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Formation of Spartina alterniflora salt marshes on the coast of Jiangsu Province, China
Ecological Engineering 23 (2004) 95–105
Formation of Spartina alterniflora salt marshes on the coast of Jiangsu Province, China R.S. Zhang∗ , Y.M. Shen, L.Y. Lu, S.G. Yan, Y.H. Wang, J.L. Li, Z.L. Zhang Institute of Ocean and Coastal Wetland Science, Nanjing Normal University, Nanjing 210097, China Received 16 June 2003; received in revised form 8 July 2004; accepted 14 July 2004
Abstract The climate, substrate, and marine hydrodynamics of Jiangsu, China, tidal flats are suitable for the growth of Spartina alterniflora. Out of 954 km coastline, a section of 410 km is protected by this plant, with a maximum width over 4 km. It functions as a new pioneer stage in plant succession, as a major coastal association, profoundly affecting the coastal environment. Field studies of topography, sedimentology, and vegetation of three typical profiles of Jiangsu coast were conducted in 2000 and 2001. TM satellite images of seven time phases between 1985 and 2001 were used to trace the process of plantation formation. Because of insufficient resolution of the satellites images before 1993 to obtain information on S. alterniflora, we only used those between 1993 and 2001 to classify three stages of their development. The first stage was between 1993 and 1995, with an annual mean expansion rate of 30%. Its area increase is due to enormous seed production and natural spread. The second stage, between 1995 and 1999, had the most rapid with an annual rate of 43%. The third stage, between 1999 and 2001, was only 10%. Its main distribution in Jiangsu lies between mean water level (MWL) and mean high water level (MHWL), on seaward fringe sparse clumps reaching about MWL. © 2004 Published by Elsevier B.V. Keywords: Spartina alterniflora; Salt marsh; Jiangsu; Tidal mud flat
1. Introduction Spartina alterniflora Loisel was introduced to China in 1979 (Chung et al., in press; Xu and Zhou, 1985). Historically, due to enormous quantity of sediments discharged by Yangtze and Yellow Rivers, the progradation of Jiangsu coastal tideland and the landward merging of offshore sands have been two processes ∗
Corresponding author. E-mail address: [email protected] (R.S. Zhang).
0925-8574/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.ecoleng.2004.07.007
of land formation. Since the 11th century about 2.5 million ha. of tideland have been reclaimed. Based on satellite images and field surveys, a general trend of accretion over erosion is clearly shown by the following events: the seaward progradation of MHWL, the land formation of Jianggang Bay, the appearance of a 0.2 km2 island in 2002 just 3 km off the shore and the disappearance of a north–south tidal waterway on western Erfenshui watershed. Mean tidal range of Jiangsu coast is between 1 and 4 km. Because of large volume of fresh water, the salinity of tidal water
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To the present time, with its area extension, S. alterniflora salt marshes with different ecological, economic and social benefits have emerged from the coast of Tianjin in northern China to Guangxi in the south. With straight and open coastlines and wide tidelands the sedimentology and wetland ecosystems of Jiangsu’s plain muddy coast differ greatly from those of the embayment muddy coast in southern China, especially in Fujian Province. As the widths and areas of S. alterniflora salt marshes in Jiangsu are the largest in China with better representative value of plain muddy coast, so we chose Jiangsu as our study site Chen (1988a, 1988b); Qin and Xie (1998).
2. Method
Fig. 1. The study area.
is relatively low, between 2.553% and 3.224%. Muddy flats are even and wide, the width being generally of 2–6 km with the widest to 13 km. The width of upper tideland suitable to S. alterniflora growth is between 1 and 4 km. Over 95% of 954 km Jiangsu coastline pertains to muddy coast, mainly in Yancheng and Nantong municipalities. Jiangsu coastal zone is located between 31◦ 33 –35◦ 07 N, with a monsoon climate ranging from warm-temperate to northern subtropical (Fig. 1). Three ecotypes of S. alterniflora from Morehead City, North Carolina, Altamaha Estuary, Georgia, and Tampa Bay, Florida, were introduced in 1979. The first nursery in Jiangsu was established in Sheyang County (Zhuo et al., 1994). Then trial plantings succeeded in other coastal counties. Previous studies dealt mainly with its roles in sedimentation, coastal protection and comprehensive utilization, whereas no research work has been carried out on its formation, expansion and distribution.
Both asexual propagation of tillering and rhizoming and seed production are very efficient. For tracing S. alterniflora’s development, treatments and analyses of TM satellite images (Yancheng charts) were conducted. Specifically, maps of seven time phases, 1985, 1988, 1993, 1995, 1997, 1999 and 2001, were used. These basically cover areas of different stages from first planting to coalescence (Table 1). For accurately reading and distinguishing Jiangsu coastal vegetation types, scopes, boundaries, and ecological conditions, we carried out environmental surveys (geomorphology, sediments, plant community, etc.) of tidelands of Bado, Wangzhu and Dongchuan polders in Dongtai and Dafeng counties between September 2000 and January 2001. In order to provide reliable ground information for analyzing satellite images, measurements of elevations of three transects together with topography and vegetation distribution were carried out (Fig. 2).
Table 1 The time phases of the TM satellite images No.
Year
Dates
1 2 3 4 5 6 7
1985 1988 1993 1995 1997 1999 2001
11 January 9 April 9 December – 28 February 19 February April
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Fig. 2. The expanding process of S. alterniflora salt-marsh (outside of the: (a) Badou Polder; (b) Dongchuan Polder; (c) Wangzhu Polder).
For satellite images of each time phase, we proceeded with standard falsecolor composite by using three wave sections: TM5, TM4, and TM3. Results showed that it was easy to distinguish dark brown S. alterniflora salt marshes from linear dyke and rose-violet tidal flat covered with fine-grained (floating mud) sediment. Further seaward silt flat tinged
gray or dark gray. Sharp contrast of colors made differentiation of S. alterniflora marsh easy, and transect survey also confirmed this result. There are extensive Phragmites australis marshes along Jiangsu coast. Their colors in falsecolor composite images resemble those of S. alterniflora marsh. As the former are located near large river mouths, these two
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can be differentiated on the basis of river meander topography. In order to reduce calculation errors of satellite images of different time phases, 20 sites of field localization, using GPS and matching with satellite images, were established. On the basis of eyesight readings digitalization of satellite images of all time phases was implemented. By using MapInfo software, measurements and calculations of plantation areas, widths and expanding scope were computed.
3. Results 3.1. Trial plantings of S. alterniflora Up to 1985, total area of trial plantings in Jiangsu only amounted to 8 × 104 m2 . In 1986, for mitigating coastal erosion, plantings of S. alterniflora on tidal flats north of Sheyang River mouth, Dalabakou, Dawagang, Shuangyanggang, etc. were made (Xu and Zhou, 1985; Zhuo et al., 1988, 1994). Up to 1989, a zone of plantation of S. alterniflora has been formed, especially on the most severely eroded sector north of Shuangyang river mouth. The 1986–1988 trial plantings in Dongtai and Dafeng aimed to increase more reclaimable lands Xu et al., 1993. 3.2. Expansion of S. alterniflora plantations 3.2.1. Expansion of tideland plantations outside Bado, Dongchuan and Wangzhu polders About 5 years after 1987, due to small size of the clumps, S. alterniflora salt marshes were unable to be shown on satellite images. Since 1993, they were clearly shown on satellite images. Fig. 2a–c were drawn based on satellite images of the five time phases from 1993 to 2001 and field works. Bado plantation was planted in 1988 on high water line 2 km south of Dongtai river sluice. Its area was only 108 m2 , but in 2001, it became 12.74 km2 of lush and dense marsh. Between Chuangshuigang sluice and Liangduo River sluice, it extended 0.8–2.0 km wide, E–W, and about 8 km long N–S. Quadrat in October 1999 showed its density 99.3 individuals/m2 , mean culm height 1.78 m, maximum 2.0 m and mean culm diameter 0.8 cm.
