Isotopic variation of fishes in freshwater and estuarine zones of a large subtropical coastal lagoon     

A.M. Garcia  D.J. Hoeinghaus  J.P. Vieira  K.O. Winemiller 《Estuarine, Coastal and Shelf Science》2007,73(3-4):399-408

We used stable C and N isotope ratios of tissues from 29 fish species from a large subtropical lagoon in southern Brazil to examine spatial variability in isotopic composition and vertical trophic structure across freshwater and estuarine habitats. Nitrogen isotope ratios indicated a smooth gradation in trophic positions among species, with most fishes occupying the secondary and tertiary consumer level. Fish assemblages showed a significant shift in their carbon isotopic signatures between freshwater and estuarine sites. Depleted carbon signatures (from −24.7‰ to −17.8‰) were found in freshwater, whereas more enriched signatures (from −19.1‰ to −12.3‰) were obtained within the estuarine zone downstream. Based on our survey of the C₃ and C₄ plants and isotopic values for phytoplankton and benthic microalgae reported for ecosystems elsewhere, we hypothesized that the observed δ¹³C differences in the fish assemblage between freshwater and estuarine sites is due to a shift from assimilating organic matter ultimately derived from C₃ freshwater marsh vegetation and phytoplankton at the freshwater site (δ¹³C ranging from −25‰ to −19‰), to C₄ salt-marsh (e.g. Spartina) and widgeon grass (Ruppia maritima), benthic microalgae and marine phytoplankton at the estuarine sites (from −18‰ to −12‰). Our results suggested that fish assemblages are generally supported by autochthonous primary production. Freshwater fishes that likely were displaced downstream into the estuary during periods of high freshwater discharge had depleted δ¹³C values that were characteristic of the upper lagoon. These results suggest that spatial foodweb subsidies can occur within the lagoon.  相似文献   

泉州湾河口湿地鸟类的种类组成与分布   总被引：10，自引：0，他引：10  

黄国勇  许文宝  刘杰斌 《台湾海峡》2002,21(2):228-233

本文根据1988-1999年进行4次泉州湾河口湿地鸟类调查资料，研究了泉州湾河口湿地自然概况，首次报道了该区鸟类13目30科108种，指出泉州湾河口地区鸟类栖息地面临的威胁因素，建议建立泉州湾河口湿地保护区以保护该区的自然生态系统和鸟类资源。  相似文献   

Sources and distribution of organic matter in a river-dominated estuary (Winyah Bay, SC, USA)   总被引：12，自引：0，他引：12  

Miguel A. Goi  Maria J. Teixeira  David W. Perkey 《Estuarine, Coastal and Shelf Science》2003,57(5-6):1023-1048

The sources and distribution of organic matter (OM) in surface waters and sediments from Winyah Bay (South Carolina, USA) were investigated using a variety of analytical techniques, including elemental, stable isotope and organic biomarker analyses. Several locations along the estuary salinity gradient were sampled during four different periods of contrasting river discharge and tidal range. The dissolved organic carbon (DOC) concentrations of surface waters ranged from 7 mg l⁻¹ in the lower bay stations closest to the ocean to 20 mg l⁻¹ in the river and upper bay samples. There was a general linear relationship between DOC concentrations and salinity in three of the four sampling periods. In contrast, particulate organic carbon (POC) concentrations were significantly lower (0.1–3 mg l⁻¹) and showed no relationship with salinity. The high molecular weight dissolved OM (HMW DOM) isolated from selected water samples collected along the bay displayed atomic carbon:nitrogen ratios ([C/N]a) and stable carbon isotopic compositions of organic carbon (δ¹³C_OC) that ranged from 10 to 30 and from −28 to −25‰, respectively. Combined, such compositions indicate that in most HMW DOM samples, the majority of the OM originates from terrigenous sources, with smaller contributions from riverine and estuarine phytoplankton. In contrast, the [C/N]a ratios of particulate OM (POM) samples varied significantly among the collection periods, ranging from low values of 5 to high values of >20. Overall, the trends in [C/N]a ratios indicated that algal sources of POM were most important during the early and late summer, whereas terrigenous sources dominated in the winter and early spring.In Winyah Bay bottom sediments, the concentrations of the mineral-associated OM were positively correlated with sediment surface area. The [C/N]a ratios and δ¹³C_OC compositions of the bulk sedimentary OM ranged from 5 to 45 and from −28 to −23‰, respectively. These compositions were consistent with predominant contributions of terrigenous sources and lesser (but significant) inputs of freshwater, estuarine and marine phytoplankton. The highest terrigenous contents were found in sediments from the river and upper bay sites, with smaller contributions to the lower parts of the estuary. The yields of lignin-derived CuO oxidation products from Winyah Bay sediments indicated that the terrigenous OM in these samples was composed of variable mixtures of relatively fresh vascular plant detritus and moderately altered soil OM. Based on the lignin phenol compositions, most of this material appeared to be derived from angiosperm and gymnosperm vascular plant sources similar to those found in the upland coastal forests in this region. A few samples displayed lignin compositions that suggested a more significant contribution from marsh C₃ grasses. However, there was no evidence of inputs of Spartina alterniflora (a C₄ grass) remains from the salt marshes that surround the lower sections of Winyah Bay.  相似文献   

