Semi-enclosed Bay Research Articles

Drivers of seasonal and decadal change on an estuarine beach in a fetch-limited temperate embayment

Beaches in estuaries and bays (BEBs) are critical landforms along many coastlines, providing vital protection to human infrastructure and ecosystem services. Like open-ocean beaches, their morphodynamics are driven by the interaction of waves and tides with the boundary conditions determined by sediment supply and geology. However, as estuaries and bays tend to be lower energy than the open ocean, and are often fetch limited, BEB behaviour is typically controlled by high magnitude events rather than modal conditions. In this study, we assess the dynamics of a BEB in a semi-enclosed bay (Port Phillip Bay, Victoria, Australia). We analyse shoreline and subaerial cross sectional beach change across a range of time scales, including in response to storm events, using a combination of aerial photography, satellite imagery and UAV-based surveys spanning multiple decades. The study assesses the impact of geological controls on beach dynamics in this estuarine/embayed setting, investigating the impact of an intertidal rocky reef and the role of sediment budgets. The rocky outcrops throughout the compartment appear to exert little long-term control on beach morphology. We find that the location of the beach with respect to the sediment compartment boundaries is fundamental to determining long-term shoreline evolution. St Leonards Beach is located near the boundary between two longshore transport systems flowing in opposite directions. This results in low sediment flux across the compartment and therefore a paucity of sand supply for beach and dune development. As a consequence, the beach is relatively stable on a seasonal scale, but has a net erosional trend over the 75-year aerial photographic record. Erosion appears to be event driven as sand is transported out of the sediment compartment during storms. This work shows the importance of understanding local boundary conditions especially local sediment budgets in estuarine environments when analysing beach dynamics.

The Role of Submarine Groundwater Discharge to the Input of Macronutrients Within a Macrotidal Subpolar Estuary

The major sources of macronutrients (nitrate, ammonium, phosphate, and silicic acid) in Jakolof Bay, Alaska are submarine groundwater discharge (SGD), rivers, and offshore water. We estimated SGD using natural geochemical tracers (radon and radium), a salt mass balance, and a two-component salinity mixing equation based on the change in groundwater salinity on falling lower low tide. Previous studies have hypothesized that the major macronutrient input into Jakolof Bay is offshore water. This study challenges that assumption by determining the relative contribution of macronutrients from SGD relative to offshore water and rivers. Here, SGD is tidally driven and, as the Northern Gulf of Alaska experiences some of the largest tidal ranges in the world, the SGD fluxes from this region are high relative to the global average regardless of local sediment type. The fluxes ranged from 596 ± 85 cm day−1 at low tide to 97 ± 83 cm day−1 at high tide and are predominantly composed of recirculated seawater (89%) rather than freshwater (11%). The major macronutrients in seawater had different input mechanisms into the semi-enclosed bay. SGD and offshore waters contend as the primary sources of nitrate, which is shown to be the limiting nutrient in this coastal area, while SGD dominates the input of silicic acid. Conversely, the aquifer is found to be a sink for phosphate, indicating that the nutrient is primarily sourced from offshore water.

Impacts of shipyard oil leakage on the PAHs and PCBs occurrence in Xiangshan Bay, China

Here, we studied the shipyard impacts on the distribution of PAHs and PCBs in the semi-enclosed Xiangshan Bay, an important mariculture zone in China. The results showed that the shipyard caused a pollution plume for PAHs but not for PCBs. As characteristic pollutants of oil leakage, the PAHs had concentrations of up to 55.82 ng L−1 in the water, 2235.04 ng g−1 in suspended particulate matter (SPM), and 1489.60 ng g−1 in sediment. The PAHs in water and SPM were dominated by phenanthrene and pyrene that were mostly derived from lubricant and diesel, while those in sediments were dominated by the high-molecular-weight PAHs, such as indeno[1,2,3-c,d]pyrene. In contrast, the PCBs concentrations reached up to 10.17 ng L−1, 79.72 ng g−1, and 124.33 ng g−1 in the seawater, SPM, and sediment samples, respectively, and they did not show spatial patterns affected by the shipyard. Moreover, the health risk assessment indicated that the shipyard discharge caused a substantial PAHs ecological risk to the adjacent and downstream water environment. Therefore, point source discharge in semi-enclosed bays should be paid close attention to due to the strong pollutant transport effect.

