River Mouth Area Research Articles

Feeding Ecology of Salton Sea Tilapia (Oreochromis spp.)

Abstract We investigated the feeding ecology of tilapia (Oreochromis spp) in the Salton Sea. Stomachs and intestines were sampled at each season. Fish foraged at the surface during the summer when dissolved oxygen was low. The proportion of plant materials in fish stomachs was higher at river mouth areas. Diatoms dominated the phytoplankton; rotifers were dominant during the spring and summer; copepods were dominant during the fall; barnacle larvae dominant during the winter. Pile worms (Neanthes succinea) were present throughout the year. Feeding activity was reduced in the summer, when dissolved oxygen was low and water temperature high.

Platinum, Rhodium, Palladium and Lead: Elements Linked to Vehicle Emissions. Their Simultaneous Voltammetric Determination in Superficial Water

The present work, regarding the determination of Pt(II), Rh(III) by square-wave adsorption stripping voltammetry (SWAdSV), Pd(II) by square-wave voltammetry (SWV) and Pb(II) by square-wave anodic stripping voltammetry (SWASV) in superficial water is an interesting example of the possibility to simultaneously, or better sequentially determine each single element in real samples. The critical comparison between peak area and peak current highlights that lower limits of detection are obtained if peak area is employed as instrumental datum. 0.6 mmol/L formaldehyde+1.2 mmol/L hydrazine (formazone complex) in 0.3 mol/L HCl and ammonia-ammonium chloride buffer pH 9.6 were employed as the supporting electrolytes. The analytical procedure was verified by the analysis of the standard reference materials: Sea Water BCR-CRM 403 and Fresh Water NIST-SRM 1643d. Precision and accuracy, expressed as relative standard deviation and relative error, respectively, were generally lower than 6% in all cases. Once set up on the standard reference materials, the analytical procedure was transferred and applied to superficial water sampled in proximity to superhighway and in the Po river mouth area. A critical comparison with spectroscopic measurements is also discussed.

Principles of Typification and Zoning of River Mouth Areas (Analytical Review)

Principles of typification and zoning of river mouth areas are discussed. Definitions of such notions as river mouth area, river mouth, delta, estuary, mouth reach of the river, andnear-shore zone of the river mouth are specified.

Seasonal variations in the characteristics of superficial sediments in a macrotidal estuary (the Seine inlet, France)

Seasonal variations in the sedimentary regime in the mouth of the Seine river, a macrotidal estuary, are described for a 3-year period. The aim of this study is to characterize and to understand the main governing mechanisms, using data from more than a thousand of superficial sediment grab samples or box cores gathered throughout the study period. Analyses of lithofacies and rheological properties were carried out. The distribution of sediments is governed by seasonal meteorological variations. The surface covered by mud reaches a maximum (40% of the total mouth area) during winter. After the winter, the soft mud deposits are progressively redistributed throughout the whole estuary area and onto the shelf. During the lowest freshwater flow at the end of summer, the fine-grained sediments cover less than 20% of the river mouth area. These seasonal variations mainly depend on the river discharge intensity, but are also linked to wave activity. In the study area, the amount of fine-grained deposits after high river flow periods depends on (1) volume of mud erodable within the estuary, (2) the duration of the flood tidal influx, and (3) the duration preceding the particular annual high river flow. During the last decades, filling of the estuary upstream from Honfleur has led to a downstream shift of the fine-grained sediment deposition area; following this, the present-day mud deposition area is in the open part of the estuary, in the subtidal shallow area. Subsequently, fresh mud deposits undergo intense hydrodynamical and meteorological effects, and are partly reworked by waves and tidal currents effects. In this study, it is shown that the behaviour of suspended matter and of superficial sediments is strongly influenced by short but intense events including high river flows and gales.

