Applied Wetlands Science - Chapter 11 pot

Buchsbaum, Robert “Coastal Marsh Management” Applied Wetlands Science and Technology Editor Donald M. Kent Boca Raton: CRC Press LLC,2001 ©2001 CRC Press LLC 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 now dry 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 mangrove swamps and salt marshes in Florida have also been destroyed ©2001 CRC Press LLC 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 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. ©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. 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. 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. ©2001 CRC Press LLC Habitat Alteration by Grid Ditching Although the most radical habitat alteration for mosquito control is filling the marsh, most mosquito control activities have involved water management of some kind. Habitat alteration for mosquito control in coastal wetlands reached the zenith of activity in the United States during the Depression (Provost, 1977). Both the Civilian Conservation Corps and the Works Progress Administration had programs to reclaim marshes by digging ditches at regular intervals on the marsh surface. Although these ditches were ostensibly intended to remove standing water from the marsh surface and to lower the water table, they really were built without regard for where pannes existed or mosquitoes actually bred. As a result, many marshes or sections of marshes that did not breed mosquitoes were ditched. At the time such considerations were not considered significant because a major purpose of the ditching projects was to put people to work. The grid ditching pattern, estimated to have occurred in over 95 percent of northeast marshes, is evident from an airplane. The effectiveness of controlling mosquitoes by grid ditching marshes, and its impacts on marsh processes, has been debated for the last 40 years (Bourne and Cottam, 1950; Lesser et al., 1976; Provost, 1977). The debate was largely initiated by the publication of observations that waterfowl use of a marsh in Kent County, DE, had declined after the marsh was subjected to grid ditching (Bourne and Cottam, 1950). Bourne and Cottam noted declines in invertebrate populations in the ditched portion of this marsh compared to an unditched section. They also noted the dom- inance of high marsh shrubs, groundsel tree ( Baccharis halmifolia ), and salt marsh elder ( Iva frutescens ) along the edge of ditches. Bourne and Cottam predicted that these high marsh shrubs would continue to spread onto the ditched marsh at the expense of the previously existing smooth cordgrass, Spartina alterniflora , as long as the ditches remained functional. This initiated a long standing debate about grid ditching between wildlife managers, whose goal was to manage salt marshes for waterfowl, and mosquito control agencies, whose goal was to reduce mosquito populations. In retrospect, there really is very little evidence on either side about the harmful effects of grid ditching on marsh wildlife (Provost, 1977). The marsh ditching debate centered on the purported lowering of water tables and gradual drying out of marshes. Clearly, a ditch that drains a panne will negatively affect wildlife that depends on that panne. But because marsh peat has such a strong affinity for water, the water table itself may only be lowered in the immediate vicinity (ca. 1 m) of the ditch (Balling and Resh, 1982). Thus, ditches are not likely to cause an overall lowering of the marsh water table. Lesser et al. (1976) reexam- ined the Kent County, DE, marsh in the 1970s and found that, contrary to the prediction of Bourne and Cottam, smooth cordgrass still dominated much of the ditched marsh even though the ditches were maintained in good working order. After the cessation of navigational dredging in the channel, which had caused a general lowering of the water table in the marsh, the area of high marsh shrubs had actually declined, and smooth cordgrass had increased (Provost, 1977). Dredging of navigable waters adjacent to marshes (Lesser et al., 1976) often complicates studies of the effect of ditching. ©2001 CRC Press LLC The most intensive studies of the effects of ditching on marsh vegetation and marsh organisms have been carried out in San Francisco Bay, New Jersey, and Delaware marshes. Putting aesthetic considerations aside, ditching a marsh obviously increases the amount of tidal water flowing into the high marsh, creating narrow bands where low marsh habitats penetrate into high marsh. Strips of smooth cordgrass penetrate salt marsh hay habitat along ditches in East Coast marshes. Ditching allows the tall ecophenotype of smooth cordgrass (Valiela et al., 1978), which dominates the lower part of the intertidal zone along the edges of tidal creeks, to extend into the high marsh. Increased productivity of marsh vegetation and invertebrates can result from this change (Shisler et al., 1975; Lesser et al., 1976; Balling and Resh, 1983). The improper placement of dredge spoils and other struc- tural alterations of the habitat, however, compromise such factors. Ditching increases the heterogeneity of the marsh, both in terms