Responses of biological traits of macrobenthic fauna to a eutrophication gradient in a semi-enclosed bay, China

The impacts of eutrophication on benthic ecological functions are of increasing concern in recent years. In order to assess the response of macrobenthic fauna to increasing eutrophication, two field sampling surveys were conducted during the summer (July–August 2020) and autumn (October–November 2020) from offshore, nearshore to estuarine sediments in Bohai Bay, northern China. Biological trait analysis was employed for the assessment of macrofaunal samples. The results indicated that there was an increase in the proportion of benthic burrowering or tube-dwelling sediment feeders and taxa with higher larval dispersal ability, but a decrease in the proportion of taxa showing high motility in areas with higher nutrient levels. Seasonal differences were also noted in the shift in biological traits, with a significantly lower similarity among the sampling areas in summer and a higher proportion of carnivorous taxa in autumn. The findings suggested that long-term disturbance can lead to the dominance of smaller body-sized benthic species and reduced sediment quality, impeding ecological recovery of benthic organisms under such harsh environment.

Tide drives nutrients variation and exchange flux in the semi-enclosed Shuidong Bay coastal water in winter, South China Sea

Nutrients play a key role in coastal ecosystems. Coastal tide is an important driver of the daily nutrient variability in semi-enclosed bay under the intensive human activities and climate change. However, the extent of tidal effects on the nutrients variation and exchange flux in the semi-enclosed bay in winter is still scarcely. In this study, seawater samples were collected by synchronous continuous observation during winter in 2021, to investigate tide drives nutrients variation and exchange flux between Shuidong Bay (SDB) and South China Sea (SCS). The results showed most nutrients were significantly impacted by the tidal variation in the SDB with the semi-diurnal cycle. Coastal flood water can increase seawater exchange capacity due to strong dilution influenced by the outer SCS water, resulting mitigate adverse effects of nutrient enrichment in the semi-enclosed bay. In addition, the concentrations of total dissolved nitrogen (TDN), total dissolved phosphorus (TDP), and silicate (DSi) were 146.75 μmol/L, 1.06 μmol/L, and 6.15 μmol/L. Besides, there was a relative excess of nitrogen, phosphorus and silicate were limiting factors in the SDB, and nutrients significantly impacted the Chlorophyll-a in coastal water. Moreover, both TDP and DSi were transported from the SDB to the SCS with a net exchange flux of 0.23 t and 1.99 t, while TDN was transported from the SCS to the SDB with a net exchange flux of 0.14 t, resulting in nutrients ratio increase in the SDB coastal water. Statistical analysis identified the tide induced hydrological variations and terrestrial inputs dominated nutrient dynamics in the SDB coastal water. This study provided a new understanding of the variation and transport of nutrients driven by tide in the SDB, which is implications for understanding the biogeochemistry of nutrients in daily scale and water quality management in the semi-enclosed bay in future.