In 1986–1990, more than 0.3 km2 were planted on tidal land outside of present Dongchuan polder (Chung et al., in press). In April 2001, a continuous plantation was formed between Chuandonggang and Chuanshuigang, N–S 9 km long, 1.0–2.0 km wide and with an area of 16.23 km2 . In 1987 3 km2 and in 1988 1 km2 were planted on tideland south of Wanggang. In April 2001, a coalesced plantation 7.5 km long, 3.3 km wide with an area of 30.39 km2 has developed. 3.2.2. Expanding rates of S. alterniflora Fig. 3a–c shows respectively marsh areas outside of three polders, total areas of S. alterniflora marshes in Jiangsu Province and respective annual expanding rate. Given A0 as S. alterniflora marsh area in a certain year, A1 as area 1 year after, A2 as area 2 years after, P% as annual expansion rate, then A1 = A0 x(1 + P%). The area data from 1993 to 2001 and the equation of A2 = A0 x(1 + P%)2 were used for calculating annual marsh expansion rates (Fig. 3c). Except trial planting period, formation of S. alterniflora salt marshes can be delineated into three stages (Fig. 3), basing upon the readable magnitude of TM satellite images (not less than 1.4 km2 ). For the first stage (1993–1995), annual mean expanding rate was 30%. For the second stage, the highest rate reached 43%, very short in Jiangsu, only 3–4 years (1995–1998). Coastal topographical ecological niches have been occupied in third stage (1998–2001) at a rate of, only 10%. 3.3. Ecological niche of S. alterniflora salt marsh Growth of S. alterniflora needs a certain tidal inundation rate; specificly its ecological niche and tidal level are closely related. On typical prograding tideland and a certain type of sediment of central Jiangsu, Fig. 4 shows results of survey and observation of three profiles. It shows vegetation distribution of upper marsh of three representative profiles and relationships with tideland elevations (Abandoned Yellow River Mouth Datum, and the same hereafter) was used and profile direction was perpendicular to sea dike. Fig. 4 shows following facts: 1. Elevation of S. alterniflora zone is lower than those of grass marsh and Saaeda salsa marshes. The lower
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Fig. 3. The area (km2 ) and expanding rate of Spartina alterniflora salt-marsh ((a) area of three areas; (b) area of whole Jiangsu; (c) annual expanding rates in 2 years).
limit of the latter and the upper limit of the former are separated by a barren flat generally 10 m wide. More than 20 years observations and fieldworks at Badou show that S. alterniflora marsh never spread landward into Imperata and Suaeda marshes. We have seen intermingling of marshes as Suaeda and Imperata in succession process. Chen, 1992 reported elevations occupied by different marshes as 4.0–5.2 m by grass marsh (Imperata cylindrical var. major–Zoysia macrocystis), 3.0–4.5 m by S. salsa marsh and 2–3 m by S. alterniflora marsh. 2. The upper limit of S. alterniflora corresponds to mean high water and its lower limit corresponds to mean sea water level, principally on upper intertidal zone. Planting experiments in Zhejiang reported 15% survival of S. alterniflora on lower tidal zone (Song, 1997). 3. Usually escarpments form on the outer fringe of S. alterniflora. Those on tidal flats near the central
part of Dongtai offshore sands usually lead formation of relatively large tidal channels, thus restricting spread of S. alterniflora Yang et al. (1996). 3.4. Expansion of S. alterniflora salt marshes along the coastline There are many rivers in Jiangsu flowing to the sea. The width, depths, and flowing velocities of lower reaches below sluices are much greater than those tidal creeks without runoffs. Those are due to a common action of fresh water discharge and tidal current. The tidal creeks below sluice lead to back and forth flowing perpendicular to the shore, impeding seeds’ dispersal alongshore. However, these can only slow down and cannot prevent seeds from crossing large tidal creeks. Tiaozini sand, the largest among Jiangsu offshore sands, is separated from its northwest, of the tidal flat off Baduo polder by a tidal channel about 1 km wide,
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Fig. 4. The ecotope of the S. alterniflora salt-marsh on 3 cross-sections of Jiangsu coast ((I) S. salsa, A. littoralis var. Sinesis; (II) I. cylmdrical var. major; (III) S. alterniflora belt; (IV) silty flat).
Sishenggang (Zhang and Chen, 1992). The seeds of S. alterniflora were carried by tidal waves to Tiaozini northwestern higher flats and germinated. At least since 1996, there emerged mottled clumps 1 km wide, 4 km long. Field observations showed that clump area ranged 5–30 m2 , mean density 50–70 culms/m2 , mean culm height 1.0 m (maximum 2.0 m) and mean culm diameter 0.45 cm (Fig. 5). Around the external margin, sparse growth of single or several seedlings and small clumps were observed. Based on satellite images the first S. alterniflora coalesced marsh was found in 2003, elliptical in shape, 2 km long and 1 km wide. Along Sishengang, dense growth of 0.153 km2 in 1999, 0.257 km2 in 2000, 0.734 in 2001, 1.224 in 2002 and 1.577 in 2003 were observed. Many clumps can be found at Erfenshui ridge and they keep on spreading southward, forming areas of sparse (7–8 individuals/m2 ) and short grasses.
3.5. Reconstruction of Jiangsu tidal salt marsh From Fig. 3b, we see that prior to 1993 the area of S. alterniflora salt marshes along Jiangsu coast was not large, whereas in 1993–1999 a rapid expansion took place. Those tidal flats suitable to its growth have been almost completely colonized. Then its expansion slowed down gradually, entering a stable expanding period adapted to a prograding rates of tideland. In 2001, (Fig. 6) total area of S. alterniflora marshes along Jiangsu coast amounted to 137 km2 , mainly distributing between north of Jianggang in Dongtai and Biandangang in Binhai (Fig. 1), forming a continuous zone of S. alterniflora. The coastlines protected by the plant have reached 410 km, 43% of Jiangsu coastline and 47% of Jiangsu muddy coastline, among which there are 80 km long eroded coastline north of Sheyang river mouth and 330 km long prograding coastline south of the river mouth. S. alterniflora salt marshes
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Fig. 5. S. alterniflora marsh on northwestern part of Tiaozini due to natural spread with clump area of 30 m2 . The white spot is a fishermen’s refuge from flooding tide.
have also been distributed between New Huai River and Guan River mouths, in the vicinity of Liezikou and along the coast of Qidong (Fig. 7). The native vegetation on higher tidal zone principally comprises S. salsa and Aulurolpus littoralis var. Sinesis and supraotidal zone with I. cylindrica var. major and Phragmites australis, Introduction of S. alterniflora has been responsible to expanding the entire upper tidal zone by pushing seaward 1–3.5 km, enhancing the widths of vegetation zone.
