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1.
Dissolved cadmium and copper species were measured in the Loire estuary and the North Biscay Bay continental shelf (France) in spring 2002. Metal behaviours along the salinity gradient, metal fluxes from the Loire system and surface distributions on the continental shelf were described and compared with the ones obtained at a period of higher discharge (i.e., winter 2001). Vertical distributions at different stations were also examined with the aim to assess whether the Loire inputs affect the Cu and Cd speciation over the continental shelf. In the Loire estuary, different metal behaviours were observed from winter. Cu and its various species mostly followed a theoretical dilution line whereas a Cd addition composed of chloro- and organic complexes was observed. According to our estimations, the Cu flux was composed, as in winter, of 40% hydrophobic organic complexes. On the other hand, Cd organic complexes accounted for less in the total dissolved metal flux than they did in winter (55 and 78% for spring and winter, respectively). On the continental shelf, a C18Cu-to-TDCu ratio of 40% was observed in the stratified area under Loire influence. For Cd, the organic fraction was relatively important in the surface waters near the mouth of the estuary and decreased deeper and seaward. Thus, the Cu and Cd speciation on the North Biscay Bay continental shelf are firstly determined by the extent of the estuarine plume. Beyond the estuarine influence, biological processes appeared to be the origin of the observed variations.  相似文献   

2.
Abstract. The population dynamics and life history characteristics of Callinectes similis and C. sapidus in the Mobile Bay-Mississippi Sound estuarine system of the northern Gulf of Mexico were studied. We report that C. similis is numerically dominant in open-bays, while C. sapidus is more abundant in shallow salt marshes. Juvenile C. similis recruit into both open-bays and salt marshes, but juvenile C. sapidus primarily recruit into shallow salt marshes. Sex ratios of C. similis and C. sapidus were generally skewed towards higher proportions of males than females. Callinectes similis appears to have a life cycle similar to that of C. sapidus. Egg-carrying C. similis migrate to higher salinity waters and presumably release larvae to nearshore shelf waters; following development, the larvae re-invade estuaries as megalopae. Juvenile C. similis grow more slowly than C. sapidus. This may be attributable to reduced feeding rates. Marked differences in fecundity and reproductive effort were found between these species. Callinectes similis and C. sapidus , respectively, produced 2.4–5.5 times 105 and 2.1–3.2 times 106 eggs and invested 24–49 and 171–372 kJ per brood. Rhizocephalan barnacle infestation by Loxothylacus texanus was encountered in C. sapidus , while sympatric C. similis were free of this rhizocephalan parasite.  相似文献   

3.
The distribution and feeding of dominant mesozooplankton species were studied in the estuary of the Ob River and adjacent inner Kara Sea shelf waters in September 2013. It was shown that the spatial distributions of Cyclops sp., Senecella siberica, Limnocalanus macrurus, Mysis oculata, Drepanopus bungei, Jashnovia tolli and Pseudocalanus sp. are related to the specific characteristics of the hydrographic regime in the estuarine frontal zone. The distributions of Cyclops sp., Senecella siberica, and Pseudocalanus sp. are mainly limited by salinity, while other species inhabit an area with a wide range of salinity values without clear preferences. Peaks of their abundance could be either consolidated or distanced in space. The populations of Jashnovia tolli, Drepanopus bungei, and Pseudocalanus sp. permanently inhabit the layer under the pycnohalocline; the populations of Cyclops sp. and Mysis oculata inhabit the upper mixed layer. Limnocalanus macrurus demonstrates a different vertical distribution pattern: the copepod undertakes diel vertical migrations in the southern part of the estuarine frontal zone; in its northern part, the population is concentrated below the pycnocline during day and night. The differences in the distributions of the studied species determine their feeding behavior and their role in phytoplankton grazing. The most intense utilization of biomass and production of autotrophic phytoplankton by zooplankton occur in the freshened water zone and the adjacent southern periphery of the estuarine frontal zone: the total daily phytoplankton consumption makes up 10–18% of the biomass and 60–380% of primary production. Daily zooplankton consumption of phytoplankton in the estuarine frontal zone decreases to 2–7% of the biomass and to 14% of primary production; in inner shelf waters, the values do not exceed 1% for both phytoplankton biomass and production.  相似文献   

