ABSTRACT: Geographic Information Systems (GIS) are currently being used by a variety of agencies in situations where accurate data on geographic information are required. In the Rhode Island Department of Environmental Management Mosquito Abatement Coordination Office we use GIS to map potential mosquito breeding habitats within salt marshes. Using this system, highly accurate maps of marsh features such as ditch networks, fish reservoirs, shallow pans and vegetation are produced. These maps can later be used to aid in the design of Open Marsh Water Management (OMWM) strategies.

INTRODUCTION

New England salt marshes were extensively ditched to control mosquito populations in the 1940s. Since then, many of these ditches have fallen into disrepair, often resulting in the creation of habitats conducive to mosquito breeding. In addition, the alteration of the water regime to marshes due to unmaintained ditches can lead to mosquito breeding habitats in shallow pools and pans where fish are unable to access. The numbers of mosquitoes generated from these areas can be quite astronomical, often in excess of 50 mosquito larvae per dipper, and occasionally up to 1000 per dip (personal observation). Recently, the Rhode Island Department of Environmental Management Mosquito Abatement Coordination Office in conjunction with the University of Rhode Island Public Health Partnership in Infectious Disease Control has begun to use geographical information systems to map salt

marshes in an effort to identify marshes with mosquito problems and to aid with the

design of OMWM strategies for these marshes. Geographical information systems (GIS) deal with geographic or locational information. GIS generates high quality maps and can analyze spatial information, such as the square footage of a particular feature. Our office uses a geographical positioning system or GPS unit to collect locational data from which maps are produced.

METHODS & MATERIALS

The protocol that our office uses is to identify marshes that might have mosquito breeding habitat and to map the geographical features of the marsh. The first map produced is a perimeter map of the marsh. The perimeter map is brought into the field and features are drawn on it as they are mapped. This serves as a double check for identification and editing purposes when the maps are finalized in the laboratory. Geographical features of the marsh (such as tidal creeks, ditches, pools of water, and vegetation) are mapped by walking each feature with the GPS unit. A typical GPS unit consists of a receiver antenna, battery pack, and hand held receiver. Additional information such as presence of fish or numbers of mosquito larvae for any particular feature can be stored in the data logger. Permanent dip stations are also established in mapped marshes in an effort to estimate the abundance of mosquito larvae and to identify areas within the marsh that have mosquito breeding problems. This information is then linked to the map via GIS software.

RESULTS AND DISCUSSION

Our office has been able to produce sub-meter accurate maps of salt marshes using GPS/GIS equipment. Figure 1 is an example of the type of map produced. The requirements for this system are a GPS unit, computer, and GIS software. A GPS unit costs anywhere between $9,000 to $11,000. A computer capable of handling GIS software costs upwards of $4,000 (standard options may include: 1 gigabyte hardrive, 32megabytes of RAM, 133 megahertz processor, 21" monitor, CD-ROM, and tape backup drive). The software required to edit, manipulate and print GIS maps is approximately $6,000. Additionally, a plotter to print the GIS maps costs $6,000-$9,000. GPS/GIS hardware and software are expensive, however much of the equipment or access to equipment may be available through cooperating universities, state or federal agencies.

ACKNOWLEDGMENTS

Thanks to Dr. Alan Gettman, Daniel Markowski and Sean Healy for their help in the field and in the laboratory. Post Doctoral Research funding to M.J. James-Pirri is from the Rhode Island Public Health Partnership in Infectious Disease Control, a partnership between the University of Rhode Island and Rhode Island Department of Environmental Management (Mosquito Abatement Coordination Office and the Narragansett Bay Estuary Project).

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