Fig. 6. S. alterniflora marsh outside of a new dyke of Dongtai, lower part of photo showing its seaward slope. Out of 2 km tideland width, 1.5 km having been embanked and 0.5 km vegetated.
Fig. 7. The distribution of S. alterniflora slat marsh on Jiangsu coast.
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4. Discussion In addition, from 1980 to 2000, 48.2 km2 S. alterniflora marshes have been reclaimed. Although many benefits have been brought from planting S. alterniflora in China, there are still a few problems due to improper planning and misunderstandings. The first problem of loss of original salt marshes in Jiangsu is due to a policy of reclamation. As during the past 50 years the Jiangsu reclaimed over 2300 km2 of tidelands and among which 1444 km2 native salt marshes in total were lost. 605 km2 S. salsa marsh, 516 km2 I. cylindrical var. major–Zoysia macrocystis marsh, and 323 km2 Phragmites australis marsh. Polder sea dyke lines in 1950–1960s mostly were above mean spring high water, mainly on Imperata–Zoysia marsh, in part on Suaeda marsh, thus a large area of original native vegetation being conserved. Not only reclamation has brought great impacts on native salt marsh ecosystems, but also from 1980 to 2000, 48.2 km2 S. alterniflora marshes were lost through reclamation. In The Netherlands, polderization increased once continuously, from 25 ha/year in the 11th century to 1800 ha/year in the 20th century. However, in the last 40 years, a combination of economic, scientific, and cultural factors have led to a halt in reclamation works. Due to a better understanding of the essential ecological functions fulfilled by natural ecosystems, projects for reflooding and removal of sea walls have been undertaken in European countries (Lefeuvre and Bouchard, 2002). Those wetland ecologists who introduced S. alterniflora to China prefer a reconciliation between development and conservation of species diversity. The European experience is very useful to us. Even nowadays, Jiangsu coastal farmers also oppose 100% reclamation for agriculture. Sheyang officials approve fish pond construction only on the condition with shore protection of waved lamping S. alterniflora zone. Farmers are happy not only with profit derived from fish ponds (about 10,000–20,000 Yuan per mu/year), but also for new tideland gained by S. alterniflora (Zuo, 2003, personal communication). The following facts show its rapid expansion compared to other plant species. A 3-year experiment of comparison with S. anglica was conducted in Manukau Harbour (37◦ S) in North Island, New Zealand in the 1960s. In side by side, S. alterniflora spread as much
as in 3 years as S. townsendii (s.1.) had done in 30 (Ranwell, 1967). In 1978–1982, Sheyang office of water works planted 198.8 ha S. anglica, but only 22 ha survived. In 1985–1986 Nanjing University and the latter started interplanting S. alterniflora in old S. anglica stand and extended seaward plantings. In 1994, a vast S. alterniflora marsh 480–500 m wide developed. However, during the period S. anglica was outcompeted by S. alterniflora and disappeared (Zhou et al., 1985). A few hundred acres of formerly freshwater marsh which became salted during canalizaion were reclaimed as useful range pasture in two growing seasons by transplanting S. alterniflora by hand at Cameron Parish, in Louisiana in the 1940s (Ranwell, 1967). S. townsendii (s.1.) has been established successfully in most of the major estuaries of England and Wales, at least 7 sites in Scotland and 16 in Ireland. In France, it was estimated from 4000 to 8000 ha in 1960s. No record was found of the deliberate plantings. It was still actively expanding in the Danish Wadden sea area and in Germany in 1960s. It was widely distributed throughout in southwest Hollond (Ranwell, 1967). According to Hubbard and Stebbings (1967) S. townsendii (s.1.) included two species: S. anglica with 12,000 ha and and S. townsendii (male sterile) with only 20 ha in the 1960s. In China we find Peunisetum purpurea with very high tillering rate of 91 after six cattings a year. A recent field study reveals S. alterniflora minimum tillers of 90 and a maximum of 692 a year in its natural state. Generally there are 5–8 rhizomes from a growing stem, 10–15 nodes, 3–7 tillers from each node. A second problem is that S. alterniflora and some mariculture sites occupy common ecological niche. There are many experimental results to convince our coastal people, because they do not know S. alterniflora detritus food web as the primary producer. The early diagram in Odum’s textbook showed a striking difference of shrimp yields from a natural area of a Texas estuary and one with disturbed salt marsh as 2.5 times more of brown shrimp and 14 times more of white shrimp (Odum, 1971). A recent study found that shrimp catches, world wide, are directly related to the area of marsh in the shrimp nursery grounds. The destruction of North Atlantic coastal marshes is at least in part responsible for the 80% decline in commercial fishery landing of estuarine dependent species since 1920 in Connecticut, New York, and New Jersey.
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Lewis also reports a 20% decline in commercial fisheries catches along Florida Gulf coast after two peaks of 61,400,000 kg in 1960 and 61,500,000 kg in 1965. During this same period, 40% of the mangroves on the main estuaries (Tampa Bay) in the area was lost due to residential and commercial fills (Lewis, 1982a). Monthly densities of juvenile blue crabs in Christmas Bay, Texas revealed the highest in sea grass (2.8– 50.6 m2 ), intermediate in salt marsh (1.3–22.1 m2 ) and the lowest on bare sand (0.6–5.6 m2 ). In West Bay, Texas, where seagrasses were absent, crab densities were intermediate in salt marsh (2.2–13.0 m2 ) to low on bare mud (0.1–1.7 m2 ) (Thomas et al., 1990). In a word, over 95% of the fish and shellfish species that are harvested commercially in the United States are wetland dependent (Mitsch and Gosselink, 2000). Fatty and stable isotopes indicated that the organic matter produced by marsh haloplnytes of Mont Saint Michel Bay, France, contributed to the diet of all tidal flat invertebrates that were studied (Creach et al., 1997), Wainright et al. (2000) using isotopic tracer method discovered in Delaware Bay both Phragmites australis and S. alterniflora being major nutrient sources of high animals (fishes) of all their respective communities. An island of Daishan County, among Zhoushan archipelago in Zhejiang, introduced S. alterniflora in 2001, for developing tourism. University experts commented it as indispensable for this purpose after witnessed its esthetic effect of the nearly coalesced fresh marsh (Zhang et al., 2003). Reports of emergence of blue crabs after S. alterniflora plantings are available from Jiangsu, Shanghai and Zhejiang. Another antagonism has been one between S. alterniflora and mangroves. According to Lewis (1990), some tidal marsh species such as smooth cordgrass are often pioneer colonizers of disturbed habitats and are replaced as other species such as mangroves naturally invade such habitats (Davis, 1940; Lewis and Dunstan, 1976; Lewis, 1982a, 1982b). Recently, the press reported that S. alterniflora on Qiao island, Zhuhai, Guangdong will be entirely wiped out by sea mulberry (Sonneratia species) within 3–5 years. The fear of endangered mangroves to be replaced by S. alterniflora is groundless. Third problem has been that S. alterniflora functions as an efficient coastal stabilizing agent except in flooding time impeding flood discharge. The Haihe River
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Board has to eradicate part of S. alterniflora overgrowth every fall. The principle of coastal plaining has been a reconciliation of development and conservation of species diversity. S. alterniflora should play more important part than previously. In the last decade, planting experiment along north Sheyang coast succeeded on where S. anglica had failed. After 8 years, S. alterniflora plantation was 22.47 km long, 136–910 m wide with an area of 1160.68 ha. Its remarkable power of damping as high as over 90% of wave energy has been measured and turned erosion to accretion (Zhang et al., 2000; Chung, 1996). Jiangsu Province spent about 10 million Yuan to rebuild and repair sea-walls destroyed by 1981 extraordinarily severe typhoon of 1981 (Chen, 1990). Tianjin lost about 400 million Yuan (RMB) in 1992 from an extraordinarily severe storm surge due to lack of extensive marsh vegetation (Qin et al., 2002). To protect coastal people from natural disasters, S. alterniflora becomes an indispensable agent, not mentioning its role as a primary producer of a detritus food web.
