Bare Mudflat Research Articles

Climate Change, Sea-Level Rise and Implications for Coastal and Estuarine Shoreline Management with Particular Reference to the Ecology of Intertidal Benthic Macrofauna in NW Europe.

In many European estuaries, extensive areas of intertidal habitats consist of bare mudflats and sandflats that harbour a very high abundance and biomass of macrobenthic invertebrates. The high stocks of macrobenthos in turn provide important food sources for the higher trophic levels such as fish and shorebirds. Climate change and associated sea-level rise will have potential to cause changes in coastal and estuarine physical properties in a number of ways and thereby influence the ecology of estuarine dependent organisms. Although the mechanisms involved in biological responses resulting from such environmental changes are complex, the ecological effects are likely to be significant for the estuarine benthic macrofauna and hence the consumers they support. This paper reviews the utilisation patterns of estuarine intertidal habitats by shorebirds, fish and crustaceans, as well as factors affecting the distribution, abundance and biomass of estuarine macrobenthos that is known to be important food source for these estuarine predators. This study also provides simple conceptual models of the likely impacts of sea-level rise on the physical and biological elements of estuarine intertidal habitats, and implications of these results are discussed in the context of sustainable long term flood and coastal management in estuarine environments.

Impacts of the invasive grass Spartina anglica on benthic macrofaunal assemblages in a temperate Australian saltmarsh

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 464:107-120 (2012) - DOI: https://doi.org/10.3354/meps09826 Impacts of the invasive grass Spartina anglica on benthic macrofaunal assemblages in a temperate Australian saltmarsh Justin Cutajar, Jeff Shimeta*, Dayanthi Nugegoda School of Applied Sciences, RMIT University, Melbourne, Victoria 3083, Australia *Email: jeff.shimeta@rmit.edu.au ABSTRACT: Reported impacts of the invasive saltmarsh grass Spartina anglica on benthic macrofaunal assemblages around the world vary considerably, and there is little understanding of the reasons for this variation. We compared macrofaunal assemblages and sediment characteristics among patches of S. anglica and adjacent uninvaded habitats (bare mudflat and native saltmarsh) in southeastern Australia. Invaded patches showed reduced species richness (by 50%) and diversity compared to both uninvaded habitats. Macrofaunal abundance in S. anglica patches was also lower than in native marsh (by 60%), but not different from mudflat. There were no differences in biomass among habitats. Ordination clearly separated the species assemblage of invaded patches from uninvaded habitats, suggesting a unique community in the Spartina habitat. Molluscs and crustaceans were the most depleted in S. anglica patches, while the polychaete Nephtys australiensis was enhanced. Infauna and epifauna were both depleted in S. anglica, although the mechanisms for these impacts should differ. Burrowing by infauna in S. anglica patches was likely impeded by dense roots and rhizomes, because the below-ground plant biomass was 72% greater than in native saltmarsh. Epifauna were likely depleted in S. anglica patches due to shading-induced inhibition of microphytobenthos growth, consistent with measured reductions of porewater salinity and increased mud content. Salinity and mud content were the sediment parameters that correlated most strongly with macrofaunal assemblage composition. These results, combined with a synthesis of published S. anglica impacts, suggest predictions of when S. anglica facilitates or inhibits macrofauna, considering infauna and epifauna separately. KEY WORDS: Spartina anglica · Invasive species · Cordgrass · Macrofauna · Saltmarsh · Estuary · Australia Full text in pdf format PreviousNextCite this article as: Cutajar J, Shimeta J, Nugegoda D (2012) Impacts of the invasive grass Spartina anglica on benthic macrofaunal assemblages in a temperate Australian saltmarsh. Mar Ecol Prog Ser 464:107-120. https://doi.org/10.3354/meps09826 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 464. Online publication date: September 19, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Intertidal bare mudflats subsidize subtidal production through outwelling of benthic microalgae

An investigation of food web structures in the northwestern soft-bottom area, including the intertidal and subtidal zones, of inner Ariake Bay, suggests that resuspended BM are substantial for offshore secondary production, and the main source of BM would be outwelling from the intertidal mudflat. Carbon and nitrogen stable isotope ratios were measured for macrobenthos samples from the intertidal mudflats, subtidal fringe and offshore subtidal zones, together with their potential food sources. Carbon and nitrogen signatures indicated that most macrobenthos assimilated offshore particulate organic matters (POM) (δ13C: −23.9 ± 0.1‰; δ15N: 8.2 ± 0.1‰) and benthic microalgae (BM) (δ13C: −16.8 ± 1.5‰; δ15N: 8.0 ± 0.4‰) among other potential sources. The relative BM contribution to filter feeders significantly decreased seaward from about 50% in the mudflats to 25% in the offshore zone, and the 99% confidence intervals of the contribution did not include zero even in the offshore zone.