珠江口浮游幼虫的生态研究     

李开枝  尹健强  黄良民  邱大俊 《海洋通报》2007,26(6):42-47

根据2002—2003年珠江口12个航次的调查资料,分析探讨了不同调查时间和区域浮游幼虫的组成类型、丰度变化和环境因子的影响。以表层盐度(S)变化将调查海域划分成三个区域:I区(S<25)、II区(2530)。12个航次的调查结果显示:调查海域共出现浮游幼虫12个类型,隶属5个动物门,II区和III区的类型数一般高于I区,软体动物门和棘皮动物门的幼虫只出现在II区和III区。其中2002年7月(夏季)、2003年1月(冬季)和4月(春季)的3个大航次结果表明珠江口浮游幼虫的平均丰度为61ind/m3,三个区域的平均丰度比较为II区(124ind/m3)>I区(33ind/m3)>III区(27ind/m3),春夏季的丰度高于冬季。另外在I区进行了9个小航次调查的研究表明:I区浮游幼虫平均丰度较高,月份之间的丰度差别明显,不同站位之间也有差别。温度和食料是影响珠江口浮游幼虫丰度变化的主要因素。  相似文献   

Spatial and temporal variations of mesozooplankton in the Pearl River estuary, China   总被引：10，自引：0，他引：10  

K.Z. Li  J.Q. Yin  L.M. Huang  Y.H. Tan   《Estuarine, Coastal and Shelf Science》2006,67(4):543-552

This paper examines spatial and temporal variations of mesozooplankton abundance, biomass and community structure during three cruises of July 2002 (summer), January 2003 (winter), and April 2003 (spring) in the Pearl River estuary, China. Zooplankton abundance and biomass fluctuated widely and showed distinct heterogeneity in the Pearl River estuary. A total of 154 species were identified during three surveys. The number of zooplankton species richness was strongly linked to salinity. Hierarchical cluster analysis identified three zooplankton groups during this study. Estuarine, neritic and pelagic groups corresponded to the upper, middle and lower reaches in the Pearl River estuary. The difference among groups could be mainly ascribed to changes in the relative contributions of the dominant species. The fluctuations in the zooplankton abundance, biomass and community structure were determined by the interactive effects of freshwater inflow, tidal and coastal currents, chlorophyll a, salinity and temperature. Significant spatial variability in the distribution of zooplankton species, abundance and biomass can be ascribed to the virtual presence of a horizontal gradient in salinity.  相似文献   

Multi-bioindicator study of a small estuary in Vendée (France)     

J. P. Debenay  P. Carbonel  M. -T. Morzadec-Kerfourn  A. Cazaubon  M. Denfle  A. -M. Lzine 《Estuarine, Coastal and Shelf Science》2003,58(4):843-860

Surficial sediment (about 5 mm) was scraped off in 15 stations selected in the Vie Estuary, a small estuary on the French Atlantic coast. The samples, prepared using the suitable methods, were used for comparing the behaviour of periphytic algae, sporopollinic and other palynologic material, ostracoda and foraminifera for proposing a synthetic evaluation of the information provided by each of them. Dinoflagellate cysts, which are found in an almost monospecific assemblage in low-salinity water, are dispersed by tidal currents, but the location of tintinnids in only the lower reaches shows a limited inward transport. Sporopollinic material is clearly related to the adjacent vegetation, indicating a local origin, and then little influence of transport on the microbenthos, even if fragments of freshwater crustaceans and of Pediastrum alga are found down to the mouth in the sporopollinic deposits. This limited transport of microbenthos allows the use of periphytic algae, benthic ostracoda and benthic foraminifera as indicators of local environmental conditions. It was then possible to determine the extent of marine influence in the estuary, to discriminate between the main channel and adjacent basins, and between different stages of evolution of the basins, from a recently dug basin to a eutrophicated one.  相似文献   

Rheological Properties and Incipient Motion of Cohesive Sediment in the Haihe Estuary of China   总被引：2，自引：1，他引：2  