Response of zooplankton to warming in a low-salinity, eutrophic bay

Warming and eutrophication are universal threats to bay ecosystems. However, the response of zooplankton varies due to diverse environmental settings and species composition. As a long and narrow semi-enclosed bay with low salinity (18–27) in the East China Sea, Xiangshan Bay (XSB) is jointly affected by global warming and the thermal drainage, which makes it an appropriate region for ascertaining the response of zooplankton to warming under low-salinity background. We examined the long-term changes in the abundance, biomass and dominant species of large mesozooplankton (LMZ; >505 μm) over four decades in XSB, and found downward trends in the annual abundance and biomass, and the biomass peak shifting from summer to spring since 2010. In addition, the relative abundance of cold-temperate species decreased, while that of warm-temperate/warm-water species and small-sized zooplankton increased. The decreased LMZ abundance and biomass in XSB were supposed to be related to low gelatinization compared with the other semi-enclosed bays in China, Jiaozhou Bay (JZB) in the Yellow Sea and Daya Bay (DYB) in the South China Sea, where the LMZ biomass and abundance increased or fluctuated mainly linked to the increase in gelatinous zooplankton. Salinity, temperature, and nutrient concentration are important factors affecting gelatinization. By comparing the background salinity and magnitudes of temperature and nutrient increases among the three bays, we speculated that the lower salinity (XSB: 18–27, JZB: 30–32, DYB: 30–34) influenced by freshwater input of the Changjiang River might be a potential factor causing the low gelatinization in XSB, as the similar upward trends in both nutrient concentration and temperature were observed in the three bays. This study suggests that miniaturization with low gelatinization and a decrease in cold-temperate species were the main responses of zooplankton to warming in the low-salinity bay in the East China Sea, which may lead to a specific pelagic ecosystem evolution.

Concentration, distribution, and bioconcentration of short- and long-chain perfluoroalkyl substances in the water, suspended particulate matter, and surface sediment of a typical semi-enclosed bay

This study investigated per- and polyfluoroalkyl substances (PFAS) levels in the surface water, suspended particulate matter (SPM), sediment, and fishes in the Laizhou Bay (LZB) and its inflow river estuaries in dry, normal, and wet seasons. The results demonstrated that the short-chain perfluoroalkyl acids (PFAA) accounted for about 60 % of the total PFAA (∑PFAA) concentration in water, while long-chain PFAA were the dominant compounds in the sediment and SPM. The levels of the ∑PFAA and their precursors decreased from the estuaries to the bay, which implied that terrigenous input (pollutant in land flowed into sea) was the main pollution source of PFAA in the LZB. The PFAAs levels in surface water were ranked as the order of dry > normal > wet season. The distribution coefficients of PFAA showed that the long-chain PFAA were more prone to be adsorbed by sediment and SPM than short-chain PFAA. The increase of ∑PFAA concentrations was in the range of 0.32–36.7 ng·L−1 after the oxidation conversion of water samples. Precursors were the important source of the PFAA in the surface water. The perfluorooctane sulfonate (PFOS) was the dominant compound in fish tissues. These results provide hints for understanding PFAS pollution in LZB.

Residual circulations and wind conditions affect the transport and distribution of Pb

Hydrodynamic conditions affect the dispersion and transportation of pollutants. In this study, 102 surface water samples were collected and numerical simulations were conducted by coupling SWAT (Soil and Water Assessment Tool) and MIKE 21 models to investigate the effect of hydrodynamic conditions on the transport and distribution of Pb in Jiaozhou Bay, China. The tidal current velocity was lowest at flood tide and highest at ebb tide in summer, mainly due to the strong runoff caused by heavy rainfall in summer. The velocity of the residual current near the bay mouth was high, with an average value of 0.32 m/s. The residual currents had alternating clockwise and counter-clockwise circulations of different diameters in the bay mouth and the northern bay. The circulation diameter in the bay mouth area was large, and the circulation extended from the bay mouth to the Yellow Sea. Due to the small circulation diameters and opposite directions of the adjacent circulations in the northern bay, pollutants were easily trapped there. The dissolved Pb particles released from the northern bay mainly migrated to the shore, while the dissolved Pb particles released from the bay mouth tended to migrate to the Yellow Sea. The dominant wind directions and residual currents were the main driving forces affecting the trajectories of the particle tracking simulations. The dissolved Pb concentration in the water was high near shore and in the southwestern bay and under the combined effects of tidal residual current, wind force, and river and wastewater inputs. The low Pb concentration near the bay mouth was mainly influenced by the high residual current velocity. These results can provide improved insights into the mechanism of Pb transport and distribution in a semi-enclosed bay.