5. Conclusion Although our climate as a whole is characterized by lower winter temperature than that of southeast U.S., yet three ecotypes of S. alterniflora from North Carolina, Georgia, and Florida have been good to their new environment. In more than twenty years total area of 137 km2 of S. alterniflora has been reached on bare flats lower than native marsh in elevation. It functions as a new pioneer association in Jiangsu salt marsh, broadening scope of wetland vegetations, as the major dominant association. S. alterniflora belt along Jiangsu coast occurs on the higher part of upper intertidal zone, whereas the most seaward clumps may approach mean tidal water. Its elevation is lower than that of native wetland marsh. Once this neophyte succeeds in rooting, it propagates very well. Based upon the recognizable scale (1.42 km2 in this study) of TM satellite images, three stages can be delineated: early annual mean expanding rate of 30%, second of 43% and third of 10%, the latter may fall farther. The sector underneath river sluice can slow down S. alterniflora’s spread along shore, but cannot prevent its spread by seed seaward dispersal. The uncoelesced
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belt of grass clumps of S. alterniflora indicates S. alterniflora marsh spread across large-scale tidal creeks. Although tidal flats soil with low contents of clay and organic matter and with high wave energy, yet they still can germinate and expand by clumps Zhuo and Xu (1985). Its multiple uses in China show a success in introduction and a bright prospect in the future. It would be interesting to find out how species zonation in China relates to spectes zonation another areas of the world. Based upon Liu et al. (1996) and Beeftink (1977), the following facts have been found. Two common species found both in China and Europe are Zostera marine and Salicornia europaea. The former species was collected by Z.T. Yang, Qingdao, Shandong. In Europe, it is essentially a sublittoral association penetrating into the intertidal belt at the most to about mean sea level. S. europaea association occurs in north ‘and east China, with a cover of 20%. It is replaced by S. sulsa association under water shortage conditions and is succeeded by with decrease soil salinity. S. salsa association occurs extensively from upper intertidal zone landward in north and east China. According to Chen (1992), it is replaced by Zoysia macrostachys under moist condition or by Auluropus littoralis var. Sinensis under dry condition. These two are succeeded by I. cylindrical var. major. In Europe, Suaeda maritime penetrates higher parts of Salicornia belt where the soil is eutrophicated by algae deposited on the mud, it could even replace Salicornia. Suaeda glauca association occurs in higher elevation than S. salsa association. It usually is replaced by A. littoralis var. Sinensis. Aster subulatus is found in I. cylindrical var. major association with a cover only of 2% in China. However, Aster tripolium in Europe plays a more important role. Under brackish, especially on heavy clay in the mesohaline parts of estuaries, a belt of the mostly biennial A. tripolium develops in this zone. It may show very luxuriant growth owing to eutrophication. This community may also develop in depressions and on low creek banks of the brackish marsh, but only when it is not grazed. Carex scabrifolia association occurs in marsh depressions in Jiangsu. It is one of the pioneer communities. It is replaced by Phragmites australis in plant succession. In Europe, Juncus gerardii-Carer extensa
association is among those communities growing between MHWS and the storm-flood zone.
Acknowledgement Funding for this study was provided by Jiangsu Office of Agricultural Resources Development, 1999 for: Engineering experiment Research of Tiaozini sand: accretion and merging with the continent. The authors thank C.H. Chung for literature cited in Section 4. Thanks also to Prof. G.J. Shen for checking the English in this manuscript.
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R.S. Zhang et al. / Ecological Engineering 23 (2004) 95–105 tive from the Mont Saint Michel bay (France). Ecol. Eng. 18, 593–606. Lewis, R.R., 1982a. Low marshes Peninsula Florida. In: Lewis, R.R. (Ed.), Creation and Restoration of Coastal Plant Communities. CRC Press, Boca Raton, FL, pp. 147–152 (Chapter 7). Lewis, R.R. (Ed.), 1982b. Creation and Restoration of Coastal Plant Communities. CRC Press, Boca Raton, FL, pp. 154–171 (Chapter 8). Lewis, R.R., 1990. Creation and restoration of coastal plain wetlands in Florida. In: Kusler, J.A., Kentula, M.E. (Eds.), Wetland Creation and Restoration. Island Press, Washington, D.C., pp. 73–101. Lewis, R.R., Dunstan, F.M., 1976. Possible role of Spartina alterniflora Loisel, in establishment of managroves in Florida. In: Lewis, R.R. (Ed.), Proceedings of the Second Annual Conference on Restoration of Coastal Vegetation in Florida. Hillsborough Community College, Tampa, FL, pp. 81–101. Liu, F.X., Cai, R.H., Tang, T.G., Liu, L., Huang, Z.Y., 1996. Herbaceous hylophytic vegetation. In: Zhao, D.C. (Ed.), Coastal Zone Vegetation of China. Ocean Press, Beijing, pp. 146–155 (in Chinese). Mitsch, W., Gosselink, J., 2000. Wetlands, third edn. John Wiley and Sons, Inc. Odum, E.P., 1971. Fundamentals of ecology. W.B. Saunders, Philadelphia, Pennsylvania, USA. Qin, P., Xie, M., 1998. Estimation of the ecological benefits of two S. alternifora plantations in north Jiangsu, China. Ecol. Eng. 11, 147–156. Qin, P., An, S.Q., Zhou, C.L., Yin, J.L., 2002. Ecological Engineering of Coastal Agriculture. Chemical Engineering Press, Beijing, p. 220 (in Chinese). Ranwell, D.S., 1967. World resources of Spartina townsendii and economic use of Spartina marshlands. J. Appl. Ecol. 4, 239–256. Song, L.Q., 1997. Spartina alterniflora and role of coastal protection. East China Sea Oceanography 15 (1), 11–19 (in Chinese). Thomas, J.L., Zimmerman, R.J., Minello, T.J., 1990. Abundance patterns of juvenile blue crabs (Callinectes supindas) in nursery habitats of two Texas bays. Bull. Mar. Sci. 46 (1), 115–125. Wainright, S.C., Weinstein, M.P., Able, K.W., Currin, C.A., 2000. Relative importance of bentbic microalgae, phytoplankton and the detritus of smooth cordgrass, Spartina alterniflora and the