BAI  Yu-chuan 《中国海洋工程》2002,16(4):483-498

The Haihe cohesive sediment, which is typical in China, is studied systematically for its basic physical and incipientmotion properties. Following the requirements of dredging works in the Haihe Estuary, cohesive sediment samples weretaken from three locations. Laboratory experiments were conducted to determine the rheological properties of these sam-ples and to examine the incipient motion of the cohesive sediment. It is found that the cohesive sediment has an obviousyield stress τb, which increases with the mud density in a manner of an exponential function, and so does the viscosityparameter η. The cohesive sediment behaves like a Bingham fluid when its density is below 1.38 ～ 1.40 g/cm3, andwhen denser than these values, it may become a power-law fluid. The incipient motion experiment also revealed that theincipient velocity of the cohesive sediment increases with the density in an exponential manner. Therefore, the incipientmotion is primarily related to the density, which is different from the case for non-cohesive sediment in which the incipi-ent motion is correlated with the diameter of sand particles instead. The incipient motion occurs in two different ways de-pending on the concentration of mud in the bottom. For sufficiently fine particles and a concentration lower than1.20 g/cm3, the cohesive sediment appears as fluidized mud, and the incipient motion is in the form of instability of aninternal wave. For a higher concentration, the cohesive sediment appears as general quasi-solid-mud, and the incipientmotion can be described by a series of extended Shields curves each with a different porosity for newly deposited alluvial mud.  相似文献   

长江河口硼的测定及分布规律研究     

韩庆平  吴玲  奚建风  陈邦林 《海洋科学》1997,21(2):35-38

采用ＨＰＴＡ方法对长江口水中硼进行分析，并与姜黄素法进行比较，方法的标准偏差为０．００５，变动系数小于５％，对长江口水样分析结果与姜黄素法相比较，其相对误差为－０．４％。  相似文献   

Seasonally Hypersaline Estuaries in Mediterranean-climate Regions     

J.L. Largier  J.T. Hollibaugh  S.V. Smith 《Estuarine, Coastal and Shelf Science》1997,45(6):789-797

Data collected in three Californian estuaries indicate that hypersaline conditions exist during the dry summers typical of a Mediterranean climate. The generalised seasonal and longitudinal hydrographic structures are described and explained. It is argued that this seasonal hypersalinity is common and that it represents a major class of estuaries. The observed accumulation of salt indicates surprisingly long residence times in small basins which have free exchange with the ocean. This semi-isolation of the inner basin leads to a large build-up or severe depletion of nutrients, pollutants and plankton in these systems. Of concern are the trends to increase pollutant loading in the same systems that are experiencing an increase in residence times owing to freshwater extraction in the watershed.  相似文献   

Implications of turbulent shear on clay floc break-up along the Atlantic estuary (Bouregreg), Morocco     

Krishnamoorthy Lakshmi Ammal Priya  Soufiane Haddout  Joan Cecilia Catubig Casila 《国际泥沙研究》2022,37(2):248-257

Water depth,salinity,current,and suspended sediment concentration(SSC)were measured along with the grain size distribution of bed sediment along an estuarine longitudinal section.The floc size increased with increase in the percentage of clay and silt,while decreased with increase in the percentage of sand content of bed sediment.The turbulent shear,G,had a direct effect on floc size with its value increasing with increase in G up to a G value of 15 s^-1,while an inverse relation existed between floc size and G at higher G(G>15 s^-1).Further,higher turbulence enabled sand to get resuspended and cause additional shear leading to the break-up of flocs.An attempt was made to modify G to account for the combined effect of water turbulence(G)and shear imparted by sand(Ga)and the impact of the modification of G on the predictability of floc size was evaluated.A new model was developed which explains floc size in terms of sediment concentration(C),salinity gradient(S),and G for different scenarios based on the value of G.Sensitivity analysis was done for observed floc size(FS)and predicted floc size using four approaches:(I)FSαC^x;(II)FSαC^xS-y;(III)FSαC^xS^-yGz for G<15 s^-1and FSαC^xS^-yG-z for G>15 s^-1;and(IV)FSαC^xS^-yG_m^-zfor G>15 s^-1and G_m=G+Ga,where x,y,and z are determined by calibration.It was observed that the predictability of the floc size improved when the turbulence was modified to account for shear imparted by sand so that the coefficient of determination was increased from 0.78 for model III to 0.89 for model IV.Further,the settling velocity was expressed as a function of suspended sediment concentration,turbulent shear,and salinity gradient.The predictability of settling velocity was improved(R2 increased from 0.77 to 0.86)when the additional turbulence created by sand was incorporated in the non-dimensional empirical equation.The study highlights the influence of sand in causing the break-up of flocs and suggests that for turbulence shear values high enough to resuspend sand,and G has to be modified to account for the additional shear imparted by sand in mixed sediment estuarine environments.  相似文献