Determination of phytoplankton community structure and biomass with HPLC-CHEMTAX and microscopic methods during winter and summer in the Qinzhou Bay of the Beibu Gulf

The Qinzhou Bay, a typical semi-enclosed bay, is facing environmental pressure from local fast-growing industrial and aquacultural development. Dominant species of phytoplankton community (based on microscopic examination) show a trend of miniaturization, while pico-phytoplankton (based on CHEMTAX analysis) is widely distributed in Qinzhou Bay. However, most previous investigations of phytoplankton community based on microscopic method that undetected small-sized cell (< 3 μm), and limited by scarce studies on CHEMTAX analysis, the long-term dynamic data of small-size phytoplankton are lacking in Qinzhou Bay. It is recognized that combining microscopic examination with CHEMTAX analysis could provide a good taxonomic reliability for large cells and valuable information about small-size groups. In this study, microscopic examination and High Performance Liquid Chromatography (HPLC)-CHEMTAX analysis were employed to characterize the spatiotemporal variability of the phytoplankton community structure in Qinzhou Bay in winter and summer of 2021. The results of microscopic observations showed that the phytoplankton community was characterized by diatoms and dinoflagellates mainly. Diatoms dominated in both seasons, of which Skeletonema costatum bloom occurred in the summer. CHEMTAX analysis not only agreed well with microscopy data for diatoms and dinoflagellates, but also helped identification of other small-sized flagellates and cyanobacteria that hard to observe by microscope. The results of CHEMTAX analysis found that diatoms, prasinophytes and cryptophytes co-dominated the total chlorophyll a in winter while diatoms became the dominant group in summer. In addition, our results indicate that the proportion of small-sized flagellates has increased in the past decade in Qinzhou Bay, especially for cryptophytes. Temperature, nutrient availability, and selective grazing of oyster affected the succession of phytoplankton community from co-dominance of diatoms and flagellates in winter to absolute diatoms dominance in summer. The distribution of prasinophytes and cryptophytes on a spatial scale were related to the location of shellfish culture area and estuary, respectively, rather than by nutrients. Eutrophication, selective grazing of oyster and warming were the driving factors of long-term changes in phytoplankton composition in Qinzhou Bay. This study enhanced our understanding of entire phytoplankton community dynamics and its relationship with environmental factors in Qinzhou Bay.

Contribution of ammonium oxidizing archaea and bacteria to intensive nitrification during summer in Mutsu Bay, Japan

Nitrification, in which ammonium is oxidized to nitrate via nitrite, is a regeneration process of bioavailable nitrogen. Ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) carry out the ammonium oxidation. Here we measured the ammonium oxidation rates (AORs), distinguishing those of AOA (VA) and AOB (VB), for two years in Mutsu Bay, a subarctic semi-enclosed bay. Nitrate and ammonium were depleted in the upper layer in summer, but a high concentration of nitrate was observed at the bottom (below 40 m), of up to 7.8 μM with a strong vertical gradient within several meters of the seafloor. A High AOR of up to 0.17 μM d−1 were observed in the bottom waters. The AOA were responsible for most of the total AOR, but the VB exceeded the VA just above the seafloor (0.3 m) in September. Removal of the suspended solids (SS) did not change the AOA’s oxidation activity but eliminated the AOB’s. This finding suggested that AOA were free-living whereas AOB were attached to the SS’s surface. It is also suggested that the sediment was this SS’s source. When ammonia mono-oxygenase, amoA, of AOA and AOB, was quantified, the copy number of AOA-amoA was an order of magnitude higher than that of AOB-amoA throughout the study period. A significant correlation (p < 0.05) was found between the AOB-amoA copy number and VB whereas no correlation was found between the AOA-amoA copy number and VA suggesting the AOA-amoA copy number did not always represent active cells. Ammonia oxidation was occurring near the bottom waters of Mutsu Bay during the summer, and it was accompanied by a dynamic balance reflecting the difference in the AOA’s and AOB’s lifestyles, free-living and particle-associated, respectively.

