breeding was likely at the predicted upland edge,
I designed ditches that were parallel to that edge. The rationale
for this was to avoid sheet flow of freshwater onto the marsh
surface and, consequently, to discourage the growth of P australis
in the post-restoration period. After implementation of Phase
1, areas around the perimeter of the newly restored marsh would
be closely monitored for evidence of breeding habitat. OMWM methods
could then be applied (if necessary) under a Phase 2 program.
Phase 1 Construction
Once the Phase 1 system had been designed, construction was initiated. Three pieces of equipment were used during the late summer of 1997. Two were low-ground- pressure track excavators equipped with rotary ditching heads specifically designed for use in OMWM. One, which also came with a bucket attachment, was provided by the U.S. Fish and Wildlife Service and the other by the State of Connecticut Wetlands Restoration Project. The third piece was a small bulldozer which was used to spread spoils and widen paths through dense vegetation; it was supplied by the Fish and Wildlife Service.
The locations of all proposed channels were flagged and trampled
to create sight lines visible from the equipment. This arduous
task was undertaken by URI researchers and members of the RI Mosquito
Abatement Office. Phase 1 channels were constructed prior to the
opening of the new culverts. The vast majority of the Phase 1
channels were finished before the equipment had to be returned
. In mid-October, the tide gates were made operational and the
Sanctuary was opened to full tidal flow.
Attempting to make predictions of mosquito breeding potential and designing control measures before wetland restoration has been achieved is an inexact science to say the very least. The unknowns far outweigh the knowns, and any proposed control measures at this point in time can only be very general in nature.
The biology and habitat requirements of salt marsh mosquito species are fairly well defined. The missing link is an accurate estimate of the type and amount of habitats that will be available to these mosquitoes for breeding. The predicted habitats map (Myshrall and Golet 1996) is the best tool available, but it is based upon tidal elevations obtained in an open estuarine
system (north of the Escape Route). Although the new culverts will allow for much greater tidal inundation in the Galilee Bird Sanctuary than prior to restoration, it is not yet clear how much water will reach each point in the Sanctuary how frequently or for how long. There seems to be some loss of tidal "head" between the culverts and the most distal portions of the Sanctuary. Such a head loss could affect the accuracy of the predicted habitats map. Consequently, the restorable area may be smaller than previously anticipated..
For these reasons, it was important to not be too specific with the initial phase of OMWM planning. Present-day thinking with regard to OMWM emphasizes the incorporation of ponds and internal channels (not connected to the tide) to maintain waterfowl habitat in the marsh. Although this is an admirable goal, the work must be done with mosquito control as the primary purpose. The addition of such designs should only be considered if large-scale breeding warrants their use. A determination as to their need and effectiveness will require several seasons of study. As an interim measure, however, it may be useful to construct spur ditches between tidal channels and selected breeding sites as early as the end of the first year of restoration. This type of work could be considered Phase 2 construction and could be implemented at the same time as the remainder of Phase 1.
Through the restoration of tidal flow, waterbird habitats at the
Galilee Bird Sanctuary can be enhanced, and this can be achieved
with a minimum threat of hordes of mosquitoes. With careful future
design and some short-term integrated pest control measures, a
potentially major public dispute can be avoided.
Applied Bio-Systems. 1991. Conceptual design report for the Galilee Bird Sanctuary Restoration/Enhancement Project. Prepared by Applied Bio-Systems, West Kingston, RI, for RI Department of Transportation, Division of Public Works. 41pp. + appendices and maps .
Bourne, W.S., and C. Cottam. 1950. Some biological effects of ditching tidewater marshes. Research Report 19. U.S. Fish and Wildlife Service. 30 pp.
Buchsbaum, R. 1994. Coastal marsh management. Pages 331-361 in D.M. Kent, Editor. Applied wetland science and technology. CRC Press, Boca Raton, Fla.
Carpenter S.J., and W.J. LaCasse. 1955. Mosquitoes of North America. University of California Press, 360 pp.
Darsie, R.F.,Jr., and R.A.Ward. 1981. Identification and geographical distribution of the mosquitoes of North America, north of Mexico. American Mosquito Control Association; Fresno, California. 313 pp.
Ferrigno, F., P.Slavin, and D. M. Jobbins. 1975. Salt marsh water management for mosquito control. Proceedings of the 62nd Annual Meeting of the New Jersey Mosquito Control Association: 32-38.
Hruby, T., W.G. Montgomery, R.A. Lent, and N. Dobson. 1985. Open marsh water management in Massachusetts: adapting to local conditions and its impact on mosquito larvae during the first season. Journal of the American Mosquito Control Association 1:85-88
Myshrall, D.H.A., and F.C. Golet. 1996. Baseline inventory and ecological profiles of coastal habitats at the Galilee Bird Sanctuary, Narragansett, RI.: Phase II. Final Report. Federal Aid in Wildlife Restoration Project No. W-23-R-38/39, Study No. III, Job No. 4. Rhode Island Division of Fish and Wildlife, Wakefield, RI. 100 pp.
US Army Corps of Engineers. 1995. Galilee salt marsh
restoration, Narragansett, Rhode Island. Feasibility (Section
1135) Report and Environmental Assessment. U.S. Army Corps of
Engineers, New England Division, Waltham, Mass.