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Tidal salt marsh restoration
Aquatic Botany, 32 (1988) 1-22
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Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
TIDAL SALT MARSH RESTORATION*
STEPHEN W. BROOME 1, ERNEST D. SENECA 2 and WILLIAM W.WOODHOUSE, Jr. 1
1Department of Soil Science, and 2Department of Botany, North Carolina State University at Raleigh, Raleigh, NC 27695 (U.S.A.) (Accepted for publication 8 September 1987)
ABSTRACT
Bro~me~S.w.~Seneca~E.D.andw~odhouse'w.w.~Jr.~988.Tidalsaltmarshrestor~i~n.Aquat. Bot.,32:l-22. Coastal salt marshes occur in the intertidal zone of moderate to low energy shorelines along estuaries, bays and tidal rivers. They have ecological value in primary production, nutrient cycling, as habitat for fish, birds and other wildlife and in stabilizing shorelines. Disturbance by development activities has resulted in the destruction or degradation of many marshes. Awareness of this loss by scientists and the public has led to an interest in restoration or creation of marshes to enhance estuarine ecosystems. Recovery of marshes after human perturbation such as dredging, discharges of wastes and spillage of petroleum products or other toxic chemicals is often slow under natural conditions and can be accelerated by replanting vegetation. The basic techniques and procedures have been worked out for the propagation of several marsh angiosperms. Factors which affect successful revegetation include elevation of the site in relation to tidal regime, slope, exposure to wave action, soil chemical and physical characteristics, nutrient supply, salinity and availability of viable propagules of the appropriate plant species. Marsh restoration technology has been applied at a variety of locations to vegetate intertidal dredged material disposal sites, stabilize shorelines, mitigate damage to natural marshes and to revegetate one marsh destroyed by an oil spill. Contractual services for marsh establishment are now available in some regions. Further research is needed to determine the success of marsh restoration and creation in terms of ecological function, including the faunal component.
INTRODUCTION
Coastal salt marsh vegetation is composed primarily of grasses, sedges, rushes and other herbaceous angiosperms which are periodically flooded by estuarine waters. These coastal marshes occur in the intertidal zone of moderate to low energy shorelines along tidal rivers and in bays and estuaries. Along steep * Paper No. 8506 of the Journal Series of the North Carolina State University Agricultural Research Service, Raleigh, NC 27695-7601. The use of trade names in this publication does not imply endorsement by North Carolina Agricultural Research Service of the products named, nor criticism of similar ones not mentioned.
0304-3770/88/$03.50
© 1988 Elsevier Science Publishers B.V.
shorelines, marshes may occupy only narrow fringes, but along gently sloping shorelines they may occupy vast areas. Marshes fix energy in the form of primary production, recycle nutrients, stabilize shorelines and provide habitat for many fishery species. Until recently, estuarine marshes have been considered useless and prime areas for waste disposal or conversion to agricultural, commercial and recreational uses. Alteration of these valuable estuarine systems has decreased as their ecological values have been recognized. Although marshes are now protected by legislation in many countries, there will always be the possibility of disturbance by national defense activities, dredging, pipelines for offshore petroleum resources, highway construction, accidental toxic material spills or willful destruction. Transplanting marsh vegetation has been a common practice in some parts of the world for many years. Ranwell (1967) reported that Spartina townsendii H. & J. Groves was transplanted extensively in Europe, particularly during the 1920's and 1930's, to reduce channel silting, for coastal erosion protection and to reclaim land for agriculture. A large and successful reclamation project involving planting S. townsendii was carried out in The Netherlands (Lambert, 1964). Planting of the 490-ha polder began in 1925 and by 1949 it was ready for production of agricultural crops. It should be noted that the fertile form of this grass came to be known as S. anglica C.E. Hubbard. Chung and Zhuo (1985) reported that S. anglica was introduced in China in 1963. Since that time > 30 000 ha have been planted, providing substantial economic, social and ecological benefits. Reported uses of Spartina marshes were bird habitat, animal fodder, pasture, aquaculture, green manure, amelioration of saline soil, coastal stabilization and land reclamation (Chung, 1982 ). Spartina alterniflora Loisel. was introduced to China in 1979 because of its potential for producing higher biomass and, after 5 years, successful plantings amounted to 260 ha (Zhuo and Xu, 1985). Experiments have tested its value as green manure for rice culture, as goat and fish feed and for paper making. The concept of marsh restoration or creation to preserve or enhance natural estuarine ecosystems is relatively new in most parts of the world. Marshes have been established in recent years to stabilize the intertidal zone of dredged material deposits, to restore areas damaged by man or natural causes, to mitigate damage or destruction of marsh and to stabilize the intertidal zone of canal banks and sandy eroding estuarine shorelines. The Coastal Engineering Research Center, U.S. Army Corps of Engineers, sponsored initiation of marsh building studies in North Carolina in 1969. Garbisch (1977) identified 105 sites where experimental or applied marsh plantings have been attempted in the continental U.S.A. A summary of information available on building salt marshes along the coasts of the continental U.S.A. was presented by Woodhouse (1979).
PERTURBATION Salt marshes may be altered by natural causes, such as severe storms, sedimentation, or changes in sea level. There are also documented cases of cyclic changes which involve dieback and recovery due apparently to natural causes, although the exact causal factor has not been identified (Linthurst and Seneca, 1980). Interactions among several environmental factors, especially drainage, sedimentation, substrate, salinity and the degree of anaerobosis, determine successional changes in salt marsh vegetation. The greatest influence on erosion of marshes is usually either rising sea level or coastal subsidence. Although restoration has been accomplished in certain cases following natural perturbation, most restoration efforts are a result of direct or indirect human perturbation of marshes. Direct perturbation includes the effects of dredging, which may influence sedimentation, erosion, or drainage. Other examples of direct perturbations include long-term discharge of industrial effluents, agricultural run-off and accidental spillage of petroleum or other toxic materials. Impact to the marsh may be rapid, as in the case of a toxic materials spill, or may be spread over a long period of time, due to cumulative effects of the material or process involved. Many activities such as diversion of water courses, damming for flood control and other water regulating actions, have indirect effects on marsh vegetation and the organisms which inhabit the marsh. These indirect effects include changes in salinity levels, sedimentation rates and nutrient pulses. Perturbations often result in significant alterations in the productivity, species composition and capacity of the marsh to provide habitat and stabilize the shoreline. Recovery of salt marshes after natural or human perturbations depends on the degree and nature of the perturbation and on chance as well as predictable events. Most angiosperms have the capacity to reproduce both sexually (by seed) and vegetatively (by rhizome fragment). The availability of disseminules (seeds and rhizome fragments) to the perturbed site and the capacity of these disseminules to become established are two important determinants in the recovery process. Recolonization of the site by bacteria and microalgae is usually a prerequisite to natural re-invasion by pioneer marsh angiosperms. Exposure of the site to open estuarine waters, storm frequency, availability of appropriate disseminules and the capacity of disseminules to tolerate the prevailing conditions and become established, all interact to determine the rate of recovery. Chance plays a large role in the re-establishment of moderately exposed sites and less of a role in recolonization of more protected sites. It is not sufficient for the disseminules to simply reach the site, germinate and begin growth; they must become established and perpetuate themselves for restoration to occur. The sequence of events necessary for successful establishment does not occur every year. Good seed crop years do not necessarily occur in
conjunction with the storm-free period required for initial establishment and growth of young seedlings. Recovery time under natural conditions may range from a few to 10 or more years, depending on the nature and degree of the perturbation and on the relative maturity of the marsh involved. Under favorable conditions, a marsh in the pioneer stages of development will obviously recover more rapidly than a relatively mature marsh with its so-called climax species and accumulated organic matter or carbon bank. Following the Amoco Cadiz oil spill and subsequent clean-up operations, it was 3 years before a pioneer annual species of Salicornia became established in large numbers at the Ile Grande marsh site along the Brittany coast of France (Seneca and Broome, 1982). Twelve years after dredge material disposal on a Spartina alterniflora marsh along the Bogue Sound shoreline in North Carolina, U.S.A., there was no natural recolonization, although much of the dredge material was in the intertidal zone (Woodhouse et al., 1976). In contrast, a 40-ha dieback area of Spartina marsh on Oak Island, North Carolina, became completely revegetated in 4 years (Linthurst and Seneca, 1980). These and other examples indicate considerable variation in marsh recovery time. Exposed and relatively isolated sites require considerably longer to recover because of the greater role of chance involved in disseminule dispersal and successful establishment. MARSHESTABLISHMENT
Site requirements Elevation and tidal regime interact to determine the extent, duration and time of submergence. It is sometimes difficult to relate the type of marsh at a given location to these three factors and in such cases it may be that the average daily submergence time is the controlling factor. In many cases, the best estimate of suitable elevations for marsh establishment may be obtained by observing and taking elevation readings on a nearby marsh of the type to be constructed. If this is not possible, trial plantings should be made extending from points well above, to those well below the zone of estimated establishment, and survival and growth determined. Where two or more species are being tested, their zones of estimated establishment can be overlapped. Experience along the North Carolina coast indicates that the lower limit of emergent marsh vegetation is about mean sea level. The upper limit of low-marsh species is near mean high water and the upper limit of high-marsh species is the mean storm tide level. Slope determines the area which can be successfully established. Within limits, the more gentle the slope, the more area on which marsh can be established. Although steep slopes may facilitate drainage and aeration, they are more difficult to plant and offer a relatively narrow zone for successful estab-
lishment. Wave energy is dissipated over a relatively narrow area, whereas with a gentle slope, wave energy is dissipated over a comparatively wider area. Slopes must be sufficient for good surface drainage to prevent ponding and subsequent increases in salinity due to evaporation. Marshes have been established on slopes from 10% to < 1%, but slopes of 1-3% are preferable. Exposure to wave action is a major factor to consider in determining the types of propagules to use and the probability of restoration. Wave climate data, which include wind speed and direction, bottom and shoreline configuration, fetch and water level, are not usually available to aid in determining the probability of successful marsh establishment. Fetch, the distance of open water over which the wind blows and waves are generated, is an important indicator of the severity of the wave climate at a given site. Woodhouse {1979 ) summarized the results of numerous plantings and advised that transplants can be used successfully at sites with fetches < 4 km and seed can be used successfully at sites with < 1 km of fetch. Knutson et al. (1981) found that fetch, shore configuration and grain size were useful indicators of wave climate severity and the probability of establishing vegetation by transplanting. Substrate characteristics Marshes occur on a wide variety of substrates ranging from coarse sands to fine clays with both high and low concentrations of organic matter. Sandy substrates are usually the easiest to plant because they provide adequate bearing strength and offer few problems to either manual or machine manipulation when making holes or tilling. These sandy substrates often have insufficient amounts of nutrients necessary for rapid plant establishment. The use of commercial fertilizer materials may be necessary to overcome these deficiencies. Finer textured substrate materials are more likely to have adequate nutrient concentrations. When the upper layers are removed, however, as in the cleanup of a toxic chemical or a petroleum product spill, the remaining substrate may contain insufficient concentrations of plant nutrients, especially nitrogen and phosphorus. Organic substrates present special problems, both physical and chemical, which make them difficult areas for marsh re-establishment. Although many marshes exist on substrates high in organic matter, these marshes were probably initiated prior to the organic matter accumulation which took place under the developing marsh through time. One of the characteristics of estuaries is salinity variation, which may range from a few parts per thousand (ppt) to full sea strength (35 ppt) in the tidal waters which flood the marshes. Owing to substrate characteristics, season, seepage from upland and the frequency of inundation, salinity in salt marsh substrates varies from almost fresh water to more than twice sea strength. Although all salt marsh plants exhibit some degree of salt tolerance, under certain conditions salinity levels may be too high for successful marsh estab-
lishment. Seeds and seedlings are usually more salt sensitive than are established plants. Under regular flooding, sandy substrates do not usually develop salt concentrations which are too high for marsh establishment. In the zone between neap tide high water and spring tide high water, however, salt concentrations may become high in newly planted or seeded areas due to concentration of salts resulting from evaporation during periods of low rainfall and high temperatures. This situation may exist in shallow bays which are influenced by wind setup in which the wind pattern results in extended periods of low water during hot weather, or in areas with large ranges in astronomic tides where the marsh is not flooded during the neap tide period. Domes of sandy material adjacent to and above the planting site, or upland areas adjacent to the site, tend to reduce salinities by accumulating precipitation which seeps outward and dilutes substrate salinities in the planting area. Although salinity tolerance varies greatly among the salt marsh plants of the world, substrate salinities greater than sea strength generally restrict growth and often decrease survival of plantings. Substrate salinities > 45 ppt may prevent establishment of Spartina alterniflora at mid-latitudes (35 °N ) along the eastern coast of the U.S.A., whereas transplants of Puccinellia maritima (Huds.) Parl. may survive this and even higher levels of substrate salinity at 50 °N along the west coast of France.