Brazil: Cadam — kaolin

Field surveys of the 350-km shoreline adjacent to the Amazon river mouth reveal three distinct types: erosional mud, accretionary sand, and accretionary mud. Formation of these zones is controlled by the delivery of Amazon suspended sediment, mediated by the hydrodynamic regime. Erosional mud shorelines extend from Rio Araguari (near the Amazon river mouth) northwestward 280 km to 3.5 °N (near Cabo Cassipore). Shoreface (<5 m water depth) retreat annually yields 1–4 × 106 tons of fine-grained sediment deposited during an earlier phase of shoreface progradation. Sandbodies up to 5 m thick overlie erosional mud shorefaces for 10–30 km downdrift of small rivers. The sand is supplied from these rivers and released by shoreline retreat of the river-mouth areas. Amazon River sand is restricted in the coastal zone from its mouth north to the Cabo Norte shoal area, where it mixes with sand carried by Rio Araguari from the Guiana Highlands.North of 3.5 °N, mud aggradation and progradation is taking place on underconsolidated, low-gradient tidal flats backed by mangrove swamps. 210Pb and 14C geochronology of vibracores from the mudflats indicate that sediment accumulation is rapid (0.24–2.0 cm/yr) landward of the 2-m isobath, supplied from a thick (50–150 cm) seasonal surface layer. Shoreface progradation is episodic, separated by decadal hiatuses. Fine-grained suspended-sediment flux from the Amazon and minor amounts of sand and mud from the local rivers supply sediment to the mudflats. Shore-normal tidal currents and solitary waves rework the surface mud layer, preferentially transporting available sand landward into the mangrove fringe, and producing very fine-grained accumulation on the tidal flat (10–12 φ mean grain size). Lateral accretion of features 10–100 km long, termed mudcapes, produces tens of kilometers of seaward coastal-plain addition along the northern coast. Similar features are identified downdrift along the Guianas coast as far as the Orinoco River (1600 km). The northern Amapa shoreface deposits are a locus of modern sediment accumulation, which progrades over subaqueous deltaic strata.

Dynamics of the Yenisei and Pur River Deltas

Variations in the mouth areas of the Yenisei and Pur rivers over the period of 50 years were revealed on the basis of comparison of topographic maps prepared in the 1950s and space images made from the Landsat satellite in 1973 (MSS System) and 1999, 2000 (ETM System). Maps of the drainage network dynamics were compiled; they show that, over a period of many years, mouth areas of northern rivers undergo slow but steady changes, which are indicative of the continuing protrusion of deltas into bays at a rate up to 20 m/year, the increment in mouth areas reaching 0.05–0.07% a year. As noted, secondary water streams die off under the condition of flow concentration in main branches, and small islands get integrated. It was found that, over the period under study, natural variations in the level of the receiving water body and human-induced changes in river basins (construction of a chain of reservoirs) did not have considerable impact on dynamic processes occurring in deltas.

An inversion method for reflectance in stratified turbid waters

Most methods for interpreting water-leaving reflectance assume vertical homogeneity in the water column. This approach is relevant to quite homogeneous waters or to very turbid waters where reflectance is related to the optical properties of a thin upper surface layer. In weakly turbid and stratified waters, water-leaving reflectance depends on the vertical profile of each optically significant component. This study presents a semi-empirical inversion method to estimate Total Suspended Matter (TSM) concentrations from reflectances in sediment-dominated and stratified waters. The method derives from the concept of a remote sensing estimate of concentration, which is calculated from the profile of suspended matter concentration and from the profile of diffuse attenuation coefficient. A simplification is introduced when the diffuse attenuation profile is not known. The simplified method can be applied to satellite data to retrieve 'optically-effective' concentrations showing better correlations with reflectances than subsurface concentrations. The method is extensively described in the paper and is applied, as an example, to field measurements and to SPOT data over the Ebro river mouth area. Its potential use in connection with numerical modelling of suspended sediment transport is also discussed.

Modelling population dynamics of the pelagic larval shrimp Metapenaeus ensis in the Osaka Bay estuary

Aiming at providing numerical tools useful to assess the impacts of coastal development pressures on marine life, a Lagrangian model for population dynamics of pelagic eggs and larvae of the greasyback shrimp, Metapenaeus ensis, in Osaka Bay was developed and improved based on laboratory experiments. The model was combined with a 3-D Eulerian numerical model that predicts physical and biological conditions of the habitat. A series of numerical experiments was done to investigate their transport processes from the spawning grounds, and the concentration process of full-grown larvae towards the mouth of Yodo River that flows into the innermost basin. Model results revealed, as a general tendency, that the early larval developmental stages through nauplius to zoea continue to drift like a passive tracer, and begin to concentrate at the river mouth area after the mysis stage, mainly avoiding low saline environment in the surface layer. This suggests that the full-grown larvae may be favored with chance to take advantage of the river-induced gravitational circulation that dominates the innermost estuarine basin. In addition, it was found that tidal condition around the spawning period also exerts a considerable influence upon the fate of pelagic larvae.

A new voltammetric method for the simultaneous monitoring of heavy metals in sea water, sediments, algae and clams: application to the Goro Bay ecosystem.

Arsenic(III), selenium(IV), copper(II), lead(II), cadmium(II), zinc(II) have been determined in sea water, sediments, algae and clams by differential pulse cathodic (DPCSV) and anodic (DPASV) stripping voltammetry. The voltammetric measurements are carried out using a conventional three-electrode cell and the ammonia-ammonium chloride buffer pH 9.2 as supporting electrolyte. The analytical procedure has been verified by the analysis of the standard reference materials (Estuarine Sediment BCR- CRM 277, Ulva Lactuca BCR-CRM 279 and Mussel Tissue BCR-CRM 278). The precision and the accuracy are less than 5%. This procedure is utilized for the monitoring of heavy metals in the Po river mouth area (Italy).

