Academic literature on the topic 'Estuary-coast gradient'

We analyzed the distribution of suspended sediments concentration (SSC) in the Yellow River Estuary based on data from GaoFen-1 (GF-1), which is a high-resolution satellite carrying a wide field-of-view (WFV) sensor and panchromatic and a multispectral (PMS) sensor on it. A new SSC retrieval model for the wide field-of-view sensor (M-WFV) was established based on the relationship between in-situ SSC and the reflectance in blue and near infrared bands. SSC obtained from 16 WFV1 images were analyzed in the Yellow River Estuary. The results show that (1) SSC in the study area is mainly 100–3500 mg/L, with the highest value being around 4500 mg/L. (2) The details of suspended sediment injection phenomenon were found in the Yellow River Estuary. The SSC distribution in the coastal water has two forms. One is that the high SSC water evenly distributes near the coast and the gradient of the SSC is similar. The other is that the high SSC water concentrates at the right side of the estuary (Laizhou Bay) with a significantly large area. Usually, there is a clear-water notch at the left side of the estuary. (3) Currents clearly influenced the SSC distribution in the Yellow River Estuary. The SSC gradient in the estuary was high against the local current direction. On the contrary, the SSC gradient in the estuary was small towards the local current direction. Eroding the coast and resuspension of the bottom sediments, together with currents, are the major factors influencing the SSC distribution in nearshore water in the Yellow River Estuary.

The present study investigated the larval fish dispersal along an estuarine–ocean gradient to explore connectivity between ocean and estuaries. During spring 2009, a combined ocean–estuarine survey was conducted along the Lima estuarine salinity gradient and in two transects off the adjacent coast (northwestern Iberian Peninsula), until the 100 m isobaths. Salinity, total particulate matter, particulate organic matter, total dissolved carbon, and dissolved organic carbon reached higher values at the ocean, and chlorophyll a and nutrients increased at the estuary. From the total 56 taxa identified, 14 were present along the gradient, including estuarine species (ES), marine stragglers (MS), and migrants (MM). Canonical correspondence analysis showed that species were separated along the gradient according to their ecological functional classification. MM associated with high salinity were separated from ES correlated with lower salinities and high chlorophyll a concentrations of inner estuary. Flounder (Platichthys flesus) showed a typical spatial gradient of MM, with abundance increasing from the ocean towards inner estuary. The dispersal of larvae along the Lima estuarine–ocean gradient was indicative of connectivity between habitats, emphasizing the need to consider this feature in management plans, mainly for species exploited by commercial fisheries.

Hangzhou Bay is a large, high-turbidity shallow bay located on the southern side of the Changjiang Estuary, China. The process and dynamic mechanisms of water and sediment transport in the bay are not yet clear. An improved three-dimensional sediment numerical model that combined various dynamic factors was established to simulate and analyze these mechanisms. The residual current cannot properly represent the net water and sediment transport, and the residual unit width water flux (RUWF) and residual unit width sediment flux (RUSF) were used to explain the water and sediment transport. The results of numerical simulations indicate that in summer, the surface RUWF from the Changjiang Estuary near Nanhui Cape flows westward along the coast, in which the major part flows southward to the Zhenhai area, and the small part flows further westward along the north coast and then turns to the south coast and eastward, forming the water transport pattern of north-landward and south-seaward, which is stronger in the spring tide than in the neap tide. The bottom RUWF near Zhenhai flows northward to Nanhui Cape in the neap tide, which is larger in the neap tide than in the spring tide. In the middle and western parts of the bay, the RUWF has the same pattern as the surface water transport and is stronger in the spring tide than in the neap tide. The pattern of RUSF is roughly similar to the water flux transport. During the spring tide, the water and sediment transport fluxes near Nanhui Cape are from the Changjiang Estuary into Hangzhou Bay, but from Hangzhou Bay into the Changjiang Estuary during the neap tide. In the winter, the distributions of RUWF, RUSF, and suspended sediment concentration (SSC) are similar to those in the summer. In addition, the distance of surface water transport westward along the north coast is shorter than that in the summer, the magnitude of the bottom RUWF is smaller than that in the summer due to the weaker salinity gradient, and the bottom RUSF near Nanhui Cape is weaker than that in the summer during the neap tide. The net transect water flux (NTWF) and the net transect sediment flux (NTSF) near Nanhui Cape are from the Changjiang Estuary into Hangzhou Bay during the spring tide; during the neap tide, the NTWF is still from the Changjiang Estuary into Hangzhou Bay, but the NTSF is from Hangzhou Bay into the Changjiang Estuary because the SSC is much higher in the bottom layer than in the surface layer. The dynamic reason for the temporal and spatial variation in RUWF and RUSF is that the barotropic pressure gradient force is larger than the baroclinic pressure gradient force during the spring tide and is the opposite during the neap tide.