Selenium in the liver facilitates the biodilution of mercury in the muscle of Planiliza haematocheilus in the Jiaozhou Bay, China

There are increasing evidences that the biodilution effect can significantly reduce the biomagnification of mercury (Hg) in fish. The significant antagonism of selenium (Se) -Hg may have a potential diluting effect on Hg in fish; however, there is still lack of knowledge on such effect. To reveal the Se-Hg interaction and its role in controlling the biodilution effect of Hg, we investigated levels of Hg and Se in the muscle and liver of redlip mullet from Jiaozhou Bay, China, an urbanized semi-enclosed bay highly impacted by human activities. In general, Hg levels in fish muscle were significantly negatively correlated to the levels of Se in the liver and fish size for fish with a size of < 200 mm, indicating that the antagonistic effect of Se on Hg increased with fish growth. This relationship was not significant for fish with a size of > 200 mm, possibly because the normal metabolism of Hg in muscle was hindered by homeostatic regulation or physiological activities such as gonadal development in vivo. Furthermore, the molar ratio of Se in the liver/Hg in the muscle was significantly increasing with Se/Hg in the liver, suggesting that the liver may be the key organ involved in Se-Hg antagonism. Moreover, both ratios continued to decrease with increasing fish size, implying that the antagonistic effect weakens with fish growth. These results indicate that Hg sequestration by liver may be a key mechanism of Se-Hg antagonism in fish and function as a driver for the biodilution effect of Hg, especially at a size of < 200 mm. These findings are further supported by the established linear model of Se-Hg antagonism at different developmental stages.

Evaluation of the taxonomic composition of phytoplankton using microscopy and CHEMTAX in Todos Santos Bay (Baja California, México) during 2017-2018

This study analyzes the spatial and temporal variability of phytoplankton biomass and taxonomic composition in the surface waters of Todos Santos Bay, a semi-enclosed bay within the upwelling zone of the Baja California peninsula (México). Two methodological approaches (microscopy and chemotaxonomy [CHEMTAX]) were used to describe the variability of some genera and species (observed under the microscope) and the importance of those groups that cannot be observed microscopically. Phytoplankton biomarker pigments were measured with high-resolution liquid chromatography and used as input to run the CHEMTAX software to determine the contribution of the main phytoplankton groups to chlorophyll-a (Chl-a). The microscopic analyses showed that diatoms and dinoflagellates comprised 65 and 33% of the total cells, respectively. Dinoflagellates were most abundant in the inner bay and during cold months; the most frequent and abundant genera were Tripos, Protoperidinium, and Prorocentrum. Among diatoms, the most frequent genera were Cylindrotheca, Guinardia, Navicula, Pseudo-nitzschia, and Chaetoceros. CHEMTAX indicated that, together with diatoms, the flagellates prymnesiophytes and chlorophytes contributed a median of 80% to Chl-a, with chlorophytes as the most important group (29.9%). The high contribution of these flagellates suggests that they are represented by small-sized cells not visible by the light microscopy used. However, CHEMTAX largely underestimated the contribution of dinoflagellates (due to the presence of many mixotrophic species). Hence, our results emphasize the importance of using both techniques for a more detailed evaluation of the taxonomic composition of phytoplankton in this and other coastal regions.