Employment of Peak Area as Instrumental Datum for Improving the Voltammetric Quantitative Analysis of Heavy Metals in Fresh and Sea Water in the Presence of Surfactants

Peak area instead of peak height is used for the simultaneous determination of Cu(II), Pb(II), Cd(II), and Zn(II) in fresh and sea water in the presence of anionic and cationic surfactants by differential pulse anodic stripping voltammetry. These species, if present, tend to make more irreversible the electrodic process of the metals. Because the employment of peak area for species having irreversible electrodic processes permits limits of detection about one or 2 orders of magnitude lower, this work shows the possibility of determining heavy metals at ultratrace level concentrations in the presence of surfactants, compounds which are always present in natural waters. The precision and accuracy of the analytical method were checked by the analysis of the standard reference materials (SRM) Fresh Water NIST-SRM 1643d, Sea Water BCR-CRM 403, and Estuarine Water BCR-CRM 505. The former, expressed as relative standard deviation (s(r)), and the latter, expressed as relative error (e), were satisfactory, being in all cases lower than 5%. The analytical procedure has been applied to fresh and sea water sampled in the Po river mouth area (Italy).

The change of characteristics of tidal wave in the Changjiang River mouth area since the post-glacial transgression maximum

During the period of the post-glacial transgression maximum (PGTM), there was a huge trumpet estuary in the modern Changjiang River Delta area. The location and the shape of the Paleo-Changjiang River Estuary (PCRE) were much different from those of the present Changjiang River Estuary. The study on the change of characteristics of tidal wave in the Changjiang River mouth area since the PGTM can help to understand better the dynamic development of the Changjiang River Delta. The course curves of tidal level and tidal current velocity during a single tidal cycle for 35 points are calculated, and characteristics of tidal waves in the PCRE and its adjacent area are compared with those of tidal waves in the modern Changjiang River mouth area. The results show that the tidal waves within the PCRE and in its adjacent area during the period of the PGTM belonged to standing wave or a mixture of standing wave and progressive wave. Since then, the tidal wave in the Changjiang River mouth become gradually to be progressive wave with the PCRE being filled and the Changjiang River mouth shifting southeastwards.

When and where rivers meet the sea

River mouth areas provide one of the most desired locations for human habitation. Although occupying only a small portion of the total length of the world’s shoreline, river mouths are dynamic and complex with highly variable physical and chemical characteristics.

Progradation of the Changjiang River delta since the mid-Holocene

Subaqueous deltaic deposits with approximately 30 radiocarbon ages show that the Changjiang River delta was strongly affected by tides and that the delta progradation rate after 2 kaBP was almost double the rate before 2 kaBP. This change in the progradation rate correlates well with the active extension of the subaerial delta plain shown by previous work. Widespread human activities, such as farming, deforestation, and dike construction, probably resulted in an increase in sediment discharge to the river-mouth area.

Colour classification of coastal waters of the Ebro river plume from spectral reflectances

This paper presents a colour classification of coastal waters from features of spectral reflectance. Experimental data were collected in coastal waters of the Ebro river mouth area during two periods of non-bloom conditions and low suspended load. Examination of the reflectance spectra reveals a few significant shapes corresponding to different apparent colours and specific values of hydrological parameters. A colour classification is proposed. An empirical method and a semi-analytical method are presented in order to retrieve suspended particulate matter concentration, namely SPM, chlorophyll a concentration, chl, sediment refractive index, mr , and absorption coefficient of yellow substance at 440 nm, a y (440). The first method is a direct application of the colour classification. It is based on correlations found for each water type between spectral features of the first derivative of reflectance and SPM, chl, mr , ay (440) values. A second method uses the inversion of a three component reflectance model. Measured reflectance spectra and typical values of mr , deduced from the colour classification, are assimilated in the model. As a result, it appears that estimates of SPM and chl are more accurate by calculating chl from the correlation technique and SPM along with ay (440) from inversion of the reflectance model.