Plant materials and techniques The ultimate goal in marsh restoration is to replace the marsh that was altered or destroyed. This statement of purpose usually translates into replacing the dominant native angiosperms, with the assumption that once the plants are re-established the animal component and other native plants will soon invade, become re-established and the marsh will return to its former undisturbed state in structure and function. Along the east coast of the U.S.A., Spartina alterniflora is the dominant angiosperm in regularly flooded marshes and is the principal species used in marsh re-establishment projects (Woodhouse et al., 1974, 1976; Garbisch et al., 1975). It has also been used effectively to stabilize shorelines along the Gulf Coast of the U.S.A. (Dodd and Webb, 1975 ). An ecologically equivalent species, S. foliosa Trin., occupies the lower portions of the intertidal zone on the southern Pacific coast of the U.S.A. and it has been planted successfully to re-establish marshes in that region (Knutson, 1976). In the U.K., the vigorous and aggressive fertile hybrid, S. anglica, has been successfully planted and has accelerated recovery of a chronically oiled marsh (Dicks and Iball, 1981 ). Along the Brittany coast of France, Halimione portulacoides (L.) Aell. and PuccineUia maritima have been transplanted successfully along intertidal creek banks and upper levels of the former marsh surface, respectively (Seneca and Broome, 1982). Many marsh angiosperms have been either considered or actually tried in marsh establishment projects. Results of selected studies along the east coast
of the U.S.A. and the European coast will serve to describe the general techniques and procedures developed with three marsh species-S, alterniflora, P. maritima and H. portulacoides. A variety of sites were investigated along the coast of North Carolina to cover the range of astronomic tides (0.2-1.4 m), salinities (10-35 ppt) and tidal exposures. Substrates were primarily sand (often > 90% ) and of gentle slope ( ~ 2% ) (Woodhouse et al., 1974 ). Studies in the Chesapeake Bay region of Virginia and Maryland, U.S.A., were conducted under somewhat lesser influences of astronomic tides, lesser salinities and on a variety of substrate textures (Garbisch et al., 1975; Garbisch, 1977). Studies on the French coast were conducted under a greater astronomic tidal range, higher substrate salinities and on finer textured substrates. Propagation techniques investigated include seeding, transplanting sprigs (tillers with attached roots and rhizome fragments, but with little substrate material), transplanting plugs (tillers with a core of intact substrate material, roots and rhizomes) and planting greenhouse-grown potted seedlings. All methods are feasible with certain species under certain prevailing site conditions. Both manual and mechanical planting procedures have been developed for many species. Techniques have also been developed for nursery production of plant materials. Protective structures have been used successfully on some exposed sites. On substrates with nutrient deficiencies, experiments have been conducted to determine sources, rates, methods of application and timing of application of fertilizer materials. The description of techniques and procedures that follows is largely developed from our work in North Carolina and supplemented by the work of others.
Seeding Seeding experiments with S. alterniflora indicate that seed should be harvested as near as possible to maturity or just prior to shattering, from late September through mid-October along the North Carolina coast. Seeds ripen earlier at more northerly latitudes and later at more southerly latitudes along the Atlantic coast of the U.S.A. Seeds (caryopses) can be harvested by hand, but mechanization is desirable to obtain adequate amounts for large-scale operations. A two-wheeled garden tractor equipped with a reel, cutting blade and a canvas catchment bag has proven satisfactory (Fig. 1) (Broome et al., 1974; Woodhouse et al., 1974). Harvested seed is transferred to large burlap sacks which are then transported to an area for temporary storage or threshing. Seed can be easily threshed in a thresher designed for small grain following storage at 1-4°C for ~ 1 month. After threshing, seed must be stored in covered containers filled with estuarine water, sea water or artificial sea water of ~ 35 ppt salinity at 2-4 ° C. Direct seeding can be accomplished from mid-April through mid-June along the North Carolina coast, earlier at more southerly latitudes and later at more northerly latitudes, by incorporating seed into the substrate to a depth of 2-3
Fig. 1. A machine built for harvesting seed heads of Spartina alterniflora and S. patens. cm. The substrate should be broken up with a rotary tiller or a spike-toothed harrow to prepare the seed bed. The area can then be hand-seeded at the rate of 100 viable seeds (as determined by germination tests) per square meter. Finally, the area should be reworked with the tillage equipment to incorporate the seed into the substrate. Results of seeding experiments indicate that direct seeding is feasible only in the upper half of the intertidal zone. W h e n seeding is successful, complete vegetative cover is established by the end of the first growing seasons. Comparison of an area in the upper half of the intertidal zone that was seeded at the rate of 100 viable seeds per square meter, with one that was transplanted at the same time with sprigs spaced 0.9 m apart, indicated similar above-ground biomass accumulations after two growing seasons. Marsh establishment from direct seeding is dependent on storm-free periods and is more likely to be successful in sheltered or protected sites t h a n in exposed areas. It is probable that most of these techniques and procedures are applicable to the European S. anglica. Seeding costs include harvesting, threshing, storage, seeding, travel, supplies and equipment. Since storage, travel, supplies and equipment vary with the facilities and equipment available, only the remaining cost items are presented here. W h e n a source of seed has been located, costs of seeding one ha are: 5
person hours to harvest seed, 2.5 person hours to thresh the seed and 7.5 person hours to prepare the seed bed and sow the seed. In actual practice, these estimates may need to be doubled to compensate for equipment failure, inexperienced personnel and unforeseen difficulties.
Transplanting sprigs On the North Carolina coast, transplanting sprigs or single-stem plants of
S. alterniflora on a 1-m spacing, in April or May, can result in substrate stabilization and marsh establishment by the end of the second growing season (Woodhouse et al., 1974). Transplanting can be accomplished manually or mechanically, depending on the size of the operation and the accessibility of the site. A farm tractor with a transplanter used for tobacco or vegetable plants has proved satisfactory on certain sandy sites (Woodhouse et al., 1974) (Fig. 2 ) and a hand-held power auger has worked well in less accessible sites (Garbisch et al., 1975). A tool (dibble) similar to that used to plant tree seedlings has worked well in manual operations. Transplanting is successful over a wider range of conditions than is seeding. Marsh can be initiated on exposed sites where seeding is not successful and from about mean sea level to about mean
Fig. 2. A mechanicaltransplanterused for transplantingmarshvegetation.
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(b)
Fig. 3. (a) An eroding shoreline near Nags Head, North Carolina was planted with sprigs of S. alterniflora and Spatens in June 1979. (b) The same shoreline after 13 months.
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Fig. 4. (a) An unvegetated creek bank in the marsh at Ile Grande, France, 19 May 1981. Vegetation was destroyed by the Amoco Cadiz oil spill that occurred in March 1978 and the clean-up operations that followed. (b) The same area in May 1982, 1 year after transplanting with Halimione portulacoides and Puccinellia maritima.