Chance and good luck led to a career studying how freshwater inflow drives estuary processes. In 1986, someone asked me: How much fresh water has to flow to a bay for it to be healthy? The question shaped my career. There is probably no better place on Earth to compare effects caused by inflow differences than the Texas coast, because the major estuarine systems lie in a climatic gradient where runoff decreases 56—fold from the Louisiana border in the northeast to the Mexico border in the southwest. This estuary—comparison experiment was used to study inflow effects. The science evolved from the idea in the 1990’s that organisms responded directly to inflow rates to the domino theory in the 2000’s of indirect effects where inflow drives estuary conditions and that organisms respond to those habitat conditions. Today it is hypothesized that climate drives hydrology, which drives estuary dynamics; and thus, climatic factors can indirectly shape estuarine structure and function. Assuming change along the inflow gradient is analogous to effects of altering estuaries over time, we can now predict ecosystem change with changing climate or land—use change.

Smaller rivers in Japan can be characterized as having short distances from the mountainous areas of the source of sediment production to the estuary and steep slopes. Therefore, sediment produced from the mountains and river channels at the time of flooding immediately contributes significantly to the sediment dynamics at the estuary and coast in a short period of time. On the other hand, there have been few observations or studies that have measured the volume of landslides and riverbed fluctuations in the mountains in the entire basin before and after the occurrence of flooding, and quantitatively linked them to the amount of landslide movement and shoreline changes in the entire basin. This paper discusses the Chitose River basin (basin area A: 30km2, river channel distance L: 0.179km, stream gradient I: 1/14) and the Niizaki River basin (A: 16km2, L: 0.213km, I:1/17), which have an estuary on the Yugawara coast in Kanagawa Prefecture. The effect of sediment production from mountains and riverbeds at the time of flooding on coastal sediment dynamics on July 3rd, 2021.

The genus Callinectes comprises seven species of blue crab found on the Brazilian coast, almost all are recorded in Cachoeira River estuary. The objective of this study is to analyse distribution of Callinectes species in the estuary of Cachoeira River (Ilhéus, Bahia). Monthly collections were conducted in the low tide of neap tide for a year and in five stations distributed according to the estuary salinity gradient. Six traps were assembled and submerged at each station for two hours. Sediment samples were collected for granulometric characterization and measuring of organic matter content. Temperature, salinity and pH were also measured in the bottom water, as well as water transparency at the start of each collection. Five species were collected: Callinectes danae, C. ornatus, C. exasperatus, C. larvatus and C. bocourti. The species presented different distribution patterns based on the salinity gradient and transversal profile of the estuary. Only C. danae was found in all collection points, and was the most abundant species throughout the study period. Callinectes ornatus was restricted to external estuarine areas, which presented higher salinity and transparency values. Callinectes larvatus predominantly occurred in the external station and estuary partitions, mainly in the margin. In spite of the occurrence of C. exasperatus throughout the entire estuary, this species was restricted to the margin. This study supports the assumption that species distribution patterns of this genus are the result of both variable influence, namely salinity, and complex intraspecific and interspecific relations between the congeneric species.

In the semiarid coast of northeast Brazil, climate change and changes in land use in drainage basins affect river hydrodynamics and hydrochemistry, modifying the estuarine environment and its biogeochemistry and increasing the mobilization of mercury (Hg). This is particularly relevant to the largest semiarid-encroached basin of the region, the Jaguaribe River. Major Hg sources to the Jaguaribe estuary are solid waste disposal, sewage and shrimp farming, the latter emitting effluents directly into the estuary. Total annual emission reaches 300 kg. In that estuary, the distribution of Hg in sediment and suspended particulate matter decreases seaward, whereas dissolved Hg concentrations increase sharply seaward, suggesting higher mobilization at the marine-influenced, mangrove-dominated portion of the estuary, mostly in the dry season. Concentrations of Hg in rooted macrophytes respond to Hg concentrations in sediment, being higher in the fluvial endmember of the estuary, whereas in floating aquatic macrophytes, Hg concentrations followed dissolved Hg concentrations in water and were also higher in the dry season. Animals (fish and crustaceans) also showed higher concentrations and bioaccumulation in the marine-influenced portion of the estuary. The variability of Hg concentrations in plants and sediments agrees with continental sources of Hg. However, Hg fractionation in water and contents in the animals respond to higher Hg availability in the marine-dominated end of the estuary. The results suggest that the impact of anthropogenic sources on Hg bioavailability is modulated by regional and global environmental changes and results from a conjunction of biological, ecological and hydrological characteristics. Finally, increasing aridity due to global warming, observed in northeast Brazil, as well as in other semiarid littorals worldwide, in addition to increased water overuse, augment Hg bioavailability and environmental risk and exposure of the local biota and the tradition of human populations exploiting the estuary’s biological resources.

