Toxins and Other Bioactive Metabolites in Deep Chlorophyll Layers Containing the Cyanobacteria Planktothrix cf. isothrix in Two Georgian Bay Embayments, Lake Huron.

The understanding of deep chlorophyll layers (DCLs) in the Great Lakes-largely reported as a mix of picoplankton and mixotrophic nanoflagellates-is predominantly based on studies of deep (>30 m), offshore locations. Here, we document and characterize nearshore DCLs from two meso-oligotrophic embayments, Twelve Mile Bay (TMB) and South Bay (SB), along eastern Georgian Bay, Lake Huron (Ontario, Canada) in 2014, 2015, and 2018. Both embayments showed the annual formation of DCLs, present as dense, thin, metalimnetic plates dominated by the large, potentially toxic, and bloom-forming cyanobacteria Planktothrix cf. isothrix. The contribution of P. cf. isothrix to the deep-living total biomass (TB) increased as thermal stratification progressed over the ice-free season, reaching 40% in TMB (0.6 mg/L at 9.5 m) and 65% in South Bay (3.5 mg/L at 7.5 m) in 2015. The euphotic zone in each embayment extended down past the mixed layer, into the nutrient-enriched hypoxic hypolimnia, consistent with other studies of similar systems with DCLs. The co-occurrence of the metal-oxidizing bacteria Leptothrix spp. and bactivorous flagellates within the metalimnetic DCLs suggests that the microbial loop plays an important role in recycling nutrients within these layers, particularly phosphate (PO4) and iron (Fe). Samples taken through the water column in both embayments showed measurable concentrations of the cyanobacterial toxins microcystins (max. 0.4 µg/L) and the other bioactive metabolites anabaenopeptins (max. ~7 µg/L) and cyanopeptolins (max. 1 ng/L), along with the corresponding genes (max. in 2018). These oligopeptides are known to act as metabolic inhibitors (e.g., in chemical defence against grazers, parasites) and allow a competitive advantage. In TMB, the 2018 peaks in these oligopeptides and genes coincided with the P. cf. isothrix DCLs, suggesting this species as the main source. Our data indicate that intersecting physicochemical gradients of light and nutrient-enriched hypoxic hypolimnia are key factors in supporting DCLs in TMB and SB. Microbial activity and allelopathy may also influence DCL community structure and function, and require further investigation, particularly related to the dominance of potentially toxigenic species such as P. cf. isothrix.

Effect of drying methods on the powder and compaction properties of microcrystalline cellulose derived from Gossypium herbaceum

The effect of drying method, a process variable, on the powder and compaction properties of microcrystalline cellulose (MCC) obtained from the partial acid hydrolysis of bleached alpha (α) cellulose content of matured linters of Gossypium herbaceum (GH) was investigated. A portion of the wet MCC obtained was fluid bed dried at 60 ± 1 ºC, inlet air of 30 m3 min-1 for 3 h (coded MCC-GossF). The second portion was lyophilized at - 45 ± 2 ºC for 6 h (coded MCC-GossL). The physicochemical, scanning electron micrographs, X ray diffraction patterns and micromeritic properties of the derived MCCs were determined using standard methods. The cohesiveness and compactibility of the powders were investigated using Kawakita model while the deformation and compressibility pattern were determined using Heckel model. Avicel® PH 102 (AV-102) was used as comparing standard. Ash values of < 2%, pH (6.54 ± 0.23 to 6.58 ± 0.08), degree of polymerization, DP (231.50) was obtained. MCC-GossF had higher moisture content, swellability, better flow indices, and lesser porosity than MCC-GossL. Kawakita model demonstrated good consolidation and compactibility for both powders. Compacts of MCC-GossL were significantly (p < 0.05) harder than those of MCC-GossF. Heckel analysis demonstrated good compressibility and deformation pattern that was comparable with AV-102. Compacts of MCC-GossL had better mechanical and tablet compression properties than MCC-GossF

Microplastics in Tampa Bay, Florida: Abundance and variability in estuarine waters and sediments.

