Bay Estuary Research Articles

Hematology and biochemistry reference intervals for American crocodiles (Crocodylus acutus) in South Florida.

The American crocodile (Crocodylus acutus) is considered a vulnerable species by the International Union for Conservation of Nature (IUCN) Red List across its range and classified as locally threatened in several countries. There is a lack of knowledge involving hematological and physiological parameters in American crocodile populations, limiting our understanding of what are considered "normal" blood analyte results for the species and how to link them with health assessments. In this study, we analyzed 40 hematological and biochemical parameters and estimated reference intervals (RIs) for 35 of them based on 436 clinically healthy wild American crocodiles caught in South Florida between 2015 and 2021. Crocodiles were captured across three areas with different levels of human influence [low = Everglades National Park (ENP), medium = Biscayne Bay Estuary (BBE), and high = Turkey Point Nuclear Power Plant (TP)]. There was very strong-to-strong evidence for an effect of where animals were caught on five analytes: basophils %, phosphorus, proportion of (pr) alpha-2 globulins, absolute count (abs) of gamma globulins, and corticosterone, so no reference values were estimated but general statistics are presented and discussed. From the remaining analytes, we found no evidence that sex or size class had an effect on red blood cell (RBC), azurophils and monocytes abs, triglycerides, and albumin abs. However, we did find moderate-to-strong evidence that sex influenced azurophils % and size class influenced white blood cell (WBC), heterophils %, monocytes %, basophils abs, creatine phosphokinase (CPK), potassium, glucose, bile acids, alpha-1 globulin abs, and alpha-2 globulin pr and abs. Finally, there was strong evidence that both sex and size class influenced PCV, lymphocytes % and abs, eosinophils % and abs, aspartate aminotransferase (AST), calcium, sodium, chloride, total protein, albumin/globulin (A/G) ratio, albumin pr, alpha-1 globulin, and beta globulin abs. Intraspecific analysis showed that size is the variable that most influenced analytes explaining up to 29% of the variation, which relates to our findings based on intraindividual analysis. We compared our results with blood parameters reported for conspecifics as well as closely related species and discussed implication of those results for clinical diagnosis and American crocodile conservation.

OSPREY SHIFT FROM NESTING IN TREES TO ARTIFICIAL STRUCTURES IN THE SAN FRANCISCO BAY AREA, CALIFORNIA.

This note documents changes in both substrate used for nest sites and distribution of nesting Ospreys in the San Francisco Bay area over the last 2 decades. Ospreys shifted from use of natural to artificial structures for nesting, as well as shifting nesting distribution from a fresh-water reservoir to the San Francisco Bay estuary. Changes in predator populations, prey, and availability of nest sites may be influencing these changes. The shift from use of natural to artificial structures for nest sites by Osprey mirrors a pattern observed in other western states.

Assessing seasonal spatial segregation by age class of beluga whales (Delphinapterus leucas) in Western Hudson Bay estuaries

Segregation of adult males from adult females and immature animals is known to occur in some beluga whale populations, but it is unclear if such segregation occurs in Hudson Bay, where the largest summering population in the world is found. Using imagery from a photographic aerial survey conducted in August 2015, we examined spatial distribution by age class with respect to several environmental variables near two of three main estuaries, Churchill and Seal River, used by Western Hudson Bay belugas in the summer season. Belugas photographed during aerial surveys were classified by age manually using an identification decision tree, and GPS coordinates of their locations were plotted in ArcGIS. Distribution by age class was examined in relation to five habitat characteristics: distance to coastal habitat, bathymetry, sea surface temperature, and extent of river plume. Habitat characteristics and the proportion of animals by age classes were similar in both estuaries, indicating no segregation, and suggesting the environmental data assessed were not associated with patterns of distribution and density of age classes at the spatial and temporal scale being investigated. Overall density of calves was almost three times higher at the Seal River; however, suggesting this location may be preferred for calf rearing in the summer season. Results provide a greater understanding of spatial patterns of beluga whale habitat use in western Hudson Bay, and information useful in conservation and management advice.

