Biological uptake and accumulation of silica on the Amazon continental shelf

Water column and seabed samples were obtained from 92 stations on the Amazon continental shelf during October of 1979. Uptake of silica near and southeast of the river mouth began at a salinity of 8%. and accounted for 17% of the riverine silica flux to this region. Uptake northwest of the river mouth began at a salinity of 20%. and resulted in 33% removal of the riverine silica flux. Examination of filtered suspended solids revealed abundant diatoms in the surface waters, including Coscinodiscus. Skeletonema, Synedra. and Thalassiosira. The biological uptake of silica appears to be dependent on three factors: turbidity, turbulence, and nutrient availability. There was no evidence of abiological removal of silica in the Amazon estuary. 75 to 88% of the silica removed from surface waters by diatoms dissolves prior to accumulation in the seabed. Based on the mean biogenic silica content of shelf sediment (0.25%) and estimates of rates of sediment accumulation, the biogenic silica accumulation rate on the shelf is 2 × 10¹² g/yr, which represents only 4% of the dissolved silica supplied by the Amazon River. Biological uptake of silica in estuarine surface waters may not accurately reflect permanent removal of biogenic silica to the seabed because of dissolution which occurs in bottom waters and near the sediment-water interface.     

Fish community ecology in an Altered River delta: Spatial patterns in species composition, life history strategies, and biomass

We sampled nearshore fishes in the Sacramento-San Joaquin Delta, California, United States, during 2001 and 2003 with beach seines and gill nets. We addressed three questions. How and why did fish assemblages vary, and what local habitat features best explained the variation? Did spatial variation in assemblages reflect greater success of particular life history strategies? Did fish biomass vary among years or, across habitats? Nonmetric multidimensional scaling showed that habitat variables had more influence on fish assemblages than temporal variables. Results from both gear types indicated fish assemblages varied between Sacramento and San Joaquin River sampling sites. Results from gill net sampling were less pronounced than those from beach seine sampling. The Sacramento and San Joaquin river sites differed most notably in terms of water clarity and abundance of submerged aquatic vegetation (SAV), suggesting a link between these habitat characteristics and fish relative abundance. Among-site differences in the relative abundance of periodic and equilibrium strategist species suggested a gradient in the importance of abiotic versus biotic community structuring mechanisms. Fish biomass varied among years, but was generally higher in SAV-dominated habitats than the turbid, open habitats in which we found highest abundances of striped bassMorone saxatilis and special-status native fishes such as delta smeltHypomesus transpacificus, Chinook salmonOncorhyncus tschawytscha, and splittailPogonichthys macrolepidotus. The low abundance of special-status fishes in the comparatively productive SAV-dominated habitats suggests these species would benefit more from large-scale restoration actions that result in abiotic variability that mirrors natural river-estuary habitat than from actions that emphasize local (site-specific) productivity.     

Comprehensive Analysis of Fish Assemblages in Relation to Seasonal Environmental Variables in an Estuarine River of Indian Sundarbans

Fish distribution in relation to environmental variables was investigated in the Matla River of Sundarban estuarine system. A total of 64 brackish water species belonging to 38 families showing tropical and subtropical affinities were obtained upon monthly sampling of 1 year. The most abundant species were Harpadon nehereus, Gudusia chapra, Coilia neglecta, Coilia ramcarati and Liza parsia. Fish assemblages showed significant seasonal variation as was revealed from MANOVA. MDS ordination plot based on similarity in the fish assemblages revealed that premonsoonal season was distinguishable from the monsoonal and postmonsoonal seasons. Notable differences were also evident between monsoon and postmonsoon. Canonical correspondence analysis indicated that salinity, acidity, inorganic phosphate concentration and dissolved oxygen were the most important environmental variables in determining the observed variation in fish assemblages. Seasonal succession of fish populations may be related to differences in life cycle and adaptation to prevalent ecological conditions. The study therefore suggests that environmental variations in terms of changing salinity and dissolved oxygen have significant influence in structuring estuarine piscine community in this region.     

