Applied Wetlands Science - Chapter 11

Buchsbaum, Robert “Coastal Marsh Management” Applied Wetlands Science and Technology Editor Donald M. Kent Boca Raton: CRC Press LLC,2001 CHAPTER 11 Coastal Marsh Management Robert Buchsbaum CONTENTS Historical Coastal Marsh Management Coastal Wetland Destruction Mosquito Control Biology of Salt Marsh Mosquitoes Habitat Alteration by Grid Ditching Pesticides and Bacterium Exploitation of Coastal Wetlands Marsh Diking Contemporary Marsh Management Recent Trends in Coastal Wetland Loss Mosquito Control by Open Marsh Water Management OMWM vs. Grid Ditching Effect of OMWM on Mosquitoes Effect of OMWM on Marsh Processes Other Potential Management Uses of OMWM Recommendations for Mosquito Control Impacts of Docks and Piers Buffer Zones and Coastal Wetlands Water Quality Aspects of Buffers Pathogenic Microorganisms Nitrogen Wildlife Habitat Aspects of Buffers Examples of Buffer Protection Programs Restoration of Degraded Wetlands with Particular Emphasis on Introduced Species Future Considerations References ©2001 CRC Press LLC HISTORICAL COASTAL MARSH MANAGEMENT When European settlers first arrived in the northeast United States, they often settled around salt marshes (Nixon, 1982). Marshes were valued as a source of food for livestock because there was little open grazing land. Native Americans of the northeastern United States, unlike their counterparts in other parts of North America, did not regularly maintain open lands. Marshes had traditionally been used for grazing sheep and cattle in Europe (Jensen, 1985), thus it was not surprising that they would be similarly valued in the New World. As more and more farmland was cleared for pasture, attitudes toward coastal wetlands changed for the worse. Marshes were at best ignored and at worst were perceived as worthless land that bred mosquitoes and other pestilence. The best use of the coastal wetlands was in being reclaimed and put to some useful purpose. Up until about the 1970s, the two most widespread management activities in coastal wetlands were outright destruction and mosquito abatement. COASTAL WETLAND DESTRUCTION Coastal wetlands have been filled and degraded to create more land area for homes, industry, and agriculture. Estimates of wetland lost since colonial times have not always distinguished coastal from inland wetlands, so we must rely to some extent on estimates of all wetland to estimate coastal wetland losses. Dahl (1990) estimated that the United States has lost 30 percent of its original wetlands acreage (53 percent if Alaska and Hawaii are excluded). An estimated 46 percent of the original wetlands area of Florida and Louisiana, the two states with the largest acreage of coastal wetlands (almost seven million ha combined), have been lost (Watzin and Gosselink, 1992). About 90 percent of California’s original area of wetlands have been destroyed (Figure 1, Watzin and Gosselink, 1992). Evaluations of coastal wetland loss suggest that over one half of the original U.S. salt marshes and mangrove forests have been destroyed, much of it between 1950 and the mid-1970s (Watzin and Gosselink, 1992). Between the mid-1950s and mid-1970s, the coterminous United States lost an estimated 373,300 acres of vege-tated estuarine wetlands, a 7.6 percent loss (Frayer et al., 1983). Such losses and modifications have been particularly acute in San Francisco Bay. Most of the bay’s tidal marshes have been filled by the activities of gold miners, agriculture, and salt production. Hydrologic changes caused by dams, reservoirs, and canals have reduced the freshwater flow to only about 60 percent of its original volume. Similar activities have occurred in other urban areas. Major airports were built on filled tide lands in New York City, Boston, and New Orleans. The upscale Back Bay section of Boston was once a shallow embayment fringed with salt marshes. Old maps of the city indicate extensive areas of water that are nowdry land. Similarly, the original shoreline of Manhattan was irregular with bays and inlets, a far cry from the present almost linear expanse of piers and highways. Marshland, with its rich, peaty soil, was often reclaimed for agriculture in Europe. Both mangroveswamps and salt marshes in Florida havealso been destroyed ©2001 CRC Press LLC Figure 1 Salt marsh dominated by pickleweek (Salicornia virginica) near Stinson Beach, CA; over 90 percent of California’s wetlands, including most of its original coastal marshes, have been destroyed. to create waterfront homes and marinas and for the construction of the Intracoastal Waterway (Florida Department of Natural Resources, 1992a, b). Over 40 percent of the salt marshes and mangroves in Tampa Bay have been lost since 1940 (Florida Department of Natural Resources, 1992a, b). Lake Worth in Palm Beach County has lost 87 percent of its mangroves and 51 percent of its salt marshes. MOSQUITO CONTROL Mosquito control activities in coastal wetlands have involved both physical alteration of the habitat to make it less suitable for mosquito breeding (source reduction), and the use of chemical and/or biological agents to directly kill adult and larval mosquitoes. Although the use of pesticides often receives the most public attention, habitat alteration is ultimately of more concern because of its potential to irreversibly alter coastal wetlands. Biology of Salt Marsh Mosquitoes Mosquito breeding areas on salt marshes and mangrove forests typically occur at the irregularly flooded upper edges of these habitats (Figure 2). Sites may include spring tides associated with the new and full moons. Mosquitoes may also breed among sporadically inundated tufts of high marsh plants, such as salt marsh hay ©2001 CRC Press LLC (Spartina patens) in East Coast marshes. Eggs of most species such as Aedes solicitans, the most common nuisance mosquito in the northeastern United States, are laid on the surface of a marsh typically in shallow depressions or along the edges of drying salt pannes at least several days after the last spring tide. The eggs incubate in the air and hatch only after the subsequent spring tide or rain refills depressions on the marsh surface. The larvae, known as wrigglers because of their corkscrew-like movements, undergo four feeding stages (instars) and a nonfeeding but active pupal stage. Adults emerge in anywhere from several days to several weeks after the eggs hatch depending on the temperature. Figure 2 Typical habitat of salt marsh mosquito larvae during a spring tide; the pools are within a short form smooth cordgrass (Spartina alterniflora) marsh and will usually dry up prior to the next spring tide precluding a permanent fish population. Salt marsh mosquitoes typically produce several broods per year and are said to be multivoltine. Because they are tied to the lunar tidal cycle, the emergence of adults from marshes tends to be synchronized. Coastal residents experience this as periodic waves of mosquitoes, which may occur every 2 or 4 weeks depending on the height of the spring tide and weather conditions. The success of mosquito breeding on a salt marsh depends on a number of factors. If the pool dries out before the larvae can complete all stages and emerge as adults, the larvae will die. Similarly, permanent pools that support predatory fish such as Fundulus spp. and Gasterosteus spp. will not support mosquito larvae and are not a suitable habitat for eggs. Low marsh areas that are flooded daily by tides are not sites of mosquito breeding because they do not provide the prolonged period of air incubation the eggs require, and they are accessible to predatory fish. ©2001 CRC Press LLC ... - tailieumienphi.vn