Estuarine Coastal and Shelf Science最新文献

Understanding the seasonal variation (annual cycle) of tides is crucial for coastal management and the planning of coastal infrastructure, as well as pivotal for navigation safety, prediction of extreme sea levels and so on. Specifically, seasonal variations of M₂ amplitudes, larger in summer and smaller in winter, have attracted widespread attention. Nevertheless, investigations into other tidal constituents, such as S₂, K₁, O₁, remain comparatively sparse. Here, seasonal variations of the four principal tidal constituents are studied in the shallow shelf regions of the China Seas and the North Sea, both acknowledged for exhibiting the most pronounced seasonal modulations of M₂ amplitude, attributable to vertical stratification. We perform a segmented Harmonic Analysis with moving average filter, to remove semi-annual cycle, at 25 tide gauge data and find a synchronized seasonal modulation of M₂ and O₁ in China, which can be explained by stratification. Whereas S₂ manifest an inverse seasonal modulation, larger in winter and smaller in summer, attributed to the sun's varying proximity to the earth. The K₁ tide displays two very different seasonal cycle, also influenced by astronomical modulation. This observed pattern basically persists in the North Sea, while O₁ shows a negative seasonal amplitude but still exists high correlation coefficient with M₂. Consequently, this study provides a deep insight into 4 principal tidal constituents' seasonal modulation and underlying mechanisms, thereby enhancing our ability to comprehend and predict water level extremes and flooding with greater precision.

Coastal lagoons are transitional areas between land and sea, particularly vulnerable to human impact. The aim of this work was to compare soft bottom macrozoobenthic communities in the Lagoon of Marano and Grado, before (past period: 1993 to 1995) and after the entry into force of the Water Framework Directive-WFD (present period: 2008 to 2021). In the present period higher richness, abundances, and diversity were observed, also considering each water type (euhaline, polihaline and mesohaline) and basin (Marano and Grado) separately. The multivariate analyses also showed differences among periods and water types. According to the AMBI index, most stations were slightly disturbed in all periods and water types, and biocoenotic affinity did not vary significantly. The frequency of echinoderms increased in all water types, whereas the frequency of the polychaete Hediste diversicolor decreased in eu- and polihaline water bodies. These changes can mainly be explained by a general increase in salinity, and therefore probably the result of a marinization process, a decreasing confinement of the lagoon. As the calculation of M-AMBI is derived from AMBI, diversity and richness, this process could lead to a better ecological status sensu WFD, but with the loss of the characteristics and ecological functions of this paralic ecosystem.

River discharge forms a plume of low-salinity water that spreads offshore, delivering terrestrial substances into the ocean and thus plays a critical role in controlling marine environments as well as the carbon cycle. This study investigated how freshwater discharged from the Changjiang impacts the physical and biological responses and oceanic uptake of carbon dioxide (CO₂) in the northern East China Sea (ECS) by combining the recently available sea surface salinity (SSS) product from the Soil Moisture Active Passive (SMAP) mission with other satellite measurements of sea surface temperature (SST) and chlorophyll-a (chl-a) concentration. The partial pressure of CO₂ (pCO₂) and its interannual variability were estimated using empirical regression with satellite-derived environmental variables. The bias-corrected SMAP SSS revealed that river discharge largely contributed to the distinct interannual SSS variations, with a seasonal cycle reaching a maximum in winter and a minimum in summer. Compared to the SST and chl-a anomalies, we observed an increase in SST and primary production in the region where sea surface freshening was robust. Freshwater from rivers contributes to sea surface warming by trapping heat from the atmosphere at the surface layer. Nutrient-enriched freshwater within the buoyant plume enhances phytoplankton production, which in turn enriches the ocean surface with chl-a. Simultaneously, the pCO₂ was relatively low in the region where the SST and primary production were high, highlighting that the heat and riverine nutrients trapped within the buoyant plume contributed to the reduction in pCO₂ by promoting the biological uptake of CO₂. The estimates conducted here illustrate the synergistic utility of multiple satellite measurements for the evaluation of CO₂ uptake capacity, complemented by in situ measurements of river-dominated marginal seas.