This study provides the first measurement of microplastic abundance and distribution in surface waters and sediments in Tampa Bay, FL. Microplastic concentrations in discrete water samples ranged from 0.25 to 7.0 particles/L with an average of 0.94 (±0.52) particles/L. Samples taken with a 330 µm plankton net had 1.2-18.1 particles/m3 with an average of 4.5 (±2.3) particles/m3. Discrete samples were 200 times higher than net samples, suggesting substantial losses or undersampling with the net. For both discrete and plankton tow samples, there were no significant differences in concentrations between stations or regions. Intense rainfall events in the summer always preceded samples with substantially higher counts. Most (>75%) microplastics were fibers. Using an average value of 1 particle/L, Tampa Bay contains ~4 billion microplastic particles. Surface sediments had an average of 280 (±290) particles/kg, ranging from 30 to 790 particles/kg. Highest concentrations of microplastics were found in sediments close to industrial sources; lowest values in Middle and Lower Tampa Bay are consistent with shorter residence times.

Distribution and ecotoxicological effects of polyhalogenated carbazoles in sediments from Jiaozhou Bay wetland.

A suite of eight polyhalogenated carbazole (PHCZ) congeners were detected in sediments of the Jiaozhou Bay wetland. 3,6-dichlorocarbazole (36-CCZ), and 3,6-dibromocarbazole (36-BCZ) were detected in all samples. The concentrations of ΣPHCZs ranged from 6.9 to 33.4 ng/g dry weight (dw). The recovery of surrogate standard ranged from 85 to 109%. Significant relationships were found between the concentrations of 36-CCZ and those of the other three detected compounds (36-BCZ, 36-ICZ, and 1368-BCZ). However, with regard to the other chemicals, only 1368-BCZ was related to 36-ICZ. The toxic equivalent (TEQ) was used to assess the relative toxicity of PHCZs, which ranged within 0.1-3.9 pg TEQ/g dw in sediment. The inventory of ΣPHCZs was 58.9 kg. These results indicate that PHCZs are widely distributed in the Jiaozhou wetland and the dyeing and finishing industries may be important contamination sources of PHCZs.

Temporal and seasonal variation and ecological risk evaluation of flame retardants in seawater and sediments from Bohai Bay near Tianjin, China during 2014 to 2017.

Seawater and sediment samples were collected from 2014 to 2017 at Bohai Bay near Tianjin, China. The median concentration of ΣOPFRs was 2202 ng/l in the seawater from 2017. ΣAlkyl-OPFRs was the predominant constitution in the seawater with a median contribution of nearly 80%, and ΣCl-OPFRs was the major component in the sediment. Regarding BFRs, BDE-209 was the principal one in the sediment. The levels of TEP, TCEP and TBEP in sediments displayed significantly seasonal variations. The summer concentration of TEP was higher than that in both the spring and autumn, and concerning TCEP and TBEP, their lowest concentration occurred in summer. The concentration of ΣOPFRs experienced a rapid increasing during 2014-2016 due to more emissions of OPFRs. The ecological risk evaluation of OPFRs and BFRs suggested a moderate and high risk to the investigated marine region under the high exposure scenario, respectively.

Occurrence of surface sand microplastic and litter in Macajalar Bay, Philippines.

Microplastics have become an emerging structural pollutant to the marine environment particularly in the Philippines owing to high plastic load. This study was carried out to determine the occurrence of microplastic and coastal litter in Macajalar Bay, Philippines. Three coastal areas were studied namely, Opol, El Salvador City, and Alubijid with three substations in each area. A total of nine surface sand sediment samples were collected for microplastic analysis. Microplastics were extracted through the flotation method and preliminary identification was carried out using a stereomicroscope. The beach litters were obtained through transect walk in a 5 m × 10 m quadrant per area. Overall, studied microplastics were mainly angular and filament type with colors varying from blue, black, light orange, pale white, and translucent. Litter analysis showed the dominance of plastics across the study area with a mean cumulative coastal clean index (CCI) of 2.40 (clean).

Characterization of organic contaminants in fjords and bays on the Kenai Peninsula Alaska.