Site fidelity of common bottlenose dolphins (Tursiops truncatus) in a highly industrialized area of the Galveston Bay estuary

AbstractCoastal common bottlenose dolphins (Tursiops truncatus) that inhabit urban estuaries are exposed to a myriad of anthropogenic threats. To manage and conserve these populations, it is imperative to understand their habitat use and residency patterns. In this study, we evaluated the site fidelity of common bottlenose dolphins in upper Galveston Bay (UGB), a heavily industrialized area of the Galveston Bay estuary. We aimed to identify groups within the population with varying affinity to UGB and to determine if there are resident dolphins in UGB. The Galveston Bay Dolphin Research Program conducted monthly photo‐identification surveys in UGB between January 2016 and December 2019. We identified 442 distinct dolphins within UGB and used their sighting histories to calculate occurrence, permanence, and periodicity. These site fidelity metrics were incorporated into a cluster analysis that revealed three groups. Group 1 (n = 192, 43%) consisted of individuals with the highest site fidelity to UGB and were classified as year‐round or seasonal long‐term residents. Group 2 (n = 141, 32%) were transients and Group 3 (n = 109, 25%) were short‐term users of UGB. This study identified resident dolphins in UGB, and we recommend that this group be monitored closely, as they are particularly vulnerable to stressors in the upper estuary.

Does Ozone Pollution Share the Same Formation Mechanisms in the Bay Areas of China?

As important regions of transition between land and sea, the three bay areas of Bohai Bay (BHB), Hangzhou Bay (HZB), and Pearl River Estuary (PRE) in China often suffer from severe photochemical pollution despite scarce anthropogenic emissions. To understand the causes of high ozone (O3) concentrations, the high O3 episode days associated with special synoptic systems in the three bays were identified via observations and simulated by the weather research and forecasting coupled with community multiscale air quality (WRF-CMAQ) model. It was revealed that the interaction between synoptic winds and mesoscale breezes resulted in slow wind speeds over the HZB and PRE, where air pollutants transported from upwind cities gained a long residence time and subsequently participated in intensive photochemical reactions. The net O3 production rates within the bay areas were even comparable to those in surrounding cities. This finding was also applicable to BHB but with lower net O3 production rates, while high levels of background O3 and the regional transport from farther upwind BHB partially elevated the O3 concentrations. Hence, these three bay areas served as O3 "pools" which caused the accumulation of air pollutants via atmospheric dynamics and subsequent intense photochemical reactions under certain meteorological conditions. The results may be applicable to other similar ecotones around the world.

Hyperspectral prediction of mangrove leaf stoichiometries in different restoration areas based on machine learning models

Mangroves play an extremely important role in purifying the atmosphere and responding to global temperature changes. The analysis of chemical elements (carbon, nitrogen, phosphorus, etc.) in mangroves is an effective way to investigate physiological activities, such as vegetation growth, development, and material metabolism. Therefore, the monitoring of mangrove stoichiometry is extremely important for mangrove restoration. Here, two mangrove species, Kandelia candel (KC) and Aegiceras corniculatum (AC), were studied in the Quanzhou Bay Estuary Wetland Nature Reserve. Two machine learning models [random forest (RF) and back propagation neural network (BPNN)] and partial least squares (PLS) were established with the original spectral data as independent variables, and the optimal model was selected by comparing the simple cross-validation VEcv, the ratio of performance to deviation, and the root mean square error (RMSE). The results showed that: (1) the contents of total phosphorous and total nitrogen decreased gradually and the content of total carbon of mangroves increased gradually with an increase in age at restoration; (2) hyperspectral modeling can invert the ecological stoichiometries of KC and AC, and it can be used to effectively monitor the growth status of the species studied; and (3) model performance ranking, PLS > RF > BPNN, where PLS (VEcv ≥ 0.60 and RMSE < 40) was significantly better than the other two models, and BPNN was the least effective and not suitable for hyperspectral inversion modeling of KC and AC ecological stoichiometries. This study provides a methodological basis for long-term and large-scale dynamic monitoring of mangrove ecological stoichiometries and mangrove restoration quality based on hyperspectral data.