The soft-bottom macrobenthos of North Carolina estuaries

The structure of macro infaunal (>0.5 mm sieve size) assemblages was examined in samples of unconsolidated substrates collected during the summers of 1994–1997 at 208 stations throughout North Carolina estuaries. Numerical classification (cluster analysis) of stations resulted in 14 distinct site groups that reflected discernible habitatrelated patterns in species distributions. Multiple discriminant analysis, performed on synoptic abiotic variables (depth, salinity, dissolved oxygen, pH, percent silt-clay), showed that the separation of site groups was related primarily to salinity. Percent silt-clay had a secondary influence on the separation of sites within similar salinity zones. Species diversity among site groups generally decreased with decreasing salinity and increasing mud content of sediment. Nodal analysis showed a wide range in constancy and fidelity of species assemblages within site groups. Some assemblages dominated by euryhaline species had no particular affinity with any one site group. The strongest affinities, as evidenced by high values of both constancy and fidelity, were displayed by an assemblage of oligochaetes, insect larvae, gammaridean amphipods, and the clamCorbicula fluminea in tidal freshwater muds; and an assemblage of haustoriid amphipods, the bivalveDonax variabilis, the polychaeteParaonis fulgens, and unidentified echinoids at high-salinity sites in outer Pamlico Sound near ocean inlets. A series of stations with impaired benthic assemblages in polluted habitats emerged from the cluster analysis and was distinguishable from other site groups that reflected a greater influence of natural controlling factors (such as salinity and sediment type) on species distributions. These results suggest that the interaction of both anthropogenic and natural environmental controlling factors is important in defining the structure of these infaunal assemblages.     

The sedimentary record of climatic and anthropogenic influence on the Patuxent estuary and Chesapeake Bay ecosystems

Ecological and paleoecological studies from the Patuxent River mouth reveal dynamic variations in benthic ostracode assemblages over the past 600 years due to climatic and anthropogenic factors. Prior to the late 20th century, centennial-scale changes in species dominance were influenced by climatic and hydrological factors that primarily affected salinity and at times led to oxygen depletion. Decadal-scale droughts also occurred resulting in higher salinities and migration of ostracode species from the deep chanel (Loxoconcha sp.,Cytheromorpha newportensis) into shallower water along the flanks of the bay. During the 19th century the abundance ofLeptocythere nikraveshae andPerissocytheridea brachyforma suggest increased turbidity and decreased salinity. Unprecedented changes in benthic ostracodes at the Patuxent mouth and in the deep channel of the bay occurred after the 1960s whenCythermorpha curta became the dominant species, reflecting seasonal anoxia. The change in benthic assemblages coicided with the appearance of deformities in foraminifers. A combination of increased nitrate loading due to greater fertilize use and increased fresh-water flow explains this shift. A review of the geochemical and paleoecological evidence for dissolved oxygen indicates that seasonal oxygen depletion in the main channel of Chesapeake Bay varies over centennial and decadal timescales. Prior to 1700 AD, a relatively wet climate and high freshwater runoff led to oxygen depletion but rarely anoxia. Between 1700 and 1700, progressive eutrophication occurred related to land clearance and increased sedimentation, but this was superimposed on the oscillatory pattern of oxygen depleton most likely driven by climatological and hydrological factors. It also seems probable that the four-to five-fold increase in sedimentation due to agricultural and timber activity could have contributed to an increased natural nutrient load, likely fueling the early periods (1700–1900) of hypoxia prior to widespread fertilizer use. Twentieth-century anoxia worsened in the late 1930s–1940s and again around 1970, reaching unprecedented levels in the past few decades. Decadal and interannual variability in oxygen depletion even in the 20th century is still strongly influenced by climatic processes influencing precipitation and freshwater runoff.     

Seasonal Cycling and Transport of Mercury and Methylmercury in the Turbidity Maximum of the Delaware Estuary

The Delaware River Estuary (DRE) is a cornerstone of industrialization, shipping, and urban usage, and has a long history of human impact on pollution and recovery. Mercury (Hg) is a contaminant of concern in the DRE based upon concentrations in some fish samples that were found to exceed State and Federal fish tissue criteria. Methylation of Hg often follows a seasonal pattern as its production is biologically mediated. Surveys were conducted in November 2011, April 2012, and July 2012 to assess this effect. We sampled surface and bottom water at six sites spanning the estuarine turbidity maximum (ETM) in the main channel of the river, plus three sediment sites at shallow, subtidal locations. Our results indicate there is a clear seasonal increase in both water column and sediment methylmercury (MeHg) and %MeHg concentrations in the ETM during July. Water-column-filtered total mercury (HgT), suspended particle HgT, and MeHg concentrations were found to fluctuate little with location or season in the ETM. In contrast, sediment MeHg, water-column-filtered MeHg, and pore water HgT varied seasonally. Furthermore, pore water MeHg levels were elevated in concert with increased k _meth rates in July. Estimated river input and sediment and atmospheric depositional MeHg flux were compared seasonally. River flux was more than an order of magnitude higher than sediment flux in April, coinciding with higher fluvial transport. However, during July, river flux decreases and sediment flux becomes a larger relative source. This trend has potential implications for fish and other biota residing in the DRE during summer.     