Tidal influence and local morphology on circulation and salt transport are investigated in the Caeté river estuary, a well-mixed estuary along the north coast of Brazil. Velocity, temperature, and salinity data were collected in three different locations along the estuary’s main channel, over three single, 13 h tidal cycles. The aim of this study was to investigate the relationship between tidal distortion and salinity by using classical methods of comparison of three cross-channel circulation characteristics, as well as computation of salt flux and vertical mixing. Findings indicate a flood-ebb asymmetry in currents, due to the distinct funneling morphology of the estuary, with shallow marginal areas being dominant towards the estuary head, while both stratification and shear dominate near the estuary mouth. The tidal currents enhanced vertical diffusion in the mid- and lower reaches, explaining the prevailing weakly stratified conditions, while the dominant well-mixed conditions in the upper estuary are a result of a combination of stronger flood currents and negligible vertical saline gradient. The predominant downstream salt transport supports the conclusion that there is little accumulation of salt in the Caeté river estuary. In addition, findings indicate that tidal correlation and Stokes drift are important components in the upper estuary, while tidal correlation played an important role in the middle estuary, with fluvial discharge most important in the lower estuary.

Abstract. Tidal marshes are sedimentary environments and are among the most productive ecosystems on Earth. As a consequence they have the potential to reduce atmospheric greenhouse gas concentrations by sequestering organic carbon (OC). In the past decades, most research on soil organic carbon (SOC) storage in marsh environments has focused on salt marshes, leaving carbon dynamics in brackish and freshwater marshes largely understudied and neglecting the diversity among tidal marshes. We therefore conducted an extensive sampling campaign to quantify and characterize SOC stock in marshes along a salinity gradient in the Scheldt estuary (Belgium and the Netherlands). We find that SOC stocks vary significantly along the estuary, from 46 in freshwater marshes to 10 kg OC m−2 in salt marshes. Our data also show that most existing studies underestimate total SOC stocks due to shallow soil sampling, which also influences reported patterns in OC storage along estuaries. In all sampled tidal marsh sediments the SOC concentration is more or less constant from a certain depth downward. However, this concentration decreases with increasing salinity, indicating that the amount of stable SOC decreases from the upper estuary towards the coast. Although the net primary production of macrophytes differs along the estuary, our data suggest that the differences in OC storage are caused mainly by variations in suspended sediment concentration and stable particulate OC (POC) content in the water along the estuary. The fraction of terrestrial suspended sediments and POC that is transported downstream of the maximum turbidity zone is very limited, contributing to smaller amounts of long-term OC sequestration in brackish and salt marsh sediments. In addition, high rates of sediment deposition on freshwater tidal marshes in the maximum turbidity zone promote efficient burial of OC in these marsh sediments.

Aims: To determine the spatial variation in physico-chemical water quality attributes in estuarine ecosystems of South Coast Kenya to inform its management. Study Design: We employed diagnostic research design where such factors as anthropogenic activities, hydrology, and accessibility were considered in choosing 12 sampling stations. A mixed sampling design (probability and non-probability) was used to sample. Place and Duration of Study: Four discharging rivers into estuarine system with a reference point were identified. 12 sampling points were earmarked and sampled for 12 months. Methodology: Nine selected water quality parameters were collected in triplicates monthly for 12 months. Temperature, dissolved oxygen, pH, conductivity, salinity and TDS were collected in situ using YSI Multiparameter meter (Professional plus) while nutrients were analyzed in the laboratory calorimetrically. Data was tested for normality and homogeneity of variances using Levene's and Shapiro-Wilk tests. Two-way analysis of variance (ANOVA), and Principal Component Analysis (PCA) were done using the 64-bit R Software version 4.3.0 to test for significant differences and correlate the parameters among the sampling sites respectively. Observed differences were considered statistically significant at P < 0.05. Results: The measured environmental variables differed significantly among the sampling stations (P < 0.05). temperature and salinity exhibited moderate to strong effect on water quality, while pH and nutrients (phosphates, nitrates, and ammonia) exhibited mixed effects with both negative and positive loadings on the Principal Components. It is demonstrated that the south coast estuary, Kenya is affected by two gradients: mineralization from the sea and the organic matter gradient at the upstream stations dominated by the fluvial inflows from the respective rivers. Conclusion: The south coast of Kenya estuary is impacted by natural processes and anthropogenic activities. we recommend for continued regular water quality assessment and monitoring to acquire sufficient data to shape policy frameworks towards its sustainable management.