4.
The goal of studies described here was to determine the responses of zooplankton taxa to phytoplankton patches which develop in and near intrusions of cold, nutrient-rich Gulf Stream water. To achieve this goal we determined the horizontal and vertical distributions of abundant mesozooplankton taxa on the south-eastern continental shelf of the USA between 29°30′ and 31°N. The study period was from June 23 to August 16, 1981. Highest concentrations of zooplankton usually occurred in and near patches of phytoplankton. Increased phytoplankton appeared to trigger the formation of patches of the calanoid copepod Temora turbinata and the cyclopoid copepods Oithona spp. and Oncaea spp. The patches of zooplankton had greater alongshore than cross-shelf dimensions. T. turbinata responded rapidly to increased concentrations of phytoplankton by reproducing and aggregating in and above intruded waters. Oithonidae which were often, but not always, abundant in phytoplankton patches eventually attained high concentrations over most of the middle and part of the inner shelf. Their concentration and that of Oncaeidae increased steadily. Oncaeidae were not abundant in recently upwelled waters, as was T. turbinata but reached high concentrations in older intrusions when the abundance of T. turbinata remained level or decreased slowly. Both cyclopoid taxa are thought to reproduce slowly (egg sacs) compared to T. turbinata. Another taxon, the doliolids, became abundant far more rapidly in intruded waters (by asexual reproduction) than did the other three taxa. Doliolids were the most opportunistic intrusion zooplankton form. They do not regularly occur in low abundance on the shelf, as do the three copepod taxa, but develop in pulses in regions where T. turbinata and Oncaea are not abundant. Of the four taxa studied the abundance of doliolids increased and decreased most rapidly, whereas Oithona and Oncaea increased slowly and did not decrease during the study period. T. turbinata and Oncaea were most abundant at 60% of all stations in the intruding water. Doliolids and Oithona on the other hand, were mostly in the thermocline and intrusion. Whereas phytoplankton patches, which developed in intrusions, were physically induced (PAFFENHÖFER and LEE, 1988), patches of zooplankton were biologically induced.  相似文献   

5.
福建漳江口红树林保护区浮游植物群落的季节变化研究   总被引：4，自引：1，他引：3  
于2001年1月～2003年1月对福建省漳江口红树林区水体浮游植物群落的季节变化进行了研究。结果表明,漳江口红树林区浮游植物以硅藻门种类为主,优势种为长菱形藻(Nitzschia longissima)和菱形藻(Nitzschia sp.1)等,同时出现多种裸藻、绿藻和甲藻。本次调查共鉴定到浮游植物31属87种(包括变种),其中硅藻门23属75种(包括变种),蓝藻门3属3种,绿藻门1属4种,金藻门1属1种,甲藻门2属2种,裸藻门1属2种。浮游植物密度变化范围为2.78×104～1.14×106个/L,平均为3.51×105个/L,季节变化为双峰型。出现大量的底栖硅藻和淡水性藻类是该水域浮游植物的一个特点。浮游植物的组成和结构表明该水域水质较好。  相似文献   

6.
Distribution patterns and trophic contributions of rotifers from freshwater through polyhaline estuarine waters were examined in the southern Chesapeake Bay and its major tributaries for a two-year period. Trichocerca marina and Synchaeta spp. were the major taxa in abundance, followed by Polyarthra vulgaris, Keratella cochlearis and Brachionus spp. There was a significant negative correlation between salinity and rotifer density, biomass, and number of species. Rotifers were a component of the microzooplankton biomass during specific periods and at particular sites, dominating summer assemblages in tidal freshwater and river–estuary transition sites, plus the winter communities in estuarine waters. This observation indicates that rotifers may play an important trophic role by seasonally replacing metazoan nauplii as a biomass source in both tidal freshwater and estuarine ecosystems. The annual contribution of rotifers to the total microzooplankton biomass exclusive of heterotrophic dinoflagellates was brief but intensive, achieving over 50% of annual biomass during a 2–3 month period. Despite the small annual mean contribution of rotifers to the total microzooplankton biomass, rotifers may have a limited, but significant impact on the trophic dynamics of the zooplankton community in Chesapeake Bay and its major tidal tributaries.  相似文献   

