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[Display omitted] • The water column showed dominance of absorption with maximum Chl-a concentration. • Scattering was dominated in water with maximum TSM. • CDOM and Chl-a showed non-conservative behavior during the pre and post ISM seasons. • Stratification plays a significant role in determining the bio-optical properties. Using ten years of in-situ data from a shallow optically complex coastal ecosystem, this study unravels the coupling between bio-optical variability and seasonally changing hydrography. The data presented is novel, as these are long-term simultaneous measurements of bio-optical properties and constituents covering a wide range of hydrographic conditions at different sampling stations in riverine, estuarine, and coastal shelf. The data represent all three seasons experienced in the region, i.e., Indian Summer Monsoon (ISM), post-ISM, and pre-ISM. It allowed us to conduct a baseline study to characterize the bio-optical variability (absorption or scattering dominated) coupled with stratification for remote sensing applications on ecological health. Four groups of sampling stations, representing varying hydrography, were identified as riverine, maximum stratification, maximum chlorophyll-a (Chl-a) concentration, and estuarine/shelf. The maximum concentrations of total suspended matter (TSM) were always collocated with the strongest stratification site, while maximum Chl-a was always located downstream of maximum stratification. Surprisingly, colored dissolved organic matter (CDOM) values were negligible in the ISM season and increased manifold in other seasons. The source of CDOM (either land-derived or in situ generated) inferred from the spectral slope revealed the dominance of land-derived CDOM in the post-ISM season. Combining the entire data into the same groups showed that groups with maximum TSM and samples from estuarine locations were scattering-dominated. In contrast, the group with maximum Chl-a was absorption dominated. The analysis revealed that the optical behavior of the sampling locations being either absorption or scattering dominated depended on the state of stratification and contribution of Chl-a to the absorption budget. [ABSTRACT FROM AUTHOR]

In the present study, it was analyzed the structure of mesozooplankton community, and their spatio-temporal variations along the Caeté River estuary (northeast of Pará, Brazil). Samples were collected during spring tides conducted in nychthemeral cycles, in three fixed sectors located along the studied estuary (inner-S1, middle-S2 and outer-S3), using conical plankton nets of 200 μm mesh size. Samplings were performed in September 2014 (dry season) and March 2015 (rainy season), totaling 54 samples. A total of 25 mesozooplankton species were recorded, being the copepods the most diversified group (21 species), mostly dominated by estuarine and coastal species. The most abundant mesozooplankton species presented significantly higher densities (p <0.0001) between the middle (Pseudodiaptomus richardi , 583.8±956.5 ind m−3, Paracalanus quasimodo, 108.9±181.4 ind m−3 and Pseudodiaptomus acutus, 23.4±66.6 ind m−3) and outer (Acartia tonsa, 476.9±1,298.8 ind m−3 and Acartia lilljeborgii (407.9±1,038.1 ind m−3 and Parasagitta tenuis , 59.9±117.1 ind m−3) sectors. The non-metric multidimensional ordination analysis highlighted that the average density of the main species varied mainly at a spatial scale, with density increasing toward the mouth of the estuary (except for P. richardi). Spearman's correlation (rs) demonstrated that the salinity, turbidity, dissolved nutrients and chlorophyll a concentrations were the prevailing environmental variables associated with significant spatial changes of mesozooplankton distribution in this area. Overall, the results showed that spatial variation in the water physicochemical characteristics of the Caeté Estuary have significant effects on the structure and succession of the mesozooplankton, which may potentially affect the functioning and biodiversity of this coastal ecosystem. [ABSTRACT FROM AUTHOR]

A massive fish mortality of the major species, viz., Mugil cephalus, Chanos chanos , and Oreochromis mossambicus , occurred on November 27, 2017 in the Adyar estuary. This catastrophe followed a spell of heavy rainfall and flash floods. A detailed study of water quality parameters (pH, water temperature, salinity, total suspended matter, dissolved oxygen, biochemical oxygen demand, and nutrients) and heavy metals, i.e., chromium (Cr), copper (Cu), cadmium (Cd), nickel (Ni), lead (Pb), and zinc (Zn), in the sediment and fish tissues were analyzed. Pollution indices like the enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), pollution load index (PLI), potential ecological risk index (PERI), and biota sediment accumulation factor (BSAF) were used to measure heavy metals. The pollution indices revealed that metals were significantly enriched in the sediments. The Igeo indicates that there was moderate contamination by Cd (2.27–3.25), whereas CF shows high contamination by Cd (7.22–9.72) and moderate contamination by Pb (2.5–3.25). The PLI (1.04–1.13) suggests that heavy metal contamination of sediments has occurred. Results showed that high concentrations of the toxic metals Pb and Cd were found in the sediment as well as in fish tissues. Length and weight of fish are significantly correlated (r2 = 0.98, p < 0.05). The study revealed that the mass fish kill was due to impulsive changes in the water quality and heavy metal pollution from untreated urban sewage discharges in this region. • Factors related to fish kills in the tropical estuary are investigated. • Cd and Pb toxicity found in the sediment and fish tissue. • The proximate cause of fish kills was due to metal pollution. • Monitoring on a seasonal basis is required in coastal waters. [ABSTRACT FROM AUTHOR]