A baseline environmental characterization of Seldovia Bay and harbor on the Kenai Peninsula, Alaska, was conducted using a sediment quality approach. The data was derived from a larger study that assessed seven distinct water bodies on the Kenai Peninsula's north side, draining into Kachemak Bay or into Lower Cook Inlet. Sampling sites for water quality measurements, sediment chemistry, and benthos were randomized within each embayment. Concentrations of 140 organic and elemental contaminants were analyzed. Habitat parameters (depth, salinity, grain size, organic carbon, etc.) that influence species and contaminant distribution were also measured at each sampling site. Concentrations of chlorinated pesticides and PCBs were uniformly low, with the exception of Seldovia Harbor, where total DDT and PCBs exceeded the lower sediment quality guidelines. Concentrations of PAHs were relatively low, except in Seldovia Harbor where concentrations exceeded lower sediment quality guidelines for PAHs, and in one location approached the upper limit. That concentration of PAHs exceeded all other measurements in the NOAA National Status & Trends database for the entire State of Alaska. Characteristics of the PAH compounds present indicate large contributions of pyrogenic sources (burned fuel and/or other organic matter). Seldovia Bay had much lower PAH concentrations than the harbor.

Geochemical sourcing of runoff from a young volcanic watershed to an impacted coral reef in Pelekane Bay, Hawaii.

Runoff of sediment and other contaminants from developed watersheds threatens coastal ecosystems and services. A sediment geochemical sourcing study was undertaken on a sediment-impacted coral reef flat to identify terrestrial sediment sources and how these changed over time. Geochemical signatures were identified for watershed soils that formed on Hawaiian basaltic and alkalic lavas using relatively immobile compatible (Ni, Sc) and incompatible (Nb, REE, Th) elements quantified by ICP-MS in total decompositions of the fine fraction of surface soils. Some soils also contained ash from late-erupting cinder cones that added alkalic geochemical signatures, resulting in distinctive mixed signatures near these geologic features. Sediment was collected in Pelekane Bay using sediment traps during winter 2010-2011 and a sediment core in order to geochemically source runoff entering the bay. Geochemical signatures in trapped sediment showed that runoff predominantly originated from the lower watershed along a highway corridor rather than from the upper watershed or areas with alkalic lavas. Soil in the highway corridor also contained Zn above levels of concern for aquatic organisms and anthropogenic Pb, indications that runoff control measures could reduce the exposure of the reef community to potentially toxic metals and other road-associated contaminants. The upper portion of a 60-yr long sediment record from Pelekane Bay was disturbed by tsunamigenic waves from the Tohoku earthquake, and the remainder was likely subject to mixing by winter waves that averaged out geochemical variations. On average, watershed regions with basaltic soils were the predominant source of runoff to the bay over the past 60 years. By linking sediment runoff to geographic regions or features in watersheds, geochemical sourcing can provide insights that allow resource managers to direct runoff mitigation and soil conservation efforts to areas where they will be most effective.

Impact of Hydrous Manganese and Ferric Oxides on the Behavior of Aqueous Rare Earth Elements (REE): Evidence from a Modeling Approach and Implication for the Sink of REE.

In this study, models were used for the first time to investigate the fate and transport of rare earth elements (REE) in the presence of hydrous manganese and ferric oxides in groundwaters from the coastal Bohai Bay (China). Results showed that REE sorption is strongly dependent on pH, as well as hydrous manganese and ferric oxide content. Higher proportions of REE were sorbed by hydrous manganese oxide as compared to hydrous ferric oxides, for example in the presence of neodymium. In this case, a mean 28% of this element was sorbed by hydrous manganese oxide, whereas an average 7% sorption was observed with hydrous ferric oxides. A contrasting REE sorption behavior was observed with hydrous manganese and ferric oxide for all investigated groundwaters. Specifically, REE bound to hydrous manganese oxides showed decreasing sorption patterns with increasing atomic number. The opposite trend was observed in the presence of hydrous ferric oxides. In addition, these results suggested that light REE (from La to Sm) rather than heavy REE (from Eu to Lu) are preferentially scavenged by hydrous manganese oxide. However, the heavy REE showed a greater affinity for hydrous ferric oxides compared to light REE. Therefore, both hydrous manganese and ferric oxide are important scavengers of REE. This study shows the implication of hydrous manganese and ferric oxide sorption for the sink of REE in groundwater.