Impact of estuaries on fluvial Cr input into the ocean: Perspectives from the Mobile Bay Estuary, Northern Gulf of Mexico

The chromium (Cr) stable isotope system has been recently developed as a promising redox proxy to study Earth’s oxygenation history. However, an incomplete understanding of the global marine Cr isotope mass balance hinders its quantitative application. Specifically, whether estuary environments can alter fluvial Cr flux into the global ocean, together with its isotopic composition, is still debated. Here, we report the first systematic redox-dependent stable Cr isotope data for an oxic estuary (the Mobile Bay Estuary in the northern Gulf of Mexico). Our data suggest that the Cr(VI) supplied by the Mobile River is completely reduced to Cr(III) before salinity reaches 5. A Rayleigh distillation model calculates an isotope fractionation factor of −0.1‰ to −0.3‰ (isotopically light Cr(VI) preferentially reduced). Approximately 15–30% of fluvial Cr(III) is removed from solution in the mixing zone, and this process likely preferentially removes isotopically heavy Cr(III). Therefore, if the face values of the Cr concentration and δ53Cr of the Mobile River were used as input terms for the Gulf of Mexico, Cr flux would have been overestimated by a factor of 5–7 and its δ53Cr overestimated by 0.3–0.7‰. A literature survey suggests that seasonally variable fluvial Cr flux is lost from solution in the majority of estuaries studied thus far. Estuary loss of Cr and annual variation combined add an order of magnitude uncertainty to the global fluvial Cr flux estimated previously. How fluvial δ53Cr is affected in an estuary environment is difficult to generalize because of the competition between partial Cr(VI) reduction that removes light isotopes and Cr(III) scavenging that likely removes heavy isotopes, and such competition likely varies among estuaries.

Impact of Suspended Sediment Diffusion from the Implementation of Arresting Facilities on Cross-Sea Bridges

In order to ensure the safety of bridges and ships, non-navigable channel arresting facilities for ships have become an important part of cross-sea bridges, and the diffusion of suspended sediment caused by their implementation has an impact on seawater quality. Taking the Jintang bridge as an example, a two-dimensional tidal current and sediment numerical model was applied to predict the distribution of suspended sediment diffusion caused by the implementation of arresting facilities, in order to analyze seawater quality. We adopted a new formula for the equivalent roughness method, to generalize the bridge piers, and obtained good results. The results showed that the zone where the SSC (suspended sediment concentration) reached 10 mg/L was concentrated in the area from 4.5 km north to 6.5 km south of the arresting facility, when it was implemented near the western channel. The sea area by the main channel was concentrated within 500 m of the arresting facility. The impact of the implementation of the arresting facility on seawater quality was relatively limited. Only the protected marine area in the Zhenhai Section of the Hangzhou Bay Estuary Coastal Wetland was affected by the suspended sediment from the construction of the western channel.

The increase of cyanobacteria and benthic diatoms over 43 years in upper San Francisco Estuary, California

The quality and quantity of phytoplankton carbon available at the base of the aquatic food web is critical to fish production in estuaries. Therefore, a decrease in chlorophyll a concentration, an estimate of phytoplankton carbon, in upper San Francisco Bay estuary over the last 43 years is hypothesized to be an important contributing factor to a long-term decline in fish production. Although a decrease in the chlorophyll a concentration is well documented for the upper estuary, the quality of carbon available to the food web due to change in the phytoplankton community composition is not. The relative change in the phytoplankton community composition and how it impacted carbon transfer within the lower San Joaquin River, lower Sacramento River and Suisun Bay, was determined with data from 6 stations sampled at 2-week to 4-week intervals between 1975 and 2017. Analysis of similarity (ANOSIM) comparisons confirmed that the relative change in carbon among phytoplankton genera across time affected the food quality index and the size structure of the phytoplankton food resource in the estuary. Between the first and last decades, phytoplankton carbon shifted from large volume cells and diatoms to small volume cells and cyanobacteria. There was also a shift from pelagic to epibenthic and benthic-pelagic diatoms between these two periods. Only 21 phytoplankton genera were responsible for most of this change based on similarity percentage analysis (SIMPER). Single and multivariate analyses confirmed a link between the phytoplankton community carbon and environmental conditions, particularly an increase in Sechhi disk depth. These analyses suggest that a full understanding of the estuarine food web dynamics over time in upper San Francisco Estuary depends on knowing the phytoplankton community composition and how it varies within pelagic and benthic habitats.