Microbial mediated nitrogen (N) transformation is subject to multiple controlling factors such as prevailing physical and chemical conditions, and little is known about these processes in sediments of wet-dry tropical macrotidal systems such as Darwin Harbour in North Australia. To understand key transformations, we assessed the association between the relative abundance of nitrogen cycling genes with trophic status, sediment partition and benthic nitrogen fluxes in Darwin Harbour. We analysed nitrogen cycling gene abundance using a functional gene microarray and quantitative PCRs targeting the denitrification gene (nosZ) and archaeal ammonia oxidation (AOA.1). We found a significant negative correlation between archaeal ammonia oxidation and silicate flux (P = 0.004), an indicator for diatom and benthic microalgal activity. It is suggested that the degradation of the diatomaceous organic matter generates localised anoxic conditions and inhibition of nitrification. Abundance of the nosZ gene was negatively correlated with nutrient load. The lowest nosZ gene levels were in hyper-eutrophic tidal creeks with anoxic conditions and increased levels of sulphide limiting the coupling of nitrification-denitrification (P = 0.016). Significantly higher levels of nosZ genes were measured in the surface (top 2 cm) compared to bulk sediment (top 10 cm) and there was a positive association with di-nitrogen flux (N 2) in surface (P = 0.024) but not bulk sediment. This suggests that denitrifiers are most active in surficial sediment at the sediment-water interface. Elevated levels of nosZ genes also occurred in the sediments of tidal creek mouths and mudflats with these depositional zones combining the diffuse and seaward supply of nitrogen and carbon supporting denitrifiers. N-cycle molecular assays using surface sediments show promise as a rapid monitoring technique for impact assessment and measuring ecosystem function. This is particularly pertinent for tropical macrotidal systems where systematic monitoring is sparse and in many cases challenged by climatic extremes and remoteness. [Display omitted] • Functional gene array applied to marine sediment and water enables identification of functionally relevant N cycle genes • NosZ qPCRs for surface sediments show promise as a monitoring tool to differentiate the trophic status of sediments • Relative abundance of nitrogen cycling genes are responsive to nutrient status and sediment partition • N-cycle molecular assays using surface sediments show promise as a rapid monitoring technique [ABSTRACT FROM AUTHOR]

This study aims to explore microplastic contamination in the sediments of Benoa Bay. Eight locations were sampled, with four duplications denoting the rainy and dry seasons. Based on observations, the microplastic concentration varied from 9.51 to 90.60 particles/kg with an average of 31.08 ± 21.53 particles/kg. The area near the landfill had the highest abundance, while the inlet and center of Benoa Bay and the Sama River had the lowest concentration. The fragments (52.2 %) and large microplastic sizes (64.7 %) were the most documented particles. We also identified 17 polymers, which dominated (37.5 %) by polyethylene, polypropylene, and polystyrene. There were no appreciable variations in abundance between seasons, although there were substantial variations in shape and size. Comprehensive investigation, adequate policies, continuous monitoring, and reducing waste from land- and sea-based sources that engage various stakeholders must be implemented urgently to prevent the release of microplastic into the aquatic ecosystem. [Display omitted] • Sediment In Benoa Bay was contaminated by microplastic. • Microplastics at Benoa Bay are dominated by secondary microplastics. • Strong positive correlation between the microplastic in sediment and water. • Landfill, rivers, and mariculture suspected as a source of microplastics. [ABSTRACT FROM AUTHOR]

The present study aimed to assess the water quality dynamics (physicochemical properties, nutrient and chlorophyll–a) in the Netravathi-Gurupur estuary, India across the space and seasons and to simplify the complex water quality dataset through a chemometric approach. The results indicated that pH, EC, temperature, alkalinity, salinity, TDS, hardness, chloride and intense mixing of suspended solids, driven by the semidiurnal tides, are the major factors affecting water quality. Spatial heterogeneity and monsoon have profound impact on nutrient distribution revealing the following values (mg l−1): phosphate-P (0.015–0.105), nitrate-N (0.016–0.094), nitrite-N (0.001–0.012), and silicate (1.83–14.50). The estuary was evaluated for suitability for brackish water fisheries. The results indicated fair water quality during pre- and post-monsoon but marginal quality in monsoon, primarily due to dilution associated with reduced salinity. The outcome of this study can be suitably utilized for the sustainable development of estuaries and their feasibility for brackish water fisheries. [Display omitted] • Surface water quality was investigated for Netravathi-Gurupur estuary, India. • Chemometric analysis indicated higher pollution load in Gurupur stretch. • Water quality index suggested fair to marginal quality for brackish water fisheries. • Study is useful to develop sustainable environmental and fisheries management plans. [ABSTRACT FROM AUTHOR]