A benthic bioindicator reveals distinct land and ocean-Based influences in an urbanized coastal embayment.

Biogeochemical maps of coastal regions can be used to identify important influences and inputs that define nearshore environments and biota. Biogeochemical tracers can also track animal movement and their diet, monitor human coastal development, and evaluate the condition of habitats and species. However, the beneficial applications of spatial biogeochemical analysis are hindered by a limited understanding of how tracer distribution is affected by different land and ocean-based influences. To help address these knowledge gaps, we determined the spatial trends of three stable isotopes (δ13C-carbon, δ15N-nitrogen, δ34S-sulfur) and 13 major and trace elements in an urbanized coastal embayment (Moreton Bay, Australia), as incorporated into the muscle tissue of a marine consumer, the eastern king prawn Melicertus plebejus. Results were used to identify unique biochemical regions within the bay and to discuss how spatial patterns in tracers could be used to indicate the relative importance of catchment, urban and offshore drivers in coastal bays. Discriminant analysis identified seven biogeochemical regions that were likely distinguished by variation in catchment, urban, and offshore input, and habitat type. δ13C and δ15N patterns suggested nearshore areas could be distinguished by increased sediment resuspension and higher wastewater inputs from catchments. High inshore lead (Pb) and copper (Cu) concentrations were likely the result of urban input. Arsenic (As) and cadmium (Cd) increased further from shore. This trend implied oceanic influences were a significant control over As and Cd bioavailability. Cobalt (Co) and rare earths were also used to differentiate some nearshore areas, but incongruent distribution patterns in Co suggested it may be less reliable. Overall, results indicated that δ15N, δ13C, Cd, Cu, Pb and rare earth elements were the most reliable tracers to differentiate nearshore and offshore environments, and catchment-based effects. We encourage future studies to consider using a similar multivariate approach in coastal spatial analysis, and to include unrelated tracers that reflect distinct coastal influences.

Heavy metal distribution, contamination and analysis of sources - Intertidal zones of Sandu Bay, Ningde, China.

Concentrations of heavy metals in sediments and seawaters from the intertidal zone are analyzed along with cage-bred fish in the Sandu Bay of Fujian Province in China. Elements measured are As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn. The concentrations of Cu and Ni found in the sediments do not meet the first standard of the Chinese National Criteria for Marine Sediment Quality. The results of Igeo, EF, and CF index calculations for the sediment samples clearly prove anthropogenic causes of contamination. The water quality standard for fisheries was exceeded by As, Hg, and Cu. Cage-bred fish show increased levels of As, Cr, and Zn. Significant associations are found for AsCu and NiZn. These findings can be related to coal and crude oil combustion and processes associated with the production of batteries, steel, and alloys. The results point to industrial source locations along discharging rivers north and northwest of the Sandu Bay.

Simulated conservative tracer as a proxy for S-metolachlor concentration predictions compared to POCIS measurements in Arcachon Bay.

The work presented here aims at comparing monitoring of S-metolachlor, the major pesticide in use in the Arcachon Bay (South West of France, transitional coastal area), by chemical analysis (monthly passive sampling) and contaminant dissipation modeling from sources (Mars-2D model). The global strategy consisted in i) identifying the major sources of S-metolachlor to the Bay, ii) monitoring these sources for 12 months, and iii) comparing modeled data in the Bay based on measured inputs, to chemical measurements made inside the Bay along with the 12-month source monitoring. Results first showed that the major S-metolachlor surface inputs to the Arcachon Bay are mainly from one single source. Modeled and measured data were in good agreement at 5 sites in the Bay, both in terms of concentration range and seasonal trends. Modeling thus offers a cost-effective solution for monitoring contaminants in transitional waters, overcoming in addition the technical limitations for measuring pg L-1 or lower levels in coastal waters. However, we highlighted that secondary sources may affect accuracy at local level.