The ecological effects of structural flood mitigation works on fish habitats and fish communities in the lower Clarence River system of South-Eastern Australia

The effects of flood mitigation structures on the quality of estuarine and freshwater fish habitats in the lower Clarence River system of south-eastern Australia were investigated. Surrounding land use, fringing vegetation, overall level of habitat disturbance, distance from the sea, salinity, and water temperature were examined and compared between four sites on natural tributary streams, four sites on channelized flood mitigation drains gated at their mouths, and ten paired sites (five below and five above floodgates) on flood mitigation drains in this system, from mid 1988 to late 1990. Quantitative sampling of the fish fauna at each of these sites was conducted quarterly over this 21/2-yr period. Juvenile fishes were sampled using netting enclosures together with application of the ichthyocide rotenone, while subadults and adults were sampled using multiple-panel gill nets. In general, fish habitats in the flood mitigation drains, and especially those above flood gates, had more intensive surrounding land uses, less natural native fringing vegetation and, overall, were more highly disturbed than those in the natural tributaries. Salinity at the various study sites was largely dependent on the pattern of seasonal (mainly summer and autumn) rainfall and distance upstream from the sea. Salinities usually differed only slightly between gated and ungated sites at similar distances from the sea, indicating that the floodgates were generally ineffective in preventing the penetration of saline river water into the drains immediately above them. These gates were, however, very effective in preventing the establishment of fringing mangrove vegetation in the drains above them. The main ecological effects of these flood mitigation works have thus been to generally degrade the overall quality of available fish habitat, particularly in terms of reductions in natural fringing vegetation (mangroves in the more estuarine-dominated areas and overhanging terrestrial trees in the more freshwater-dominated areas often being replaced by grassess and rushes), and to increase the intensity of surrounding land use (natural forest often being cleared and wetlands drained for cattle grazing and sugarcane growing), both of these factors contributing to increases in generalized aquatic habitat disturbance. Results from the study of the fish assemblages in these natural and man-altered habitats revealed the following general patterns. Highest fish species numbers and abundances occurred in the ungated natural tributaries and in drains downstream of floodgates. These habitats also contained the largest proportions of both commercial fish species and individuals as well as the majority of species and individuals with marine-estuarine affinities. Both total and commercial fish species numbers generally declined with decreasing salinity and increasing distance of the sampling sites from the sea. Even through saline waters from the main river system penetrated the majority of the floodgates during most of the study period, fish passage through these gates was found to be very restricted. Fish assemblages above such gates were generally dominated by primarily freshwater species, as compared with primarily saltwater (estuarine-marine) species below. The conversion of the great majority of small mangrove-fringed tributaries in the lower reaches of this river system into uniform floodgated drainage channels has thus resulted in the destruction of, and impeded fish access to, large areas of previously available estuarine fish nursery and feeding habitat. These drainage changels are now dominated by terrestrial-freshwater vegetation above where they are cut off from the main river channels by the floodgates, and the period of their construction has coincided with that of reported declines in fish catches in this river system. On the basis of the above findings, it is recommended that these floodgates be left fully open at all times except immediately prior to and during floods in the river system, thus facilitating the re-establishment of fringing mangrove vegetation along the banks of the artificial drains in the lower reaches, generally improving flushing and thus water quality in these drains, and allowing the establishment of primarily estuarine-marine fish communities, including more species of economic importance, in them.     

Sediment Accretion in Tidal Freshwater Forests and Oligohaline Marshes of the Waccamaw and Savannah Rivers,USA

Sediment accretion was measured at four sites in varying stages of forest-to-marsh succession along a fresh-to-oligohaline gradient on the Waccamaw River and its tributary Turkey Creek (Coastal Plain watersheds, South Carolina) and the Savannah River (Piedmont watershed, South Carolina and Georgia). Sites included tidal freshwater forests, moderately salt-impacted forests at the freshwater–oligohaline transition, highly salt-impacted forests, and oligohaline marshes. Sediment accretion was measured by use of feldspar marker pads for 2.5 year; accessory information on wetland inundation, canopy litterfall, herbaceous production, and soil characteristics were also collected. Sediment accretion ranged from 4.5 mm year^?1 at moderately salt-impacted forest on the Savannah River to 19.1 mm year^?1 at its relict, highly salt-impacted forest downstream. Oligohaline marsh sediment accretion was 1.5–2.5 times greater than in tidal freshwater forests. Overall, there was no significant difference in accretion rate between rivers with contrasting sediment loads. Accretion was significantly higher in hollows than on hummocks in tidal freshwater forests. Organic sediment accretion was similar to autochthonous litter production at all sites, but inorganic sediment constituted the majority of accretion at both marshes and the Savannah River highly salt-impacted forest. A strong correlation between inorganic sediment accumulation and autochthonous litter production indicated a positive feedback between herbaceous plant production and allochthonous sediment deposition. The similarity in rates of sediment accretion and sea level rise in tidal freshwater forests indicates that these habitats may become permanently inundated if the rate of sea level rise increases.     

