Estuarine Coastal and Shelf Science最新文献

Characterizing the origin and quality of the organic matter (OM) present in estuaries, as well as its export toward the ocean, is a key issue to better understanding the carbon cycle and its impact on global change. In this study, fatty acid markers and δ¹³C and δ¹⁵N values were used to characterize the particulate and sedimentary organic matter composition in the large mangrove-dominated Parnaíba Delta, known as a large reservoir of blue carbon. The presence of some long-chain fatty acids and other mangrove OM markers, such as the 18:2ω6 and 18:3ω3, indicated that the material produced in mangroves contributed largely to the particulate organic matter of water and sediments of the delta. Their presence in further oceanic stations also reveals the mangrove material is exported to the adjacent coastal ocean. In the main river channel, the higher contribution of 18:2ω6 in the sediments than in the mangrove regions, indicated an additional source related to anthropogenic activities, probably agriculture. The branched fatty acids found in the samples point to the presence of bacteria and indicated the intense modifications of the organic matter in the region, reflecting the heterotrophic nature of the delta. In addition, the predominance of saturated fatty acids in the delta suggests that the organic matter exported to the coastal ocean is dominated by detrital material.

This study investigates the response of salt transport to freshwater discharge events and tides in the Waitematā Estuary. The salt transport is assessed by both observations and numerical simulations using a gridded salt balance and isohaline salt transport. The Waitematā Estuary represents a unique type of estuary in parameter space: it varies between well-mixed and strain-induced periodic stratification during the spring-neap tidal cycle. Spring tides often lead to a net inflow of salt when the freshwater discharge is below average. Higher freshwater discharge (>10 m³s^-1) results in net downstream salt transport regardless of the amplitude of the tides. The estimates of estuarine parameters show that the whole estuary becomes partially-mixed when the freshwater discharge increases by another order of magnitude (100 m³s^-1). Based on future regional climate projections of less average rainfall with more intense events and rising temperatures, the estuary is expected to experience less frequent but stronger salt outflow. This study contributes observations from a previously undocumented part of estuarine parameter space.

Studies that focus on the flow dynamics in multi-channel estuaries using detailed field measurements are rarely reported. Hence, this study investigates the effect of changes in topographic features on the upstream fluvial patterns and downstream salinity intrusion at the multi-channel Tanintharyi River estuary (TRE), Myanmar. The outcomes were compared with the multi-channel Chikugo River estuary (CRE) and Arakawa River estuary (ARE) of Japan using the data presented in previous studies. Continuous measurements of velocity and discharge distributions were conducted at 12-h intensive surveys (30-min intervals) at the upstream confluence area of TRE during spring and neap tides. The velocity in the TRE was vertically uniform during spring and neap tides. The maximum horizontal velocity was found at the middle area of the main channel and at the thalweg area of the branch. In TRE, the discharge ratio of the branch to total discharge was temporally changed during a tidal cycle while the area ratio was stable. Conversely, the discharge ratio of the branch to total discharge in the CRE was nearly equal to the area ratio of the branch. This may be due to the influence of channel sinuosity. The mean velocity in the upstream estuarine channel reduced with an increase in sinuosity index (SI) in both TRE and CRE. Hence, the SI has a negative influence on the upstream fluvial flow. Further, the saltwater travel distance in the three multi-channel estuaries (TRE, CRE, and ARE) increased with a decrease in SI. Conversely, the salinity intrusion length in all three estuaries increased with an increase in SI. This shows that the SI has a negative influence on the saltwater travel distance and a positive influence on the salinity intrusion length. In conclusion, the topographic features of estuaries have a strong and different impact on the flow dynamics in their upstream and downstream.