7.
In this paper we describe results of a study designed to test the hypothesis that coastal regions with weak subtidal flow (i.e., coastal null zones) may serve as retention areas for estuarine larval forms. Our investigation assessed the distribution of 3 taxa of crab larvae (Callinectes sapidus, Uca spp., and Hexapanopeus angustifrons) within a 200-km2 region encompassing the mouth of Delaware Bay (ca. 39° N, 75° W). Previous studies had shown that larvae of C. sapidus and Uca spp. are exported to the coastal ocean, while larvae of H. angustifrons are retained within the estuary. In the present investigation, we conducted simultaneous plankton tows at 3 stations during peak spawning season. Samples were collected from a depth of 1 m every 30 min throughout a complete tidal cycle. One station was located 15 km within the bay and was subjected to strong flow at tidal frequency. A second station was located within a southward-flowing coastal current near the southern terminus of the bay at Cape Henlopen. A final station was located in a coastal area of weak subtidal flow near Cape May at the northern terminus of the bay. Results provide a unique synoptic view of larval distributions in 3 distinct hydrographic regimes in the mouth of a major estuary. The coastal-current station was characterized by low concentrations of newly hatched C. sapidus and Uca zoeae, while the null-zone station had high densities of both early and advanced larval stages of these two taxa. In contrast, the station located within the bay had few C. sapidus or Uca zoeae and was dominated by both early and advanced stages of the mud crab H. angustifrons. These data provide clear evidence for the retention of exported larval forms in a coastal null zone associated with the circulation of a large estuary and thus are consistent with our hypothesis.  相似文献   

8.
The Sofala Bank, a wide shelf located along the central coast of Mozambique, hosts tides with high amplitudes. The Regional Ocean Modelling System (ROMS) was used to analyse the tidal currents on the bank and to investigate their effects on the stratification and generation of tidal fronts. During spring tides, barotropic tidal currents with maximum values ranging from 40 cm s–1 to 70 cm s–1 are found on the central bank. The major axis of the tidal ellipses for M2 and S2 follow a cross-shelf direction with mainly anticlockwise rotation. Similar to observations, three distinct regimes occur: (i) a warm well-mixed region on the inner shelf where the depths are <30 m; (ii) a wellmixed colder region above the shelf edge; and (iii) a stratified region offshore. The model shows that the tides lead to cooling where two criteria are satisfied: the Simpson and Hunter parameter log10(h/U3) <3.2 and the depth h >30 m. The shelf edge of the bank is important for internal tide generation. Two frontal structures result, one offshore between cooler mixed waters and warmer stratified waters and the other in shallow inshore waters, between cooler mixed waters and solar heated mixed waters.  相似文献   

9.
Results of a three-year survey of the occurrence of Callinectes sapidus larvae in the mouth of Delaware Bay indicated that stage I zoea larvae were most abundant insurface water as compared to mid-depths and near bottom. The major peak in abundance of stage I zoea larvae occurred in early August with a secondary peak in early September. Peaks in abundance of megalopae occurred five weeks after the respective peaks in zoeal abundance. Zoea stages II–VIII were not collected in the bay mouth. Results of sampling every 3 h over consecutive tidal cycles showed that stage I zoea larvae were most common in the water column on ebbing tidal currents. Megalopae were most common in the water column on flooding tidal currents, suggesting a tidally related, vertical migration. It was concluded that stage I zoea larvae are flushed from the estuary and undergo development on the continental shelf. Megalopae are then transported back to inshore waters by a combination of winds and currents and invade the estuary by means of migration into the water column on flooding tidal currents and migration to the bottom on ebbing tidal currents.  相似文献   

10.
The spatial distribution, abundance, and assemblage structure of macrozoobenthos were examined at 45 stations in a brackish lagoon (Idoura Lagoon, Japan) to examine the animal–environmental relations in estuarine soft-bottom habitats. We found a total of 23 taxa; the polychaetes Heteromastus sp., Hediste spp., and Prionospio japonica and the isopod Cyathura muromiensis numerically dominated the community. Cluster analysis and one-way analysis of similarity (ANOSIM) identified seven groups of stations that had significantly different macrozoobenthic communities; these were subsequently consolidated into five habitat groups according to their association with environmental characteristics. Canonical correspondence analysis (CCA) showed that salinity, silt-clay content, and the oxidation–reduction potential (ORP) of the sediment strongly affected the macrozoobenthos distribution pattern in the lagoon, whereas other factors (e.g., relative elevation of the habitat and sediment organic content) had much weaker effects. Similarity percentages (SIMPER) procedures indicated that the polychaete Notomastus sp. and the bivalve Macoma contabulata were specific to habitats with low salinity and reduced mud, whereas the bivalve Nuttallia olivacea was specific to sandy bottoms. Heteromastus sp. and Hediste spp. achieved their highest densities in rather oxidized sediments. The acid-volatile sulfide (AVS) content in the sediment was suggested as another possible factor affecting macrozoobenthic density. Our results clearly demonstrate that macrozoobenthic assemblages in estuarine soft-bottoms have high spatial heterogeneity on a small scale (e.g., hundreds of meters) related to physical and chemical environmental changes. Our data also suggested the importance of sediment redox condition (e.g., ORP and AVS content) and sediment grain size as structuring factors in estuarine soft-bottom communities as well as the salinity in the habitat.  相似文献   