Modern and Holocene hydrographic characteristics of the shallow Kara Sea shelf (Siberia) as reflected by stable isotopes of bivalves and benthic foraminifera

River discharge of Ob and Yenisei to the Kara Sea is highly variable on seasonal and interannual time scales. River water dominates the shallow bottom water near the river mouths, making it warmer and less saline but seasonally and interannually more changeable than bottom water on the deeper shelf. This hydrographic pattern shows up in measurements and modelling, and in stable isotope records (δ¹⁸O, δ¹³C) along the growth axis of bivalve shells and in multiple analyses of single benthic foraminiferal shells. Average isotope ratios increase, but sample-internal variability decreases with water depth and distance from river mouths. However, isotope records of bivalves and foraminifera of a sediment core from a former submarine channel of Yenisei River reveal a different pattern. The retreat of the river mouth from this site due to early Holocene sea level rise led to increasing average isotope values up core, but not to the expected decrease of the in-sample isotope variability. Southward advection of cold saline water along the palaeo-river channel probably obscured the hydrographic variability during the early Holocene. Later, when sediment filled the channel, the hydrographic variability at the core location remained low, because the shallowing proceeded synchronously with the retreat of the river mouth.     

Responses of fish and macrobenthic assemblages to hydrologic disturbances in Tijuana Estuary and Los Peñasquitos Lagoon,California

Changes in the assemblages of fishes and benthic macro-invertebrates were evaluated in relation to wastewater inflows at Tijuana Estuary and impounded streamflows and mouth closure at Los Peñasquitos Lagoon. Freshwater from sewage spills or winter rains lowered water salinities and had major impacts on the channel organisms of both southern California coastal wetlands. Benthic infaunal assemblages responded more rapidly to reduced salinity than did fishes, with continued salinity reduction leading to the extirpation of most species. Both the fish and benthic invertebrate assemblages became dominated by species with early ages of maturity and protracted spawning seasons. Between-system comparisons showed that good tidal flushing reduced negative impacts on both the fish and benthic assemblages.     

Modeling diagnosis of suspended sediment transport in tidal estuarine system

A three-dimensional, time-dependent hydrodynamic and suspended sediment transport model was performed and applied to the Danshuei River estuarine system and adjacent coastal sea in northern Taiwan. The model was validated with observed time-series salinity in 2001, and with salinity and suspended sediment distributions in 2002. The predicted results quantitatively agreed with the measured data. A local turbidity maximum was found in the bottom water of the Kuan-Du station. The validated model then was conducted with no salinity gradient, no sediment supply from the sediment bed, wind stress, and different freshwater discharges from upstream boundaries to comprehend the influences on suspended sediment dynamics in the Danshuei River estuarine system. The results reveal that concentrations of the turbidity maximum simulated without salinity gradient are higher than those of the turbidity maximum simulated with salinity gradient at the Kuan-Du station. Without bottom resuspension process, the estuarine turbidity maximum zone at the Kuan-Du station vanishes. This suggests that bottom sediment resuspension is a very important sediment source to the formation of estuarine turbidity maximum. The wind stress with northeast and southwest directions may contribute to decrease the suspended sediment concentration. When the freshwater discharges increase at the upstream boundaries, the limits of salt intrusion pushes downriver toward river mouth. Suspended sediment concentrations increase at the upriver reaches in the Danshuei River to Tahan Stream, while decrease at Kuan-Du station.     