Abstract Sedimentary organic matter (SOM) plays an important role in hosting and reducing HgII in marine/estuarine sediment. This study provides a better understanding on the influence of nature of SOM, in regulating sedimentary mercury (Hg) and elemental mercury (Hg0) distribution, and speciation in the Zuari and Mandovi Estuaries that are representative of monsoon fed tropical estuaries, located in the central west coast of India. Salinity of the overlying water column controlled the physical and chemical characteristics of SOM in the estuarine systems. The high molecular weight (MW) SOM dominated at the mid and upstream (low salinity region) of the estuaries, whereas, the low MW SOM prevailed at the downstream (high salinity region). Sediment Hg showed more affinity towards the SOM of high MW. Increasing MW of SOM increased total sedimentary Hg T in both the estuaries. SOM with low MW in the estuarine sediment displayed a negative relationship with the sediment Hg concentration. Distribution of Hg0 concentration in the estuarine sediment suggests that reduction of HgII in presence low MW SOM was a dominant process. It was also found that distribution and speciation of Hg0 in the estuarine sediment depends on the quantity, quality of the SOM, and the total sediment Hg loading. This study demonstrated that the competition between Hg-SOM complexation and HgII reduction by SOM controls HgII/Hg0 distribution in tropical estuarine sediment systems. Graphical abstract Unlabelled Image Highlights • The biogeochemical cycling of Hg in estuarine sediment was investigated. • Quantity and quality of SOM controlled dispersal of Hg T in estuarine sediment • High MW-SOM > at middle and upstream locations, >low MW downstream • Hg preferentially adsorbed to SOM of high MW, Hg0 > with low MW • Competition between HgII reduction and complexation by SOM control Hg T [ABSTRACT FROM AUTHOR]

Abstract Sampling strategies and methodological procedures are a theme of discussion in all areas of Science, considering their potential impacts on results, interpretations, and conclusions. In the case of ecological studies based on recent foraminifera, most of papers vary on collecting single samples or replicates, on counting living and/or dead assemblages, and on the depth of the sediment layer collected. In this study we discussed the implications of the following questions, especially in the intertidal zone of a tropical estuary: (i) Do collecting a single sample or replicates affect results and interpretations? (ii) Are there differences in results and interpretations generated from counting living (stained) or dead assemblages?; and (iii) Do varying the sampling depth of sediment layers influence the results and interpretations? We defined three collection points along the mangrove margins associated to the Itapanhaú River (Bertioga, State of São Paulo, Brazil). In each point, we drilled three microcores with the depth of 20 cm, laterally distant 30 cm from each other. In each microcore sediment samples (3 mL) were extracted in the layer intervals of 0–1, 4–5, 9–10, 14–15, and 19–20 cm. Foraminifera from all the samples were compared regarding absolute abundances, species composition, diversity, evenness and, communities similarities. We observed that replicates produce better results than single samples, both for the living and dead assemblages. Pseudoreplication simulation produced divergent results. Replicates make possible the application of more accurate inferential statistical analysis because the spatial variations of the species are captured. There were significant differences in ecological indicators and respective interpretations between analyzes based on counting living and dead assemblages so that they should not be considered directly comparable to each other. Counting living foraminifera requires higher effort for collecting and picking tests to reach the statistical minimum recommended. Regarding sampling depth, the first centimeter seems to be sufficient to find the vast majority of living foraminifera, mainly to estimate species richness. However, thicker sediments result in a longer time interval integrated into the sample, so the time-scale and variables that control foraminifera may change for interpretation. Our findings are consistent with previous studies carried out in subtropical estuaries, also expanding methodological recommendations to tropical estuaries. Future studies should explore the best distances among replicates. Highlights • Methodological issues were mostly assessed in subtropical environments; only a few report data from tropical estuaries. • Replicates are better than single samples, producing more accurate results. • Pseudoreplication procedure should never be adopted as sampling strategy. • Ecological indicators based on living and dead assemblages differ significantly. • The uppermost centimeter of sediment seems to be enough to estimate species richness. [ABSTRACT FROM AUTHOR]

Abstract Estuaries are highly productive ecosystems, defined by salt-freshwater exchanges that are significantly altered by changes upstream and in adjacent coastal areas. Tropical estuaries are characterized by the periodic advance and retreat of saline intrusion, depending on seasonality, episodic river flows and flooding events. Salt-water intrusion due to the estuarine dynamics might be affected by dam systems, which could modify the hydrological regime of the estuary in relation to other stressors, such as land use changes. For this purpose, field measurements of salinity, temperature, river-discharge and flow velocities were conducted over a year to analyze the current hydrological regime in the upper estuary of the Grijalva River in the southern Gulf of Mexico, part of the Biosphere Reserve "Pantanos de Centla", one of the most biodiverse areas in the world. Analysis of land use and vegetation cover was performed. Historical implications of the hydrological performance of the four-dam system (1957 to 2014) are presented, together with the upstream-induced changes (i.e. discharge and seasonal water volumes variations): before, between and after the full operation of the dam system. A general loss of seasonality in the river discharge was identified (1974–1987), when critical mean annual water discharges were registered (Q mean from 263.56 to 126.49 m3/s). Chronological changes in the estuary and in the surrounding area due to the introduction of large extensions of cultivated grassland (~1020 km2), reduction in mangrove cover (~223 km2) and tular (~1340 km2) were noticed. These modifications mostly occurred before conservation strategies were implemented, such as the designation of the Biosphere Reserve (1992). This study contributes to a better understanding of the response of estuarine systems to anthropic perturbations and the development of long-term management plans that could take into account climate change and the increase of hydropower development. Graphical abstract Unlabelled Image Highlights • An upper-estuary in Southern Gulf of Mexico is analyzed through field measurements. • Characterization of the current seasonal dependency of the salt-wedge is provided. • Dam implications on salt-wedge and land use changes are identified. • Loss on hydrological seasonality is the major direct impact to the upper-estuary. • System-stress is induced by cultivated grasslands despite conservation policies. [ABSTRACT FROM AUTHOR]