11.
Human encroachment on the coastal zone has led to concern about the impact of anthropogenic nitrogen (N) on estuarine and continental shelf waters. Western North Atlantic watershed budgets suggest that the export of human-derived N from estuaries to shelf waters off the east coast of the US may be significant; however, models based on water inputs and estimates of upwelling of deepwater nutrients to surface waters of the mid-Atlantic bight indicate that estuarine N may be a relatively minor component of the overall shelf N budget. Stable N isotope ratios could provide a means to assess the relative input of anthropogenic N to shelf waters, particularly since dissolved N from human sources has elevated δ15N values (range: 7–30‰). We collected particulate material from surface shelf waters off the US east coast from 2000 to 2005 at near-shore sample sites proximal to the mouth of six estuaries and corresponding sites farther offshore. Near-shore (mean 33.7 km from estuary mouth) δ15N values ranged from 5.5 to 7.7‰ Offshore values (mean 92.4 km from estuary mouth) were consistently lower than near-shore sites (average 4.7 ± 1.0‰ versus 6.8 ± 1.1‰), suggesting different N sources to near and offshore stations. Near-shore regions are often more productive, as mean monthly chlorophyll-a concentrations from the sea-viewing wide field-of-view sensor (SeaWiFS) were significantly higher at near-shore sites near the mouth of three of the six estuaries. A mass balance using a concentration-dependent mixing model with chlorophyll-a concentrations as a surrogate for dissolved inorganic nitrogen can account for all of the nitrogen at near-shore sites south of Cape Cod with estuarine nitrogen estimated to contribute 45–85% of the nitrogen to the near-shore surface particulate material. Our results support the hypothesis that estuarine nitrogen is influencing continental shelf ecosystems, and also provide preliminary evidence of the spatial extent of its influence on shelf waters in the mid-Atlantic bight.  相似文献   

12.
The occurrence of harmful epiphytic dinoflagellates is of concern to scientists, the aquaculture industry, and government due to their toxicity not only to marine organisms but also to humans. There have been no studies on the abundance of the epiphytic dinoflagellates in Korean waters. We explored the presence of epiphytic dinoflagellates in the coastal waters off Jeju Island, southwestern Korea. Furthermore, we measured the abundance of epiphytic dinoflagellates on the thalli of 24 different macroalgae, collected from five different locations in October 2009. Five epiphytic dinoflagellate genera Amphidinium, Coolia, Gambierdiscus, Ostreopsis, and Prorocentrum were found. These five genera were observed on the thalli of the macroalgae Chordaria flagelliformis, Martensia sp., Padina arborescens, and Sargassum sp., while none were observed exceptionally on Codium fragile. The abundance of Ostreopsis spp. was highest on Derbesia sp. (8,660 cells/g wet weight), while that of Gambierdiscus spp. was highest on Martensia sp. (4,870 cells/g-ww). The maximum abundances of Amphidinium spp., Coolia spp., and Prorocentrum spp. were 410, 710, and 300 cells/g-ww, respectively. The maximum abundance of Coolia spp., Gambierdiscus spp., and Ostreopsis spp. obtained in the present study was lower than for other locations reported in literature. The results of the present study suggest that the presence and abundance of epiphytic dinoflagellates may be related to the macroalgal species of the coastal waters of Jeju Island.  相似文献   

13.
Vertical distributions of phyllosoma larvae were examined in waters east of the Philippines or west of the Mariana Islands (18°56′ N to 19°04′ N; 129°10′ E to 129°35′ E) based on zooplankton samples collected with an Isaacs-Kidd Midwater Trawl on September 22–24, 1986. Phyllosoma larvae belonged to the two families Scyllaridae and Palinuridae comprising 4 genera and 9 species. Of the collected phyllosoma larvae, those of Scyllarus cultrifer and Panulirus longipes were most abundant and showed similar vertical distributions: (1) both species were collected from the mixed layer at night but not in the day, (2) their vertical distributions did not change with their stages, and (3) the upper limit of their vertical distributions during the day accorded with the base of mixed layer. Furthermore, their vertical distributions were similar to those of lepthocephalus larvae which were collected using the same sampling stations and gear in the present study. Vertical distributions of phyllosoma larvae were discussed in relation to their horizontal distributions. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