L’impact anthropique lié à l’augmentation du CO2 atmosphérique a été observé à l’échelle globale océanique, avec comme conséquence l’acidification des océans (AO). Comme l’océan ouvert, les écosystèmes côtiers sont soumis à l’AO. Ces écosystèmes ne représentent que 7% de la surface océanique mais ils sont responsables d’un tiers de la production primaire océanique mondiale, jouant ainsi un rôle clé dans le cycle du carbone global. Les environnements côtiers sont très hétérogènes et influencés par des apports continentaux, ce qui complexifie l’étude du cycle du CO2. Cette thèse étudie à différente échelle spatiale et temporelle la variabilité du cycle du carbone dans les milieux méga tidaux côtiers du nord-ouest de l’Europe. Entre 2015 et 2019, nous avons installé un capteur autonome de pCO2 sur une bouée cardinale de la côte de Roscoff, au sud de la Manche. Les observations proximales et plus au large des paramètres du système CO2 ainsi que de l’ensemble des paramètres physico-chimiques, nous ont permis de décrire précisément l’écosystème et de quantifier la variabilité tidale, diurne et interannuelle. Dans un second temps, nous avons suivi la variabilité de ces paramètres à l’échelle décennale, en se basant sur les prélèvements réguliers réalisés entre 2008 et 2018 dans deux milieux côtiers très proches géographiquement (Brest et Roscoff), mais sous influence plus ou moins importante des rivières. Enfin, nous avons quantifié la dynamique de deux gaz climatiquement actifs dissous le long de deux gradients estuariens : le CO2 et le CH4. Ce dernier, bien que peu étudié, apparaît comme un composé central pour la compréhension du fonctionnement des écosystèmes côtiers
The anthropogenic impact of the raise of atmospheric CO2 has been observed on the global oceanic scale, resulting in the Ocean Acidification (OA). Largely present in the coastal ecosystems, a decrease of their population could have significant socio-economic consequences. Coastal ecosystems represent only 7% of the global ocean but host a third of the total primary production of the oceans, playing a key role in the global carbon cycle. They are highly diversified and influenced by continental inputs, which complexifies the study of the CO2 cycle. This PhD thesis investigated at different spatial and temporal scales the variability of the carbon cycle in megatidal environments of the North Western European Shelves. From 2015 to 2019, we installed an autonomous sensor of pCO2 (Sunburst SAMI-CO2) on a cardinal buoy located off Roscoff, in the south of the English Channel. Coupled with additional proximal and offshore observations of the carbon cycle and biogeochemical parameters, we were able to describe precisely this ecosystem and assess the tidal, diurnal and interannual variability. Secondly, we followed the variability of these parameters at the decadal scale, based on regular sampling from 2008 to 2018 in two coastal environments very close geographically (Brest and Roscoff, NWES), but with different freshwater influence. Finally, since methane is increasingly considered as a key player in the understanding of the coastal ecosystem functioning and Climatically-Actives Gas cycles, we quantified the driving processes of CO2 and CH4 air-sea exchanges in two mega-tidal estuaries influencing our study region

<em>Abstract</em>.-Telemetered adult striped bass <em>Morone saxatilis </em>(<em>n </em>= 170) in two small nonnatal U.S. Atlantic coast estuaries, the Mullica River-Great Bay in New Jersey and the Saco River in Maine, displayed a variety of movements relative to migration and habitat use. Individual presence in both systems ranged from hours to many months from spring through fall but seldom during the winter. Some made upriver runs during the presumed spawning season. An absence of eggs, larvae, or juvenile stage striped bass or suitable spawning grounds suggests that fish utilizing both systems are members of migrant contingents originating elsewhere. In both systems, some seasonal residents occupied individual "home" ranges throughout the salinity gradient, but others were plastic in their behavior and utilized several sites or visited the estuary either briefly or for a whole season in different years. Movement of fish between study sites and recaptures away from them indicated wide dispersal during time away from the study estuaries. The above supports the idea that migratory and seasonal residence behaviors of migrant striped bass are not compulsive or predictive but reactive or learned. Despite long seasonal occurrence in these small estuaries by some individuals, none appeared to become full-time residents. Small estuaries may lack the year-round resources for spawning and feeding to enable this. However, the observed behaviors could promote recolonization of spawning stocks with residents in larger restored rivers and estuaries where they have been previously extirpated. Localized fishery depletion of small estuaries could occur quickly but would be temporary in the absence of stock wide depletion.