Abstract Understanding the variability in organism's immunological response is crucial for predicting changes at population or community level. The present study investigated the immunoecology of a commercially valuable clam Paphia malabarica in a tropical monsoon-influenced estuary. Clams were collected monthly during a year cycle, which coincided with pre-monsoon (February–May), monsoon (June–September) and post-monsoon seasons (October–January). For assessment of immune functioning, selected hemocyte parameters (total hemocyte concentration, hemocyte mortality, lysosomal content, esterase activity, reactive oxygen species production, and phagocytic activity) were analyzed using flow cytometry. Simultaneously, clam's condition index, nutrients, chlorophyll a , dissolved oxygen, pH, temperature and bacterial density were also measured at the sampling site. Our results exhibited seasonal patterns in hemocyte functioning with the highest activity during the pre-monsoon season (suggestive of a suitable harvesting period) and lowest during monsoon (suggestive of a critical biological period). The critical biological period for P. malabarica was marked with compromised immune parameters inflicted by low salinity, food availability, and possibly high bacterial abundance. Also, the involvement of reproductive stress altering the hematological functioning in P. malabarica cannot be ruled out. Nutrients, dissolved oxygen, pH and temperature could not explain much of the hemocyte variability. The present study has further validated the usefulness of hemocyte as a suitable marker for understanding immunoecology of P. malabarica which is of prime importance, especially in a monsoon-influenced tropical estuarine environment. The findings of our research will be constructive in monitoring natural as well as cultivated bivalve populations of economic and ecological relevance. Highlights • Immunoecological investigation of a commercially valuable clam Paphia malabarica in a tropical monsoon-influenced estuary. • Seasonal pattern in hemocyte functioning influenced by environmental as well as physiological factors. • The compromised immune parameters during monsoon suggestive of a critical biological period. • Improved hematological activity during pre-monsoon season suggestive of a suitable harvesting period. [ABSTRACT FROM AUTHOR]

Abstract The trophic structure of a community is used to infer ecosystem functioning (e.g. energy transfer and nutrient cycling). Here the trophic structure of the benthic infaunal and epifaunal communities in the Brunei Estuary are characterized, and their distribution along an estuarine pH gradient is analyzed using univariate and multivariate techniques. This analysis revealed that surface deposit feeders (e.g., polychaetes) were numerically dominant within the infaunal communities whereas in the epifaunal communities filter feeders (e.g., bivalves) were highly abundant. Species richness for almost all trophic groups increased toward the lower estuary, except for omnivores in the epifaunal communities, which decreased markedly. Both Analysis of Variance (ANOVA) and Analysis of Similarities (ANOSIM) detected significant differences in the density of respective trophic groups among stations. Within infaunal communities, both Biological and Environmental procedure (BIO-ENV) and Canonical Correspondence Analysis (CCA) showed that trophic shifts were associated with environmental gradients. Surface-deposit feeders and omnivores were the most abundant macrobenthos of the upper estuary characterized by low salinity, low pH, and a higher percentage of mud particles. The proportion of filter feeders and carnivores increased with salinity/pH and sand. A more uniform distribution of trophic structure was found in the lower estuary, with high salinity and pH over sandy habitat. In contrast, within epifaunal trophic groups, the percentage of surface deposit feeders and omnivores declined, but filter feeders remarkably increased toward the sea. The proportion of carnivores remained similar at all stations. Non-Metric Multidimensional Scaling (nMDS) ordination for epifaunal trophic groups clearly demarcated higher salinity/pH stations from lower salinity/pH stations, suggesting different trophic compositions along the estuarine pH gradient. [ABSTRACT FROM AUTHOR]

Globally, a key ecosystem service provided by sedimentary estuarine habitats is the regulation of nutrient cycles. The nitrogen (N) cycle is driven by complex biogeochemical transformations within these sediments—including nitrogen fixation, denitrification, assimilation and anaerobic ammonia oxidation—mediated by microorganisms. Evaluating ecosystem processes and their functional value is a knowledge gap for the wet-dry tropics and even more limited for macrotidal estuaries. The capacity of these important environments to withstand and assimilate increasing nitrogenous loads as a consequence of accelerating development pressures in tropical Australia is largely unknown. Because of the critical role nitrogen cycling plays in estuarine ecosystems, identifying important habitats that underpin N cycling, particularly denitrification known to mitigate anthropogenic N inputs, is important. Detailed benthic habitat mapping of the Darwin-Bynoe region of northern Australia has provided a rare opportunity to demarcate its key habitats, such as intertidal mudflats, seagrass, mangroves, reef and saltmarsh. Combined with new measurements of benthic nitrogen fluxes, it has been possible for the first time to map these processes and develop a simple integrated functional value for N cycling across key benthic habitats of a tropical macrotidal estuary. Maps generated in this process have provided broadscale identification of the functional importance of habitats with relevance to N removal processes. The role of intertidal sediments in denitrification has been highlighted. Furthermore, the study emphasises connectivity across benthic seascapes, where multiple services are likely to interact, in supporting overall function and ecosystem health. The distillation of composite processes in this mapping format allows resource managers and scientists to communicate outputs visually with a simple classification scheme which could be superimposed with additional data to support environmental assessment and management. • Denitrification hot spots that provide important ecosystem services were identified and mapped. • Intertidal habitats provide valuable zones for biogeochemical processes in the wet-dry tropics. • Connectivity across benthic seascapes is critical for preserving the interaction of multiple ecosystem services. • Mapping tools facilitate management and conservation decisions. [ABSTRACT FROM AUTHOR]