Anthropogenic Ecological Change and Impacts on Mosquito Breeding and Control Strategies in Salt-Marshes, Northern Territory, Australia

Darwin, in the tropical north of Australia, is subject to high numbers of mosquitoes and several mosquito-borne diseases. Many of Darwin's residential areas were built in close proximity to tidally influenced swamps, where long-term storm-water run-off from nearby residences into these swamps has led to anthropogenic induced ecological change. When natural wet-dry cycles were disrupted, bare mud-flats and mangroves were transformed into perennial fresh to brackish-water reed swamps. Reed swamps provided year-round breeding habitat for many mosquito species, such that mosquito abundance was less predictable and seasonally dependent, but constant and often occurring in plague proportions. Drainage channels were constructed throughout the wetlands to reduce pooled water during dry-season months. This study assesses the impact of drainage interventions on vegetation and mosquito ecology in three salt-marshes in the Darwin area. Findings revealed a universal decline in dry-season mosquito abundance in each wetland system. However, some mosquito species increased in abundance during wet-season months. Due to the high expense and potentially detrimental environmental impacts of ecosystem and non-target species disturbance, large-scale modifications such as these are sparingly undertaken. However, our results indicate that some large scale environmental modification can assist the process of wetland restoration, as appears to be the case for these salt marsh systems. Drainage in all three systems has been restored to closer to their original salt-marsh ecosystems, while reducing mosquito abundances, thereby potentially lowering the risk of vector-borne disease transmission and mosquito pest biting problems.

Changes in diatom patch‐size distribution and degradation in a spatially self‐organized intertidal mudflat ecosystem

Self-organized spatial patterns have been proposed as possible indicators for regime shifts in ecosystems. Until now, this hypothesis has only been tested in drylands. Here, we focus on intertidal mudflats where regular spatial patterns develop in early spring from the interaction between diatom growth and sedimentation but disappear when benthic herbivore abundance increases in early summer, accompanied by a dramatic shift to a bare mudflat. We followed the patch-size distributions of diatom biofilms during this degradation process. As time progressed, we found a temporal change in the spatial configuration occurring simultaneously with the loss of the diatom-sediment feedback. This indicates a gradual failure in time of the self-organization process that underlies regular patterning in this ecosystem. The path to degradation co-occurred with the loss of the larger patches in the ecosystem, which resulted in a decrease of the truncation in the patch-size distribution. Hence, our study in mudflat ecosystems confirms the general hypothesis that spatial patterns can provide important clues about the level of degradation. Nevertheless, our study highlights the need for thorough study about the type of spatial patterns and the nature of the underlying feedbacks before a reliable assessment of ecosystem status can be made, as changes in patch-size distribution differed markedly with those observed in other ecosystems.