12 high water. Closer-spaced plantings have some advantages in establishing stands on marginal sites (Broome et al., 1986). An example of shoreline erosion control using single-stem field-dug transplants is shown in Fig. 3a and b. This planting was carried out in 1979 along the Roanoke Sound shoreline near Nags Head, North Carolina. After 8 years, the planting was still effective in preventing erosion, while the adjacent unvegetated shoreline continued to recede. Costs of transplanting include travel, supplies and equipment in addition to digging plants and transplanting. As with seeding, costs of transport, storage, supplies and equipment vary considerably. Manual digging and planting efforts require: 1 person hour to dig and separate 180-200 transplants and 1 person hour to plant an equal number of transplants. Mechanized costs are: 1 person hour to dig and separate 400 plants using a tractor-drawn shallow plow and about an equal number can be transplanted per person hour using a tractor-drawn planter. Labor costs for manual transplanting of one ha with plants on a 1-m spacing, or 10 000 plants, are ~ 50 person hours for digging and preparing transplants and about the same amount of time for planting. Mechanized costs for an equivalent operation are about half those required in the manual operation for both digging and planting, or a total of ~ 50 person hours for the combined operations. Transplanting sprigs of H. portulacoides 0.5 m apart along intertidal creek banks at Ile Grande, France, in May, resulted in complete cover by the end of the second growing season (Seneca and Broome, 1982 ) (Fig. 4a and b). Transplanting was accomplished manually using a 6.5-cm diameter soil auger which worked well in the high organic matter substrate. Sprigs were dug at the rate of ~ 180 per person hour and planted at the rate of ~ 50 person hour. Based on these digging and planting time requirements only, ~ 1020 person hours (220 person hours to dig sprigs plus 800 person hours to plant) would be required to plant 1 ha on a 0.5-m spacing (40 000 transplants).
Greenhouse-grown potted seedlings Seedlings of S. alterniflora and several other marsh angiosperms have been grown in large numbers in a mixture of equal parts of sand, top soil and either peat moss or vermiculite in plastic trays with 5-cm compartments. Each tray contains 36 planting units (Fig. 5a and b). These transplants initiate marsh development as well or better than sprigs or plugs. They are especially successful on sites with irregular flooding regimes, due mainly to the moisture retention capacity of the potting medium, which is also an advantage in establishment during periods of low rainfall. These greenhouse-grown plants can be used in situations where field-grown plants are unavailable. Because seed must be collected and germinated to grow these plants, at least one year of planning and preparation prior to transplanting is necessary. Extensive plantings utilizing greenhouse-grown potted seedlings have been conducted in the Chesapeake Bay region (Garbisch et al., 1975).
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Fig. 5. (a) Seedlings of Spartina species growing in a greenhouse. (b) A tray of S. cynosuroides seedlings ready for transplanting. The picture was taken 3 months after seeding.
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Fig. 6. (a) An unvegetated site at Kerlavos, France, after planting with alternate rows of sprigs and plugs of Puccinellia maritima (May 1979 ). (b) The same site after 2 years (May 1981 ).
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Transplanting plugs Transplanting plugs (5-7-cm diameter, 15-cm depth core of root and substrate material intact) of P. maritima on a 0.5-cm spacing at Ile Grande, France, produced good results (Fig. 6a and b). Cover was complete by the end of three growing seasons (Seneca and Broome, 1982). Transplanting was accomplished manually using a 6.5-cm diameter soil auger to open holes for the plugs in substrates which ranged from coarse sand to silt to those with high concentrations of organic matter. Above-ground growth spread radially at the rate of ~ 10 cm annually. These plugs were dug at the rate of ~ 75 per person hour and planted at the rate of ~ 50 per person hour. Based on these digging and planting time requirements only, ~ 1330 person hours (530 person hours to dig plants plus 800 person hours to plant) would be required to plant 1 ha on a 0.5-m spacing.
Fertilizer materials Because of the uncertainty of storm-free periods and adequate precipitation during the establishment period, the human-initiated marsh should be established as quickly as possible. Both conventional and slow-release fertilizer materials have been used successfully to facilitate marsh establishment at sites
Fig. 7. T h e effect of fertilizer on growth of Spartina alterniflora planted along a n eroding shoreline of the Neuse River in N o r t h Carolina. T h e row on t h e right received no fertilizer while the rows on the left a n d the center were fertilized with N, P a n d K at planting.
16 TABLE 1 Means ± 1 standard error comparing growth measurements of a transplanted (carried out in 1974 ) and adjacent natural marsh. Data for the first 2 years for above-ground and the first 3 years for below-ground growth were not included to eliminate bias created by effects of the initial establishment period
Above-ground means Years averaged Numbers of stems m -2 Number of flowering stems m -2 Height (cm) Basal area (cm2 m-2) Dry weight (g m -e) Below-ground means Years averaged Dry weight (gm -2) {0-30 cm)
Transplanted marsh
Natural marsh
1976-1983
1974-1983
745 ± 97 29 ± 6 96 _+6 176 +, 11 849 +,48
719 +,58 77 +, 19 100 +_5 157 +, 7 793 ± 67
1977-1983
1974-1983
2274± 73
1957+, 140
t-test for significant difference
NS ** NS NS NS
Adapted from Broome et al. (1986). *Significant at the 0.05 probability level. **Significant at the 0.01 probability level. where s u b s t r a t e s were deficient in n i t r o g e n a n d / o r p h o s p h o r u s . E v e n on sites w i t h o u t deficiencies in t h e s e n u t r i e n t s , fertilizer a m e n d m e n t s o f t e n result in increased p l a n t growth a n d t h e r e b y s h o r t e n t h e critical e s t a b l i s h m e n t period. On exposed sites, rapid p l a n t growth a n d early e s t a b l i s h m e n t are critical to successful m a r s h d e v e l o p m e n t . Application of t h e e q u i v a l e n t of 112 kg h a -1 N a n d 49 kg h a -1 P, in the p l a n t i n g hole or b y banding, results in good g r o w t h of S. alterniflora in N o r t h Carolina ( B r o o m e et al., 1983 ) (Fig. 7). B o t h c o n v e n t i o n a l soluble a m m o n i u m sulfate plus c o n c e n t r a t e d s u p e r p h o s p h a t e a n d slow-release O s m o c o t e are desirable sources. T h e soluble sources should n o t be placed in direct c o n t a c t with the p l a n t roots. F i r s t y e a r growth can usually be increased significantly by b r o a d c a s t application of a m m o n i u m sulfate plus c o n c e n t r a t e d s u p e r p h o s p h a t e at the same rates in m i d - s u m m e r . T h e same sources, rates a n d m e t h o d of application have also p r o d u c e d significant g r o w t h responses in the s e c o n d growing season. In the finer t e x t u r e d d i s t u r b e d s u b s t r a t e s at Ile G r a n d e , F r a n c e , slow-release Osmocote, placed in t h e p l a n t i n g hole at t h e rate of 2.8 g N a n d 1.2 g P, produced the best growth of H. portulacoides a n d P. maritima. Puccinellia maritima was the m o r e fertilizer d e p e n d e n t of t h e s e two species.
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Long-term development An important aspect of determining the success of marsh restoration projects is long-term measurements. Above- and below-ground standing crops of S. alterniflora transplanted along a shoreline of Bogue Banks, North Carolina, were sampled annually over a 10-year period and compared with a similar adjacent natural marsh (Broome et al., 1986). Results indicated that aboveground biomass was equivalent or greater in the transplanted marsh at the end of the second growing season. Below-ground biomass in the two marshes was equivalent at the end of four growing seasons. Measurements of above-ground growth in the transplanted marsh for Years 3-10 were not significantly different from the natural marsh except for number of flowering stems (Table 1 ). Below-ground biomass was greater in the transplanted area. This sampling was sufficient to document that the restored marsh was persistent and selfsustaining. APPLICATIONOF TECHNOLOGY Although techniques and procedures for marsh establishment have been developed relatively recently and are still being perfected, their use has progressed beyond the purely experimental stage. These procedures have been used to establish marsh successfully under a variety of substrate and tidal conditions along the Atlantic, Gulf and Pacific coasts of the U.S.A. and along the coasts of the U.K. and France. The examples chosen for the discussion to follow illustrate both the usefulness and demand for the technology, in a contractual framework and the need for and application of the technology to real world pollution and marsh destruction problems.
Restoration after an oil spill Marsh establishment techniques and procedures developed along the east coast of the U.S.A. were adapted to the Brittany coast of France to restore marsh that was damaged and destroyed by the Amoco Cadiz oil spill and subsequent cleanup operations (Seneca and Broome, 1982). Preliminary experiments were necessary to compare types of transplants, fertilizer materials and planting seasons and to determine the feasibility of field nursery production for several marsh angiosperms. Although several small-scale plantings were established earlier, larger scale plantings were not begun until one year after the spill. Planting was subsequently continued over a 3-year period. All transplants were spaced 0.5 m apart. Results from these experiments indicated that H. portulacoides and P. maritima survived better and grew more rapidly than the other plants tested. Survival and growth data further indicated that plug-type transplants of P.