黄河下游窄河段挖河固堤启动工程减淤效果研究

根据1997年实施的黄河下游窄河段挖河固堤启动工程的观测资料,分析了挖河对河道冲淤变化及水面线调整的影响。研究表明,在一定的时段和一定河段内,挖河对于减少河道淤积及降低洪水位都有较好效果。对挖沙减淤效果的基本概念也作了讨论。     

珠江口磨刀门枯季水文特征及河口动力过程

根据磨刀门2003年12月9~15日的大、中潮同步水文观测资料,分析了磨刀门枯季的潮汐、潮流、余流、悬移质含沙量、盐度等水文特征,并对枯季河口动力过程,如咸淡水混合、河口射流等进行了初步研究。在枯季由于径流较弱,潮流成为主要动力。表层由于受径流和风的影响余流基本上沿河道走向向下游,中层以下有稳定的向上的余流存在。枯季磨刀门含沙量较小(<1 kg/m3),盐度在平面上和垂向上均有一定变化。磨刀门枯季咸淡水混合类型为缓混合型,各站盐度分层参数均在0.01~1.0。从实测流速的分布情况来看,河口下层有反向的水流,存在明显的因密度差而形成的密度环流。根据枯季实测资料计算所得的密度弗劳德数,磨刀门枯季以浮力射流为主。     

Hydrological and biogeochemical dynamics of the minor and trace elements in the St. Lawrence River

Surface water samples from the St. Lawrence River were collected in order to study the processes controlling minor and trace elements concentrations (Al, Fe, Mn, Cd, Co, Cu, Ni and Zn), and to construct mass balances allowing estimates of the relative importance of their natural and anthropogenic sources. The two major water inputs, the upper St. Lawrence River, which drains waters originating from the Lake Ontario, and the Ottawa River were collected fortnightly over 18 months. In addition, other tributaries were sampled during the spring floods. The output was monitored near Quebec City at the river mouth weekly between 1995 and 1999. Dissolved metal concentrations in the upper St. Lawrence River carbonated waters were lower than in the acidic waters of the tributaries draining the crystalline rocks of the Canadian shield and the forest cover. Biogeochemical and hydrodynamic processes occurring in Lake Ontario drive the seasonal variations observed in the upper St. Lawrence River. Biogeochemical processes relate to biological uptake, regeneration of organic matter (for Cd and Zn) and oxyhydroxide formation (for Mn and Fe), while hydrodynamic processes mainly concern the seasonal change in vertical stratification (for Cd, Mn, and Zn). In the Ottawa River, the main tributary, oxyhydroxide formation in summer governs seasonal patterns of Al, Fe, Mn, Cd, Co and Zn. The downstream section of the St. Lawrence River is a transit zone in which seasonal variations are mainly driven by the mixing of the different water masses and the large input of suspended particulate matter from erosion. The budget of all dissolved elements, except Fe and Zn, was balanced, as the budget of particulate elements (except Cd and Zn). The main sources of metals to the St. Lawrence River are erosion and inputs from tributaries and Lake Ontario. Direct anthropogenic discharges into the river accounted for less than 5% of the load, except for Cd (10%) and Zn (21%). The fluxes in transfer of dissolved Cd, Co, Cu and Zn species from the river to the lower St. Lawrence estuary were equal to corresponding fluxes calculated for Quebec City since the distributions of dissolved concentrations of these metals versus salinity were conservative. For Fe, the curvature of the dilution line obtained suggests that dissolved species were removed during early mixing.     

An estuarine benthic index of biotic integrity for the Mid-Atlantic region of the United States. I. Classification of assemblages and habitat definition

An objective of the Mid-Atlantic Integrated Assessment Program (MAIA) of the U.S. Environmental Protection Agency is to develop an index for assessing benthic community condition in estuaries of the mid-Atlantic region of the United States (Delaware Bay through Pamlico Sound). To develop such an index, natural unimpaired communities must first be identified and variability related to natural factors accounted for. This study focused on these two objectives; Lnansó et al. (2002) describe the index. Using existing data sets from multiple years, classification analyses of species abundance and discriminant analysis were employed to identify major habitat types in the MAIA region and evaluate the physical characteristics that structure benthic infaunal assemblages. Sampling was restricted to soft bottoms and to the index development period, July through early October. The analyses revealed salinity and sediment composition as major factors structuring infaunal assemblages in mid-Atlantic estuaries. Geographical location was a secondary factor. Nine habitat classes were distinguished as a combination of 6 salinity classes, 2 sediment types, and the separation of North Carolina and Delaware-Chesapeake Bay polyhaline sites. The effect of sediment types on faunal assemblages was restricted to polyhaline sites, which were separated into two sediment groups above and below 90% sand content. Assemblages corresponding to each of these 9 habitats were identified in the context of widely recognized patterns of dominant taxa. Differences between North Carolina and Delaware-Chesapeake Bay polyhaline assemblages were attributed to the relative contributions of species and not to differences in species composition. No zoogeographic discontinuities could be identified. Our results reinforce the findings of recent studies which suggest that, with respect to estuarine benthic assemblages, the boundary between the Virginian and the Carolinian Provinces be moved to a new location south of Pamlico Sound.     