of physical characteristics and the biota. The banks of the mosquito ditches are characterized by lowered salinities compared to the adjacent high marsh because regular tidal flushing prevents the build up of hypersaline conditions (Balling and Resh, 1982). In addition, the substratum along the edge of ditches is likely to be better oxygenated than areas further back because of the lowered water table at low tide (Mendelssohn et al., 1981; Howes et al., 1981; Balling and Resh, 1982). In San Francisco Bay, pickleweed ( Salicornia virginica ), a low marsh species, tends to have higher pro- ductivity along ditches than elsewhere on the marsh (Balling and Resh, 1983). Balling and Resh attribute this higher productivity to the tendency of near-ditch areas to have lower salinities than the surrounding marsh. In less saline marshes, the tendency of pickleweed to be outcompeted by baltic rush ( Juncus balticus ), a brackish water species, is also attributed to lower average salinities along ditches. The response of invertebrates to ditching in San Francisco Bay varies seasonally. The diversity of arthropods decreased away from ditches during the dry season in San Francisco Bay salt marshes (Balling and Resh, 1982). The reverse was true during the wet season except in a natural channel and an old ditch that had relatively greater biomass of vegetation and more complex structure than most of the ditches present (Balling and Resh, 1982). Balling and Resh conclude that the arthropod community adjacent to mosquito ditches will eventually resemble that adjacent to natural channels. Along the east coast, a number of studies indicate that ditching has no marked effect on invertebrate populations of salt marshes (Shisler and Jobbins, 1975; Lesser et al., 1976; Clarke et al., 1984). Lesser et al., for example, found an increase in populations of fiddler crabs ( Uca spp.) and the salt marsh snail ( Melampus biden- tatus ) in ditched marshes compared to controls. Ditching may very likely enhance fish populations of salt marshes. Fish density and diversity increased in ponds when these were connected to a ditching system ((Resh and Balling, 1983). As long as ponds are not drained, ditching increases the amount of available marsh habitat to fish by increasing the amount of open water at high tide. It also allows the fish access to parts of the marsh that are normally not available to them. The ditches serve as corridors by which fish may enter the vegetated surface of the marsh at high tides (Rozas et al., 1988). This movement of fish, particularly the mummichog ( Fundulus heteroclitus ), is important to the productivity of marsh fish in that it allows ©2001 CRC Press LLC the fish to feed on invertebrates of the marsh surface, resulting in more rapid growth rates (Weissberg and Lotrich, 1982). Ecologically, it is a mechanism by which the productivity of the vegetated surface of the marsh is transported into the surrounding estuarine habitats as these fish become prey for larger fish or birds. Using flume nets, more than 3 times as many individual fish and 14 times the fish biomass per area were caught in intertidal rivulets of tidal freshwater marshes than in larger creek banks (Rozas et al., 1988). These intertidal rivulets are structurally similar to mosquito ditches. Ditching of salt marshes has historically been considered harmful to populations of salt marsh birds (Urner, 1935; Bourne and Cottam, 1950). Clarke et al. (1984) found lower numbers of shorebirds, waders, terns, and swallows on ditched marshes compared to adjacent control marshes that had substantial areas of pannes. Because there were no differences in invertebrate populations, they attributed this observation to difficulty of foraging along ditches, possibly because of their steep sides. Other than swallows, the number of passerines (songbirds) was unaffected. Perhaps the most destructive aspect of ditching to salt marsh ecosystems has been related to the placement of dredge spoils. In many cases, spoils have simply been left along the side of the excavated creek bank where they form levees that are rarely, if ever, inundated by the tides. These levees are typically colonized by species of plants normally found at the upland edge of the marsh, such as the salt marsh elder in east coast marshes. If the levees are high enough, the normal flow of high tides over the surface of the marsh is impeded. The negative impact of dredge spoil dispersal can be avoided by proper man- agement procedures designed to ensure that the spoils do not form levees along the border of mosquito ditches. A rotary ditcher, for example, spreads dredge spoils thinly over the marsh surface and has a temporary fertilizing effect (Burger and Shisler, 1983). Using the dredge spoils from ditches to create small islands that do not impede the general sheet flow of water over a marsh during a high tide may actually be beneficial to wildlife that require a mixture of upland and wetland habitats. Shisler et al. (1978) found that clapper rails ( Rallus longirostris ) frequently nested on spoil islands in New Jersey marshes. Pesticides and Bacterium Pesticides are still used to control salt marsh and mangrove mosquitoes. Broad- spectrum