Spatial distribution and temporal trends of cyclic and linear siloxanes in sediment from semi-enclosed and industrialized bays of Korea, in 2013 and 2021

Although siloxanes are contaminants of emerging concerns, limited studies have been conducted on contamination and time trends in siloxanes from aquatic environments worldwide. To date, most previous studies have focused on the environmental relevance of cyclic siloxanes in coastal environments. In the present study, cyclic and linear siloxanes were measured in sediment collected from semi-enclosed bays in Korea in 2013 and 2021 to assess occurrence, spatial distribution, temporal trends, and ecological risks. Almost all siloxanes were detected in all sediment samples, indicating continuous contamination for the last decade. The concentrations of cyclic siloxanes in sediment were approximately two times higher than those of linear siloxanes. Decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6) were predominantly detected in all sediment samples, possibly due to their high consumption and strong resistance. The overall concentrations of siloxanes in sediment gradually decreased from inner to outer parts of the bays, suggesting that industrial activities largely contributed to siloxane contamination. Moreover, the highest concentrations of siloxanes in both sampling years were observed in sediment near the outfall of wastewater treatment plant, implying a potential source in the coastal environment. Siloxane concentrations in sediment were significantly correlated with sedimentary organic carbon. The concentrations of siloxanes in sediment were not significantly different between 2013 and 2021, indicating ongoing contamination. The concentrations of D5 and D6 in our sediment samples showed a limited potential to pose a threat to benthic organisms.

On the effectiveness of tributyltin ban part II: Temporal and spatial trends of organotin pollution in intense sediment accumulation areas and dumping sites of the Baltic Sea

Based on the knowledge gained from our previous study, our aim is to observe the current levels of butyltin (BTs) pollution, changes during different seasons, and the factors that affect these trends in the areas of highest concern. These areas include semi-enclosed bays in the Port that were previously affected by large tributyltin (TBT) inputs, as well as the dumping sites of dredged sediment in the Baltic Sea. Compared to previous studies, there has been a significant decrease in the levels of BTs in the Klaipeda Port. However, the sediment in the semi-enclosed bays still contained BTs, ranging from less than 0.5 ng Sn g−1 dw to as high as 728.5 ng Sn g−1 dw. Some BTs were also detected in the currently exploited dumping sites of the Baltic Sea. Moreover, butyltin degradation index (BDI) revealed occasional fresh TBT input or slow degradation both in the Port and in the Sea. Some trends in butyltin concentrations were indicative of the impact of climate change in Lithuania, which are consistent with global trends. We also found that variations in BTs concentrations were closely related to dredging and cleaning activities taking place in the Klaipeda Port. Correlation, principal component, and cluster analysis revealed close relationship between TBT and its degradation products, as well as between TBT and Zn, Pb, Cu. Ship cleaning/maintenance activities were identified as the main source of pollution in the study area. Despite the gradually decreasing BTs concentration in the Klaipeda Port, the problem is not yet completely solved.

Variations in fish community composition and trophic structure under multiple drivers in the Beibu Gulf

IntroductionBeibu Gulf is a semi-enclosed bay with important ecological and economic value of the northwestern South China Sea (SCS). It proved to be a stressed ecosystem and therefore clearly vulnerable to further external disturbances.MethodsData from 26 fishery bottom trawl surveys in the Beibu Gulf from 2006 to 2018 are analyzed to reveal changes in the fish abundance, dominant species composition, diversity, mean trophic level (MTL), and fishing-in-balance (FiB) index.ResultsFish abundance decreased significantly (p&amp;lt; 0.05) with increased anthropogenic disturbance (e.g., fishing intensity and land-derived pollutants), with catch per unit effort (CPUE) decreasing from 40.69 kg·h−1 in 2006 to 15.84 kg·h−1 in 2018. Dominant species composition has changed dramatically from 2006 to 2018, with fish communities shifting from demersal to pelagic species, and from large and high-trophic-level species to small and low-trophic-level species. Meanwhile, Margalef’s richness and Shannon–Wiener diversity indexes trend downward. The MTL declines from 3.82 in 2006 to 3.71 in 2018 (at 0.08 trophic level per decade), and decreasing with the decrease of the proportion of high-trophic fish and demersal fish in total catch (p&amp;lt; 0.05). A FiB index tends to be less than 0, this index declines with decreasing MTL and fish abundance (p&amp;lt; 0.05).DiscussionOverall, fish stocks in the Beibu Gulf continue to decline and are currently overexploited. Multiple external disturbances, such as fishing (including overfishing, dominance of trawl fishery, and ‘skipper effect’), habitat disturbance, pollution, and temperature changes, may have contributed to significant changes in fish communities and trophic structure in the Beibu Gulf.