Holocene hydrographical changes of the eastern Laptev Sea (Siberian Arctic) recorded in δO profiles of bivalve shells

Oxygen isotope profiles along the growth axis of fossil bivalve shells of Macoma calcarea were established to reconstruct hydrographical changes in the eastern Laptev Sea since 8400 cal yr B.P.. The variability of the oxygen isotopes (δ¹⁸O) in the individual records is mainly attributed to variations in the salinity of bottom waters in the Laptev Sea with a modern ratio of 0.50‰/salinity. The high-resolution δ¹⁸O profiles exhibit distinct and annual cycles from which the seasonal and annual salinity variations at the investigated site can be reconstructed. Based on the modern analogue approach oxygen isotope profiles of radiocarbon-dated bivalve shells from a sediment core located northeast of the Lena Delta provide seasonal and subdecadal insights into past hydrological conditions and their relation to the Holocene transgressional history of the Laptev Sea shelf. Under the assumption that the modern relationship between δ¹⁸O_w and salinity has been constant throughout the time, the δ¹⁸O of an 8400-cal-yr-old bivalves would suggest that bottom-water salinity was reduced and the temperature was slightly warmer, both suggesting a stronger mixture of riverine water to the bottom water. Reconstruction of the inundation history of the Laptev Sea shelf indicates local sea level ∼27 m below present at this time and a closer proximity of the site to the coastline and the Lena River mouth. Due to continuing sea level rise and a southward retreat of the river mouth, bottom-water salinity increased at 7200 cal yr B.P. along with an increase in seasonal variability. Conditions comparable to the modern hydrography were achieved by 3800 cal yr B.P.     

Web-based application for estimating water quality impacts due to environmental dredging

A Web-based dredge plume simulation software has been developed for estimating sediment transport and contaminant release from dredging operations. This application software comprises a near-field source model and far-field sediment transport model, combined with the settling analysis of flocculent particles. It is designed to run on all computing platforms with a standard Web browser and is accessible over the Internet. This paper describes its internal software structures and the major features of the application software. In addition, an example application of sediment transport in the Savannah River, GA, is included to illustrate typical input and output screens and to demonstrate the accuracy of the model. The water quality assessment software developed herein will greatly enhance the ability of the predictive tool for estimating sediment transport and resuspension during dredging operations.     

The ichthyofauna and abiotic hydrological environment of the Ria de Aveiro,Portugal

The abiotic hydrological environment and the community dynamics of the fish fauna were investigated in the Ria de Aveiro, an estuarine coastal lagoon system (43 km²), which has both marine and fluvial influences. Abiotic hydrological and fish community parameters were recorded routinely during 12 months at ten stations. Temperature ranged between 9.5°C and 26.0°C, salinity between 0.0‰ and 32.0‰, dissolved oxygen between 0.8 mg 1^?1 and 15.4 mg 1^?1, pH between 6.1 and 9.4, and transparency between 4.4% and 100.0%. No significant differences were observed in temperature and dissolved oxygen among stations, or in seasonal variation in transparency. Nineteen thousand thirty-one fish specimens comprising 55 species were sampled. Abundance, biomass, and species richness were highest in summer and late winter at stations near the lagoon entrance. Sedentary species were most numerous, marine migratory species had the highest biomass, and the category “occasional species” had the highest number of species. Atherinidae, Mugilidae, and Gobiidae were the most important families. Eight species represented about 80% of the total fish abundance and biomass but only six species occurred in all the months and at all the stations. It was concluded that the Ria de Aveiro, with high seasonal and spatial abiotic variation, has a very rich and representative fish community compared with temperate and tropical estuaries and estuarine coastal lagoons around the world.     

黄河河口段一维水流泥沙数学模型

针对黄河河口段河道来水来沙特性和河道冲淤演变特点,综合考虑了断面上水沙分布和冲淤分布不均匀,阻力变化、河口三角洲淤积延伸等问题,建立了黄河利津以下河口段一维水流泥沙数学模型。用该模型对多年汛期和冬季河口段内水沙进行验证计算表明:计算结果与实测结果基本吻合。本模型可用来预测河口段内沿程不同时刻水位、含沙量及河床冲淤的变化过程。