pesticides, such as organophosphates (e.g., malathion) or pyrethroids (e.g., resmethrin), are sprayed on marshes in an attempt to kill emerging adults as they fly off the marsh. In Essex County, Massachusetts, malathion use has been timed to coincide with the emergence of adults from the marsh before they have had a chance to disperse to upland habitats (personal communication, W. Montgomery, Essex County Mosquito Control Project). These pesticides break down relatively quickly in the environment compared to those in wide use 20 years ago, such as organochlo- rines (e.g., DDT, dieldrin). However, organophosphates are toxic to nontarget organ- isms, particularly aquatic invertebrates and fish. Bacillus thuringiensis israelensis (Bti) is a bacterium that produces a protein toxin that affects mosquito larvae. Bti may be spread by hand or aerially over salt ©2001 CRC Press LLC pannes that contain mosquito larvae. Although more specific than pesticides, Bti may still have some impact on nontarget dipterans that may occur in marshes, particularly chironomids (Lacey and Undeen, 1986). Chironomid larvae are an important item in the diet of sticklebacks (Ward and Fitzgerald, 1983). Bti treatment of salt marsh pools may potentially impact the food sources of these fish that are essential in the trophic structure of salt marshes because they are consumed by other fish, birds, and mammalian predators. Bti is less toxic to chironomid larvae than to mosquito larvae (Lacey and Undeen, 1986), thus avoiding nontarget effects on chironomids requires judicious measurement of final concentrations. EXPLOITATION OF COASTAL WETLANDS When coastal wetlands were not being destroyed outright, or ditched for mos- quito control, they were sometimes managed to provide useful products. Humans have used the vegetation itself. Salt marsh hay is still cut from northeast marshes. Although not the most ideal fodder for livestock, it has the advantage of containing virtually no weed seeds; thus, it is much sought after by gardeners for mulch. Nixon (1982) cited a 19th century survey that showed that farmers in Rhode Island cut 1557 metric tons of salt marsh hay from more than 1015 ha of marsh in 1875. The salt marsh hayers benefited from the creation of mosquito ditches that drained pannes and created a regular grid pattern on the marsh, making it easier to move equipment around on the marsh. As the hayer’s were primarily interested in the salt marsh hay, a high marsh species, they would sometimes build dikes or other barriers to restrict regular tidal inundation. Marshes have also been managed to provide wildlife for hunting. Typically, impoundments have been created on salt marshes to provide open water habitat for waterfowl. Impoundments often create a new set of problems, most notably invasion by aggressive, alien plant species such as common reed ( Phragmites australis ) and purple loosestrife ( Lythrum salicaria ) that are more tolerant of brackish conditions. Impoundments may reduce the exchange of tidal water into the marsh and, thus, reduce the ability of coastal wetlands to export organic matter into surrounding coastal waters (Montague et al., 1987). They also act as barriers to the movement of marsh fish, as well as anadromous fish, that may be passing through marshes. In tropical regions, tannins are extracted from mangrove bark, and the wood is used for charcoal. Mangrove swamps, however, have not historically been managed to the extent that salt marshes have. MARSH DIKING Diking of marshes has been carried out to create impoundments for wildlife, for flood control, to create pleasure boating and swimming areas, and for the construc- tion of causeways for roads and railroads. Often this causes habitat degradation behind the dike because tidal flushing is reduced and the water stagnates. ©2001 CRC Press LLC Diking can have drastic effects on marsh vegetation and, by extension, seriously alter populations of marsh fauna. If salinities behind the dike are diminished due to reduced tidal flushing, aggressive brackish water species such as the common reed and cattails ( Typha spp.) will replace the natural salt marsh vegetation (Figure 3; Niering and Warren, 1980; Roman et al., 1984; Beare and Zedler, 1987). Overall productivity of the vegetation may increase in response to lowered salinities or decrease if the tidally restricted area becomes hypersaline (Zedler et al. 1980). Often, marsh creeks behind dikes have lower water quality than those seaward. Portnoy (1991) observed lower dissolved oxygen and higher than normal levels of sulfides behind a dike on the Herring River in Wellfleet, MA. This area is plagued by periodic fish kills and high numbers of mosquitoes, both consequences of stag- nation. In the past, road construction on fill over marshes did not plan for mainte- nance of adequate tidal flushing in their design. Roads block sheet flow of tidal water over the marsh surface, and culverts for tidal creeks are often too small to maintain the normal tidal range and flushing. Flood and ebb tides behind a road across a marsh may be delayed several hours by an inadequately sized culvert compared to that seaward of the road, and the tidal range may be reduced by 25 per cent or more. Restoring the normal tidal circulation to a formerly diked area can reverse these negative effects. Slavin and Shisler (1983) noted substantial increases in wading birds, waterfowl, shorebirds, and gulls in a marsh when the dike of a tidally restricted salt marsh hay farm was breached. Conversely, the number of passerines declined. They also observed increases in smooth cordgrass and declines in salt marsh hay. Figure 3 Common reed ( Phragmites australis ) encroaching on salt marsh cordgrass; such scenes are common along the upland edge of East Coast marshes, particularly where tidal flow has been restricted. [...]