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maritima, with 5-7-cm cores of root and substrate material intact, were superior to sprigs. Sprigs ofH. portulacoides survived and grew well. There was considerable variation in response to fertilizer materials and rates, but both nitrogen and phosphorus were required for good transplant growth on the disturbed sites tested. Above-ground growth of P. maritima spread radially at the rate of ~ 10 cm annually and that of H. portulacoides at about twice this rate. At these rates of spread, planting ofH. portulacoides and P. maritima on a 0.5m spacing would achieve complete substrate cover in ~ 2 and 3 years after planting, respectively. Nursery areas were successfully established for both species and transplants of each species were obtained within 2 years. Twoyear-old nursery plants of H. portulcoides produced an average of eight sprigtype transplants, while those of P. maritima produced an average of 20 plugtype transplants. Based on these results and utilizing both field-dug and nursery-grown plants, ~ 12 000 transplants (~3500 P. maritima and 8500 H. portulacoides) were strategically planted along creek banks and other disturbed sites to restore the marsh. A major effort was devoted to reclaiming areas from which the uppermost marsh substrate was removed during the cleanup operations. Results of these studies suggest that no planting should be conducted on heavily oiled areas (cleaned or uncleaned) within a 6-month period following a major spill. Further, planting along the Brittany coast should be delayed until May after this interval of time. Although removal of oil from the marsh following a severe spill is justified, the marsh surface with the root mat itself should not be removed, The recommended planting procedure along the Brittany coast is to plant two rows of H. portulacoides sprigs spaced 0.5 m apart along the intertidal creek banks with two rows of P. maritima at the same spacing immediately adjacent to the H. portulacoides. The planting of H. portulacoides should receive the highest priority since stabilization of the creek banks is critical to marsh restoration. Comparison of plant cover on planted and unplanted sites 4 years after the spill indicated that natural reinvasion of these damaged sites has been very limited and that restoration was necessary. Contractual marsh establishment Perhaps the most experience in contractual marsh establishment has been gained by E.W. Garbisch of Environmental Concern, Inc., who has been involved in> 220 marsh establishment efforts over the past 15 years, mostly within the Chesapeake Bay region of Virginia and Maryland and the Northeastern U.S.A. Based on sales over the past 4 years by his organization, the number of potted plants sold, including > 20 herbaceous and 30 woody species of marsh plants, has ranged from 100 000 to 700 000 per year. For other vegetative propagules (sprigs, tubers, rhizomes and bulbs), numbers range from 50 000 to 100 000 per year. Seeds cold stored for internal use and for sale have
19 ranged from 900 to 1700 1 per year. These numbers of propagules reflect the size of the operation and the demand for the plant materials and technology involved. Cost estimates generated from this work are probably more realistic and representative of prevailing economics than those generated by research and government agencies. The total cost of marsh establishment includes costs associated with planning and design, negotiating for the site, preparing the site, constructing any necessary protective structures, planting and maintaining the site during the establishment period (Garbisch, 1982). The costs for planting and maintenance during the period of establishment vary depending on site conditions. The cost of potted seedlings for planting 1 ha with plants spaced 0.6 m apart (based on 1987 prices of $0.55 per plant) was ~ $15 400. Slow-release fertilizer material for application at planting to 1 ha costs ~ $2000 and one broadcast application for conventional soluble fertilizer material during the establishment period costs ~ $400 for the same area. The comparable costs for seed to cover 1 ha, o r ~ 1.2 X 106 seeds, were ~ $2400. About 10 person hours are required for broadcasting the seed and cultivation of 1 ha. About 150 person hours are required for transplanting sprigs or potted plants over 1 ha on a 0.6m spacing using a mechanical auger to drill holes. A fully mechanized operation would require about half the time. Fertilization at planting, for plants spaced 0.6 m apart, requires ~ 40 person hours and one broadcast application of fertilizer after planting, ~ 5 person hours. For maintenance during the May-October establishment period, a total of> 200 person hours are required for 1 ha assuming that 20% of the site will have to be replanted due to transplant mortality. Cost evaluation A cost estimate was made based on 1987 plant and fertilizer materials costs. Assumptions were a moderate labor cost of $5 per person hour and a combination of potted plants, slow-release fertilizer at planting and one broadcast fertilizer application after planting. Labor costs to plant 1 ha on 0.6-m spacing ( ~ 28 000 transplants) and maintain the planting for 1 year were~S18 800. Travel, per diem, overhead and profit should then be added, plus 20% of the total costs for a guarantee of the job, making the cost more realistically ~ $34 000. Although it is difficult to quantify wetland values, the cost of planting marsh compares favorably with the values of natural marshes, as estimated by various methods of evaluation (Pope and Gosselink, 1973; Gosselink et al., 1974; Mitsch and Gosselink, 1986). These estimates of marsh establishment costs were based on figures from a contractual organization engaged in this type of work full time and estimates of the values of marshland are cited in the literature and in court cases. Thus, the cost-benefit ratio for marsh establishment practices can realistically be used as justification to restore or replace damaged systems, to develop new
20 productive marshes where none exist, in mitigation when marshlands undergo alteration and to stabilize eroding estuarine shorelines as an alternative to or in conjunction with engineering structures. FUTURE RESEARCH IN MARSH RESTORATION The basic techniques and procedures for establishing estuarine marshes have been worked out for several marsh angiosperms. Rates of establishment and recovery after perturbation are needed to add a predictive dimension to our present knowledge. Selected marsh establishment sites should be monitored for at least a decade. Research should include information on the animal, sedimentation and nutrient components of the marsh as well as the plants. For the dominant marsh angiosperms, tolerance levels to major acute and chronic pollutants, such as petroleum products, should be determined. There is no substitute for obtaining this much needed information prior to serious environmental impacts. In most cases involving toxic materials spills, we do not know how long to wait before attempting to restore the damaged system. Laboratory and greenhouse studies are needed to determine sequential transplant response to substrates contaminated by probable marshland toxic materials. POLICY RECOMMENDATIONS FOR MARSH RESTORATION Although marshes are recognized as valuable estuarine systems and are protected by legislation in many regions of the world, there will always be the possibility of perturbation. Technology for marsh restoration exists for certain geographic areas and the costs to restore marshland are reasonable as compared to its estimated value as a natural resource. Given this situation, it is reasonable to recommend hectare-for-hectare restoration of marsh in the case of projected alteration of these systems whether for public interest projects, in mitigation for disturbance, or for other unavoidable, accidental or willful damage. It is usually necessary to replace all the species, but certainly those perennials that will hasten the return of the originally dominant species in a successional sequence should be planted. Annuals should be used only in exceptional cases as a stepping stone to the establishment of the dominant perennials. The contractor should be required to guarantee the work and replanting should be included in the project plans as a safeguard against damage by natural disasters. The project should be monitored for at least 3-5 years to determine the course of the restoration effort. ACKNOWLEDGMENTS This paper is based on research sponsored by the North Carolina Agricultural Research Service, NOAA and the Coastal Engineering Research Center,
21
U.S. Army Corps of Engineers. Appreciation is extended to Mr. C.L. Campbell, Jr. and Mr. L.L. Hobbs for assistance in field work.
REFERENCES Broome, S.W., Woodhouse, W.W., Jr. and Seneca, E.D., 1974. Propagation of smooth cordgrass, Spartina alterniflora, from seed in North Carolina. Chesapeake Sci., 15: 214-221. Broome, S.W., Seneca, E.D. and Woodhouse, W.W., Jr., 1983. The effects of source rate and placement of nitrogen and phosphorus fertilizers on growth of Spartina alterniflora transplants in North Carolina. Estuaries, 6: 212-226. Broome, S.W., Seneca, E.D. and Woodhouse, W.W., Jr., 1986. Long-term growth and development of transplants of the salt-marsh grass Spartina alterniflora. Estuaries, 9: 63-74. Chung, H.C., 1982. Low Marshes, China. In: R.R. Lewis III (Editor), Creation and Restoration of Coastal Plant Communities. CRC Press, Inc., Boca Raton, FL, pp. 131-145. Chung, H.C. and Zhuo, R., 1985. Twenty-two years ofSpartina anglica Hubbard in China. Journal of Nanjing University, Research Advances in Spartina, pp. 31-35. Dicks, B. and Iball, K., 1981. Ten years of saltmarsh monitoring of the case history of a Southampton Water saltmarsh and a changing refinery effluent discharge. In: Proceedings of the 1981 World Oil Spill Conference, EPA/API/USCG, Atlanta, GA, pp. 361-374. Dodd, J.D. and Webb, J.W., 1975. Establishment of vegetation for shoreline stabilization in Galveston Bay. U.S. Army, Coastal Engineering Research Center, Fort Belvoir, VA, Miscellaneous Paper 6-75. Garbisch, E.W., Jr., 1977. Recent and planned marsh establishment work throughout the contiguous United States. A survey and basic guidelines. CR D-77-3, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi. Garbisch, E.W., Jr., 1982. Highways and wetlands. Compensating wetland losses. U.S. Department of Transportation, Federal Highway Administration, Office of Research and Development, Washington, DC. Garbisch, E.W., Jr., Woller, P.B. and McCallum, R.J., 1975. Salt marsh establishment and development. U.S. Army, Coastal Engineering Research Center, Fort Belvoir, VA, Tech. Memo. 52. Gosselink, J.G., Odum, E.P. and Pope, R.M., 1974. The value of the tidal marsh. Center for Wetland Resources, Louisiana State University, Baton Rouge, Publication LSU-SG-74-03. Knutson, P.L., 1976. Development of intertidal marshlands upon dredged material in San Francisco Bay. Proceedings of the Seventh World Dredging Conference, San Francisco, CA, pp. 103-118. Knutson, P.L., Ford, J.C., Inskeep, M.R. and Ozler, J., 1981. National survey of planted salt marshes (vegetative stabilization and wave stress). Wetlands, 1: 129-157. Lambert, J.M., 1964. The Spartina story. Nature (London), 204: 1136-1138. Linthurst, R.A. and Seneca, E.D., 1980. Dieback of salt-water cordgrass (Spartina alterniflora Loisel.) in the lower Cape Fear Estuary of North Carolina: An experimental approach to reestablishment. Environ. Conserv., 7: 59-66. Mitsch, W.J. and Gosselink, J.G., 1986. Wetlands. Van Nostrand Reinhold Company, New York, 539 pp. Pope, R.M. and Gosselink, J.G., 1973. A tool for use in making land management decisions involving tidal marshland. Coastal Zone Manag. J., 1: 65-74. Ranwell, D.S., 1967. World resources of Spartina townsendii (sensu lato) and economic use of Spartina marshland. J. Appl. Ecol., 4: 239-256. Seneca, E.D. and Broome, S.W., 1982. Restoration of marsh vegetation impacted by the Amoco Cadiz oil spill and subsequent cleanup operations at Ile Grande, France. Interim Report to the
22 Department of Commerce, National Oceanic and Atmospheric Administration, Washington, DC. Woodhouse, W.W., Jr., 1979. Building salt marshes along the coasts of the continental United States. U.S. Army, Coastal Engineering Research Center, Fort Belvoir, VA, Special Report 4. Woodhouse, W.W., Jr., Seneca, E.D. and Broome, S.W., 1974. Propagation of Spartina alterniflora for substrate stabilization and salt marsh development. U.S. Army, Coastal Engineering Research Center, Fort Belvoir, VA, Technical Memo 46. Woodhouse, W.W., Jr., Seneca, E.D. and Broome, S.W., 1976. Propagation and use of Spartina alterniflora for shoreline erosion abatement. U.S. Army, Coastal Engineering Research Center, Fort Belvoir, VA, Technical Report 76-2. Zhuo, R. and Xu, G., 1985. A note on trial planting experiments of Spartina alterniflora. Journal of Nanjing University, Research advances in Spartina, pp. 352-354.