14.
This paper reports on the composition, abundance and distribution of the larval fish assemblage in the nearshore coastal waters off the St Lucia Estuary mouth, South Africa. Ichthyoplankton samples were collected over a 12 month period from five stations located along a transect up to 2·5 km offshore, and from two stations north and south of the estuary mouth, respectively. In all, 6126 fish larvae, representing 89 families and 186 species, were collected. Larvae in the families Myctophidae and Tripterygiidae comprised 21% and 16% of the total catch, respectively. The most abundant species were an unidentified triplefin, Tripterygiid 1 and the lanternfish Benthosema fibulatum, together which contributed nearly 18% of the total catch. Larvae of marine spawners independent of estuaries dominated the catch both in terms of density (90%) and in terms of number of taxa (89%). Some larvae of estuarine-associated species were present, in addition to a few specimens of estuarine resident species. Overall the dominant environmental variable affecting larval densities was temperature, particularly for Trypterygiid 1 where temperature contributed to 9% of the variance model. Densities of fish larvae peaked in November and December 1990 (late spring and early summer) and were lowest from January to June 1991 (summer, autumn an early winter). Different taxa dominated the catch each month with reef- and shelf-associated species accounting for the peak in August and September 1990, oceanic species in November 1990 and a mixture of the two groups in December. Overall larval densities were significantly higher in bottom samples with a trend of increasing densities offshore for reef and shelf taxa. The larvae of reef and shore taxa were predominantly preflexion larvae, whilst the few estuarine spawner species that were collected were mainly postflexion. Ontogenetic patterns related to depth and distance offshore were evident for the dominant species in each estuarine-association category.The present study has shown that temporal and spatial variations in the larval fish assemblage off St Lucia are related to environmental conditions and ontogenetic behavioural patterns of certain species. The origin of many of the larvae in the assemblages off the coast of St Lucia is probably from both local spawning populations in the shelf waters off KwaZulu-Natal and spawning populations farther north in shelf waters off Mozambique. Additional studies with more detailed oceanographic measurements will further our understanding of the physical processes that supply larvae to the St Lucia region.  相似文献   

15.
南海北部上层鱼类浮游生物多样性和丰度的季节变化   总被引：1，自引：0，他引：1  
The objective of this study was to investigate the seasonal variations of ichthyoplankton diversity and abun-dance in the northern South China Sea based on the data collected during summer, winter and spring. In total, 95 taxa of larval fishes were identified. The greatest number of species was recorded in spring, followed by summer and winter. The number of species was distributed mainly in the coastal waters from the east of Leizhou Peninsula to the southeast of Hainan Island during the surveyed periods of summer and spring, but in the offshore waters during winter. The abundance of larval fish was lowest in winter, increased in spring, and reached the maximum in summer. High abundance of larval fish was generally restricted to coastal waters with the isobaths less than 50 m. Seasonal variations of larval fish richness, abundance and diversity index were significant （P〈0.001）. Carangidae was the most common and abundant taxon in summer and winter, whileSardinella sp.,Thrissa mystax andLeiognathus sp. were dominant in spring. High diversity and abundance of larval fish might be attributed to increased temperature and coastal upwelling in spring and summer.  相似文献   

16.
Abstract. The waters surrounding the Pribilof Islands are an important nursery ground for juvenile walleye pollock (Theragra chalcogramma), an important forage fish in the pelagic food web of the productive Bering Sea shelf region. The diet of juvenile pollock was studied in two consecutive years along a transect line crossing from a well‐mixed coastal domain, through a frontal region to stratified water farther offshore. Variability in stomach fullness was high and evidence for increased feeding intensity in the front was weak. Prey diversity and prey size generally increased with increasing fish size, shifting from predominantly small copepods to larger, more evasive prey items such as euphausiids, crab megalopae and fish. The diet of the fish reflected changes in the relative abundance of copepods and euphausiids in the prey fields between years. Juvenile pollock showed increased feeding rates at dusk, and stomach fullness as well as prey condition were generally lowest just before sunrise; however, the proportion of euphausiids increased in the diet of pollock caught at night, suggesting that some food was also ingested during darkness. Juvenile pollock and their euphausiid prey both vertically migrated above the thermocline at night, although each had a different daytime depth.  相似文献   

