Estuarine Coastal and Shelf Science最新文献

Understanding the mechanisms that spread freshwater away from small river systems and form turbid, low-salinity coastal plumes is crucial for assessing water quality in coastal waters. We present an analysis of 15 years (January 2004 to December 2018) of daily MODIS Aqua satellite data and in situ instrument data on the turbid freshwater plume that forms off the Russian River (California, USA), a prototypical Mediterranean-climate, small mountainous river system (SMRS). We present per-pixel statistical metrics and regression analyses to identify and quantify the controls on the extent and configuration of the plume exerted by river discharge, waves, winds, and tides. While freshwater outflow exhibits a persistent signal in nearshore waters, a large-scale plume only extends offshore into coastal waters during high river flow, when plume turbidity can be detected more than 10 km offshore from the river mouth. Our results show times when wave radiation stress exceeds outflow inertia, confining the plume within the surf zone and leading to an absence of detectable plume turbidity in coastal waters. Although tidal currents significantly influence the plume near the inlet, wind forcing is the primary control on plume shape and extent in coastal waters, deflecting the turbid outflow more than 30 km upcoast or downcoast of the river mouth with respective wind directions. Coriolis forcing is also significant and observed most clearly during periods of high river discharge and low wind forcing. In addition to introducing novel remote sensing methodology for SMRS plume analyses, these findings highlight the complex interplay of forcing related to tides, river discharge, winds, and waves in shaping the behavior of SMRS plumes. New insights include the impact of tides on larger discharges, the role of Coriolis forcing in SMRS plumes, and the effect of cross-shore winds on plume compression. Further, by considering the Russian River as a model for SMRS, this study can be used to ground-truth existing numerical models of small river plumes and to contribute to understanding critical for managing coastal water quality and nearshore ecosystems.

In an era of accelerating biological globalization and climatic warming, it is vital to understand how introduced species integrate. Pacific Manila clams Ruditapes philippinarum were introduced for aquaculture to Europe in the 1970s, spread and became harvested from the Mediterranean Sea to British coasts. From the Dutch Rhine Delta, Manila clams immigrated stepwise into the southern Wadden Sea, and by long distance jump dispersal they arrived in the northern Wadden Sea in the 2010s. Encounters remained few until 2021, when live clams were often found in intertidal seagrass beds and around mixed beds of Pacific oysters with native mussels. Shell lengths reached up to 74 mm with a longevity of 7–8 years. Adult abundances remained low (<10 clams m⁻²), although larval numbers substantially increased in 2022 and 2023. Strong predation on spat may constitute ecological resistance to the immigrant. Haplotype diversity at mtDNA COI gene fragments is high and its composition is mixed from dominant haplotypes of other European sites, suggesting multiple introductions or an unknown source with an already mixed population. Currently, this is the most northern (55° N) population of R. philippinarum in continental Europe, but with the rapid expansion of this genetically variable population, further northward spread can be expected.

Marine seabed mapping is an important element in marine spatial and conservation planning. Recent large scale mapping programmes have greatly increased our knowledge of the seafloor, yet at finer resolutions, large gaps remain. Loch Eriboll, Scotland, is an area of conservation interest with a diverse marine environment supporting habitats and species of conservation importance. Here we test and present strategies for a predictive seabed substrata map for Loch Eriboll using drop down Stereo Baited Remote Underwater Video (SBRUV) imagery collected as part of systematic underwater survey of the Loch. A total of 216 SBRUV deployments were made across the study site in depths of 3 m–117 m, with six seabed classes identified using an adaptation of the EUNIS (European Nature Information System) hierarchical habitat classification scheme. Four statistical learning approaches were tested, we found, Generalised Additive Models (GAMs) provided the optimal balance between over- and underfitted predictions. We demonstrate the creation of a predictive substratum habitat map covering 63 km² of seabed which predicts the probability of presence and relative proportion of substratum types. Our method enables naturally occurring edges between habitat patches to be described well, increasing the accuracy of mapping habitat boundaries when compared to categorical approaches. The predictions allow for both defined boundaries such as those between sand and rock and fuzzy boundaries seen among fine mixed sediments to exist in the same model structure. We demonstrate that SBRUV imagery can be used to generate cost effective, fine scale predictive substrata maps that can inform marine planning. The modelling procedure presented has the potential for a wide adoption by marine stakeholders and could be used to establish baselines for long term monitoring of benthic habitats and further research such as animal distribution and movement work which require detailed benthic maps.