Assessment of trace metals contamination in surficial sediments along Lebanese Coastal Zone.

A Characterization and assessment study was conducted for trace metals pollution in surface sediments at six sites including harbors, bays and river input along Lebanese coast (LCZ). A particular attention was given to Tripoli Port in order to identify the main sources of trace metals pollution inside this harbor. Total metals concentrations were compared with those reported for the shale. The results revealed that trace metals (Cd, Pb, Zn, and Cr) contamination was significantly localized at Beirut Port, which is classified as the most highly polluted site. At Tripoli Port site, metals contamination was classified as moderate; it is affected by shipping, ship maintenance activities and sewage outfall. According to the SQGs guideline, the biological adverse effect of Cd, Pb and Zn were expected to occur frequently at Beirut Port. The results obtained would be helpful in developing more effective harbor management strategies to control and monitor the metal discharges.

An environmental magnetism approach to assess impacts of land-derived sediment disturbances on coral reef ecosystems (Cartagena, Colombia).

We used environmental magnetism methods to study recently deposited marine sediments from the estuarine ecosystems on the Caribbean coast of Colombia. Cartagena region has undergone an increasing sediment load during the last decades via sediment plumes from Magdalena River and its distributary man-made channel. Concentration dependent magnetic parameters show an increasing abundance of ferrimagnetic minerals on the uppermost sediments on sites located close to the continent (remanent magnetization SIRM = 5.4-9.5 × 10-3Am2 kg-1) as well as faraway sites (SIRM = 0.5-1.7 × 10-3Am2 kg-1 near Rosario Islands coral reef complex). The magnetic grain size and mineralogy along the cores are variable, showing the dominance of the magnetite-like minerals (remanent coercivity Hcr = 34.3-45.3 mT), with a minor contribution of high-coercivity minerals (Hcr = 472-588 mT). In addition, there is a moderate enrichment of elements Cu, Mo, and Zn (enrichment factor EF = 1.5-3.8) that indicates the additional land-derived contribution on sediments. The environmental magnetism approach, which shows significant signals of magnetic minerals and trace elements, is a reliable tool to prove the presence of continental sediment supply in coral reef ecosystems.

Fish assemblages in three fringed mangrove bays of Santa Cruz Island, Galapagos Marine Reserve / Ensamblaje de peces en tres bahías con bordes de manglar en la Isla Santa Cruz, Reserva Marina de Galápagos

Abstract Mangrove-fringed bays are highly variable ecosystems that provide critical habitats for fish species. In this study we assessed the fish assemblage in three mangrove-fringed bays (Punta Rocafuerte, Saca Calzón and Garrapatero) in the Southeast side of Santa Cruz Island, Galapagos Marine Reserve. Using gillnets, we carried out a total of 108 fieldtrips from January 2010 to December 2011. A total of 1 773 bony and 740 cartilaginous fishes belonging to 26 species and 15 families were identified at the same sampling sites. Species richness was higher in the protected bay (Garrapatero) than in those open to fishing (Punta Rocafuerte, Saca Calzón). Blacktip sharks (Carcharhinus limbatus, n= 729), Thoburn's mullets (Mugil thoburni, n= 492), Peruvian mojarras (Diapterus peruvianus, n= 440), milkfish (Chanos chanos, n= 206) and the yellow fin mojarras (Gerres cinereus, n= 197) were the most common species across sites and season (cold and warm). The abundance of the most common species varied seasonally, with C. limbatus and C. chanos being more abundant in the warm season (December to April), and M. thoburni, C. limbatus and G. cinereus in the cold season (June to October). Temperature was the most important driver of abundance in C. limbatus and C. chanos, while salinity influenced Umbrina galapagorum. This study represents the first evaluation of the fish assemblage composition and dynamics in mangrove-fringed bays in the Galapagos Marine Reserve. Rev. Biol. Trop. 66(2): 674-687. Epub 2018 June 01.