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common reed. Phragmites australis to brackish-marsh food webs. Mar. Ecol. Progr. Ser. 200, 77–91. Xu, G.W., Zhou, R.Z., 1985. Preliminary studies of introduced Spartina alteriflora Loisel in China. J. Nanjing Univ. Adv. Spartina Res., 212–225 (in Chinese with English summary). Xu, G.W., Zhou, R.E., Chung, C.H., 1993. A study of effects of accelerating Dongtai coastal tideland sedimentation by Spartina alterniflora plantation. J. Nanjing Univ., 228–231 (Second Special Issue on the Causes and Countermeasures of Natural Disasters) (in Chinese with English summary). Yang, C.C., Wang, B.C., Dai, J.C., Liu, L.T., Ye, R.H., 1996. Ecological benefits of Spartina alternaflora and its agricultural utilization ways. In: Dong, B.R. (Ed.), Comprehensive Developmental Techniques of Newly Embanked Tideland of Zhejiang. Chinese Agricultural Science and Technology Press, Beijing, p. 246 (in Chinese). Zhang, C.T., Qin, P., Wan, S.W., 2000. A study of resource pattern of S. alterniflora ecological engineering from the angle of emergy benefit. Chin. Acta Ecol. 20 (6), 1045–1049 (in Chinese). Zhang, R.S., Chen, C.J., 1992. Evolution of Jiangsu Offshore Banks and Probability of Tiaozini Sands Merged into Mainland. Ocean Press, Beijing, 124 pp. (in Chinese). Zhang, R.S., Yan, S.G., Shen, Y.M., 2003. Reclamation activities of Jiangsu prograding tidelands and fluctuations of salt marsh vegeation. Chin. Popul. Resour. Environ. 13, 118–120 (Special Issue of Sustainable Theory and Practice) (in Chinese). Zhou, D., Wang, X.R., Zhou, A.H., Wang, B.K., Pan, D.M., Zhang, E.R., 1985. A preliminary report of mercary enrichment by Spartina alterniflora Loisel and Spartina anglica Hubbard. J. Nanjing Univ. Res. Adv. Spartina, 116–123 (in Chinese with English summary). Zhuo, R.Z., Xu, G.W., 1985. A note on trial planting experiments. J. Nanjing Univ. Res. Adv. Spartina, 353–354 (in Chinese with English summary). Zhuo, R.Z., Xu, G.W., Li, X.G., 1988. Introduction, acclimatization and uses of Spartina alterniflore Loisel along the Chinese coastline. In: Proceedings of the International Symposium on the coastal zone, Beijing, August 1988, pp. 632–637. Zhuo, R.Z., Xu, G.W., Xue, G.J., Xie, T.S., Jee, R.E., 1994. A study of planting technique of Spartina alterniflora on eroded tidelands, p. 11 (in Chinese, mimeographed).
Formation of Spartina alterniflora salt marshes on the coast of Jiangsu Province, China R.S. Zhang∗ , Y.M. Shen, L.Y. Lu, S.G. Yan, Y.H. Wang, J.L. Li, Z.L. Zhang Institute of Ocean and Coastal Wetland Science, Nanjing Normal University, Nanjing 210097, China Received 16 June 2003; received in revised form 8 July 2004; accepted 14 July 2004
Abstract The climate, substrate, and marine hydrodynamics of Jiangsu, China, tidal flats are suitable for the growth of Spartina alterniflora. Out of 954 km coastline, a section of 410 km is protected by this plant, with a maximum width over 4 km. It functions as a new pioneer stage in plant succession, as a major coastal association, profoundly affecting the coastal environment. Field studies of topography, sedimentology, and vegetation of three typical profiles of Jiangsu coast were conducted in 2000 and 2001. TM satellite images of seven time phases between 1985 and 2001 were used to trace the process of plantation formation. Because of insufficient resolution of the satellites images before 1993 to obtain information on S. alterniflora, we only used those between 1993 and 2001 to classify three stages of their development. The first stage was between 1993 and 1995, with an annual mean expansion rate of 30%. Its area increase is due to enormous seed production and natural spread. The second stage, between 1995 and 1999, had the most rapid with an annual rate of 43%. The third stage, between 1999 and 2001, was only 10%. Its main distribution in Jiangsu lies between mean water level (MWL) and mean high water level (MHWL), on seaward fringe sparse clumps reaching about MWL. © 2004 Published by Elsevier B.V. Keywords: Spartina alterniflora; Salt marsh; Jiangsu; Tidal mud flat
1. Introduction Spartina alterniflora Loisel was introduced to China in 1979 (Chung et al., in press; Xu and Zhou, 1985). Historically, due to enormous quantity of sediments discharged by Yangtze and Yellow Rivers, the progradation of Jiangsu coastal tideland and the landward merging of offshore sands have been two processes ∗
Corresponding author. E-mail address: [email protected] (R.S. Zhang).
0925-8574/$ – see front matter © 2004 Published by Elsevier B.V. doi:10.1016/j.ecoleng.2004.07.007
of land formation. Since the 11th century about 2.5 million ha. of tideland have been reclaimed. Based on satellite images and field surveys, a general trend of accretion over erosion is clearly shown by the following events: the seaward progradation of MHWL, the land formation of Jianggang Bay, the appearance of a 0.2 km2 island in 2002 just 3 km off the shore and the disappearance of a north–south tidal waterway on western Erfenshui watershed. Mean tidal range of Jiangsu coast is between 1 and 4 km. Because of large volume of fresh water, the salinity of tidal water
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To the present time, with its area extension, S. alterniflora salt marshes with different ecological, economic and social benefits have emerged from the coast of Tianjin in northern China to Guangxi in the south. With straight and open coastlines and wide tidelands the sedimentology and wetland ecosystems of Jiangsu’s plain muddy coast differ greatly from those of the embayment muddy coast in southern China, especially in Fujian Province. As the widths and areas of S. alterniflora salt marshes in Jiangsu are the largest in China with better representative value of plain muddy coast, so we chose Jiangsu as our study site Chen (1988a, 1988b); Qin and Xie (1998).
2. Method
Fig. 1. The study area.
is relatively low, between 2.553% and 3.224%. Muddy flats are even and wide, the width being generally of 2–6 km with the widest to 13 km. The width of upper tideland suitable to S. alterniflora growth is between 1 and 4 km. Over 95% of 954 km Jiangsu coastline pertains to muddy coast, mainly in Yancheng and Nantong municipalities. Jiangsu coastal zone is located between 31◦ 33 –35◦ 07 N, with a monsoon climate ranging from warm-temperate to northern subtropical (Fig. 1). Three ecotypes of S. alterniflora from Morehead City, North Carolina, Altamaha Estuary, Georgia, and Tampa Bay, Florida, were introduced in 1979. The first nursery in Jiangsu was established in Sheyang County (Zhuo et al., 1994). Then trial plantings succeeded in other coastal counties. Previous studies dealt mainly with its roles in sedimentation, coastal protection and comprehensive utilization, whereas no research work has been carried out on its formation, expansion and distribution.