... Hemond, H F and Benoit, J., Cumulative impacts on water quality functions of wetlands, Environ Manage., 12, 639, 1988 Heufelder, G., Bacterial monitoring in Buzzards Bay, EPA 503/ 4-8 8-0 01, U.S Environmental Protection Agency, Region 1, Boston, MA, 1988 Howes, B., Howarth, R., Teal, J M., and Valiela, I., Oxidation-reduction potentials in a salt marsh Spatial patterns and interactions with primary production,... existing wetland area in 1973 and represents a decline in the rate of loss from the mid-1950s through the mid-1970s An increase of 4670 ha occurred in nonvegetated estuarine wetlands, such as tidal flats Recent losses have been subtler than those of the past, consisting primarily of a transformation of estuarine vegetated wetlands to deepwater habitat rather than conversion to urban or agricultural land... make a case by case approach unrealistic The rationale for protecting coastal and inland wetlands is that they perform certain functions that are valuable to the public Coastal wetlands enhance the water quality of coastal waters by removing potentially harmful constituents before they reach open water Coastal wetlands are also rich habitats for fish, shellfish, and wildlife Water quality and habitat... numerical index of wetland value based on comparing the site-specific wetland to a standard evaluation scheme Criteria comprising the value index include presence or absence of endangered species, vegetation quality, surface water quality, water quality maintenance, wildlife habitat, and socio-cultural values Potential localized, cumulative, and watershed-wide impacts, and the slope, are all considered in deriving... incremental losses of small pieces of coastal habitats, and increases in recreational-related structures and activities that impact coastal wetlands Management and mismanagement of coastal wetlands in the past and present have occurred on a local scale in which decisions have focused on protecting (or not protecting) individual wetlands The most significant future management issues will be related to global... including activities in wetland buffers, and restoration of degraded coastal wetlands Recent Trends in Coastal Wetland Loss Losses of coastal wetlands still occur, albeit at a slower rate than prior to 1970 The U.S Fish and Wildlife Service’s National Wetlands Inventory Project estimated that a net loss of 28,665 ha of vegetated estuarine wetlands occurred in the coterminous United States between 1974 and 1983... deficiency in Spartina alterniflora roots: metabolic adaptations to anoxia, Science, 214, 439, 1981 Mendelssohn, I A and McKee, K L., Spartina alterniflora die-back in Louisiana: time course investigation of soil waterlogging effects, J Ecol., 76, 509, 1988 Miller, W B and Egler, F E., Vegetation of the Weqetequock-Pawcatuck tidal-marshes, Conn Ecol Monogr., 20, 143, 1950 Mitchell, R and Chamberlain, C.,... Berg, G., Ed., Ann Arbor Science, Ann Arbor, MI, 1978, 15 Montague, C L., Zale, A V., and Percival, H F., Ecological effects of coastal marsh impoundments: a review, Environ Manage., 11, 743, 1987 Niering, W A and Scott Warren, R., Vegetation patterns and processes in New England salt marshes, BioScience, 30, 301, 1980 Nixon, S., The Ecology of New England High Salt Marshes, FWS/OBS-81–55, U.S Fish and... coastal wetlands is important for providing the seclusion a number of species of waterfowl need to nest free from predation and disturbance Kirby (1988) states that, “It has long been recognized that lands adjacent to areas managed for waterfowl play a major role in the entire management scheme.” Black ducks (Anas rubripes) nest either on islands in wetlands or in areas immediately adjacent to wetlands. .. Monahan, T J., Bowden, D C., and Graybill, F A., Status and Trends of Wetlands and Deepwater Habitats in the Coterminous United States, Department of Forest and Wood Science, Colorado State University, Ft Collins, 1983 Frenkel, R E and Boss, T R., Introduction, establishment and spread of Spartina patens on Cox Island, Siuslaw Estuary, Oregon, Wetlands, 8, 33, 1988 Hagedorn, C., Microbiological aspects of . Robert “Coastal Marsh Management” Applied Wetlands Science and Technology Editor Donald M. Kent Boca Raton: CRC Press LLC,2001 ©2001 CRC Press LLC CHAPTER 11 Coastal Marsh Management Robert. 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. measurement of final concentrations. EXPLOITATION OF COASTAL WETLANDS When coastal wetlands were not being destroyed outright, or ditched for mos- quito control, they were sometimes managed to provide