Applicability of taxonomic sufficiency of macrofaunal assemblages in benthic ecological quality assessments: Insights from a semi-enclosed bay

To explore the applicability of taxonomic sufficiency in benthic ecological quality assessments, we analyzed the similarity of data matrices under different taxonomic levels and transformations based on macrofaunal data sampled from a semi-enclosed bay. The data matrix similarity revealed a highly significant correlation among the similarity matrices at the species level and those at the higher taxonomic levels (genus, family and order), while the correlation coefficients among the matrices decreased with increasing taxonomic levels. Second-stage CLUSTER plots showed that the quantitative genus level was the closest to the quantitative species level. The loss of family level data varied among seasons. The results of the response to environmental factors at the genus and family levels were similar to those at the species level. In the assessment of the benthic ecological quality of semi-enclosed bays, the level of macrofauna identification can be at the genus or family level to improve the cost performance, depending on logistical conditions.

Using the two-way nesting technique AGRIF with MARS3D V11.2 to improve hydrodynamics and estimate environmental indicators

Abstract. In the ocean, mesoscale or submesoscale structures and coastal processes are associated with fine scales. The simulation of such features thus requires the hydrodynamic equations to be solved at high-resolution (from a few hundred meters down to a few tens of meters). Therefore, local mesh refinement is a primary issue for regional and coastal modeling. The AGRIF (adaptive grid refinement in Fortran) library is committed to tackling such a challenge for structured grids. It has been implemented in MARS3D (Model for Application at Regional Scale), a semi-implicit, free-surface numerical model developed by Ifremer (the French Research Institute for Exploitation of the Sea) for coastal environmental research and studies. As its time scheme uses an alternating-direction implicit (ADI) algorithm, the two-way nesting implementation differs from the one in explicit models. The present paper describes the specifics of the AGRIF introduction and how the nesting preserves some essential properties (mass, momentum and tracer conservations) along with the induced constraints (bathymetric coherence between grids and increase in computation cost). The use and the performance of this new tool are detailed over two configurations that illustrate the wide range of scales and resolutions typically targeted by coastal applications. The first one is based on multiple high-resolution (500 m) grids that pave the coastal ocean over thousands of kilometers, allowing a continuum between the regional and coastal scales. The second application is more local and has a finer resolution (50 m). It targets a recurrent question for semi-enclosed bays, i.e., the renewal time indicator. Throughout these configurations, the paper intends to compare the two-way nesting method with the traditional one-way approach. It highlights how the MARS3D-AGRIF tool proves to be an efficient way to both improve the physical hydrodynamics and unravel ecological challenges.

Influence of biodeposition by suspended cultured oyster on the distributions of trace elements in multiple media in a semi-enclosed bay of China

It remains unclear how the suspended non-fed bivalve mariculture will alter the coastal transfer and cleaning process of trace elements, the non-degradable contaminants, which have been reported to accumulate in sediment from bivalve mariculture areas. Herein, we set up a field in situ comparative test in the suspended oyster (Crassostrea plicatula) farming area (OF) and reference area (RA) of Xiangshan Bay to verify our hypothesis that the biodepositon of suspended oysters would consolidate trace elements from the water column and transport them to the sediment. Distribution of trace elements in multiple media of biodeposits (BDs), settling particles (SPs), sediments (SEs), and seawater demonstrate that the accelerated deposition of BDs which enriched trace elements from the water column by oysters filtering suspended particles led to trace elements accumulation in SEs from OF. Additionally, As, Cd, Co, Cr, Cu, Ni, V, and Zn were strongly regulated by this process with significant (p<0.05) higher concentrations in SEs from OF (10.96, 0.20, 13.98, 82.40, 38.47, 38.22, 108.57, and 111.20μg/g, repectively) than those from RA (9.43, 0.13, 11.76, 63.30, 30.34, 29.55, 86.59, and 100.24μg/g, repectively), but the extent was different for Mn, Mo, Pb, and W with concentrations in SEs from OF (737.37, 0.81, 30.98, and 3.96μg/g, repectively) and RA (765.25, 0.69, 31.27, and 3.34μg/g, repectively), especially for Rb and Sr with concentrations in SEs from OF (131.13 and 96.24μg/g, repectively) and RA (142.21 and 161.10μg/g, repectively), due to their geochemical and geophysical properties. Moreover, the harvest of hyper-accumulated oysters as a sink for removing trace elements from water column cannot hide the impact of this process.