Both asexual propagation of tillering and rhizoming and seed production are very efficient. For tracing S. alterniflora’s development, treatments and analyses of TM satellite images (Yancheng charts) were conducted. Specifically, maps of seven time phases, 1985, 1988, 1993, 1995, 1997, 1999 and 2001, were used. These basically cover areas of different stages from first planting to coalescence (Table 1). For accurately reading and distinguishing Jiangsu coastal vegetation types, scopes, boundaries, and ecological conditions, we carried out environmental surveys (geomorphology, sediments, plant community, etc.) of tidelands of Bado, Wangzhu and Dongchuan polders in Dongtai and Dafeng counties between September 2000 and January 2001. In order to provide reliable ground information for analyzing satellite images, measurements of elevations of three transects together with topography and vegetation distribution were carried out (Fig. 2).
Table 1 The time phases of the TM satellite images No.
Year
Dates
1 2 3 4 5 6 7
1985 1988 1993 1995 1997 1999 2001
11 January 9 April 9 December – 28 February 19 February April
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Fig. 2. The expanding process of S. alterniflora salt-marsh (outside of the: (a) Badou Polder; (b) Dongchuan Polder; (c) Wangzhu Polder).
For satellite images of each time phase, we proceeded with standard falsecolor composite by using three wave sections: TM5, TM4, and TM3. Results showed that it was easy to distinguish dark brown S. alterniflora salt marshes from linear dyke and rose-violet tidal flat covered with fine-grained (floating mud) sediment. Further seaward silt flat tinged
gray or dark gray. Sharp contrast of colors made differentiation of S. alterniflora marsh easy, and transect survey also confirmed this result. There are extensive Phragmites australis marshes along Jiangsu coast. Their colors in falsecolor composite images resemble those of S. alterniflora marsh. As the former are located near large river mouths, these two
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can be differentiated on the basis of river meander topography. In order to reduce calculation errors of satellite images of different time phases, 20 sites of field localization, using GPS and matching with satellite images, were established. On the basis of eyesight readings digitalization of satellite images of all time phases was implemented. By using MapInfo software, measurements and calculations of plantation areas, widths and expanding scope were computed.
3. Results 3.1. Trial plantings of S. alterniflora Up to 1985, total area of trial plantings in Jiangsu only amounted to 8 × 104 m2 . In 1986, for mitigating coastal erosion, plantings of S. alterniflora on tidal flats north of Sheyang River mouth, Dalabakou, Dawagang, Shuangyanggang, etc. were made (Xu and Zhou, 1985; Zhuo et al., 1988, 1994). Up to 1989, a zone of plantation of S. alterniflora has been formed, especially on the most severely eroded sector north of Shuangyang river mouth. The 1986–1988 trial plantings in Dongtai and Dafeng aimed to increase more reclaimable lands Xu et al., 1993. 3.2. Expansion of S. alterniflora plantations 3.2.1. Expansion of tideland plantations outside Bado, Dongchuan and Wangzhu polders About 5 years after 1987, due to small size of the clumps, S. alterniflora salt marshes were unable to be shown on satellite images. Since 1993, they were clearly shown on satellite images. Fig. 2a–c were drawn based on satellite images of the five time phases from 1993 to 2001 and field works. Bado plantation was planted in 1988 on high water line 2 km south of Dongtai river sluice. Its area was only 108 m2 , but in 2001, it became 12.74 km2 of lush and dense marsh. Between Chuangshuigang sluice and Liangduo River sluice, it extended 0.8–2.0 km wide, E–W, and about 8 km long N–S. Quadrat in October 1999 showed its density 99.3 individuals/m2 , mean culm height 1.78 m, maximum 2.0 m and mean culm diameter 0.8 cm.
In 1986–1990, more than 0.3 km2 were planted on tidal land outside of present Dongchuan polder (Chung et al., in press). In April 2001, a continuous plantation was formed between Chuandonggang and Chuanshuigang, N–S 9 km long, 1.0–2.0 km wide and with an area of 16.23 km2 . In 1987 3 km2 and in 1988 1 km2 were planted on tideland south of Wanggang. In April 2001, a coalesced plantation 7.5 km long, 3.3 km wide with an area of 30.39 km2 has developed. 3.2.2. Expanding rates of S. alterniflora Fig. 3a–c shows respectively marsh areas outside of three polders, total areas of S. alterniflora marshes in Jiangsu Province and respective annual expanding rate. Given A0 as S. alterniflora marsh area in a certain year, A1 as area 1 year after, A2 as area 2 years after, P% as annual expansion rate, then A1 = A0 x(1 + P%). The area data from 1993 to 2001 and the equation of A2 = A0 x(1 + P%)2 were used for calculating annual marsh expansion rates (Fig. 3c). Except trial planting period, formation of S. alterniflora salt marshes can be delineated into three stages (Fig. 3), basing upon the readable magnitude of TM satellite images (not less than 1.4 km2 ). For the first stage (1993–1995), annual mean expanding rate was 30%. For the second stage, the highest rate reached 43%, very short in Jiangsu, only 3–4 years (1995–1998). Coastal topographical ecological niches have been occupied in third stage (1998–2001) at a rate of, only 10%. 3.3. Ecological niche of S. alterniflora salt marsh Growth of S. alterniflora needs a certain tidal inundation rate; specificly its ecological niche and tidal level are closely related. On typical prograding tideland and a certain type of sediment of central Jiangsu, Fig. 4 shows results of survey and observation of three profiles. It shows vegetation distribution of upper marsh of three representative profiles and relationships with tideland elevations (Abandoned Yellow River Mouth Datum, and the same hereafter) was used and profile direction was perpendicular to sea dike. Fig. 4 shows following facts: 1. Elevation of S. alterniflora zone is lower than those of grass marsh and Saaeda salsa marshes. The lower
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Fig. 3. The area (km2 ) and expanding rate of Spartina alterniflora salt-marsh ((a) area of three areas; (b) area of whole Jiangsu; (c) annual expanding rates in 2 years).
limit of the latter and the upper limit of the former are separated by a barren flat generally 10 m wide. More than 20 years observations and fieldworks at Badou show that S. alterniflora marsh never spread landward into Imperata and Suaeda marshes. We have seen intermingling of marshes as Suaeda and Imperata in succession process. Chen, 1992 reported elevations occupied by different marshes as 4.0–5.2 m by grass marsh (Imperata cylindrical var. major–Zoysia macrocystis), 3.0–4.5 m by S. salsa marsh and 2–3 m by S. alterniflora marsh. 2. The upper limit of S. alterniflora corresponds to mean high water and its lower limit corresponds to mean sea water level, principally on upper intertidal zone. Planting experiments in Zhejiang reported 15% survival of S. alterniflora on lower tidal zone (Song, 1997). 3. Usually escarpments form on the outer fringe of S. alterniflora. Those on tidal flats near the central
part of Dongtai offshore sands usually lead formation of relatively large tidal channels, thus restricting spread of S. alterniflora Yang et al. (1996). 3.4. Expansion of S. alterniflora salt marshes along the coastline There are many rivers in Jiangsu flowing to the sea. The width, depths, and flowing velocities of lower reaches below sluices are much greater than those tidal creeks without runoffs. Those are due to a common action of fresh water discharge and tidal current. The tidal creeks below sluice lead to back and forth flowing perpendicular to the shore, impeding seeds’ dispersal alongshore. However, these can only slow down and cannot prevent seeds from crossing large tidal creeks. Tiaozini sand, the largest among Jiangsu offshore sands, is separated from its northwest, of the tidal flat off Baduo polder by a tidal channel about 1 km wide,
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Fig. 4. The ecotope of the S. alterniflora salt-marsh on 3 cross-sections of Jiangsu coast ((I) S. salsa, A. littoralis var. Sinesis; (II) I. cylmdrical var. major; (III) S. alterniflora belt; (IV) silty flat).