1
Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands
TIDAL SALT MARSH RESTORATION*
STEPHEN W. BROOME 1, ERNEST D. SENECA 2 and WILLIAM W.WOODHOUSE, Jr. 1
1Department of Soil Science, and 2Department of Botany, North Carolina State University at Raleigh, Raleigh, NC 27695 (U.S.A.) (Accepted for publication 8 September 1987)
ABSTRACT
Bro~me~S.w.~Seneca~E.D.andw~odhouse'w.w.~Jr.~988.Tidalsaltmarshrestor~i~n.Aquat. Bot.,32:l-22. Coastal salt marshes occur in the intertidal zone of moderate to low energy shorelines along estuaries, bays and tidal rivers. They have ecological value in primary production, nutrient cycling, as habitat for fish, birds and other wildlife and in stabilizing shorelines. Disturbance by development activities has resulted in the destruction or degradation of many marshes. Awareness of this loss by scientists and the public has led to an interest in restoration or creation of marshes to enhance estuarine ecosystems. Recovery of marshes after human perturbation such as dredging, discharges of wastes and spillage of petroleum products or other toxic chemicals is often slow under natural conditions and can be accelerated by replanting vegetation. The basic techniques and procedures have been worked out for the propagation of several marsh angiosperms. Factors which affect successful revegetation include elevation of the site in relation to tidal regime, slope, exposure to wave action, soil chemical and physical characteristics, nutrient supply, salinity and availability of viable propagules of the appropriate plant species. Marsh restoration technology has been applied at a variety of locations to vegetate intertidal dredged material disposal sites, stabilize shorelines, mitigate damage to natural marshes and to revegetate one marsh destroyed by an oil spill. Contractual services for marsh establishment are now available in some regions. Further research is needed to determine the success of marsh restoration and creation in terms of ecological function, including the faunal component.
INTRODUCTION
Coastal salt marsh vegetation is composed primarily of grasses, sedges, rushes and other herbaceous angiosperms which are periodically flooded by estuarine waters. These coastal marshes occur in the intertidal zone of moderate to low energy shorelines along tidal rivers and in bays and estuaries. Along steep * Paper No. 8506 of the Journal Series of the North Carolina State University Agricultural Research Service, Raleigh, NC 27695-7601. The use of trade names in this publication does not imply endorsement by North Carolina Agricultural Research Service of the products named, nor criticism of similar ones not mentioned.
0304-3770/88/$03.50
© 1988 Elsevier Science Publishers B.V.
shorelines, marshes may occupy only narrow fringes, but along gently sloping shorelines they may occupy vast areas. Marshes fix energy in the form of primary production, recycle nutrients, stabilize shorelines and provide habitat for many fishery species. Until recently, estuarine marshes have been considered useless and prime areas for waste disposal or conversion to agricultural, commercial and recreational uses. Alteration of these valuable estuarine systems has decreased as their ecological values have been recognized. Although marshes are now protected by legislation in many countries, there will always be the possibility of disturbance by national defense activities, dredging, pipelines for offshore petroleum resources, highway construction, accidental toxic material spills or willful destruction. Transplanting marsh vegetation has been a common practice in some parts of the world for many years. Ranwell (1967) reported that Spartina townsendii H. & J. Groves was transplanted extensively in Europe, particularly during the 1920's and 1930's, to reduce channel silting, for coastal erosion protection and to reclaim land for agriculture. A large and successful reclamation project involving planting S. townsendii was carried out in The Netherlands (Lambert, 1964). Planting of the 490-ha polder began in 1925 and by 1949 it was ready for production of agricultural crops. It should be noted that the fertile form of this grass came to be known as S. anglica C.E. Hubbard. Chung and Zhuo (1985) reported that S. anglica was introduced in China in 1963. Since that time > 30 000 ha have been planted, providing substantial economic, social and ecological benefits. Reported uses of Spartina marshes were bird habitat, animal fodder, pasture, aquaculture, green manure, amelioration of saline soil, coastal stabilization and land reclamation (Chung, 1982 ). Spartina alterniflora Loisel. was introduced to China in 1979 because of its potential for producing higher biomass and, after 5 years, successful plantings amounted to 260 ha (Zhuo and Xu, 1985). Experiments have tested its value as green manure for rice culture, as goat and fish feed and for paper making. The concept of marsh restoration or creation to preserve or enhance natural estuarine ecosystems is relatively new in most parts of the world. Marshes have been established in recent years to stabilize the intertidal zone of dredged material deposits, to restore areas damaged by man or natural causes, to mitigate damage or destruction of marsh and to stabilize the intertidal zone of canal banks and sandy eroding estuarine shorelines. The Coastal Engineering Research Center, U.S. Army Corps of Engineers, sponsored initiation of marsh building studies in North Carolina in 1969. Garbisch (1977) identified 105 sites where experimental or applied marsh plantings have been attempted in the continental U.S.A. A summary of information available on building salt marshes along the coasts of the continental U.S.A. was presented by Woodhouse (1979).
PERTURBATION Salt marshes may be altered by natural causes, such as severe storms, sedimentation, or changes in sea level. There are also documented cases of cyclic changes which involve dieback and recovery due apparently to natural causes, although the exact causal factor has not been identified (Linthurst and Seneca, 1980). Interactions among several environmental factors, especially drainage, sedimentation, substrate, salinity and the degree of anaerobosis, determine successional changes in salt marsh vegetation. The greatest influence on erosion of marshes is usually either rising sea level or coastal subsidence. Although restoration has been accomplished in certain cases following natural perturbation, most restoration efforts are a result of direct or indirect human perturbation of marshes. Direct perturbation includes the effects of dredging, which may influence sedimentation, erosion, or drainage. Other examples of direct perturbations include long-term discharge of industrial effluents, agricultural run-off and accidental spillage of petroleum or other toxic materials. Impact to the marsh may be rapid, as in the case of a toxic materials spill, or may be spread over a long period of time, due to cumulative effects of the material or process involved. Many activities such as diversion of water courses, damming for flood control and other water regulating actions, have indirect effects on marsh vegetation and the organisms which inhabit the marsh. These indirect effects include changes in salinity levels, sedimentation rates and nutrient pulses. Perturbations often result in significant alterations in the productivity, species composition and capacity of the marsh to provide habitat and stabilize the shoreline. Recovery of salt marshes after natural or human perturbations depends on the degree and nature of the perturbation and on chance as well as predictable events. Most angiosperms have the capacity to reproduce both sexually (by seed) and vegetatively (by rhizome fragment). The availability of disseminules (seeds and rhizome fragments) to the perturbed site and the capacity of these disseminules to become established are two important determinants in the recovery process. Recolonization of the site by bacteria and microalgae is usually a prerequisite to natural re-invasion by pioneer marsh angiosperms. Exposure of the site to open estuarine waters, storm frequency, availability of appropriate disseminules and the capacity of disseminules to tolerate the prevailing conditions and become established, all interact to determine the rate of recovery. Chance plays a large role in the re-establishment of moderately exposed sites and less of a role in recolonization of more protected sites. It is not sufficient for the disseminules to simply reach the site, germinate and begin growth; they must become established and perpetuate themselves for restoration to occur. The sequence of events necessary for successful establishment does not occur every year. Good seed crop years do not necessarily occur in
conjunction with the storm-free period required for initial establishment and growth of young seedlings. Recovery time under natural conditions may range from a few to 10 or more years, depending on the nature and degree of the perturbation and on the relative maturity of the marsh involved. Under favorable conditions, a marsh in the pioneer stages of development will obviously recover more rapidly than a relatively mature marsh with its so-called climax species and accumulated organic matter or carbon bank. Following the Amoco Cadiz oil spill and subsequent clean-up operations, it was 3 years before a pioneer annual species of Salicornia became established in large numbers at the Ile Grande marsh site along the Brittany coast of France (Seneca and Broome, 1982). Twelve years after dredge material disposal on a Spartina alterniflora marsh along the Bogue Sound shoreline in North Carolina, U.S.A., there was no natural recolonization, although much of the dredge material was in the intertidal zone (Woodhouse et al., 1976). In contrast, a 40-ha dieback area of Spartina marsh on Oak Island, North Carolina, became completely revegetated in 4 years (Linthurst and Seneca, 1980). These and other examples indicate considerable variation in marsh recovery time. Exposed and relatively isolated sites require considerably longer to recover because of the greater role of chance involved in disseminule dispersal and successful establishment. MARSHESTABLISHMENT
Site requirements Elevation and tidal regime interact to determine the extent, duration and time of submergence. It is sometimes difficult to relate the type of marsh at a given location to these three factors and in such cases it may be that the average daily submergence time is the controlling factor. In many cases, the best estimate of suitable elevations for marsh establishment may be obtained by observing and taking elevation readings on a nearby marsh of the type to be constructed. If this is not possible, trial plantings should be made extending from points well above, to those well below the zone of estimated establishment, and survival and growth determined. Where two or more species are being tested, their zones of estimated establishment can be overlapped. Experience along the North Carolina coast indicates that the lower limit of emergent marsh vegetation is about mean sea level. The upper limit of low-marsh species is near mean high water and the upper limit of high-marsh species is the mean storm tide level. Slope determines the area which can be successfully established. Within limits, the more gentle the slope, the more area on which marsh can be established. Although steep slopes may facilitate drainage and aeration, they are more difficult to plant and offer a relatively narrow zone for successful estab-
lishment. Wave energy is dissipated over a relatively narrow area, whereas with a gentle slope, wave energy is dissipated over a comparatively wider area. Slopes must be sufficient for good surface drainage to prevent ponding and subsequent increases in salinity due to evaporation. Marshes have been established on slopes from 10% to < 1%, but slopes of 1-3% are preferable. Exposure to wave action is a major factor to consider in determining the types of propagules to use and the probability of restoration. Wave climate data, which include wind speed and direction, bottom and shoreline configuration, fetch and water level, are not usually available to aid in determining the probability of successful marsh establishment. Fetch, the distance of open water over which the wind blows and waves are generated, is an important indicator of the severity of the wave climate at a given site. Woodhouse {1979 ) summarized the results of numerous plantings and advised that transplants can be used successfully at sites with fetches < 4 km and seed can be used successfully at sites with < 1 km of fetch. Knutson et al. (1981) found that fetch, shore configuration and grain size were useful indicators of wave climate severity and the probability of establishing vegetation by transplanting. Substrate characteristics Marshes occur on a wide variety of substrates ranging from coarse sands to fine clays with both high and low concentrations of organic matter. Sandy substrates are usually the easiest to plant because they provide adequate bearing strength and offer few problems to either manual or machine manipulation when making holes or tilling. These sandy substrates often have insufficient amounts of nutrients necessary for rapid plant establishment. The use of commercial fertilizer materials may be necessary to overcome these deficiencies. Finer textured substrate materials are more likely to have adequate nutrient concentrations. When the upper layers are removed, however, as in the cleanup of a toxic chemical or a petroleum product spill, the remaining substrate may contain insufficient concentrations of plant nutrients, especially nitrogen and phosphorus. Organic substrates present special problems, both physical and chemical, which make them difficult areas for marsh re-establishment. Although many marshes exist on substrates high in organic matter, these marshes were probably initiated prior to the organic matter accumulation which took place under the developing marsh through time. One of the characteristics of estuaries is salinity variation, which may range from a few parts per thousand (ppt) to full sea strength (35 ppt) in the tidal waters which flood the marshes. Owing to substrate characteristics, season, seepage from upland and the frequency of inundation, salinity in salt marsh substrates varies from almost fresh water to more than twice sea strength. Although all salt marsh plants exhibit some degree of salt tolerance, under certain conditions salinity levels may be too high for successful marsh estab-
lishment. Seeds and seedlings are usually more salt sensitive than are established plants. Under regular flooding, sandy substrates do not usually develop salt concentrations which are too high for marsh establishment. In the zone between neap tide high water and spring tide high water, however, salt concentrations may become high in newly planted or seeded areas due to concentration of salts resulting from evaporation during periods of low rainfall and high temperatures. This situation may exist in shallow bays which are influenced by wind setup in which the wind pattern results in extended periods of low water during hot weather, or in areas with large ranges in astronomic tides where the marsh is not flooded during the neap tide period. Domes of sandy material adjacent to and above the planting site, or upland areas adjacent to the site, tend to reduce salinities by accumulating precipitation which seeps outward and dilutes substrate salinities in the planting area. Although salinity tolerance varies greatly among the salt marsh plants of the world, substrate salinities greater than sea strength generally restrict growth and often decrease survival of plantings. Substrate salinities > 45 ppt may prevent establishment of Spartina alterniflora at mid-latitudes (35 °N ) along the eastern coast of the U.S.A., whereas transplants of Puccinellia maritima (Huds.) Parl. may survive this and even higher levels of substrate salinity at 50 °N along the west coast of France.