Impact on the Yangtze (Changjiang) Estuary from its drainage basin: Sediment load and discharge

This paper focuses on the sediment transport and freshwater discharging from upper Yangtze drainage basin downstream, primarily on the basis of multiyear hydrological data collected from three major hydrological gauge stations (Yichang, Hankou and Datong). Data indicate highest sediment load in Yichang (5.6 × 108 t/a), lowest in Hankou (5.1× 108 t) and second highest in Datong (5.4 ×108 t). This fluctuations are identical with what has been observed from the annual flood season. About one thirds of the sediment load are trapped in the middle Yangtze River course, where meandering river pattern prevails; rest of them are directly transported to the river mouth area via lower Yangtze River channel, where the river is typically confined by the exposed base rock and almost none is being trapped, instead, minor being drained to the mainstream from the local tributaries. To recognize this sediment delivery and river flow media is vital, because it can highlight morphologic/topographic correlation between the upper drainage basin and the estuary and the erosion and siltation in the river mouth area, where extensive coast has been exclaimed and or being exclaimed, and new navigation channel and port is being constructed. It is particularly crucial for monitoring the impact on estuarine change after 3-Gorges dam being closed in 2009. Data also indicate an increase in freshwater discharging downstream (>7.7 × 1111 m3/a), of which ∼50% derived from the upstream and another half concentrated from the local tributaries. The result shows that this numerous freshwater has constantly flowed into the river mouth area to support the estuarine aquaculture and ecosystem, where it is confronted with huge amount of tidal prism (>10 times more than that of the annual runoff) transforming from offshore. Thus, a great concern for saltwater intrusion especially during the dry season is aroused, largely due to the intense upstream agriculture irrigation and large water transfer project, such as the well-planned South-North Water Transfer project.

Wind-induced Variations in Water Level in River Mouths

The principal factors that control the character of deformation variations in water level in mouth areas of rivers are considered. The role of wind regime and the sea level variations in the formation of positive and negative setups is assessed. River mouth zones are classified in terms of the predominance of positive or negative variations in water level. Specific features of the positive or negative setup regimes in the mouth zones of the Neva, Don, and Volga rivers are discussed.

Hydrological Regime and Morphodynamics of the Yangtze River Mouth Area

The features of the hydrological regime, modern morphological structure, fluviomorphological processes, and the history of formation of the Yangtze River mouth area are discussed. The influence of the huge river water and sediment runoff and tides on the hydrological and morphological processes in the Yangtze River mouth is shown. The possible impact of construction of the large waterworks “Three Gorges” on the hydrological and morphological processes in the Yangtze River mouth is roughly evaluated.

Colour classification of coastal waters of the Ebro river plume from spectral reflectances

This paper presents a colour classification of coastal waters from features of spectral reflectance. Experimental data were collected in coastal waters of the Ebro river mouth area during two periods of non-bloom conditions and low suspended load. Examination of the reflectance spectra reveals a few significant shapes corresponding to different apparent colours and specific values of hydrological parameters. A colour classification is proposed. An empirical method and a semi-analytical method are presented in order to retrieve suspended particulate matter concentration, namely SPM, chlorophyll a concentration, chl, sediment refractive index, mr , and absorption coefficient of yellow substance at 440 nm, a y (440). The first method is a direct application of the colour classification. It is based on correlations found for each water type between spectral features of the first derivative of reflectance and SPM, chl, mr , ay (440) values. A second method uses the inversion of a three component reflectance model. Measured reflectance spectra and typical values of mr , deduced from the colour classification, are assimilated in the model. As a result, it appears that estimates of SPM and chl are more accurate by calculating chl from the correlation technique and SPM along with ay (440) from inversion of the reflectance model.

Study of red tide prediction model for the Changjiang Estuary

This paper based on field data (on red tide water quality monitoring at the Chaggjiang River mouth and Hutoudu mariculture area in Zhejiang Province from May to August in 1995, and May to September in 1996) presents an effective model for short term prediction of red tide in the Changjiang Estuary. The measured parameters include: depth, temperature, color diaphaneity, density, DO, COD and nutrients (PO4−P, NO2−N, NO3−N, NH4−N). The model was checked by field-test data, and compared with other related models.

A Three-Component Model of Ocean Color and Its Application in the Ebro River Mouth Area

A three-component reflectance model that takes into account the contributions of dissolved organic matter, phytoplankton, and mineral particles is described. The principle of inversion of the model, in terms of chlorophyll a plus phaeopigments concentration, chl, sediment refractive index, m r , and absorption coefficient of yellow substance at 440 nm, a y (440), is exposed. The inversion procedure is applied to experimental data collected in the Ebro river plume area. The obtained estimates of chl are accurate only in order of magnitude. However, we demonstrate that m r and a y (440) determinations are robust against chl variations within −50%, +100% of experimental values. Investigation of possible variations with wavelength of m r , using measured concentrations and a y (440) estimates, evidences a slight dependency as was previously observed. We support in conclusion that the inversion procedure could be exploited in a two-step process. First a y (440) and the mean value of m r are estimated from measured water quality parameters. Then m r is calculated at each wavelength, considering a y (440) value determined in the first step.