Sishenggang (Zhang and Chen, 1992). The seeds of S. alterniflora were carried by tidal waves to Tiaozini northwestern higher flats and germinated. At least since 1996, there emerged mottled clumps 1 km wide, 4 km long. Field observations showed that clump area ranged 5–30 m2 , mean density 50–70 culms/m2 , mean culm height 1.0 m (maximum 2.0 m) and mean culm diameter 0.45 cm (Fig. 5). Around the external margin, sparse growth of single or several seedlings and small clumps were observed. Based on satellite images the first S. alterniflora coalesced marsh was found in 2003, elliptical in shape, 2 km long and 1 km wide. Along Sishengang, dense growth of 0.153 km2 in 1999, 0.257 km2 in 2000, 0.734 in 2001, 1.224 in 2002 and 1.577 in 2003 were observed. Many clumps can be found at Erfenshui ridge and they keep on spreading southward, forming areas of sparse (7–8 individuals/m2 ) and short grasses.
3.5. Reconstruction of Jiangsu tidal salt marsh From Fig. 3b, we see that prior to 1993 the area of S. alterniflora salt marshes along Jiangsu coast was not large, whereas in 1993–1999 a rapid expansion took place. Those tidal flats suitable to its growth have been almost completely colonized. Then its expansion slowed down gradually, entering a stable expanding period adapted to a prograding rates of tideland. In 2001, (Fig. 6) total area of S. alterniflora marshes along Jiangsu coast amounted to 137 km2 , mainly distributing between north of Jianggang in Dongtai and Biandangang in Binhai (Fig. 1), forming a continuous zone of S. alterniflora. The coastlines protected by the plant have reached 410 km, 43% of Jiangsu coastline and 47% of Jiangsu muddy coastline, among which there are 80 km long eroded coastline north of Sheyang river mouth and 330 km long prograding coastline south of the river mouth. S. alterniflora salt marshes
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Fig. 5. S. alterniflora marsh on northwestern part of Tiaozini due to natural spread with clump area of 30 m2 . The white spot is a fishermen’s refuge from flooding tide.
have also been distributed between New Huai River and Guan River mouths, in the vicinity of Liezikou and along the coast of Qidong (Fig. 7). The native vegetation on higher tidal zone principally comprises S. salsa and Aulurolpus littoralis var. Sinesis and supraotidal zone with I. cylindrica var. major and Phragmites australis, Introduction of S. alterniflora has been responsible to expanding the entire upper tidal zone by pushing seaward 1–3.5 km, enhancing the widths of vegetation zone.
Fig. 6. S. alterniflora marsh outside of a new dyke of Dongtai, lower part of photo showing its seaward slope. Out of 2 km tideland width, 1.5 km having been embanked and 0.5 km vegetated.
Fig. 7. The distribution of S. alterniflora slat marsh on Jiangsu coast.
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4. Discussion In addition, from 1980 to 2000, 48.2 km2 S. alterniflora marshes have been reclaimed. Although many benefits have been brought from planting S. alterniflora in China, there are still a few problems due to improper planning and misunderstandings. The first problem of loss of original salt marshes in Jiangsu is due to a policy of reclamation. As during the past 50 years the Jiangsu reclaimed over 2300 km2 of tidelands and among which 1444 km2 native salt marshes in total were lost. 605 km2 S. salsa marsh, 516 km2 I. cylindrical var. major–Zoysia macrocystis marsh, and 323 km2 Phragmites australis marsh. Polder sea dyke lines in 1950–1960s mostly were above mean spring high water, mainly on Imperata–Zoysia marsh, in part on Suaeda marsh, thus a large area of original native vegetation being conserved. Not only reclamation has brought great impacts on native salt marsh ecosystems, but also from 1980 to 2000, 48.2 km2 S. alterniflora marshes were lost through reclamation. In The Netherlands, polderization increased once continuously, from 25 ha/year in the 11th century to 1800 ha/year in the 20th century. However, in the last 40 years, a combination of economic, scientific, and cultural factors have led to a halt in reclamation works. Due to a better understanding of the essential ecological functions fulfilled by natural ecosystems, projects for reflooding and removal of sea walls have been undertaken in European countries (Lefeuvre and Bouchard, 2002). Those wetland ecologists who introduced S. alterniflora to China prefer a reconciliation between development and conservation of species diversity. The European experience is very useful to us. Even nowadays, Jiangsu coastal farmers also oppose 100% reclamation for agriculture. Sheyang officials approve fish pond construction only on the condition with shore protection of waved lamping S. alterniflora zone. Farmers are happy not only with profit derived from fish ponds (about 10,000–20,000 Yuan per mu/year), but also for new tideland gained by S. alterniflora (Zuo, 2003, personal communication). The following facts show its rapid expansion compared to other plant species. A 3-year experiment of comparison with S. anglica was conducted in Manukau Harbour (37◦ S) in North Island, New Zealand in the 1960s. In side by side, S. alterniflora spread as much
as in 3 years as S. townsendii (s.1.) had done in 30 (Ranwell, 1967). In 1978–1982, Sheyang office of water works planted 198.8 ha S. anglica, but only 22 ha survived. In 1985–1986 Nanjing University and the latter started interplanting S. alterniflora in old S. anglica stand and extended seaward plantings. In 1994, a vast S. alterniflora marsh 480–500 m wide developed. However, during the period S. anglica was outcompeted by S. alterniflora and disappeared (Zhou et al., 1985). A few hundred acres of formerly freshwater marsh which became salted during canalizaion were reclaimed as useful range pasture in two growing seasons by transplanting S. alterniflora by hand at Cameron Parish, in Louisiana in the 1940s (Ranwell, 1967). S. townsendii (s.1.) has been established successfully in most of the major estuaries of England and Wales, at least 7 sites in Scotland and 16 in Ireland. In France, it was estimated from 4000 to 8000 ha in 1960s. No record was found of the deliberate plantings. It was still actively expanding in the Danish Wadden sea area and in Germany in 1960s. It was widely distributed throughout in southwest Hollond (Ranwell, 1967). According to Hubbard and Stebbings (1967) S. townsendii (s.1.) included two species: S. anglica with 12,000 ha and and S. townsendii (male sterile) with only 20 ha in the 1960s. In China we find Peunisetum purpurea with very high tillering rate of 91 after six cattings a year. A recent field study reveals S. alterniflora minimum tillers of 90 and a maximum of 692 a year in its natural state. Generally there are 5–8 rhizomes from a growing stem, 10–15 nodes, 3–7 tillers from each node. A second problem is that S. alterniflora and some mariculture sites occupy common ecological niche. There are many experimental results to convince our coastal people, because they do not know S. alterniflora detritus food web as the primary producer. The early diagram in Odum’s textbook showed a striking difference of shrimp yields from a natural area of a Texas estuary and one with disturbed salt marsh as 2.5 times more of brown shrimp and 14 times more of white shrimp (Odum, 1971). A recent study found that shrimp catches, world wide, are directly related to the area of marsh in the shrimp nursery grounds. The destruction of North Atlantic coastal marshes is at least in part responsible for the 80% decline in commercial fishery landing of estuarine dependent species since 1920 in Connecticut, New York, and New Jersey.