The cosmopolitan species Ficopomatus enigmaticus is one of the most prominent providers of polychaete reefs in shallow and brackish waters. The effects of polychaete reefs on the environment can be positive or negative subject to their structural complexity and vary with local environmental conditions and over time. The Coorong is a large temperate estuarine and lagoonal system with extensive polychaete reefs built by F. enigmaticus. The aims of this study were to (1) classify polychaete reefs based on size and morphology, (2) quantify reef density, (3) assess their spatial distribution and (4) assess the correlation between reefs (e.g., density, size) with the environmental gradient. Structural morphologies of F. enigmaticus were classified as either halo, circular, irregular, platform or fringing reef types. The largest densities of polychaete reefs were recorded in the vicinity of the mouth of the estuary with 224 reefs per ha compared to the lagoon (62 reefs per ha). The most common reef morphology was circular and largest sizes in the lagoon were positively correlated with salinity, chlorophyll a, TRIX (trophic index) and bicarbonate. The largest reef diameter recorded was 11.3 m, exceeding previously known F. enigmaticus circular reef formations globally. The growth of large circular reefs may have benefitted from low flows and eutrophic conditions in the Coorong during the last two decades. This study serves as an important baseline for future assessments of reef change in a Ramsar listed wetland. Furthermore, this study highlights reef characteristics of F. enigmaticus across an environmental gradient, which can be informative for the management of flow and eutrophication in estuaries and coastal lagoons.

The introduction of alien species in marine ecosystems is often driven by the increasing demand of fishery resources. This is the case of the Manila clam (R. philippinarum), imported in Europe from Japan since the 1970s, to meet the growing demand for clams that the native species, the grooved carpet shell clam (Ruditapes decussatus), could not satisfy. Alien species introduction could threaten the genetic diversity and integrity of the native clam, also causing hybridization (i.e., gene flow from one species into the gene pool of another). Since R. philippinarum recently spread in a few important Mediterranean coastal areas, a combined approach based on morphological characteristics, length differences of two nuclear species-specific markers (ITS2, 5SrDNA) and the sequence of the mitochondrial gene cytochrome c oxidase subunit I (COI), was used to investigate the presence of hybrids in six Mediterranean wetlands (Sardinia, Italy). Eight individuals morphologically identified as R. decussatus were hybrids, having sequences specific to both R. decussatus and R. philippinarum in their nuclear DNA (ITS2 and 5SrDNA). Most of these individuals were found to be post-first generation (F1) hybrids indicating that F1-hybrids may be fertile. Secondly, to study the genetic diversity of R. decussatus in the Sardinian wetlands as well as in its whole distribution area, >380 new COI sequences from the eastern Atlantic Ocean and Mediterranean Sea were analysed along with those available from public databases. Mitochondrial COI data revealed variable haplotype and nucleotide diversities in different areas, which were not dependent on sample sizes. The aquaculture breeding activities and clam transplantation between different countries, along with the long pelagic larval dispersal and the commercial import of other bivalve species might have promoted gene exchange between different sites and thus higher diversity levels in a few wild populations. Our research, evaluating the genetic makeup of wild and hatchery stocks and clarifying the degree of hybridization, can contribute to develop further recommendations for conserving the genetic integrity of R. decussatus.

Tidal flows play a crucial role in connecting coastal lagoons to the sea through channels, in this way determining the hydrological dynamics of these environments. The Punta Rasa Natural Reserve (Ramsar site) is located in a transitional zone between the outer limit of the estuary of the Río de la Plata and the open sea. In this work, we study the northernmost lagoon at the end of the spit, which is connected to the sea by a narrow tidal channel. Wetlands are developing at the edges of the lagoon and in lower lying sectors. The aim of this study is to develop a conceptual model that explains the tidal connectivity of the coastal lagoon and to assess how it affects the marsh environments. Detailed topographic surveys were performed using Structure from Motion Multi-View Stereo from a UAV, while sea level data was analyzed using recordings at 20-min intervals over a five-year period. This dataset facilitated an analysis of the frequency of exceedances for threshold values of 0.8, 1.0, 1.2 and 1.4 m. The frequency analysis reveals that the highest exceedances of these thresholds occur during the summer months. When the water level reaches 1 m, the lagoon is fully connected to the sea via the tidal channel, resulting in complete inundation of the low marshland and the margins of the high marshland. At a tidal level of 1.4 m, the high marsh connected to the tidal channel and the coastal lagoon experience flooding. The results obtained in this study provides insights into modelling hydrological connectivity between marshes and the sea, as well as determining the frequency of tidal inundation in each wetland.