Cluster analysis reveals latent structure in stakeholder interests relevant to the management of Blueskin Bay estuary, Otago, Aotearoa New Zealand

ABSTRACT Community participation is increasingly embedded into environmental policy with the aim of accelerating transformative change towards sustainable management. A common approach to engaging with communities is through key stakeholders, who are still often selected ad hoc based on their activities. We tested an analytical approach for identifying distinct groups of community preferences as part of a case study to develop a community-led management plan for Blueskin Bay estuary and its catchment. We interviewed 36 community members to elicit their preferences for predefined management objectives following a standardised protocol. Using an agglomerative hierarchical analysis, we determined value-preference clusters for high-level management objectives and more specific objectives. At both levels combined, preference clusters were attributed to some of the commercial interests, such as cockle harvesting, forestry or tourism, which we also identified ad hoc based on their activities in the Blueskin Bay area. However, in addition, cluster analyses revealed five additional preference types: Urban Development Advocates, Cultural Environmentalists, Economic Environmentalists, Integrative Thinkers and those with Diverse Interests. We conclude that cluster analysis more objectively and specifically maps community preferences and, consequently, increases the robustness of collaborative environmental management processes, such as the one underway for Blueskin Bay estuary.

Phytoplankton Diversity in Jakarta Bay Estuary, Indonesia

Phytoplankton plays an important role in aquatic ecosystems and is one of the biological parameters that can be used as bioindicators to describe conditions, quality, and environmental changes. Jakarta Bay is polluted by various wastes originating from industry, domestic, and sea transportation for fishing activities, which causes a decrease in water quality in Jakarta Bay. This study aims to reveal the composition of phytoplankton and its relationship with the physical and chemical parameters of the waters that empty into Jakarta Bay. The study was conducted in September 2021 at three sampling stations in estuary areas. Station 3 was the most polluted area from industrial waste, only found phytoplankton from the group of Cyanophyta (61.57%) and Euglenophyta (38.43%). Meanwhile, station 2 with the highest concentration of chlorophyll-a, contaminated with domestic waste was dominated by Cyanophyta (29.26%), Euglenophyta (11.79%), Chrysophyta (39.74%), and Chlorophyta (19.21%) groups. The water quality of the two sampling stations greatly affects the composition and abundance of phytoplankton.

Diatom-based paleoenvironmental reconstruction from the coast of Northern Patagonia, Argentina