Denitrification: an ecosystem service provided by salt marshes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 448:79-92 (2012) - DOI: https://doi.org/10.3354/meps09526 Denitrification: an ecosystem service provided by salt marshes Ana I. Sousa1,2,*, Ana I. Lillebø2, Nils Risgaard-Petersen3, Miguel A. Pardal4, Isabel Caçador1 1Centre of Oceanography (CO), Faculty of Sciences, University of Lisbon, Campo Grande, 1749-016 Lisbon, Portugal 2Department of Biology & CESAM, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal 3Institute of Biological Science, Center for Geomicrobiology, Aarhus University, Ny Munkegade, Building 1540, 8000 Aarhus C, Denmark 4Centre for Functional Ecology (CFE), Department of Life Sciences, University of Coimbra, Apartado 3046, 3001-401 Coimbra, Portugal *Email: aisousa@fc.ul.pt ABSTRACT: We hypothesized that denitrification rates, as an N removal process, would be enhanced in salt marsh rhizosediments as compared to sediments without vegetation (bare mudflats). Denitrification rates (measured by the 15N-isotope pairing technique), potential nitrification, and nutrient fluxes were seasonally quantified in a Spartina maritima salt marsh and in adjacent bare mudflats. Potential nitrification rates were significantly higher in autumn and winter, but there were no significant differences between the bare mudflats and S. maritima vegetated sediment. Seasonally, denitrification rates in vegetated sediments under dark conditions were significantly higher in winter (676 ± 497 µmol N2 m−2 h−1, mean ± SD), whereas bare mudflats showed a maximum rate of 151 ± 24 µmol N2 m−2 h−1 in summer. The high denitrification rates recorded in winter may be due to many abiotic and biotic factors, namely higher potential nitrification and nitrate availability in the water column, lower competition for nitrogen within the sediment, and less competition between plants, microphytobenthos, and nitrifiers, especially in dark conditions. Hence, during winter, there was a higher contribution of S. maritima marshes to N removal through denitrification, highlighting the role of the marshes in this ecosystem service. As a whole, considering the seasonal variations of the studied processes, it cannot be concluded whether or not annual denitrification was significantly different between the vegetated sediment and the bare mudflats. KEY WORDS: Denitrification · Salt marshes · Ecosystem services · Eutrophication · Spartina maritima · 15N-isotope pairing technique Full text in pdf format PreviousNextCite this article as: Sousa AI, Lillebø AI, Risgaard-Petersen N, Pardal MA, Caçador I (2012) Denitrification: an ecosystem service provided by salt marshes. Mar Ecol Prog Ser 448:79-92. https://doi.org/10.3354/meps09526 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 448. Online publication date: February 23, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Spatial and seasonal variations of atmospheric N2O and CO2 fluxes from a subtropical mangrove swamp and their relationships with soil characteristics

Marine ecosystems are a known net source of greenhouse gases emissions but the atmospheric gas fluxes, particularly from the mangrove swamps occupying inter-tidal zones, are characterized poorly. Spatial and seasonal fluxes of nitrous oxide (N2O) and carbon dioxide (CO2) from soil in Mai Po mangrove swamp in Hong Kong, South China and their relationships with soil characteristics were investigated. The N2O fluxes averaged from 32.1 to 533.7μgm−2h−1 and the CO2 fluxes were between 10.6 and 1374.1mgm−2h−1. Both N2O and CO2 fluxes in this swamp showed large spatial and seasonal variations. The fluxes were higher at the landward site than the foreshore bare mudflat, and higher fluxes were recorded in warm, rather than cold, seasons. The landward site had the highest content of soil organic carbon (OC), total Kjeldahl nitrogen (TKN), nitrate (NO3−–N) and total phosphorus (TP), while the bare mudflat had the highest ammonium nitrogen (NH4+–N) concentration and soil denitrification potential activity. The N2O flux was related, positively, to CO2 flux. Soil NO3−–N and TP increased N2O flux, while soil OC and TP concentrations contributed to the CO2 flux. The results indicated that the Mai Po mangrove swamp emitted significant amounts of greenhouse gases, and the N2O emission was probably due to soil denitrifcation.

Adaptive differences in digestive enzyme activity in the crab Neohelice granulata in relation to sex and habitat

Neohelice granulata (Dana, 1851) is a semi-terrestrial burrowing crab that inhabits estuaries and saltmarshes feeding on grasses or sediment depending on the microhabitat they occupy (vegetated saltmarsh or bare mudflat). Specific cellulolytic, amylolytic, and proteolytic enzyme activities were analyzed in midgut gland homogenates of males and females from each microhabitat fed in the laboratory with Spartina densiflora leaves and sediment, respectively, in order to detect sex, food and microhabitat related differences. The presence of β-1,4-glucosidase, endo-β-1,4-glucanase, α amylase, trypsin and chymotrypsin were confirmed. Specific cellulolytic activity was higher in crabs fed on leaves than in those fed on sediment or in no fed controls and variable differences between sexes were observed. Specific amylase activity of crabs fed on leaves was the lowest recorded. Trypsin and chymotrypsin specific activities were higher in saltmarsh crabs fed on leaves than in mudflat crabs fed on sediment. Different mechanisms of enzyme regulation to explain the observed differences among groups were suggested. Additionally, differences between sexes suggest different metabolic needs related to gonad maturation. It is concluded that N. granulata has the ability to adapt digestive enzyme production to support its physiological and metabolic needs based on the different food sources available at each microhabitat.