Plant materials and techniques The ultimate goal in marsh restoration is to replace the marsh that was altered or destroyed. This statement of purpose usually translates into replacing the dominant native angiosperms, with the assumption that once the plants are re-established the animal component and other native plants will soon invade, become re-established and the marsh will return to its former undisturbed state in structure and function. Along the east coast of the U.S.A., Spartina alterniflora is the dominant angiosperm in regularly flooded marshes and is the principal species used in marsh re-establishment projects (Woodhouse et al., 1974, 1976; Garbisch et al., 1975). It has also been used effectively to stabilize shorelines along the Gulf Coast of the U.S.A. (Dodd and Webb, 1975 ). An ecologically equivalent species, S. foliosa Trin., occupies the lower portions of the intertidal zone on the southern Pacific coast of the U.S.A. and it has been planted successfully to re-establish marshes in that region (Knutson, 1976). In the U.K., the vigorous and aggressive fertile hybrid, S. anglica, has been successfully planted and has accelerated recovery of a chronically oiled marsh (Dicks and Iball, 1981 ). Along the Brittany coast of France, Halimione portulacoides (L.) Aell. and PuccineUia maritima have been transplanted successfully along intertidal creek banks and upper levels of the former marsh surface, respectively (Seneca and Broome, 1982). Many marsh angiosperms have been either considered or actually tried in marsh establishment projects. Results of selected studies along the east coast
of the U.S.A. and the European coast will serve to describe the general techniques and procedures developed with three marsh species-S, alterniflora, P. maritima and H. portulacoides. A variety of sites were investigated along the coast of North Carolina to cover the range of astronomic tides (0.2-1.4 m), salinities (10-35 ppt) and tidal exposures. Substrates were primarily sand (often > 90% ) and of gentle slope ( ~ 2% ) (Woodhouse et al., 1974 ). Studies in the Chesapeake Bay region of Virginia and Maryland, U.S.A., were conducted under somewhat lesser influences of astronomic tides, lesser salinities and on a variety of substrate textures (Garbisch et al., 1975; Garbisch, 1977). Studies on the French coast were conducted under a greater astronomic tidal range, higher substrate salinities and on finer textured substrates. Propagation techniques investigated include seeding, transplanting sprigs (tillers with attached roots and rhizome fragments, but with little substrate material), transplanting plugs (tillers with a core of intact substrate material, roots and rhizomes) and planting greenhouse-grown potted seedlings. All methods are feasible with certain species under certain prevailing site conditions. Both manual and mechanical planting procedures have been developed for many species. Techniques have also been developed for nursery production of plant materials. Protective structures have been used successfully on some exposed sites. On substrates with nutrient deficiencies, experiments have been conducted to determine sources, rates, methods of application and timing of application of fertilizer materials. The description of techniques and procedures that follows is largely developed from our work in North Carolina and supplemented by the work of others.
Seeding Seeding experiments with S. alterniflora indicate that seed should be harvested as near as possible to maturity or just prior to shattering, from late September through mid-October along the North Carolina coast. Seeds ripen earlier at more northerly latitudes and later at more southerly latitudes along the Atlantic coast of the U.S.A. Seeds (caryopses) can be harvested by hand, but mechanization is desirable to obtain adequate amounts for large-scale operations. A two-wheeled garden tractor equipped with a reel, cutting blade and a canvas catchment bag has proven satisfactory (Fig. 1) (Broome et al., 1974; Woodhouse et al., 1974). Harvested seed is transferred to large burlap sacks which are then transported to an area for temporary storage or threshing. Seed can be easily threshed in a thresher designed for small grain following storage at 1-4°C for ~ 1 month. After threshing, seed must be stored in covered containers filled with estuarine water, sea water or artificial sea water of ~ 35 ppt salinity at 2-4 ° C. Direct seeding can be accomplished from mid-April through mid-June along the North Carolina coast, earlier at more southerly latitudes and later at more northerly latitudes, by incorporating seed into the substrate to a depth of 2-3
Fig. 1. A machine built for harvesting seed heads of Spartina alterniflora and S. patens. cm. The substrate should be broken up with a rotary tiller or a spike-toothed harrow to prepare the seed bed. The area can then be hand-seeded at the rate of 100 viable seeds (as determined by germination tests) per square meter. Finally, the area should be reworked with the tillage equipment to incorporate the seed into the substrate. Results of seeding experiments indicate that direct seeding is feasible only in the upper half of the intertidal zone. W h e n seeding is successful, complete vegetative cover is established by the end of the first growing seasons. Comparison of an area in the upper half of the intertidal zone that was seeded at the rate of 100 viable seeds per square meter, with one that was transplanted at the same time with sprigs spaced 0.9 m apart, indicated similar above-ground biomass accumulations after two growing seasons. Marsh establishment from direct seeding is dependent on storm-free periods and is more likely to be successful in sheltered or protected sites t h a n in exposed areas. It is probable that most of these techniques and procedures are applicable to the European S. anglica. Seeding costs include harvesting, threshing, storage, seeding, travel, supplies and equipment. Since storage, travel, supplies and equipment vary with the facilities and equipment available, only the remaining cost items are presented here. W h e n a source of seed has been located, costs of seeding one ha are: 5
person hours to harvest seed, 2.5 person hours to thresh the seed and 7.5 person hours to prepare the seed bed and sow the seed. In actual practice, these estimates may need to be doubled to compensate for equipment failure, inexperienced personnel and unforeseen difficulties.
Transplanting sprigs On the North Carolina coast, transplanting sprigs or single-stem plants of
S. alterniflora on a 1-m spacing, in April or May, can result in substrate stabilization and marsh establishment by the end of the second growing season (Woodhouse et al., 1974). Transplanting can be accomplished manually or mechanically, depending on the size of the operation and the accessibility of the site. A farm tractor with a transplanter used for tobacco or vegetable plants has proved satisfactory on certain sandy sites (Woodhouse et al., 1974) (Fig. 2 ) and a hand-held power auger has worked well in less accessible sites (Garbisch et al., 1975). A tool (dibble) similar to that used to plant tree seedlings has worked well in manual operations. Transplanting is successful over a wider range of conditions than is seeding. Marsh can be initiated on exposed sites where seeding is not successful and from about mean sea level to about mean
Fig. 2. A mechanicaltransplanterused for transplantingmarshvegetation.
I0
(b)
Fig. 3. (a) An eroding shoreline near Nags Head, North Carolina was planted with sprigs of S. alterniflora and Spatens in June 1979. (b) The same shoreline after 13 months.
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Fig. 4. (a) An unvegetated creek bank in the marsh at Ile Grande, France, 19 May 1981. Vegetation was destroyed by the Amoco Cadiz oil spill that occurred in March 1978 and the clean-up operations that followed. (b) The same area in May 1982, 1 year after transplanting with Halimione portulacoides and Puccinellia maritima.