Urbanization impacts, especially stormwater runoff and pollutant discharge, pose ecological threats to coastal ecosystems globally. Long-term environmental monitoring datasets and assessments are used to quantify anthropogenic impacts on ecosystem health. This study synthesized twenty years (2002–2021) of water quality data from the National Estuarine Research Reserve System-wide Monitoring Program at the understudied Masonboro Island Reserve (North Carolina, United States) and provided an analytical methodology that can be applied to other Reserves and monitoring programs world-wide. Time series and correlation analyses of biological, chemical, and physical water quality parameters were used to identify spatiotemporal trends of nutrient dynamics and phytoplankton biomass at three stations within a 5-km stretch of the Atlantic Intracoastal Waterway. Heterogenous water quality conditions were observed between stations, especially for chlorophyll a, and were influenced by the relative proximity to marine waters, human developments, and urban tidal creeks. Long-term trends indicated significant water quality changes (i.e., increased chlorophyll a, reduced pH and salinity) related to anthropogenic influences. An unexpected and rapid shift in nutrient dynamics occurred around 2007, marked by significantly decreased ammonium and orthophosphate concentrations, which considerably reduced DIN/DIP ratios. This positive change was potentially influenced by sewage infrastructure improvements and stormwater wetland construction, removing waste-derived nutrients that previously entered the ecosystem. Impacts of major storms were also observed with weeks of hypoxia and low salinity following Hurricane Florence. These findings emphasized the value of long-term trend analyses of monitoring program data at multiple sites and provided insights into the significant water quality impacts of urbanization and benefits from wetland protection. This study further encourages the evaluation of long-term water quality monitoring datasets in estuarine environments globally.

The Qiongzhou Strait (QS) throughflow is affected by the seasonal circulation in both the northern South China Sea (SCS) shelf and the Beibu Gulf. The water masses with distinct properties between these two regions signify the baroclinic processes in the QS. In this study, a high-resolution unstructured-grid Finite Volume Community Ocean Model (FVCOM) was used to investigate the features and dynamic mechanisms of baroclinic-induced currents (BCC) in the QS. Different forcings were considered such as tides, river discharges, winds, and remote forcings (low-frequency sea surface level and current variations). The model results indicate that the volume transport of the BCC contributes to 31.26% of the total in the QS, determining the transport direction in summer. The baroclinic response to low-frequency remote forcings is most pronounced during the summer-autumn season, but less than winds during the winter-spring season. This finding underscores the importance of low-frequency remote forcings on the QS throughflow, which has often been overlooked in previous studies. Momentum balance suggests that the BCCs are predominantly driven by both the barotropic and baroclinic pressure gradient forces. Decrease (increase) in either of these two forces will lead to an intensified eastward (westward) flow. The contribution of the horizontal advection is relatively weak but cannot be ignored. This study highlights the baroclinic responses of QS throughflow to different forcings, which is important when investigating the circulation in the northern SCS, especially in the Beibu Gulf.

Mangrove forests are known as coastal carbon sinks, but the long-term (millennium-scale) preservation processes of organic matter (OM) in their soils and the role of sulphur in these processes are still not fully understood. These processes are crucial for better estimating the impact of sea-level variations on the carbon dynamics in mangrove forests, which are particularly sensitive to sea-level changes due to their direct hydrological interactions with coastal waters. This study focuses on a soil layer enriched in mangrove-derived OM that accumulated during a stable sea-level period of the Holocene in New Caledonia (South Pacific). Radiocarbon dating situates this enriched layer at approximately 4000 cal BP. The aim of this study is to characterize the enriched OM layer using bulk (Rock-Eval), isotopic (δ¹³C and δ¹⁵N), and molecular (lignin and neutral carbohydrates) analyses. This OM has undergone diagenetic processes such as dehydrogenation, and the loss of components such as the main neutral carbohydrates: glucose, xylose, and galactose. However, some Rock-Eval parameters, the total lignin content, and carbon and nitrogen isotopic ratios are characteristic of well-preserved OM, suggesting differential decomposition/preservation processes. In addition, SEM observations highlighted the presence of pyrite associated to preserved root material. Along with high S_org/TOC ratio, these results suggest potential processes of OM sulfurization preserving it from decomposition. Prolonged sea-level stability in addition to anoxic and sulfidic soil conditions enhanced OM accumulation and long-term sequestration in mangrove soils.

Coilia nasus was once an economically important fish in the Yangtze River estuary, but overfishing and other anthropogenic factors have severely depleted its population. To conserve and restore C. nasus, there is an urgent need to determine its precise spatiotemporal distribution. However, as a typical anadromous species, C. nasus seasonally uses estuarine habitats, resulting in a very high proportion of nulls in some seasons and posing a great challenge to predicting abundance. This study compared three commonly used tree methods (gradient boosting machine (GBM), random forest (RF), and conditional random forest (CRF)) to predict the abundance of C. nasus in the Yangtze River estuary using trawl resource monitoring survey data from 2013 to 2018. Based on the survey data, 16 explanatory variables, including temperature, salinity, pH, and chemical oxygen demand, were used as predictors, and the coefficient of determination (R²), root mean square error (RMSE), and root mean square logarithmic error (RMSLE) were used to evaluate the performance of the three tree methods. Three metrics were used to assess the performance difference between interpolation and extrapolation for the three tree methods when modeling by season and combining seasons. The results showed that (1) compared with combined modeling, seasonal modeling could accurately determine the high- and low-abundance regions in interpolation, and the quarterly model greatly improved the extrapolation prediction accuracy. (2) Almost all metrics indicated that the interpolation RF model had the best performance, while CRF and GBM were significantly worse than other methods for some indicators, and the RF model had better robustness and could be applied to the abundance of all seasons. (3) The model performance in extrapolation was significantly lower than that of interpolation, RF was also the best method, and RF could still identify high-abundance areas when the amount of data was much smaller than that used for interpolation. The findings of our study can be generalized to species distribution modeling of other migratory species in the Yangtze River estuary or estuarine ecosystems in the Northwest Pacific Ocean.

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.