We developed an Ecopath model for the Estuary of Sirinhaém River (SIR), a small-sized system surrounded by mangroves, subject to high impact, mainly by the sugar cane and other farming industries in order to describe the food web structure and trophic interactions. In addition, we compared our findings with those of 20 available Ecopath estuarine models for tropical, subtropical and temperate regions, aiming to synthesize the knowledge on trophic dynamics and provide a comprehensive analysis of the structures and functioning of estuaries. Our model consisted of 25 compartments and its indicators were within the expected range for estuarine areas around the world. The average trophic transfer efficiency for the entire system was 11.8%, similar to the theoretical value of 10%. The Keystone Index and MTI (Mixed Trophic Impact) analysis indicated that the snook ( Centropomus undecimalis and Centropomus parallelus ) and jack ( Caranx latus and Caranx hippos ) are considered as key resources in the system, revealing their high impact in the food web. Both groups have a high ecological and commercial relevance, despite the unregulated fisheries. As result of the comparison of ecosystem model indicators in estuaries, differences in the ecosystem structure from the low latitude zones (tropical estuaries) to the high latitude zones (temperate system) were noticed. The structure of temperate and sub-tropical estuaries is based on high flows of detritus and export, while tropical systems have high biomass, respiration and consumption rates. Higher values of System Omnivory Index (SOI) and Overhead (SO) were observed in the tropical and subtropical estuaries, denoting a more complex food chain. Globally, none of the estuarine models were classified as fully mature ecosystems, although the tropical ecosystems were considered more mature than the subtropical and temperate ecosystems. This study is an important contribution to the trophic modeling of estuaries, which may also help the knowledge of the role of key ecosystem processes in SIR. [ABSTRACT FROM AUTHOR]

The present study evaluated the origin and distribution of polycyclic aromatic hydrocarbons (PAHs) and the organic matter (OM) in the surface sediment of the São Paulo River estuary, Todos os Santos Bay (TSB), Brazil. The samples were collected in the rainy (CP1) and the dry (CP2) seasons. We analyzed the 16 PAHs from the United States Environmental Protection Agency (US EPA) priority pollutant list, total organic carbon (TOC), total nitrogen (N), and stable carbon isotope (δ 13 C). The total concentration of PAHs ranged from 11.45 ± 1.28 to 1825.35 ± 107.96 ng g − 1 , while TOC ranged from 3.8 to 27.7 g kg − 1 . CP1 showed the highest concentrations for all parameters. The δ 13 C ratio indicated terrigenous OM (− 23.81 to − 26.63‰). The TOC/N ratio (C/N) indicated transitional OM (12.32 to 24.39), in addition to the continental origin. The diagnostic ratios of PAHs origin revealed only pyrolytic source, although close to areas with a history of petroleum contamination. [ABSTRACT FROM AUTHOR]

As the nexus where rivers and oceans meet, estuaries are vulnerable to microplastic (MP) pollution derived from rivers. However, few studies have focused on the pollution status of MPs in small estuarine areas. Here, the abundance and characteristics of MPs in surface water and sediment samples from a small estuary, the Wanquan River estuary, were studied. The average abundance of MPs was 6573 ± 2659 n/m3 in surface water and 1065 ± 696 n/kg dw in sediment samples from the Wanquan River estuary. Most of the MPs in water samples and sediments were red (92.9 % and 88.1 %) fragments (87.4 % and 95.5 %) with sizes <1.0 mm (90.8 % and 92.4 %) made up of antifouling paint particles (APPs) (83.5 % and 89.8 %), respectively. A significant positive correlation (p < 0.01) was found between the concentration of Cu2+ and the abundance of APPs in sediment samples from the Wanquan River estuary. The APPs in the sediments can act as a continuous source of toxic chemicals (e.g., Cu2+) to marine environments. The results of this study expand our knowledge about MP pollution in small estuaries, and the ecological risk of APPs in the Wanquan River estuary to aquatic organisms should not be ignored. [Display omitted] • The abundance and characteristics of MPs in the Wanquan River estuary were studied. • Red antifouling paint fragments with sizes <1 mm were the main constituent of MPs. • MPs abundance in surface water was 1.22–26.2 times higher than that in sediment. • The spatial heterogeneity of MPs was caused by the unique hydrological features. [ABSTRACT FROM AUTHOR]