Hydrodynamics in the tidal flat in semi-enclosed Xiangshan Bay

Tidal flats provide a foundation for biological diversity and marine economy. Xiangshan Bay is a semi-enclosed bay that shelters large areas of tidal flats, and is known for its aquaculture. In this study, field trips were conducted in late autumn to measure the water level, current, water temperature, tidal flat temperature, and turbidity data of the tidal flat in the bay during Typhoon Lingling. The field data were well calibrated and used to investigate the hydrodynamics, temperature, and turbidity of the tidal flat. The results showed that the spring-neap tidal cycles at the sea surface level were well captured at both stations. The maximum tidal range was 5.5 m and 1.5 m during spring and neap tides, respectively. The tidal flat was occasionally exposed to air occasionally (30 min). The current velocity (&amp;lt;0.2 m/s) and waves (&amp;lt;0.15 m) at the field stations were weak, and the direction of flow was controlled by the geomorphology, even during Typhoon Lingling. Water was more turbid at station S2 (&amp;lt;0.8 kg/m3) than at station S1 (&amp;lt;0.2 kg/m3). The sea water temperature and tidal flat temperature were affected by tidal cycles, with larger variations occurring during spring tides than during neap tides. The maximum value of seawater temperature at S1 station was greater than that at station S2 during spring tides. The intrinsic mode functions (IMFs) of sea water temperature and surface tidal flat temperature were similar, as they are both subject to sea-air-tidal flat interactions. The IMFs of the middle and bottom layers in the tidal flat were less correlated. Temperature fluctuations in seawater and tidal flats were mainly affected by air temperature and tides. Small-scale features (&amp;gt;0.5 Hz) were important for water and tidal flat temperatures, particularly during typhoons. These findings provide field data for future studies on eco-hydrology and coastal engineering in tidal flats.

Impact of Land Reclamation on Coastal Water in a Semi-Enclosed Bay

Land reclamation has a profound impact on coastal environments. On the Chinese coast, the new Xiang’an International Airport has been built on newly reclaimed land. The impact of the massive land reclamation project (finished in 2018) on water quality and coast conditions in a nearby semi-enclosed bay is investigated using remotely sensed data. Factors affecting surface water quality and coast conditions are further analyzed using multiple regression. All water quality and coast condition indices show no long-term trend from 2005 to 2021. The suspended solid concentration (with a maximum value of 96.11 mg/L) is much lower than the threshold of 188 mg/L. When considering variations in sediment concentration, the probability that the concentration reaches the threshold is less than 1×10−6%; therefore, suspended solids have little threat to the local oyster-growing industry. The trend of dissolved inorganic nitrogen concentration is steady, implying little alteration to nutrient circulation in the semi-enclosed bay. Within the observation timeframe of 2005–2021, a recent sedimentation trend (surrogated by the normalized difference water index) appears after 2018 but it needs to be confirmed by a longer observation. Statistical models based on multiple regression highlight the following links: (1) the sediment source is outside the bay, (2) the overland runoff from newly claimed land dilutes nutrient concentrations, and (3) the coast conditions are mainly affected by tides and rainfall. Neither actively reclaimed or cumulative reclaimed areas form a direct causal relationship to water quality or coast conditions in the semi-enclosed bay.