Resumen Las bahías de manglar son ecosistemas muy variables que proveen hábitats críticos para especies de peces. En este estudio se evaluó los ensamblajes de peces de tres bahías de manglar (Punta Rocafuerte, Saca Calzón y Garrapatero) ubicadas en el sureste de la isla Santa Cruz, Reserva Marina de Galápagos. Usando redes de trasmallos iguales a los usados por la pesca artesanal, se llevaron a cabo un total de 108 salidas de campo entre enero 2010 y diciembre 2011. Un total 1 773 peces óseos y 740 peces cartilaginosos correspondiendo a 26 especies y 15 familias fueron capturados, identificados y liberados con vida. La riqueza de especies fue mayor en Garrapatero (sitio protegido) que en Punta Rocafuerte y Saca Cazón (sitios abiertos a la pesca). Las mayores capturas estuvieron representadas por el tiburón punta negra (Carcharhinus limbatus; n= 729), seguido la lisa rabo negro (Mugil thoburni; n= 492), la mojarra peruana (Diapterus peruvianus; n= 440), la diabla (Chanos chanos; n= 206) y la mojarra rayada (Gerres cinereus; n= 197). A pesar que éstas especies fueron consistentemente las más importantes a través de los sitios y temporadas (caliente y fría), se observó una mayor abundancia de C. limbatus y C. chanos durante la temporada caliente (enero a abril), y de M. thoburni, C. limbatus y G. cinereus durante la temporada fría (junio a octubre). La temperatura fue determinada como el factor más importante que influye en la abundancia de C. limbatus y C. Chanos, mientras la salinidad lo fue para Umbrina galapagorum. Este estudio representa una importante contribución para el entendimiento de la composición de los ensamblajes de peces en las bahías de manglar de la Reserva Marina de Galápagos.

Determining representative ranges of point sensors in distributed networks.

Distributed networks of stationary instruments provide high temporal scope (i.e., range/resolution) observations but are spatially limited as a set of point measurements. Measurement similarity between points typically decays with distance, which is used to set interpolation distances. The importance of analyzing spatiotemporal data at equivalent spatial and temporal scales has been identified but no standard procedure is used to interpolate space using temporally-indexed observations. Using concurrent mobile and stationary active acoustic, fish density data from a tidal energy site in Puget Sound, WA, USA, six methods are compared to estimate the range at which stationary measurements can be spatially interpolated. Four methods estimate the representative range of the mean using autocorrelation or paired t-test and repeated measures ANOVA. Accuracy of resulting sensor density estimates was modeled as departures from interpolated linear and aerial estimates. Two methods were used to estimate representative range of the variance by comparing theoretical spectra or by determining equivalent spatial and temporal scales. Representative ranges of means extended from 30.57 to 403.9 m. Estimation error (i.e., standard deviation) ranges of linearly interpolated or aerially extrapolated values ranged from 42.5 to 82.3%. Representative ranges using variance measurements differed by a factor of approximately two (scale equivalence = 648.7 m, theoretical = 1388.1 m). A six-step decision tree is presented to guide identification of monitoring variables and choice of method to calculate representative ranges in distributed networks. This approach is applicable for networks of any size, in aquatic or terrestrial environments, and monitoring the mean or variance of any quantity.

Determination of phthalate esters in seawater of Chabahar Bay using dispersive liquid-liquid microextraction coupled with GC-FID.

Phthalate esters (PEs), a group of environmental pollutants which are possibly carcinogenic to humans, have been detected in seawater. Seven PEs in seawater were quantitatively determined by using gas-chromatography flame ionizing detection after executing dispersive liquid-liquid microextraction. The suggested method is optimized for microextraction and determination of PEs in artificial sea water. Factors affecting the microextraction procedure such as the type and volume of extracting and dispersive solvents (carbon tetrachloride, 20 µL; methanol, 0.5 mL), extraction time and pH (7) were investigated. Under optimum conditions, the limit of detection of the analytes were obtained between 0.04 and 4.52 µg·L-1, and linearity and linear range were of 0.999 ≥ R2 ≥ 0.994 and 10-560 µg·L-1 respectively. Enrichment factors were found in the range of 761-827 fold, while the relative standard deviations of the analytes were between 0.17 and 7.5% (n = 6) for real sea water samples. Using this method, total PEs content of seawater from several locations in Chabahar Bay (the southeast part of Iran) was estimated 2.33-90.45 µg·L-1.