Summer fluxes of atmospheric greenhouse gases N 2O, CH 4 and CO 2 from mangrove soil in South China

The atmospheric fluxes of N 2O, CH 4 and CO 2 from the soil in four mangrove swamps in Shenzhen and Hong Kong, South China were investigated in the summer of 2008. The fluxes ranged from 0.14 to 23.83 μmol m − 2 h − 1, 11.9 to 5168.6 μmol m − 2 h − 1 and 0.69 to 20.56 mmol m − 2 h − 1 for N 2O, CH 4 and CO 2, respectively. Futian mangrove swamp in Shenzhen had the highest greenhouse gas fluxes, followed by Mai Po mangrove in Hong Kong. Sha Kong Tsuen and Yung Shue O mangroves in Hong Kong had similar, low fluxes. The differences in both N 2O and CH 4 fluxes among different tidal positions, the landward, seaward and bare mudflat, in each swamp were insignificant. The N 2O and CO 2 fluxes were positively correlated with the soil organic carbon, total nitrogen, total phosphate, total iron and NH 4 +-N contents, as well as the soil porosity. However, only soil NH 4 +-N concentration had significant effects on CH 4 fluxes.

Sulfur storage changed by exotic Spartina alterniflora in coastal saltmarshes of China

For the purpose of ecological engineering, Spartina alterniflora was introduced to China in 1979 and now covers about 112,000 ha of China's coastal lands. It was hypothesized that S. alterniflora could actively change the habitat environment, thus facilitating its competition over native species. In Yancheng Nature Reserve, sulfur storage of sediments and plant tissues was compared among marshes dominated by the exotic S. alterniflora and adjacent native Suaeda salsa and Phragmites australis and bare mudflat. Results showed that the S. alterniflora marsh contained the highest content of water-soluble, adsorbed, carbonate-occluded and total sulfur in the sediment. The sulfur levels were higher in the center than at the edges of the S. alterniflora marsh. Native marshes showed no significant difference in sediment sulfur levels. With greater biomass and higher tissue sulfur concentrations, plant sulfur storage of S. alterniflora vegetation was also larger than those of the native vegetations. Because higher concentrations of sulfur increase the competitive advantage of S. alterniflora over native halophytes, the results of the research showing that S. alterniflora increased marsh sulfur storage may shed light on the mechanism of expansion of monospecific vegetation in coastal China.

Molluscan assemblages of seagrass-covered and bare intertidal flats on the Banc d'Arguin, Mauritania, in relation to characteristics of sediment and organic matter

The Banc d'Arguin, a non-estuarine area of shallows and intertidal flats off the tropical Saharan coast of Mauritania, is characterised by extensive intertidal and subtidal seagrass beds. We examined the characteristics of intertidal seagrass ( Zostera noltii) meadows and bare areas in terms of the presence and abundance of molluscs (gastropods and bivalves). To explain observed differences between molluscan assemblages in seagrass and bare patches, some aspects of the feeding habitat (top-5 mm of the sediment) and of food (organic materials) of molluscs were examined. The novelty of this study is that phytopigments were measured and identified to assess source and level of decay (freshness) of organic material in the sediment and to study their importance as an explanatory variable for the distribution of molluscs. Over an area of 36 km 2 of intertidal flats, at 12 sites, paired comparisons were made between seagrass-covered and nearby bare patches. Within seagrass meadows, dry mass of living seagrass was large and amounted to 180 ±10 g AFDM m − 2 (range 75–240). Containing twice the amount of silt per unit dry sediment mass, seagrass sediments were muddier than bare areas; the relative amount of organic material was also larger. The total number of species of bivalves and gastropods amounted to 27, 14 of which were found only in seagrass areas, 4 only in bare and 9 in both types of habitat. Among the three numerically most abundant species, the bivalves Anadara senilis, Dosinia hepatica and Loripes lacteus, the first was numerically most abundant in bare and the other two in seagrass-covered areas. Bare intertidal areas had greater mean total biomass of molluscs (80.5 g AFDM m − 2 ) than seagrass meadows (30.0 g AFDM m − 2 ). In both habitats, the bulk of the biomass was made up by A. senilis. Excluding this species, bare mudflats contained on average only 3.1 g AFDM m − 2 and seagrass meadows 6.9 g AFDM m − 2 . As compared to previous surveys in 1980–1986, the biomass of A. senilis had increased almost 10-fold and D. hepatica, previously found in very small numbers, had become the most numerous species. However, the total biomass excluding that of A. senilis was similar. Concentrations of phytopigments were similar to those observed at temperate mudflats, indicating that the Banc d'Arguin might not be as oligotrophic as previously thought. Per unit of dry sediment mass, smaller amounts of phytopigments were found in bare than in seagrass areas. Per unit of dry organic material, bare sediments contained most (fresh) phytopigments. This suggests that in seagrass-covered meadows the organic material is more degraded than in bare sediments. Overall, the composition of phytopigments, quite surprisingly, indicated a benthic-diatom-dominated trophic system. Multivariate statistics revealed that patterns of zoobenthic assemblages were correlated with patterns of a combination of four environmental parameters: grain size of the sediment, amount of fresh phytopigments and amounts of leaves and roots of seagrass.