Marine dissolved organic matter (DOM) plays a key role in the carbon cycle. There is growing interest for its chemical and ecological properties but its variability in the very heterogeneous coastal environments is poorly documented. In this study, we assess the spatial and temporal variations in marine coastal DOM chemical properties and its potential to fuel the growth of the heterotrophs in the planktonic food-web. We sampled two northwestern Mediterranean coastal stations under contrasting terrestrial and human influences. From January to July 2022, dissolved organic carbon (DOC) concentration progressively increased, although highly variable spatially. DOM composition varied temporally rather than spatially. These variations appeared related to a combination of direct freshwater inputs (tracked by salinity variations), direct human contaminations (tracked by concentrations in copper and lead), and primary production (tracked by concentrations in chlorophyll a). An incubation experiment was used at each sampling date to evaluate the growth potential of heterotrophic prokaryotes and compare it to variations in DOM properties. Significantly higher growth was observed with DOM from a site under higher terrestrial and human influences. Water temperature exerted a higher control on growth than DOM properties. Correlation analysis with DOM sources suggested the uncoupling of phytoplanktonic production and growth of heterotrophic prokaryotes, which appeared better supported by human contaminations and, to a lesser extent, freshwater inputs. Sediment resuspension in harbors and antifouling paints could represent two important sources of bioavailable resources, favoring fast heterotrophic growth and higher net production, respectively. This work suggests that human activities and constructions in harbors have the potential to strengthen the heterotrophic basis of the planktonic food web.

Intense wind-driven setdowns can cause extensive drying of the shallow Taganrog Bay in the Azov Sea, significantly impacting the marine infrastructure and ecosystem. Satellite measurements of MSI Sentinel-2 and OLI Landsat 8 during 2015–2021 were used to identify 28 intense cases of such processes. Using a simple difference method based on near-infrared measurements, we calculated the area of a drying zone (S) and investigated its relation with storm intensity and duration. Our findings indicate that S in the estuarine part of the bay can exceed 300 km². Setdowns most often occurred in the autumn during intense and persistent easterly winds with wind speed exceeding 8 m/s. The largest areas of drying zone (S > 100 km²) were observed during continuous winds lasting more than 10 days. The correlation between the integral action of wind stress and S was 0.74, and for prolonged events (more than 5 days) it was 0.92.

Further, satellite data was used to validate the results of ADCIRC numerical modelling. Based on the modeling data, we investigated the influence of wind speed on the area of bottom drying in order to obtain a simple parameterization of this process. At the initial moment of setdown, the sea level decreases as t^1/2 and linearly depends on the square root of the integral wind stress, while the drying zone increases as t^1/4. The relation between sea level and wind speed was universal for different wind amplitude until an equilibrium state is reached. Interestingly, during most intense winds (>20 m/s), the drying zone decreases, which is related to the drying out of the banks located at the entrance of the Taganrog Bay limiting water outflow from the bay.

Understanding population connectivity via fish movement and the appropriate scale for management is amplified by the use of tagging techniques. Natural fish markers provide unique signatures that reflect distinct environmental and physiological characteristics of populations, allowing us to determine the degree of connectivity among them. Different markers function within defined spatiotemporal ranges with specific advantages and limitations. We tested whether applying multiple markers would increase the power of assessing population structure and connectivity of black bream Acanthopagrus butcheri from 12 estuaries across southern Australia. We utilised a range of natural markers, including genetics, otolith shape, otolith isotopic composition, and otolith elemental composition, to determine the effectiveness of each marker independently and through integration. For this estuarine-dependent species, combining genetics and otolith-based techniques was complementary in increasing the accuracy of our results but not all marker integrations were consistently beneficial, highlighting the importance of appropriate marker selection. The maximum classification accuracy to collection site of 95% (a combination of genetics, otolith shape, and otolith isotopic composition) emphasised the species’ estuarine dependency and limited connectivity across the sampling range, suggesting location-specific management is needed for this commercially important species.

Heavy metal contamination in the estuarine wetlands of tropical islands is becoming increasingly severe. This study focused on four typical estuarine wetlands of Hainan Island, including the mangrove and seagrass areas in Lingshui County, the mangrove and seagrass areas in Xinying Port, the mangrove area in Sibi Wan, and the seagrass area in Huachang Wan. By analyzing the heavy metal content in the surface sediments of these wetlands, we investigated the distribution characteristics and levels, explored their influencing factors, and assessed ecological risk of heavy metals in these areas. It was found the accumulation of heavy metals was high from obvious sampling sites of human activities, the type of sediment could affect the adsorption of heavy metals, with silty mudflats accumulating more. TOC/TN indicated that the organic sources of mangroves were diverse, included environmental impacts and human interference. According to the soil accumulation index and potential ecological risk index in these areas, almost all heavy metals were unpolluted except for As, which showed moderate pollution levels. The overall ecological risk in these areas was relatively low. The results of principal component analysis and correlation analysis indicated that Pb, Cu, and As were primarily sourced from human activities, while Cr was mainly of natural origin. Moreover, the distribution of heavy metals in the study areas was principally affected by TOC and salinity.