Sri Lanka's extensive 1740-km shoreline boasts a wealth of carbon-sequestering marine habitats, encompassing coastal forests, underwater meadows, and tidal wetlands. This review paper discussed the current status, recent changes, and future potential of the trio of carbon-rich coastal habitats in Sri Lanka. As with other countries in South Asia, including India and Bangladesh, mangrove research in Sri Lanka has advanced well, and regional-scale quantitative analyses of mangrove distribution, biomass, and carbon stocks have been conducted in many coastal areas of Sri Lanka. However, studies on seagrass meadows and saltmarshes are limited to a few sites and the objectives of these studies were mostly restricted to species diversity and distribution. This study analysis focuses on Sri Lankan studies related to mangroves, salt marshes, seagrass, and blue carbon ecosystems. Economic analysis of blue carbon ecosystems, and country-level quantification of carbon stocks in mangrove forests, seagrass meadows, and saltmarshes are yet to be conducted in the country. Moreover, most of the blue carbon ecosystems in Sri Lanka are in degraded conditions or under threat. Therefore, it is essential to enhance knowledge about carbon-sequestering coastal habitats within the nation and develop effective preservation and rehabilitation strategies, to guarantee responsible stewardship of Sri Lanka's shorelines. While there is some very good data available insufficient attention has been given to studying seagrasses and saltmarshes in Sri Lanka, despite their ecological value.

An estuary is a complex system that encompasses numerous, complex interactions between environmental factors and processes that are directly or indirectly influenced by human activities. A well-studied estuary is the Elbe estuary, which is under pressure from human activities. About 2300 publications focus on scientific aspects of its hydrology, morphodynamics, biology, chemistry or a combination of these, covering water, sediment and human interventions, among other topics. While it is important to understand the processes, selecting actions to improve the system should be based on a deep understanding of the estuary system as a whole and a confrontation with the complex interrelationship of the components that make up the estuary. This can be overwhelming, as most humans are able to understand only three or four indirectly related parameters simultaneously, whereas numerous variables are interlinked and affect each other in the environment. The resulting reluctance to address such an issue combined with a lack of common language of citizens, scientists and planning authorities can hamper public acceptance of management measures.

In this paper, we use the software iModeler to describe the Elbe estuary in its complexity as a stressed system and present results from the application of the model by a group of scientists from different backgrounds. This model is not intended to be an alternative to – for example – mathematical-hydrological modelling. It also does not claim to be factually correct, and it is certainly not complete. It should be seen as an exercise to deal with complex interactions in a simple way and to develop a deeper understanding of the system. Participants in the exercise defined 46 factors and 112 direct linkages. The model identified contaminant availability, turbidity and nutrient concentrations as the stressors with the greatest impact on the quality of the Elbe estuary. Dredging of shipping channels was the activity with the greatest negative impact, and extending nature protection areas would have the highest positive effect.

The results of the model, although subjective to some extent, were plausible when compared to the literature. The possibility of describing a more differentiated cause-effect relationship for some factors and their direct connection would have been beneficial. However, such collaborative qualitative modelling facilitates knowledge sharing, can reveal indirect effects and raises awareness of those factors that are strongly interwoven within system, and would have a large cumulative effect on the respective goal.

Age and growth of little tunny (Euthynnus alletteratus) were assessed by examination of annual growth increments in cross-section of first dorsal spines from 207 fish (85–1030 mm Straight Fork Length, SFL) sampled between 2017 and 2021 from the northeastern Atlantic and Mediterranean Sea. Some analysis and recommendations are provided for using the first dorsal fin spine for age estimation of little tunny. The comparative analysis of the sectioning location, with transverse sections collected at 0.5, 1.0, and 1.5 times the width of the condyle base measured from the base of the spine, showed that the 1.0 cross-section distance proved to be the most reliable option. Fish ages ranged 0–10 years old and the growth parameters estimates based on standard von Bertalanffy growth function were (for sexes combined): L_∞ (asymptotic length) = 99.77 cm; k (growth coefficient) = 0.445 year⁻¹; and t₀ (age at zero length) = − 0.072 year⁻¹. In order to ensure comparable results, it is crucial to implement a reproducible protocol for future studies on the age and growth of little tunny.

Colored dissolved organic matter (CDOM) is an indicator and optical proxy of terrestrial processes such as land use with allochthonous material fluxes, biogeochemical cycles, and water quality in coastal zones influenced by rivers. However, the role of land use changes on the spatial and temporal availability of CDOM has been poorly explored in Chile. Here, we studied two watersheds with similar climates and contrasting land use patterns in northern Patagonia considering the sampling of CDOM in their estuarine and adjacent coastal ocean. An empirical algorithm with the coefficients adjusted to our study areas to estimate CDOM was applied to Landsat 7 and 8 images to examine temporal variability of CDOMest from 2001 to 2011 and 2013–2020. Our results showed an increasing trend of CDOMest in both areas. Different trends in land use patterns between the two watersheds showed a significant correlation with CDOMest and contrasting associations with environmental variables. Higher humification was found in Yaldad in comparison with Colu. In both areas, allochthonous materials predominated, especially during austral spring according to the low values of the Fluorescence Index (FI). Our results highlight the potential of CDOMest to parameterize biogeochemical cycling models and to further understand the dynamics of CDOM in coastal ecosystems.