Carrying capacity for shorebirds during migratory seasons at the Jiuduansha Wetland, Yangtze River Estuary, China

The carrying capacity of food resources for migrating shorebirds was estimated at a stopover site in the Yangtze River Estuary during the two migratory seasons (spring and autumn). From March to May and September to November 2005, the macrobenthos resources of the Jiuduansha Wetland were investigated, and most of the macrobenthos species in the newly-formed shoal were found to be appropriate food for shorebirds. Biomass measurements showed that the total food resource was about 4541.20 kg AFDW (Ash-Free Dry Weight) in spring and about 2279.64 kg AFDW in autumn. Calculations were also done in the available habitats (intertidal bare mudflat and Scirpus × mariqueter/Scirpus triqueter zones) for the shorebirds. The food resources in the available areas were about 3429.03 kg AFDW in spring and about 1700.92 kg AFDW in autumn. Based on the classification (by lean weight, basic metabolic rate and body length) of the shorebird community, and using the energy depletion model, it was theorized that all of the food resources in the Jiuduansha Wetland could support about 3.5 million shorebirds during spring season and 1.75 million shorebirds during autumn season. The shorebird carrying capacities in terms of the available food were about 2.6 million and 1.3 million birds during the two respective migration seasons. Considering the effect of intake rate, the potential carrying capacity was about 0.13–0.26 million shorebirds in the study area. The main factor restricting use of the area by shorebirds was the scarcity of available habitats for roosting at high tide rather than availability of food supply. We recommend restoring some wading pools in the dense Phragmites australis and Spartina alterniflora zones for shorebirds to roost in, to improve shorebirds’ utilization efficiency of the resources in the Jiuduansha Wetland.

Evidence of former Holocene sea level in the Marennes-Oléron Bay (French Atlantic coast)

Both sedimentological and mollusc death assemblage analyses from a 14C-dated core, coupled with seismic stratigraphical analysis within the Marennes-Oléron Bay (French Atlantic coast), provide a detailed record of environmental changes during the end of the Holocene rapid sea-level rise. Lithofacies and mollusc fauna changes evidence the transition from a former intertidal bare mudflat to a subtidal environment. The newly shown former sea-level record, computed from radiocarbon-dated Scrobicularia plana shell, matches previously published local sea-level curves. This drowned mudflat belongs to an incised valley-fill that provides new insights into valley-fill successions along the French Atlantic coast.

Use of Willapa Bay, Washington, by shorebirds and waterfowl after Spartina control efforts

ABSTRACT Over the past 15 yr, an invasive cordgrass, Spartina alterniflora, has covered more than 5000 ha of tidal mudflats in Willapa Bay, Washington, threatening key shorebird habitat on the Pacific Flyway. Although chemical and mechanical control methods have been used to manage Spartina in Willapa Bay, little is known about how these methods affect subsequent use by shorebirds and waterfowl. During 2003–2004, four sites were monitored for 10-min periods for use by shorebirds [Dunlin (Calidris alpina), Western Sandpiper (C. mauri), Least Sandpiper (C. minutilla), Black-bellied Plovers (Pluvialis squatarola) and Long-billed and Short-billed dowitchers (Limnodromus sp.)] and waterfowl [Mallard (Anas platyrhynchos), Gadwall (A. strepera), American Wigeon (A. americana), Green-winged Teal (A. crecca), and Canada Goose (Branta canadensis)]. The four sites were bare mudflat (never infested with Spartina), tilled Spartina meadow (free of live Spartina and dead stubble), herbicide-sprayed Spartina meadow (10% living Spartina and 30% dead stubble), and an untreated Spartina meadow. Untreated Spartina meadow was rarely used by birds, with a mean of seven small Calidris sandpipers (peeps) and 0.8 waterfowl ha−1. Mean numbers of peeps and waterfowl observed using the herbicide-treated Spartina meadow were 62 and 16 ha−1, and the tilled Spartina meadow were 700 and 27 ha−1, respectively. Mean use of the adjacent bare mud site by peeps and waterfowl was 450 and 11 ha−1, respectively. The untreated Spartina meadow, sprayed meadow, tilled meadow and the bare mud site had mean densities of Black-bellied Plovers and dowitchers of 26, 24, 6, and 0 ha−1, and 0.8, 6, 0.3, and 0 ha−1, respectively. Our results demonstrate that, within several years of removal of invasive Spartina from mudflats in a large Washington estuary by either mechanical or chemical means, use by shorebirds and waterfowl will increase dramatically.