Estuaries and deltas are common along modern coasts and are well represented in the geologic record because of the high preservation of their deposits. Worldwide, estuaries are more abundant than deltas because of the relatively short time available for Holocene coastal sedimentation due to sea level variations. The evolution of estuaries and deltas during the recent geological past can be reliably reconstructed. Among others, paleostudies in estuaries aim to reconstruct sea level and freshwater input variations, and the timing and frequency of extreme events (e.g., tsunamis). A significant number of studies have been published in the past 20 years, which used preserved remains of microorganisms accumulated during long intervals in sediments. The preserved record of fossil remains evidences the response of microorganisms to environmental changes at the time of their deposition. Among the proxies preserved in sediments, diatoms are one of the most reliable bioindicators to trace environmental changes. Due to rapid reproduction rate under favourable conditions and their siliceous frustule, they are abundant in recent and older sediments from estuaries and deltas. In this manuscript, results from previous studies were reviewed, integrated and statistically analyzed with the aim to reconstruct Holocene coastal changes in relation to sea level curves. These studies were conducted along a latitudinal transect on four estuarine mesotidal systems from Northern Patagonia, Argentina: Colorado River delta (39°40′S; 62°08′W), San Blas Bay (40°33′S; 62°13′W), Negro River (40°57′S; 62°49′W) and Chubut River estuaries (43°22′S; 65°03′W). The focus is on the preserved diatom assemblages and the paleoecological information they represent. Seven coastal sedimentary cores were correlated. Based on multivariate analysis (NMDS), fossil and modern diatom assemblages were integrated and compared. These estuary systems are dominated by littoral drift, where the plains became flooded by the sea about 7000 14C years BP ago. When the sea transgression occupied the area, Colorado delta and San Blas Bay evolved from tidal channels flooded to tidal flats, sand flats and marshes during the late Holocene regression. At Colorado River, the gradually increase of the fluvial influence is associated with the eastward progradation of the deltaic lobe during the last ca. 7000 14C years BP. At the Negro River estuary, a shallow vegetated brackish/freshwater environment evolved into marine conditions, tidal channels and marshes during the last 2000 14C years BP. A marine coastal environment (estuary) at ca. 4400 14C years BP that evolved into a salt marsh was inferred at the inlet of the Chubut River. Diatom salinity-preferences showed how connections between the wetland and the sea varied over time with sea level changes and gradual infilling. Diatom-inferred paleoenvironments and radiocarbon dates allowed reconstruction of the coastline position to the east in the Early Holocene and to the west during transgressive-regressive events.

Stand structure, biomass, and net primary productivity of planted and natural mangrove forests in Batan Bay Estuary, Philippines

Stand structure, biomass, and net primary productivity of planted and natural mangrove forests in Batan Bay Estuary, Philippines

Analysis of trophic status in estuaries in Banten Bay

The fish population could expand in a healthy habitat with adequate water quality and fertile conditions. Banten bay estuaries were known as an area with high fishing activities and were a source of income for fishermen. Many human activities occur in the vicinity of estuaries, which can impact water quality and aquatic fertility. This study aims to determine the trophic status of the fourth estuary in Banten Bay. Water was sampled in the estuarine area of the Banten Bay, namely Wadas, Karangantu, Cengkok, and Pamong, in May, July, and October 2013, as well as in April 2021. pH, water temperature, salinity, conductivity, turbidity, and dissolved oxygen are all measured in situ. Other values like nitrite, nitrate, ammonia, chlorophyl-a, Total Nitrogen, and Total Phosphorous were measured in the lab. TRIX techniques were used to determine trophic status. In four Banten Bay estuaries, a nutrient-rich water environment could still support an abundance of fish.

Trends in surface elevation and accretion in a retrograding delta in coastal Mississippi, USA from 2012–2016

The Grand Bay estuary is in the north-central Gulf of Mexico and lacks riverine sediment input for marsh elevation maintenance. This study quantified trends in surface elevation change and accretion along an elevation gradient within the estuary. Elevation change rates were compared to short (13.71 mm/yr; 95% CI: -2.38–29.81), medium (6.97 mm/yr; 95% CI: 3.31–10.64), and long-range (3.50 mm/yr; 95% CI: 2.88–4.11) water level rise (WLR) rates for the region. Elevation change rates ranged from 0.54 mm/yr (95% CI: -0.63–1.72) to 5.45 mm/yr (95% CI: 4.27–6.62) and accretion rates ranged from 0.82 mm/yr (95% CI: -0.16–1.80) to 3.89 mm/yr (95% CI: 2.90–4.89) among marsh zones. Only the elevation change rate at a Juncus roemerianus marsh located high in the tidal frame was lower than long- (P < 0.001) and medium-range WLR rates (P < 0.01). The elevation change rate at a lower elevation J. roemerianus marsh was higher than the long-range WLR rate (P < 0.05). No marsh zones had elevation change rates that were significantly different from short-range WLR. These results suggest that J. roemerianus marshes higher in the tidal frame are the most vulnerable to increases in sea level. Lower elevation marshes had higher rates of elevation change driven by sediment accretion and biogenic inputs. Other local research suggests that shoreline erosion is a threat to marsh persistence but provides elevation capital to interior marshes. Marsh migration is a potential solution for marsh persistence in this relatively undeveloped area of the Gulf Coast.