The Japanese seabass Lateolabrax japonicus, an important commercial fishery species, exhibits partial migration, where some individuals migrate upstream into rivers, and others inhabit estuarine and coastal areas within the same population. Although this migratory behavior has been documented in juvenile seabass, the prevalence of river use and the ecological significance of partial migration in subsequent developmental stages remain unclear. To understand the river use of subadult and adult Japanese seabass, we estimated the river use history using otolith Sr/Ca ratios from individuals captured in both marine and riverine environments. Based on hierarchical clustering with Dynamic Time Warping, Sr/Ca ratios at age 0 were clustered into three habitat use patterns: coastal resident, estuarine resident, and river migrant. Groups that used coastal and riverine habitats at age 0 tended to use coastal and riverine habitats, respectively, from spring to fall of age 1 and above, with overlapping distributions during winter. Subadult and adult river use patterns were linked to juvenile river use, indicating a carryover effect. Additionally, seasonal migration between the sea and rivers became less active with age, and the high growth sustained by river use also declined with age, suggesting that the benefits of river use are less for older (subadult and adult) seabass. This study highlights that juvenile habitat use experience drives subadult and adult partial migration of Japanese seabass, with individuals seeking environments adapted from past experiences. Our findings indicate that the seabass population consists of individuals adapted to various environments, from the sea to the rivers, maximizing the use of biological productivity.

Information about stomach content composition of fish species of a temperate coastal fish community (western Dutch Wadden Sea) over the period 1930–2019 was analysed to reconstruct long-term trends in trophic position of individual species. Stomach data were not evenly distributed but clustered both with respect to years as well as fish species. For 18 fish species, all being omnivorous and belonging to different functional groups (pelagic, benthopelagic, demersal) and guilds [(near)-resident, juvenile marine migrants, marine seasonal visitiors], prey consumption and trophic position over time could be analysed. Prey occurrence in the stomachs of different fish species showed variability over time, most likely due to fluctuations in prey abundance, but without a trend. For all species, individual fish showed variablity in trophic position in the order of 1 unit or even more both within and between years. However, in all 18 species, no significant trend in mean trophic position over time could be found, despite the serious anthropogenic stress (pollution, eutrophication events, climate change) and the decrease in fish abundance in the area during the last 50 years. The present study does not indicate any changes in trophic position of individual species in the western Dutch Wadden Sea over the last 80 years. At the community level, trophic structure varies due to interannual fluctuations in species composition and year-to year fluctuations in the relative abundance of the various fish species. At the ecosystem level the trophic role of the fish community has been degraded due to the decrease in total fish biomass in the area.

Field observations in the Pearl River Estuary (PRE) indicate that vertical structures of tidal currents vary in different regions, which is associated with freshwater-induced stratification. A three-dimensional unstructured grid model (PRE-model) based on FVCOM is developed to study the mechanism of vertical structural changes in tidal currents. With the effect of freshwater, the amplitude of tidal currents increases in the upper layers and decreases in the bottom layers, and in regions with geometrical complexity, it is maximum in the middle depths. Momentum analysis indicates that vertical friction (VF), pressure gradient forces (PGF), and momentum advection (ADV) are the main factors leading to changes in tidal vertical structures. Variations of VF induced by stratification lead to an increase of tidal currents amplitude in the upper layers while a decrease in the bottom layers. Changes in PGF and ADV can also have significant impacts on tidal currents. Tidal frequency variations of density gradients result in pronounced tidal frequency baroclinic PGF in the bottom depths and enlarge total PGF. The amplitude of tidal currents increases at corresponding depths, which leads to subsurface maxima of tidal currents. ADV is special as its phase is variable relative to tidal currents, which can enhance or weaken tidal currents in different regions. The generation of tidal frequency baroclinic PGF is highly correlated with nonlinear processes, and the horizontal advection is considered the primary source of baroclinic PGF. The similar sources of ADV and baroclinic PGF also make them dominant in regions with geometrical complexity or large river plumes.