Transport timescales (TTS), namely residence time and exposure time, were computed for adjacent shallow meso-tidal tropical estuarines system using the Lagrangian model D-Waq Part coupled with the hydrodynamic model Delft3D-Flow, and the Constituent-oriented Age and Residence time Theory, CART. The main results are threefold: (a) The TTS differs more between releases at high or low tide than between those at spring and neap tides. The exposure time was also calculated and found to be larger than the residence time by a few days. (b) The exposure and residence times were used to evaluate the return coefficient ( r ) for different scenarios. As with residence and exposure times, the return coefficient was found to differ more between releases at high or low tide than between those at spring and neap tides. (c) For the Caravelas Estuary, where the river inflow was low (~4 m 3 s −1 ), the residence time was found to be much larger than for the Peruípe Estuary, where the river discharge was greater and nearly constant during the sampling period (~20 m 3 s −1 ). These results shows the importance of advection in decreasing TTS in the Peruípe Estuary compared to the Caravelas Estuary. The influence of the advection and dispersion agrees with previous simple estimates obtained using the newly modified Land Ocean Interaction Coastal Zone (LOICZ) model by Andutta et al. (2014) . [ABSTRACT FROM AUTHOR]

Estuarine ecosystems in SE Asia have been poorly studied when compared to other tropical environments. Important gaps exist particularly in the understanding of their biogeochemical function and contribution to global change. In this work we looked into N-turnover in the water column and sediments of the Bangpakong estuary (13°N). A seasonal sampling program was performed along the salinity gradient covering different stretches of the estuary (68 km). Key physical and chemical characteristics were also monitored in order to unravel possible environmental controls. Results showed the occurrence of active denitrification in sediments (5.7–50.9 nmol N-N 2 /(cm 3 ·hr)), and water column (3.5–1044 pmol N-N 2 /(cm 3 ·hr)). No seasonal or spatial variability was detected for denitrification potential in sediment samples. However, in the water column, the denitrification activity peaked during the transition season in the downstream sites coinciding with high turbidity levels. Therefore, in that period of the year, the water column compartment may be an important contributor to nitrate reduction within the estuary. The rather low nitrification rates detected were not always measurable, probably due to the reduced oxygen content and high siltation. This study is one of the few dealing simultaneously with sediments and water column processes in a highly turbid tropical estuary. Therefore, it emerges as a valuable contribution for the understanding of the dynamics of the nitrogen cycle in tropical environments by exploring the role of estuarine N microbial activity in reducing the effects of increased nitrogen loads. [ABSTRACT FROM AUTHOR]

A comparative study of fish assemblages of a marine protected area and an exploited area was carried out in the Sine Saloum estuary (Senegal, West Africa). Data were collected at these two sites between 2008 and 2011. The two areas are morphologically similar, and comparison of the physicochemical parameters (salinity, transparency, temperature and percentage of saturation of dissolved oxygen) showed that the water masses are similar. The bio-ecological indicators and ecological, trophic and size structures were also compared. Given the environmental similarity of the two sites, their differences in bio-ecological characteristics and fish assemblage organization can be explained by the protection status of the MPA. The species richness and fish abundance per sampling unit were higher in the exploited site, but the mean trophic level and the observed maximum size of individuals were higher in the MPA. Although slightly higher for the MPA, the differences observed for biomass and average size between the two sites were not significant. The beta diversity in the MPA was higher than in the exploited site. The fish assemblage was dominated in terms of abundance by two pelagic herbivores Ethmalosa fimbriata (80%) and Sardinella maderensis (12.3%) and in terms of biomass by E. fimbriata (37.4%) and a benthic predator, Arius latiscutatus (23.7%). The assemblage of the MPA had a marine affinity characterized by the presence of piscivorous or generalist predators; large individuals were not uncommon. In the exploited site, the fish assemblage was relatively stable, dominated in abundance by E. fimbriata (33.4%) and S. maderensis (32.8%). In terms of biomass, a species of mullet, Liza dumerili , ranked first (26.2%), followed by E. fimbriata (22.4%) and S. maderensis (14.9%). The assemblage in the exploited site had a more estuarine affinity, dominated by detritivorous or phytophagous herbivores. Individuals observed there were mostly of small or medium size. This study confirms that the establishment of MPA is an effective tool for restoring marine biodiversity and trophic structure of fish assemblages. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are widely distributed in marine ecosystems, and their ubiquitous presence is raising concern, particularly about possible impacts on fisheries resources. In tropical regions, shellfish fisheries represent an essential source of income and subsistence for traditional communities, and adverse effects on these resources may have severe consequences on human health. In the present study, bivalve molluscs of the species Anomalocardia flexuosa , captured in the region of the Itapessoca estuary in Pernambuco, Brazil, were analysed. A total of 90% of the individuals presented MP particles in their tissue. We observed an average of 5.15 ± 3.80 MP particles per individual, and for each gram of soft tissue, 3.66 ± 2.59 MP particles were found. Our results showed that MPs are present in clams captured on the Pernambuco coast and that the species studied proved to be suitable for monitoring the levels of microplastic pollution. • This is the first record of microplastic in Anomalocardia flexuosa in South America. • Microplastics were present in 90% of the specimens analysed. • For each gram of A. flexuosa soft tissue, 3.66 ± 2.59 microplastic particles were found. • Anomalocardia flexuosa can be used to monitor the levels of MP contamination. [ABSTRACT FROM AUTHOR]