A novel approach to evaluate potential risk of organic enrichment in marine aquaculture farms: a case study in Sanggou Bay.

A novel approach was proposed to evaluate the potential risk of organic enrichment in marine aquaculture farms without obvious environmental degradation. The approach was based on historical environmental records preserved in sediment cores, and potential risk of organic enrichment can be effectively evaluated by comparing burial fluxes of marine organic carbon (OCM) during times before and after large-scale aquaculture. A case study was conducted in Sanggou Bay. The change trends on burial fluxes of organic carbon in sediment over the past 150 years were rebuilt. OCM burial fluxes have greatly increased since the beginning of large-scale aquaculture in 1980s, reaching 16.0~16.5 times higher than that before large-scale aquaculture. The results indicate that aquaculture activities have resulted in obvious accumulation of aquacultural organic matters, although sedimental environment has not degraded seriously. Besides, if the OCM burial fluxes further increase to 3.5~7.0 times higher than that in present, sedimental environment may degrade obviously. Therefore, potential risks of organic enrichment still exist with aquaculture development in Sanggou Bay.

Modeling the exposure time in a tidal system: the impacts of external domain, tidal range, and inflows.

Exposure time is an important characteristic for hydrodynamics that has simultaneous impacts on the biochemical processes in tidal systems. To eliminate man-made errors, decrease computational effort, and increase simulation efficiency, exposure time was evaluated under different hydrodynamic conditions for a bay to investigate the impact of the external domain on the accuracy of the computational results for exposure time. The exposure time was explicitly defined and computed using a hydrodynamic model and tracer experiments for a set of ten external domain sizes (EDS), five external domain lengths (EDL), and three special hydrodynamic conditions. The results indicated that the external domain had a significant influence on the exposure time, and the intensity of this influence was related to hydrodynamic conditions. The sensitivity of the exposure time to the external domain increased with increasing tidal range, while freshwater inflows decreased this sensitivity. However, the variation trends for exposure time with different EDS and EDL were independent of the hydrodynamic conditions. Considering the computational efficiency (maximum), the calculated error (minimum) of the exposure time, and the impact of the boundary conditions (minimum), the recommended EDS and EDL range from 9 to 13 times the initial domain size and 1.30 to 1.45 times the length in the bay, respectively. The research regarding exposure time and external domains not only helps to eliminate the errors caused by man-made factors and reduce the computational effort but also provides a reference for understanding the interrelationship between coastal waters, reciprocating flow, and the water environment.

Anthropogenic activities and coastal environmental quality: a regional quantitative analysis in southeast China with management implications.

Regional analysis of environmental issues has always been a hot topic in the field of sustainable development. Because the different levels of economic growth, urbanization, resource endowments, etc. in different regions generate apparently different ecological responses, a better description and comparison across different regions will provide more valuable implications for ecological improvement and policymaking. In this study, seven typical bays in southeast China that are a rapid developing area were selected to quantitatively analyze the relationship between socioeconomic development and coastal environmental quality. Based on the water quality data from 2007 to 2015, the multivariate statistical method was applied to analyze the potential environmental risks and to classify the seven bays based on their environmental quality status. The possible variation trends of environmental indices were predicted based on the cross-regional panel data by Environmental Kuznets Curve. The results showed that there were significant regional differences among the seven bays, especially Quanzhou, Xiamen, and Luoyuan Bays, suffered from severer artificial disturbances than other bays, despite their different development patterns. Socioeconomic development level was significantly associated with some water quality indices (pH, DIN, PO4-P); the association was roughly positive: the areas with higher GDP per capita have some worse water quality indices. In addition, the decreasing trend of pH values and the increasing trend of nutrient concentration in the seven bays will continue in the foreseeable future. In consideration of the variation trends, the limiting nutrient strategy should be implemented to mitigate the deterioration of the coastal environments.