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Lewis also reports a 20% decline in commercial fisheries catches along Florida Gulf coast after two peaks of 61,400,000 kg in 1960 and 61,500,000 kg in 1965. During this same period, 40% of the mangroves on the main estuaries (Tampa Bay) in the area was lost due to residential and commercial fills (Lewis, 1982a). Monthly densities of juvenile blue crabs in Christmas Bay, Texas revealed the highest in sea grass (2.8– 50.6 m2 ), intermediate in salt marsh (1.3–22.1 m2 ) and the lowest on bare sand (0.6–5.6 m2 ). In West Bay, Texas, where seagrasses were absent, crab densities were intermediate in salt marsh (2.2–13.0 m2 ) to low on bare mud (0.1–1.7 m2 ) (Thomas et al., 1990). In a word, over 95% of the fish and shellfish species that are harvested commercially in the United States are wetland dependent (Mitsch and Gosselink, 2000). Fatty and stable isotopes indicated that the organic matter produced by marsh haloplnytes of Mont Saint Michel Bay, France, contributed to the diet of all tidal flat invertebrates that were studied (Creach et al., 1997), Wainright et al. (2000) using isotopic tracer method discovered in Delaware Bay both Phragmites australis and S. alterniflora being major nutrient sources of high animals (fishes) of all their respective communities. An island of Daishan County, among Zhoushan archipelago in Zhejiang, introduced S. alterniflora in 2001, for developing tourism. University experts commented it as indispensable for this purpose after witnessed its esthetic effect of the nearly coalesced fresh marsh (Zhang et al., 2003). Reports of emergence of blue crabs after S. alterniflora plantings are available from Jiangsu, Shanghai and Zhejiang. Another antagonism has been one between S. alterniflora and mangroves. According to Lewis (1990), some tidal marsh species such as smooth cordgrass are often pioneer colonizers of disturbed habitats and are replaced as other species such as mangroves naturally invade such habitats (Davis, 1940; Lewis and Dunstan, 1976; Lewis, 1982a, 1982b). Recently, the press reported that S. alterniflora on Qiao island, Zhuhai, Guangdong will be entirely wiped out by sea mulberry (Sonneratia species) within 3–5 years. The fear of endangered mangroves to be replaced by S. alterniflora is groundless. Third problem has been that S. alterniflora functions as an efficient coastal stabilizing agent except in flooding time impeding flood discharge. The Haihe River
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Board has to eradicate part of S. alterniflora overgrowth every fall. The principle of coastal plaining has been a reconciliation of development and conservation of species diversity. S. alterniflora should play more important part than previously. In the last decade, planting experiment along north Sheyang coast succeeded on where S. anglica had failed. After 8 years, S. alterniflora plantation was 22.47 km long, 136–910 m wide with an area of 1160.68 ha. Its remarkable power of damping as high as over 90% of wave energy has been measured and turned erosion to accretion (Zhang et al., 2000; Chung, 1996). Jiangsu Province spent about 10 million Yuan to rebuild and repair sea-walls destroyed by 1981 extraordinarily severe typhoon of 1981 (Chen, 1990). Tianjin lost about 400 million Yuan (RMB) in 1992 from an extraordinarily severe storm surge due to lack of extensive marsh vegetation (Qin et al., 2002). To protect coastal people from natural disasters, S. alterniflora becomes an indispensable agent, not mentioning its role as a primary producer of a detritus food web.
5. Conclusion Although our climate as a whole is characterized by lower winter temperature than that of southeast U.S., yet three ecotypes of S. alterniflora from North Carolina, Georgia, and Florida have been good to their new environment. In more than twenty years total area of 137 km2 of S. alterniflora has been reached on bare flats lower than native marsh in elevation. It functions as a new pioneer association in Jiangsu salt marsh, broadening scope of wetland vegetations, as the major dominant association. S. alterniflora belt along Jiangsu coast occurs on the higher part of upper intertidal zone, whereas the most seaward clumps may approach mean tidal water. Its elevation is lower than that of native wetland marsh. Once this neophyte succeeds in rooting, it propagates very well. Based upon the recognizable scale (1.42 km2 in this study) of TM satellite images, three stages can be delineated: early annual mean expanding rate of 30%, second of 43% and third of 10%, the latter may fall farther. The sector underneath river sluice can slow down S. alterniflora’s spread along shore, but cannot prevent its spread by seed seaward dispersal. The uncoelesced
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belt of grass clumps of S. alterniflora indicates S. alterniflora marsh spread across large-scale tidal creeks. Although tidal flats soil with low contents of clay and organic matter and with high wave energy, yet they still can germinate and expand by clumps Zhuo and Xu (1985). Its multiple uses in China show a success in introduction and a bright prospect in the future. It would be interesting to find out how species zonation in China relates to spectes zonation another areas of the world. Based upon Liu et al. (1996) and Beeftink (1977), the following facts have been found. Two common species found both in China and Europe are Zostera marine and Salicornia europaea. The former species was collected by Z.T. Yang, Qingdao, Shandong. In Europe, it is essentially a sublittoral association penetrating into the intertidal belt at the most to about mean sea level. S. europaea association occurs in north ‘and east China, with a cover of 20%. It is replaced by S. sulsa association under water shortage conditions and is succeeded by with decrease soil salinity. S. salsa association occurs extensively from upper intertidal zone landward in north and east China. According to Chen (1992), it is replaced by Zoysia macrostachys under moist condition or by Auluropus littoralis var. Sinensis under dry condition. These two are succeeded by I. cylindrical var. major. In Europe, Suaeda maritime penetrates higher parts of Salicornia belt where the soil is eutrophicated by algae deposited on the mud, it could even replace Salicornia. Suaeda glauca association occurs in higher elevation than S. salsa association. It usually is replaced by A. littoralis var. Sinensis. Aster subulatus is found in I. cylindrical var. major association with a cover only of 2% in China. However, Aster tripolium in Europe plays a more important role. Under brackish, especially on heavy clay in the mesohaline parts of estuaries, a belt of the mostly biennial A. tripolium develops in this zone. It may show very luxuriant growth owing to eutrophication. This community may also develop in depressions and on low creek banks of the brackish marsh, but only when it is not grazed. Carex scabrifolia association occurs in marsh depressions in Jiangsu. It is one of the pioneer communities. It is replaced by Phragmites australis in plant succession. In Europe, Juncus gerardii-Carer extensa
association is among those communities growing between MHWS and the storm-flood zone.
Acknowledgement Funding for this study was provided by Jiangsu Office of Agricultural Resources Development, 1999 for: Engineering experiment Research of Tiaozini sand: accretion and merging with the continent. The authors thank C.H. Chung for literature cited in Section 4. Thanks also to Prof. G.J. Shen for checking the English in this manuscript.
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