Professor Arthur J. Willis (1922–2006)

Professor Arthur J. Willis (1922–2006)

Wave attenuation in coastal mangroves in the Red River Delta, Vietnam

Wave attenuation was studied in a coastal mangrove system in the Red River Delta, Vietnam on the coast north of Do Son. From sea towards land the study area consisted of a bare mudflat, covered by a sandy layer with embryonic cheniers, abruptly changing into a muddy tidal flat overgrown with mangroves. Three instrumented tripods (A–C) placed in a cross-shore profile, were used to measure current velocity and water level, at the open tidal flat, at the beginning of the mangrove vegetation, and in the mangrove vegetation, respectively. Measurements were conducted in the wet season in July and August 2000. The elevation of the area was surveyed using a levelling instrument. Over the bare sandy surface of the mudflat, the incoming waves are reduced in height (and energy density) due to bottom friction. This reduction decreases with increasing water depth. In the mangrove vegetation, the bottom friction exerted by the clay particles is very low. However, the dense network of trunks, branches and above ground roots of the mangrove vegetation causes a much higher drag force. For the mangrove vegetation which mainly consists of Kandelia candel, the drag force can be approached by the function C D = 0.6e 0.15 A (with A being the projected cross-sectional area of the under water obstacles at a certain water depth). For the same muddy surface without mangroves the function would be C D = 0.6.

Sedimentation in an estuarine mangrove system

Sediment dynamics were studied in a mangrove system in the Ba Lat estuary of the Red River, Vietnam. The study area was situated on a riverbank, which consisted of a bare mudflat containing a vegetation gradient from pioneering mangroves to 5- to 7-year-old mangroves. Measurements were conducted in the dry season (February/March 2000) and in the wet season (July/August 2000). Actual sedimentation rates were measured using sediment traps and the elevation of the area was surveyed in both periods. Two undisturbed sediment cores were taken in the densely vegetated area for 210Pb-dating analysis and showed long-term sedimentation rates of 0.22 g cm −2 yr −1 and 0.36 g cm −2 yr −1. Sedimentation rates recorded by the sediment traps in the vegetated area were 2.94 g cm −2 yr −1 in the dry season and 3.46 g cm −2 yr −1 in the wet season. In both seasons, the sedimentation rates on the bare mudflat were five to ten times higher than in the densely vegetated area. However, the elevation of the mudflat was slightly lower in the wet season than in the dry season. This implies that erosion must have taken place between March and July. This study demonstrates that the bare mud bank of an estuary is highly dynamic until mangroves cover it. Sediment delivery to the vegetated zones is low but the protective effect of vegetation against erosion by waves and currents is strong. This results in small but steady actual sedimentation rates under mangroves and therefore sustained long term accretion. The study further identifies the need for similar measurements to be made in different seasons covering the effects of periodic storm events.

IDENTIFICATION OF THE SPECTRAL CHARACTERISTICS OF SALTMARSH VEGETATION USING INDIRECT ORDINATION: A CASE STUDY FROM CHONGMING DONGTAN, SHANGHAI