12 high water. Closer-spaced plantings have some advantages in establishing stands on marginal sites (Broome et al., 1986). An example of shoreline erosion control using single-stem field-dug transplants is shown in Fig. 3a and b. This planting was carried out in 1979 along the Roanoke Sound shoreline near Nags Head, North Carolina. After 8 years, the planting was still effective in preventing erosion, while the adjacent unvegetated shoreline continued to recede. Costs of transplanting include travel, supplies and equipment in addition to digging plants and transplanting. As with seeding, costs of transport, storage, supplies and equipment vary considerably. Manual digging and planting efforts require: 1 person hour to dig and separate 180-200 transplants and 1 person hour to plant an equal number of transplants. Mechanized costs are: 1 person hour to dig and separate 400 plants using a tractor-drawn shallow plow and about an equal number can be transplanted per person hour using a tractor-drawn planter. Labor costs for manual transplanting of one ha with plants on a 1-m spacing, or 10 000 plants, are ~ 50 person hours for digging and preparing transplants and about the same amount of time for planting. Mechanized costs for an equivalent operation are about half those required in the manual operation for both digging and planting, or a total of ~ 50 person hours for the combined operations. Transplanting sprigs of H. portulacoides 0.5 m apart along intertidal creek banks at Ile Grande, France, in May, resulted in complete cover by the end of the second growing season (Seneca and Broome, 1982 ) (Fig. 4a and b). Transplanting was accomplished manually using a 6.5-cm diameter soil auger which worked well in the high organic matter substrate. Sprigs were dug at the rate of ~ 180 per person hour and planted at the rate of ~ 50 person hour. Based on these digging and planting time requirements only, ~ 1020 person hours (220 person hours to dig sprigs plus 800 person hours to plant) would be required to plant 1 ha on a 0.5-m spacing (40 000 transplants).
Greenhouse-grown potted seedlings Seedlings of S. alterniflora and several other marsh angiosperms have been grown in large numbers in a mixture of equal parts of sand, top soil and either peat moss or vermiculite in plastic trays with 5-cm compartments. Each tray contains 36 planting units (Fig. 5a and b). These transplants initiate marsh development as well or better than sprigs or plugs. They are especially successful on sites with irregular flooding regimes, due mainly to the moisture retention capacity of the potting medium, which is also an advantage in establishment during periods of low rainfall. These greenhouse-grown plants can be used in situations where field-grown plants are unavailable. Because seed must be collected and germinated to grow these plants, at least one year of planning and preparation prior to transplanting is necessary. Extensive plantings utilizing greenhouse-grown potted seedlings have been conducted in the Chesapeake Bay region (Garbisch et al., 1975).
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Fig. 5. (a) Seedlings of Spartina species growing in a greenhouse. (b) A tray of S. cynosuroides seedlings ready for transplanting. The picture was taken 3 months after seeding.
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Fig. 6. (a) An unvegetated site at Kerlavos, France, after planting with alternate rows of sprigs and plugs of Puccinellia maritima (May 1979 ). (b) The same site after 2 years (May 1981 ).
15
Transplanting plugs Transplanting plugs (5-7-cm diameter, 15-cm depth core of root and substrate material intact) of P. maritima on a 0.5-cm spacing at Ile Grande, France, produced good results (Fig. 6a and b). Cover was complete by the end of three growing seasons (Seneca and Broome, 1982). Transplanting was accomplished manually using a 6.5-cm diameter soil auger to open holes for the plugs in substrates which ranged from coarse sand to silt to those with high concentrations of organic matter. Above-ground growth spread radially at the rate of ~ 10 cm annually. These plugs were dug at the rate of ~ 75 per person hour and planted at the rate of ~ 50 per person hour. Based on these digging and planting time requirements only, ~ 1330 person hours (530 person hours to dig plants plus 800 person hours to plant) would be required to plant 1 ha on a 0.5-m spacing.
Fertilizer materials Because of the uncertainty of storm-free periods and adequate precipitation during the establishment period, the human-initiated marsh should be established as quickly as possible. Both conventional and slow-release fertilizer materials have been used successfully to facilitate marsh establishment at sites
Fig. 7. T h e effect of fertilizer on growth of Spartina alterniflora planted along a n eroding shoreline of the Neuse River in N o r t h Carolina. T h e row on t h e right received no fertilizer while the rows on the left a n d the center were fertilized with N, P a n d K at planting.
16 TABLE 1 Means ± 1 standard error comparing growth measurements of a transplanted (carried out in 1974 ) and adjacent natural marsh. Data for the first 2 years for above-ground and the first 3 years for below-ground growth were not included to eliminate bias created by effects of the initial establishment period
Above-ground means Years averaged Numbers of stems m -2 Number of flowering stems m -2 Height (cm) Basal area (cm2 m-2) Dry weight (g m -e) Below-ground means Years averaged Dry weight (gm -2) {0-30 cm)
Transplanted marsh
Natural marsh
1976-1983
1974-1983
745 ± 97 29 ± 6 96 _+6 176 +, 11 849 +,48
719 +,58 77 +, 19 100 +_5 157 +, 7 793 ± 67
1977-1983
1974-1983
2274± 73
1957+, 140
t-test for significant difference
NS ** NS NS NS
Adapted from Broome et al. (1986). *Significant at the 0.05 probability level. **Significant at the 0.01 probability level. where s u b s t r a t e s were deficient in n i t r o g e n a n d / o r p h o s p h o r u s . E v e n on sites w i t h o u t deficiencies in t h e s e n u t r i e n t s , fertilizer a m e n d m e n t s o f t e n result in increased p l a n t growth a n d t h e r e b y s h o r t e n t h e critical e s t a b l i s h m e n t period. On exposed sites, rapid p l a n t growth a n d early e s t a b l i s h m e n t are critical to successful m a r s h d e v e l o p m e n t . Application of t h e e q u i v a l e n t of 112 kg h a -1 N a n d 49 kg h a -1 P, in the p l a n t i n g hole or b y banding, results in good g r o w t h of S. alterniflora in N o r t h Carolina ( B r o o m e et al., 1983 ) (Fig. 7). B o t h c o n v e n t i o n a l soluble a m m o n i u m sulfate plus c o n c e n t r a t e d s u p e r p h o s p h a t e a n d slow-release O s m o c o t e are desirable sources. T h e soluble sources should n o t be placed in direct c o n t a c t with the p l a n t roots. F i r s t y e a r growth can usually be increased significantly by b r o a d c a s t application of a m m o n i u m sulfate plus c o n c e n t r a t e d s u p e r p h o s p h a t e at the same rates in m i d - s u m m e r . T h e same sources, rates a n d m e t h o d of application have also p r o d u c e d significant g r o w t h responses in the s e c o n d growing season. In the finer t e x t u r e d d i s t u r b e d s u b s t r a t e s at Ile G r a n d e , F r a n c e , slow-release Osmocote, placed in t h e p l a n t i n g hole at t h e rate of 2.8 g N a n d 1.2 g P, produced the best growth of H. portulacoides a n d P. maritima. Puccinellia maritima was the m o r e fertilizer d e p e n d e n t of t h e s e two species.
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Long-term development An important aspect of determining the success of marsh restoration projects is long-term measurements. Above- and below-ground standing crops of S. alterniflora transplanted along a shoreline of Bogue Banks, North Carolina, were sampled annually over a 10-year period and compared with a similar adjacent natural marsh (Broome et al., 1986). Results indicated that aboveground biomass was equivalent or greater in the transplanted marsh at the end of the second growing season. Below-ground biomass in the two marshes was equivalent at the end of four growing seasons. Measurements of above-ground growth in the transplanted marsh for Years 3-10 were not significantly different from the natural marsh except for number of flowering stems (Table 1 ). Below-ground biomass was greater in the transplanted area. This sampling was sufficient to document that the restored marsh was persistent and selfsustaining. APPLICATIONOF TECHNOLOGY Although techniques and procedures for marsh establishment have been developed relatively recently and are still being perfected, their use has progressed beyond the purely experimental stage. These procedures have been used to establish marsh successfully under a variety of substrate and tidal conditions along the Atlantic, Gulf and Pacific coasts of the U.S.A. and along the coasts of the U.K. and France. The examples chosen for the discussion to follow illustrate both the usefulness and demand for the technology, in a contractual framework and the need for and application of the technology to real world pollution and marsh destruction problems.
Restoration after an oil spill Marsh establishment techniques and procedures developed along the east coast of the U.S.A. were adapted to the Brittany coast of France to restore marsh that was damaged and destroyed by the Amoco Cadiz oil spill and subsequent cleanup operations (Seneca and Broome, 1982). Preliminary experiments were necessary to compare types of transplants, fertilizer materials and planting seasons and to determine the feasibility of field nursery production for several marsh angiosperms. Although several small-scale plantings were established earlier, larger scale plantings were not begun until one year after the spill. Planting was subsequently continued over a 3-year period. All transplants were spaced 0.5 m apart. Results from these experiments indicated that H. portulacoides and P. maritima survived better and grew more rapidly than the other plants tested. Survival and growth data further indicated that plug-type transplants of P.