Development and Application of Landsat-Based Wetland Vegetation Cover and UnVegetated-Vegetated Marsh Ratio (UVVR) for the Conterminous United States

Effective management and restoration of salt marshes and other vegetated intertidal habitats require objective and spatially integrated metrics of geomorphic status and vulnerability. The unvegetated-vegetated marsh ratio (UVVR), a recently developed metric, can be used to establish present-day vegetative cover, identify stability thresholds, and quantify vulnerability to open-water conversion over a range of spatial scales. We developed a Landsat-based approach to quantify the within-pixel vegetated fraction and UVVR for coastal wetlands of the conterminous United States, at 30-m resolution for 2014–2018. Here we present the methodology used to generate the UVVR from spectral indices, along with calibration, validation, and spatial autocorrelation assessments. We then demonstrate multiple applications of the data across varying spatial scales: first, we aggregate the UVVR across individual states and estuaries to quantify total vegetated wetland area for the nation. On the state level, Louisiana and Florida account for over 50% of the nation’s total, while on the estuarine level, the Chesapeake Bay Estuary and selected Louisiana coastal areas each account for over 6% of the nation’s total vegetated wetland area. Second, we present cases where this dataset can be used to track wetland change (e.g., expansion due to restoration and loss due to stressors). Lastly, we propose a classification methodology that delineates areas vulnerable to open-water expansion based on the 5-year mean and standard deviation of the UVVR. Calculating the UVVR for the period-of-record back to 1985, as well as regular updating, will fill a critical gap for tracking national status of salt marshes and other vegetated habitats through time and space.

Movement patterns of juvenile green sturgeon (Acipenser medirostris) in the San Francisco Bay Estuary

Little is known about the distribution and ecology of juvenile green sturgeon throughout their range and specifically within California’s Central Valley and the San Francisco Bay Estuary. The objective of our study was to identify rearing movement patterns of juvenile green sturgeon and their interaction with Delta and Bay habitats. Acoustic biotelemetry was used to record juvenile movements and residence within different regions of this highly modified watershed. We document a diversity of movements exhibited by 31 acoustically tagged juvenile green sturgeon monitored over a 9-month period. The juvenile sturgeon either (1) remained in the Delta or moved (2) into the Carquinez Straits, (3) into San Pablo Bay, (4) into San Pablo Bay but returned to Delta, (5) through the estuary and likely left through the mouth of the bay, (6) or left the estuary only to return later. Spatiotemporal habitat quality varies within and between Delta and Bay habitats. Variation in water year and hydrologic connectivity are likely to influence habitat quality and quantity, and behaviors may be differentially optimized for fitness in response to environmental variation. Our results provide initial evidence supporting multiple behavioral movement patterns and a broad use of regional habitats for green sturgeon in the California Central Valley. This apparent behavioral diversity observed through movement patterns may ensure long-term success of all population segments over time in an extremely variable environment, ultimately supporting overall population stability (i.e., the portfolio effect). Enhanced conservation efforts may be needed to protect juvenile green sturgeon and the habitats they rely upon.