Remote sensing is a major source of spatial information of the attributes of the earth's surface, and remote sensing technology has become a primary tool for vegetation classification at large scales. The relationship between vegetation and their spectral characteristics is key for interpreting remote sensing images. This study related characteristics of saltmarsh vegetation at the intertidal zone of Chongming Dongtan Nature Reserve, Shanghai, to patterns of their spectral reflectance. Paired measurements of saltmarsh community and spectral characteristics were carried out along three transects covering the major variations in vegetation and environment within the study area. The spectral characteristics were measured by a ground FieldSpec Pro JR spectroradiometer and the spectral data were converted to simulate the 10 bands of Compact Airborne Spectrographic Imager (CASI) bandset. The spectral data sets were then ordinated using Principal Component Analysis (PCA), an indirect ordination technique. The eigenvalue of the first PCA axis was 19.9, which represented 98.5% of the variation in the spectral data. A sequence of bare mudflat, Scirpus mariqueter community, Spartina alterniflora community and Phragmites australis community changed along the first ordination axis showed a strong correspondence with variation in the bands six to ten, i.e. the simulated CASI wavebands covering the 736 to 870 nm wavelengths. A significant relationship between the first axis PCA scores for the spectral data of quadrats and their percentage community cover and height also was identified. The second axis accounted for only 1.4% of the variation in the spectral data and it proved impossible to demonstrate any close link between any specific plant community type and a distinct set of spectral characteristics because of its low representation of the variation in the spectral data. Our study has demonstrated that the variation in the spectral data of saltmarsh vegetation at Chongming Dongtan Nature Reserve can be identified using the indirect ordination technique of PCA and then applying correlation and regression analyses to explain the relationships between the variation in the spectral data with the vegetation and ecological data. Our results indicate that PCA is of value for identifying relationships between community types and the spectral data of CASI bandsets for saltmarsh vegetation. This could provide an effective and practical approach for classification of saltmarsh vegetation at large scales and for monitoring spatio_temporally dynamic patterns of saltmarshes at Chongming Dongtan Nature Reserve. Further work is required in order to test these conclusions. The method has been evaluated for a single season with a limited sample of saltmarsh plant communities, and the application of PCA and spectral data of CASI bandsets to other saltmarsh vegetation as well as multi_seasonal spectral data are necessary to determine whether similar patterns emerge and whether the approach has more general applicability in terms of characterizing remote sensing/spectral imagery and community types in saltmarsh vegetation.

Effects of Hydrology, Herbivory and Sediment Disturbance on Plant Recruitment in a Lake Erie Coastal Wetland

Coastal wetlands of the Laurentian Great Lakes provide many valuable ecological functions and, currently, there are extensive efforts to preserve and manage remaining habitats. We examined plant recruitment in a Lake Erie coastal marsh on bare mudflats exposed during 2 y of below average water levels. In 2000 mudflat vegetation was sampled in shallow, medium and deep water transects and compared to germinable seeds found in sediments from 0–15 cm below the surface. Effects of sediment disturbance and herbivory on plant recruitment were tested in 1 m2 quadrats in 2000 and vegetation was sampled in 2001 to assess how well the disturbance/herbivory experiment predicted plant communities that became established on the mudflats. In 2000, 18 species were found on mudflats and 19 species were reared from the seedbanks. Seed densities (∼3000 seedlings/m2) were comparable to other freshwater wetlands and did not differ by sediment depth. Taxa richness was highest in sediments 0–5 cm below the surface. Most plants on the mudflats were found in the shallow transect, but seed abundance and richness were highest in deep transects. Sediment disturbance decreased taxa richness and herbivory decreased both plant cover and richness; however, responses varied among plant taxa. Our results indicate that abundant seedbanks exist in this wetland, but plant recruitment will be restricted to shallow areas due to turbidity. Communities in 2001 were more diverse (40 species) than predicted from vegetation in 2000 probably because propagules were introduced from nearby habitats. Communities in 2001 were most similar to ungrazed and undisturbed quadrats in 2000 because these had the most species.

Combinaison d'un projet portuaire et d'un projet environnemental d'amorce de réhabilitation de l'estuaire de la Seine

ABSTRACT Port 2000 consists in developing a new site with harbour facilities designed to receive the largest container vessels under optimum conditions. Situated on the extreme north-west tip of the Seine estuary, the works take into account an estuarine environment forming an habitat which is interfacial in nature (involving river, land and marine environments), enabling the simultaneous existence of a wide range of complementary biotopes (sand banks, mudflats either bare or colonized by plants, marshes and wetlands), thereby ensuring the cohesion of the food chain. As a result of the evolution of the estuary, the most fragile and most threatened link in the food chain appears to be that formed by the bare mudflats, found at a level between the mean sea level and the high tide level. The Port 2000 project includes supportive environmental measures (45,74 M€ i.e. 300 MF) included themselves in a global management plan for the whole of Seine Estuary with notably the starting of a true rehabilitation over t...