18
maritima, with 5-7-cm cores of root and substrate material intact, were superior to sprigs. Sprigs ofH. portulacoides survived and grew well. There was considerable variation in response to fertilizer materials and rates, but both nitrogen and phosphorus were required for good transplant growth on the disturbed sites tested. Above-ground growth of P. maritima spread radially at the rate of ~ 10 cm annually and that of H. portulacoides at about twice this rate. At these rates of spread, planting ofH. portulacoides and P. maritima on a 0.5m spacing would achieve complete substrate cover in ~ 2 and 3 years after planting, respectively. Nursery areas were successfully established for both species and transplants of each species were obtained within 2 years. Twoyear-old nursery plants of H. portulcoides produced an average of eight sprigtype transplants, while those of P. maritima produced an average of 20 plugtype transplants. Based on these results and utilizing both field-dug and nursery-grown plants, ~ 12 000 transplants (~3500 P. maritima and 8500 H. portulacoides) were strategically planted along creek banks and other disturbed sites to restore the marsh. A major effort was devoted to reclaiming areas from which the uppermost marsh substrate was removed during the cleanup operations. Results of these studies suggest that no planting should be conducted on heavily oiled areas (cleaned or uncleaned) within a 6-month period following a major spill. Further, planting along the Brittany coast should be delayed until May after this interval of time. Although removal of oil from the marsh following a severe spill is justified, the marsh surface with the root mat itself should not be removed, The recommended planting procedure along the Brittany coast is to plant two rows of H. portulacoides sprigs spaced 0.5 m apart along the intertidal creek banks with two rows of P. maritima at the same spacing immediately adjacent to the H. portulacoides. The planting of H. portulacoides should receive the highest priority since stabilization of the creek banks is critical to marsh restoration. Comparison of plant cover on planted and unplanted sites 4 years after the spill indicated that natural reinvasion of these damaged sites has been very limited and that restoration was necessary. Contractual marsh establishment Perhaps the most experience in contractual marsh establishment has been gained by E.W. Garbisch of Environmental Concern, Inc., who has been involved in> 220 marsh establishment efforts over the past 15 years, mostly within the Chesapeake Bay region of Virginia and Maryland and the Northeastern U.S.A. Based on sales over the past 4 years by his organization, the number of potted plants sold, including > 20 herbaceous and 30 woody species of marsh plants, has ranged from 100 000 to 700 000 per year. For other vegetative propagules (sprigs, tubers, rhizomes and bulbs), numbers range from 50 000 to 100 000 per year. Seeds cold stored for internal use and for sale have
19 ranged from 900 to 1700 1 per year. These numbers of propagules reflect the size of the operation and the demand for the plant materials and technology involved. Cost estimates generated from this work are probably more realistic and representative of prevailing economics than those generated by research and government agencies. The total cost of marsh establishment includes costs associated with planning and design, negotiating for the site, preparing the site, constructing any necessary protective structures, planting and maintaining the site during the establishment period (Garbisch, 1982). The costs for planting and maintenance during the period of establishment vary depending on site conditions. The cost of potted seedlings for planting 1 ha with plants spaced 0.6 m apart (based on 1987 prices of $0.55 per plant) was ~ $15 400. Slow-release fertilizer material for application at planting to 1 ha costs ~ $2000 and one broadcast application for conventional soluble fertilizer material during the establishment period costs ~ $400 for the same area. The comparable costs for seed to cover 1 ha, o r ~ 1.2 X 106 seeds, were ~ $2400. About 10 person hours are required for broadcasting the seed and cultivation of 1 ha. About 150 person hours are required for transplanting sprigs or potted plants over 1 ha on a 0.6m spacing using a mechanical auger to drill holes. A fully mechanized operation would require about half the time. Fertilization at planting, for plants spaced 0.6 m apart, requires ~ 40 person hours and one broadcast application of fertilizer after planting, ~ 5 person hours. For maintenance during the May-October establishment period, a total of> 200 person hours are required for 1 ha assuming that 20% of the site will have to be replanted due to transplant mortality. Cost evaluation A cost estimate was made based on 1987 plant and fertilizer materials costs. Assumptions were a moderate labor cost of $5 per person hour and a combination of potted plants, slow-release fertilizer at planting and one broadcast fertilizer application after planting. Labor costs to plant 1 ha on 0.6-m spacing ( ~ 28 000 transplants) and maintain the planting for 1 year were~S18 800. Travel, per diem, overhead and profit should then be added, plus 20% of the total costs for a guarantee of the job, making the cost more realistically ~ $34 000. Although it is difficult to quantify wetland values, the cost of planting marsh compares favorably with the values of natural marshes, as estimated by various methods of evaluation (Pope and Gosselink, 1973; Gosselink et al., 1974; Mitsch and Gosselink, 1986). These estimates of marsh establishment costs were based on figures from a contractual organization engaged in this type of work full time and estimates of the values of marshland are cited in the literature and in court cases. Thus, the cost-benefit ratio for marsh establishment practices can realistically be used as justification to restore or replace damaged systems, to develop new
20 productive marshes where none exist, in mitigation when marshlands undergo alteration and to stabilize eroding estuarine shorelines as an alternative to or in conjunction with engineering structures. FUTURE RESEARCH IN MARSH RESTORATION The basic techniques and procedures for establishing estuarine marshes have been worked out for several marsh angiosperms. Rates of establishment and recovery after perturbation are needed to add a predictive dimension to our present knowledge. Selected marsh establishment sites should be monitored for at least a decade. Research should include information on the animal, sedimentation and nutrient components of the marsh as well as the plants. For the dominant marsh angiosperms, tolerance levels to major acute and chronic pollutants, such as petroleum products, should be determined. There is no substitute for obtaining this much needed information prior to serious environmental impacts. In most cases involving toxic materials spills, we do not know how long to wait before attempting to restore the damaged system. Laboratory and greenhouse studies are needed to determine sequential transplant response to substrates contaminated by probable marshland toxic materials. POLICY RECOMMENDATIONS FOR MARSH RESTORATION Although marshes are recognized as valuable estuarine systems and are protected by legislation in many regions of the world, there will always be the possibility of perturbation. Technology for marsh restoration exists for certain geographic areas and the costs to restore marshland are reasonable as compared to its estimated value as a natural resource. Given this situation, it is reasonable to recommend hectare-for-hectare restoration of marsh in the case of projected alteration of these systems whether for public interest projects, in mitigation for disturbance, or for other unavoidable, accidental or willful damage. It is usually necessary to replace all the species, but certainly those perennials that will hasten the return of the originally dominant species in a successional sequence should be planted. Annuals should be used only in exceptional cases as a stepping stone to the establishment of the dominant perennials. The contractor should be required to guarantee the work and replanting should be included in the project plans as a safeguard against damage by natural disasters. The project should be monitored for at least 3-5 years to determine the course of the restoration effort. ACKNOWLEDGMENTS This paper is based on research sponsored by the North Carolina Agricultural Research Service, NOAA and the Coastal Engineering Research Center,
21
U.S. Army Corps of Engineers. Appreciation is extended to Mr. C.L. Campbell, Jr. and Mr. L.L. Hobbs for assistance in field work.
REFERENCES Broome, S.W., Woodhouse, W.W., Jr. and Seneca, E.D., 1974. Propagation of smooth cordgrass, Spartina alterniflora, from seed in North Carolina. Chesapeake Sci., 15: 214-221. Broome, S.W., Seneca, E.D. and Woodhouse, W.W., Jr., 1983. The effects of source rate and placement of nitrogen and phosphorus fertilizers on growth of Spartina alterniflora transplants in North Carolina. Estuaries, 6: 212-226. Broome, S.W., Seneca, E.D. and Woodhouse, W.W., Jr., 1986. Long-term growth and development of transplants of the salt-marsh grass Spartina alterniflora. Estuaries, 9: 63-74. Chung, H.C., 1982. Low Marshes, China. In: R.R. Lewis III (Editor), Creation and Restoration of Coastal Plant Communities. CRC Press, Inc., Boca Raton, FL, pp. 131-145. Chung, H.C. and Zhuo, R., 1985. Twenty-two years ofSpartina anglica Hubbard in China. Journal of Nanjing University, Research Advances in Spartina, pp. 31-35. Dicks, B. and Iball, K., 1981. Ten years of saltmarsh monitoring of the case history of a Southampton Water saltmarsh and a changing refinery effluent discharge. In: Proceedings of the 1981 World Oil Spill Conference, EPA/API/USCG, Atlanta, GA, pp. 361-374. Dodd, J.D. and Webb, J.W., 1975. Establishment of vegetation for shoreline stabilization in Galveston Bay. U.S. Army, Coastal Engineering Research Center, Fort Belvoir, VA, Miscellaneous Paper 6-75. Garbisch, E.W., Jr., 1977. Recent and planned marsh establishment work throughout the contiguous United States. A survey and basic guidelines. CR D-77-3, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi. Garbisch, E.W., Jr., 1982. Highways and wetlands. Compensating wetland losses. U.S. Department of Transportation, Federal Highway Administration, Office of Research and Development, Washington, DC. Garbisch, E.W., Jr., Woller, P.B. and McCallum, R.J., 1975. Salt marsh establishment and development. U.S. Army, Coastal Engineering Research Center, Fort Belvoir, VA, Tech. Memo. 52. Gosselink, J.G., Odum, E.P. and Pope, R.M., 1974. The value of the tidal marsh. Center for Wetland Resources, Louisiana State University, Baton Rouge, Publication LSU-SG-74-03. Knutson, P.L., 1976. Development of intertidal marshlands upon dredged material in San Francisco Bay. Proceedings of the Seventh World Dredging Conference, San Francisco, CA, pp. 103-118. Knutson, P.L., Ford, J.C., Inskeep, M.R. and Ozler, J., 1981. National survey of planted salt marshes (vegetative stabilization and wave stress). Wetlands, 1: 129-157. Lambert, J.M., 1964. The Spartina story. Nature (London), 204: 1136-1138. Linthurst, R.A. and Seneca, E.D., 1980. Dieback of salt-water cordgrass (Spartina alterniflora Loisel.) in the lower Cape Fear Estuary of North Carolina: An experimental approach to reestablishment. Environ. Conserv., 7: 59-66. Mitsch, W.J. and Gosselink, J.G., 1986. Wetlands. Van Nostrand Reinhold Company, New York, 539 pp. Pope, R.M. and Gosselink, J.G., 1973. A tool for use in making land management decisions involving tidal marshland. Coastal Zone Manag. J., 1: 65-74. Ranwell, D.S., 1967. World resources of Spartina townsendii (sensu lato) and economic use of Spartina marshland. J. Appl. Ecol., 4: 239-256. Seneca, E.D. and Broome, S.W., 1982. Restoration of marsh vegetation impacted by the Amoco Cadiz oil spill and subsequent cleanup operations at Ile Grande, France. Interim Report to the
22 Department of Commerce, National Oceanic and Atmospheric Administration, Washington, DC. Woodhouse, W.W., Jr., 1979. Building salt marshes along the coasts of the continental United States. U.S. Army, Coastal Engineering Research Center, Fort Belvoir, VA, Special Report 4. Woodhouse, W.W., Jr., Seneca, E.D. and Broome, S.W., 1974. Propagation of Spartina alterniflora for substrate stabilization and salt marsh development. U.S. Army, Coastal Engineering Research Center, Fort Belvoir, VA, Technical Memo 46. Woodhouse, W.W., Jr., Seneca, E.D. and Broome, S.W., 1976. Propagation and use of Spartina alterniflora for shoreline erosion abatement. U.S. Army, Coastal Engineering Research Center, Fort Belvoir, VA, Technical Report 76-2. Zhuo, R. and Xu, G., 1985. A note on trial planting experiments of Spartina alterniflora. Journal of Nanjing University, Research advances in Spartina, pp. 352-354.