Spatiotemporal assessment of potential drivers of salt marsh dieback in the North Inlet-Winyah Bay estuary, South Carolina (1990–2019)

Previous studies in the Gulf of Mexico and Atlantic states have suggested that a suite of possibly abiotic and biotic attributes is responsible for salt marsh dieback, e.g., drought, soil waterlogging, soil chemistry, top-down consumers control, etc. However, there are no conclusive answers in current literature explaining what led to marsh dieback in past decades, especially from the spatiotemporal perspective. Exploring all Landsat-retrieved marsh dieback events in 1990–2019, this research investigates the spatiotemporal relationships between the dieback series and the associated environmental variables in an intertidal marsh in South Carolina (SC). Based on our previous study, a series of marsh dieback events in the past 30 years were identified and dieback pixels in the estuary were extracted. Among these were the most severe marsh dieback events (1991, 1999, 2000, 2002, 2004, and 2013). Daily Evaporative Demand Drought Index (EDDI), daily precipitation data from Parameter Elevation Regressions on Independent Slopes Model (PRISM), and station-based water quality observations (dissolved oxygen, specific conductivity, salinity, turbidity, pH, and temperature) in the estuary were retrieved. Integrated with the proof-by-exhaustion method, statistical analysis showed marsh dieback were highly related to moisture imbalance in a period of 90 days before the dieback events. Respectively, pH for Clambank and Debidue Creek, salinity and turbidity for Thousand Acre were found to be the key water quality variables influencing marsh dieback besides drought. This study cogitates the environmental influence on coastal marsh dieback from a spatiotemporal perspective using a long-term satellite time series analysis. The findings could provide insights into marsh ecological resilience and facilitate coastal ecosystem management.

Dynamics and Mass Balance of Polycyclic Aromatic Hydrocarbons in and Around the Seto Inland Sea, Japan

Polycyclic aromatic hydrocarbons (PAHs) were analyzed to elucidate the distribution, ecological risk, pathways, and fluxes of these pollutants in and around the Seto Inland Sea, an industrialized coastal region of Japan. High molecular weight PAHs (5-6 rings) were primarily found in regions close to the bay estuaries, and their proportions decreased at distances further from the estuaries (offshore areas), where low molecular weight PAHs (2-4 rings) were more ubiquitous. Screening-level risk assessments revealed that the PAHs found in the sediments should have no adverse effects on benthic communities. A mass balance for PAHs in the Seto Inland Sea, calculated based on data collected in the field and published literature findings, showed the PAH flux into the Seto Inland Sea from atmospheric deposition were ca. 6 times higher than that from riverine inflows. Comparison of the amount of the PAH mass flux between the Seto Inland Sea and the sea of the Europe and Asian countries indicated that the Seto Inland Sea is less polluted than the Gulf of Lion, the Mediterranean Sea, and the Bohai Sea, China and more polluted than the Yellow Sea. This paper is the first to determine the fluxes of PAHs in the coastal region of Japan.

Contribution of the reservoir backflow to the eutrophication of its tributary: a case study of the Xiangxi River, China

AbstractBased on the routine water quality monitoring data of the Xiangxi River and its main monitoring section from January 2014 to May 2016, the monthly dynamics of nutrient concentrations and fluxes were analyzed, and the relationship between the water exchange between the reservoir and the tributaries and the changes of nutrient fluxes in the river was established. The results showed that the nutrient flux in the Xiangxi bay estuary was negatively correlated with the reservoir reflux intensity, and the overall correlation coefficient was −0.52. Four nutrient indexes, total nitrogen, total phosphorus, ammonia nitrogen (), and soluble phosphorus, all showed the same regularity and characteristics, among which was particularly prominent. It can be concluded that the variation of nutrient salts in the water body of the tributary bay is mainly determined by the water exchange between the reservoir and the tributary. In addition, the change of chemical oxygen demand and chlorophyll a flux in the Xiangxi Bay and water exchange in the reservoir area were analyzed. We found that changes in the hydraulic conditions of the return flow in the reservoir area can destroy the suitable flow environment necessary for the survival of algae, thus preventing the proliferation of harmful algae. Therefore, by controlling the hydrodynamic conditions between the reservoir area and the tributaries and changing the degree of water exchange between them, the objective of improving the water environment in the Xiangxi Bay can be achieved to a large extent.