17.
Spring phytoplankton bloom in the fronts of the East China Sea   总被引：2，自引：0，他引：2  
Frontal areas between warm and saline waters of the Kuroshio currents and colder and diluted waters of the East China Sea (ECS) influenced by the Changjiang River were identified from the satellite thermal imagery and hydrological data obtained from the Coastal Ocean Process Experiment (COPEX) cruise during the period between March 1st and 10th, 1997. High chlorophyll concentrations appeared in the fronts of the East China Seas with the highest chlorophyll-a concentration in the southwestern area of Jeju Island (~2.9 mg/m3) and the eastern area of the Changjiang River Mouth (~2.8 mg/m3). Vertical structures of temperature, salinity and density were similar, showing the fronts between ECS and Kuroshio waters. The water column was well mixed in the shelf waters and was stratified around the fronts. It is inferred that the optimal condition for light utilization and nutrients induced both from the coastal and deep waters enhances the high phytoplankton productivity in the fronts of the ECS. In addition, the high chlorophyll-a in the fronts seems to have been associated with the water column stability as well.  相似文献   

18.
The composition and distribution of the macrobenthic communities in the Ob estuary and the adjacent Kara Sea shelf were studied during the 54th cruise of the R/V Akademik Mstislav Keldysh. With the transition from the Ob River’s mouth to the open parts of the sea, the gradual changes of the bottom biocenoses included changes in the leading taxa. Along with the increase in the salinity, the freshwater and brackish water taxa are replaced by related forms adapted to dwelling in seawater. The comparison of the original data with the results of the previous investigations revealed considerable spatial and temporal variations of the bottom communities in the studied area. The main environmental factors determining the fauna distribution in the estuarine zone are discussed. The extensive biocenosis dominated by Portlandia aestuariorum in the Ob estuary was found for the first time.  相似文献   

19.
Differences in the biological and ecological strategies of two tropical flatfishes, Etropus crossotus (fringed flounder) and Citharichthys spilopterus (bay whiff) are discussed. The comparative analysis was based on the seasonal distribution of relative abundance of the two species and flatfish movements utilizing estuarine plume influenced areas as part of their life cycles. Growth parameters of the von Bertalanffy equation and recruitment were estimated (FISAT software) to compare life cycle patterns. The recruitment patterns illustrate the key difference between “estuarine-dependent” and “estuarine-related” nekton strategies. Both species have a short life cycle with a continuous recruitment activity. E. crossotus is an estuarine-related species, with two recruitment pulses (winter frontal season), in the estuarine plume on the shelf. C. spilopterus is an estuarine-dependent species, with a main recruitment pulse during the rainy season in the estuarine plume, and a residual secondary pulse inside the adjacent estuarine system (Terminos Lagoon). The results show that the ecological success of these tropical coastal marine flatfish, with similar biological patterns, is based upon the sequential use (in time and space) of estuarine plume influenced habitats, suggesting that fish migration to shallow waters is related to food availability changes as a strategy towards optimum recruitment.  相似文献   

20.
To examine the source and preservation of organic matter in the shelf sediments of the East China Sea (ECS), we measured bulk C/N and isotopes, organic biomarkers (n-alkanes and fatty acids) and compound-specific (fatty acids) stable carbon isotope ratios in three sediment cores collected from two sites near the Changjiang Estuary and one in the ECS shelf. Contrasting chemical and isotopic compositions of organic matter were observed between the estuarine and shelf sediments. The concentrations of total n-alkanes and fatty acids in the shelf surface sediments (0–2 cm) were 5–10 times higher than those in estuarine surface sediments but they all decreased rapidly to comparable levels below the surface layer. The compositions of n-alkanes in the estuarine sediments were dominated by C26-C33 long-chain n-alkanes with a strong odd-to-even carbon number predominance. In contrast, the composition of n-alkanes in the shelf sediment was dominated by nC15 to nC22 compounds. Long-chain (>C20) fatty acids (terrestrial biomarkers) accounted for a significantly higher fraction in the estuarine sediments compared to that in the shelf sediment, while short-chain (<C20) saturated and unsaturated fatty acids were more abundant in the shelf surface sediments than in the estuarine sediments. Stable carbon isotopic ratios of individual fatty acids showed a general positive shift from estuarine to shelf sediments, consistent with the variations in bulk δ 13CTOCTOC. These contrasts between the estuarine and shelf sediments indicate that terrestrial organic matter was mainly deposited within the Changjiang Estuary and inner shelf of ECS. Post-depositional diagenetic processes in the surface sediments rapidly altered the chemical compositions and control the preservation of organic matter in the region.  相似文献   

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