Abstract: The 3-day diurnal dynamics of carbonate system and related parameters on Luhuitou fringing reef of Sanya Bay-adjacent to the South China Sea (SCS) were observed in December of 2009 (early winter), April (spring), July (summer) and November (late-autumn) of 2010. The Luhuitou fringing reef ecosystem was generally dominated by macro and planktonic algae throughout the year except by coralline algae in winter. The system parameters showed distinct diurnal trends in the four seasons. Averaged ranges of diurnal variation for dissolved oxygen and partial pressure of CO2 (pCO2) were higher in the autumn, 4.67mgL−1 and 218.2μatm, respectively than other seasons. Averaged ranges of diurnal variation for normalized total alkalinity (NTA) was higher in the winter (61.3μmolkg−1), and lower in the spring (16.0μmolkg−1). The diurnal variations are mainly controlled by biological activities, especially by the processes of photosynthesis and respiration in the reef ecosystem. In winter, however, calcification and dissolution contributed more to the diurnal variations, compared with the other three seasons. Total alkalinity was largely related to seasonal changes in river inflow rates. Dissolved oxygen, pH, total CO2 and aragonite saturation also showed seasonal variations. These variations were mainly controlled by the seasonal changes of photosynthesis and respiration, which were mainly affected by changes in benthic community structure, temperature and river inflow rates. The oversaturated pCO2 in the reef ecosystem with respect to the atmosphere in the winter and summer resulted in CO2 discharge from the reef ecosystem to the SCS. The whole system served as net source of CO2 to the atmosphere and the adjacent South China Sea on an annual time scale. [Copyright &y& Elsevier]

Abstract: The Hooghly River estuary provides a unique experimental site to understand the effect of monsoonal river discharge on freshwater and seawater mixing. Water samples collected bi-weekly for a duration of 17months were analyzed for salinity, δ18O, δ13CDIC, as well as δD to investigate the differential mixing of freshwater and seawater. The differences in salinity and δ18O of samples collected during low and high tides on the same day are strongly correlated suggesting a well mixed water column at our sampling site. Low salinity and depleted δ18O during monsoon is consistent with increased river discharge as well as high rainfall. We identified different slopes in a δ18O versus salinity plot for the estuary water samples collected during monsoon and non-monsoon seasons. This is driven by composition of the freshwater source which is dominated by rainwater during monsoon and rivers during non-monsoon months. Selected δD analyses of samples indicate that groundwater contributes significantly to the Hooghly Estuary during low rainfall times of the year. δ13CDIC measured in the water recorded low values towards the end of monsoon indicating low productivity (i.e. increased organic respiration) while progressively increasing δ13CDIC values from October till January as well as during some of the pre-monsoon months can be explained by increasing productivity. Very low δ13CDIC (~−20‰) suggests involvement of carbon derived from anaerobic oxidation of organics and/or methane with potential contribution from increased anthropogenic water supply. An estimate of seawater incursion into the Hooghly Estuary at different times of the year is obtained by using salinity data in a two-component mixing model. Presence of seawater was found maximum (31–37%) during February till July and lowest (less than or equal to 6%) from September till November. We notice a temporal offset between Ganges River discharge farther upstream at Farakka and salinity variation at the Hooghly Estuary. We believe that this time lag is a result of the physical distance between Farakka and Kakdweep (our sampling location) and put constraints on the travel time of river water during early monsoon. [Copyright &y& Elsevier]

Abstract: In this work, two field campaigns were performed in July 2008 (wet season) and March 2009 (dry season) to produce original data on the concentration, partition and distribution of mercury and butyltin compounds along the tropical Bach Dang Estuary located in North Vietnam (Haiphong, Red River Delta). The results demonstrate that mercury and butyltin speciation in the surface waters of this type of tropical estuary is greatly affected by the drastic changes in the seasonal conditions. During high river discharge in the wet season, there was a large estuarine input of total Hg and tributyltin, while the longer residence time of the waters during the dry season promotes increasing MMHg formation and TBT degradation. Although most of the Hg and TBT is transported into the estuary from upstream sources, tidal cycle measurements demonstrate that this estuary is a significant source of TBT and MMHg during the wet (∼3kgTBT/day) and dry (∼3gMMHg/day) seasons. [Copyright &y& Elsevier]

Abstract: Breakdown of mangrove litter, adjacent to Hooghly-Matla estuarine ecosystem, plays a major role in regulating the fish population of the estuary. For last several decades, there has been a gradual decline in fish population due to over exploitation of resource but the exact cause of this decrease in production is still not known. To know this cause, an eleven compartment holistic model of nutrient source to estuary and grazing food chain is constructed. Model results depict the role of mangroves in regulating fish population dynamics of the estuary and predation rate of carnivorous fish on detritivorous fish is sensitive parameter in maintaining the balance between grazing food chain and detritus food chain. [Copyright &y& Elsevier]

Abstract: This paper reports for the first time upon the effects of increasing CO2 concentrations on a natural phytoplankton assemblage in a tropical estuary (the Godavari River Estuary in India). Two short-term (5-day) bottle experiments were conducted (with and without nutrient addition) during the pre-monsoon season when the partial pressure of CO2 in the surface water is quite low. The results reveal that the concentrations of total chlorophyll, the phytoplankton growth rate, the concentrations of particulate organic matter, the photosynthetic oxygen evolution rates, and the total bacterial count were higher under elevated CO2 treatments, as compared to ambient conditions (control). δ13C of particulate organic matter (POM) varied inversely with respect to CO2, indicating a clear signature of higher CO2 influx under the elevated CO2 levels. Whereas, δ13CPOM in the controls indicated the existence of an active bicarbonate transport system under limited CO2 supply. A considerable change in phytoplankton community structure was noticed, with marker pigment analysis by HPLC revealing that cyanobacteria were dominant over diatoms as CO2 concentrations increased. A mass balance calculation indicated that insufficient nutrients (N, P and Si) might have inhibited diatom growth compared to cyanobacteria, regardless of increased CO2 supply. The present study suggests that CO2 concentration and nutrient supply could have significant effects on phytoplankton physiology and community composition for natural phytoplankton communities in this region. However, this work was conducted during a non-discharge period (nutrient-limited conditions) and the responses of phytoplankton to increasing CO2 might not necessarily be the same during other seasons with high physicochemical variability. Further investigation is therefore needed. [Copyright &y& Elsevier]

Estuaries provide enumerable ecosystem services to mankind in terms of provisional, regulating, supporting, recreational and information services. However, the persistent human-environment interactions for these services altered the ecological integrity of estuaries. Although the small estuaries receive little attraction in scientific studies due to their low surface area and regional importance, these ecosystems are more vulnerable to anthropogenic pressures and require urgent attention from the scientific fraternity. The Terekhol Estuary (TRE) is a small tropical estuary situated along Goa, west coast of India, gaining recognition in recent years due to the pollution risk from tourism activities. Moreover, the estuary also behaves as an extension of the marine realm during the dry season. The food web structure and network flow indices of the TRE was assessed to reveal its present ecological status. The Ecopath modelling approach was employed to delineate the ecosystem structure and trophic functioning of the estuary distributed in 22 ecological compartments from 2018 to 2019. The trophic level of the food web ranged from detritus (TL-1) to sharks (TL- 4.53). The ecosystem structure demonstrated a grazing chain (herbivory) based organization over the detritus-based pathway. The proportion of exports to the total flows was 35% for the TRE. The model has a high total system throughput (12,043.6 t km−2 year−1), low system omnivory index (0.17) and connectance index (0.21), and a moderate relative ascendency (45.1%). Finn's cycling index (2.17%) indicated very low recycling in the system. All these indicators along with the eco-exergy index (8567.22 g detritus equivalent m−2), specific eco-exergy (38.25) and robustness index (0.11) classified the estuary as be immature, less stable and less organized and is in the initial stages of its development. The ecological indicators analyzed here point towards a medium to a high level of impact in the TRE due to anthropogenic activities. We also highlight the management measures to be implemented in order to restore the ecological quality of the TRE. [Display omitted] • The food web model of a small tropical estuary, Terekhol along the west coast of India was constructed. • A grazing chain based on herbivory followed by detritivory was identified in the estuary. • The estuary is identified as an immature, low recycling and developing ecosystem. • The health and stability indices indicated a less stable and less organized stature of the ecosystem. [ABSTRACT FROM AUTHOR]

The present study aimed to determine the total organic carbon (TOC), total nitrogen (TN), the carbon‑nitrogen ratio (TOC/TN), carbon isotope (δ13C), and nitrogen isotope (δ15N) in five sediment cores collected from upstream to downstream of the Rio Serinhaem estuary, State of Bahia, Northeast Brazil, in order to investigate the origin of the deposited organic matter (OM).Significant positive correlation was found between TOC and NT (r s = 0.75); TOC/TN and TOC (r s = 0.64); δ15N and TOC (r s = 0.72); and δ15N and TOC/TN (r s = 0.63). The values of δ13C and δ15N found are characteristic of terrestrial sources. The TOC/TN ratio confirmed the data found for δ13C and δ15N, which recorded the origin of organic matter from terrestrial C3 type plants. Upstream of the estuary, the highest means of TOC/TN were found (T1 = 36.9 and T2 = 24.4), as reflected by the increase in TOC content or reduction in TN. The OM along the estuary is predominantly from plants with a C3 photosynthetic pattern, indicating that the Serinhaem River estuary is considered a relatively well-preserved environment. [Display omitted] • Grain size does not influence the distribution of TOC in the sediments. • The organic matter on the estuary is predominantly from C3 plants. • The highest TOC and TN values occur close to the city of Ituberá. • The TOC/TN, δ13C and δ15N ratios do not indicate anthropogenic contribution. [ABSTRACT FROM AUTHOR]

Abstract: Experimental estimates of gear selectivity by age used for estimating stock size and measuring fishing impact have been scarcely documented in small-scale fisheries from Latin-America and the Caribbean. In order to improve stock assessment and fisheries management in such fisheries, an experimental approach was designed to estimate the selective performance of the encircling gillnet “boliche” used in the tropical small-scale fishery of the Ciénaga Grande de Santa Marta, Colombia. Similar to covered cod-end hauls, an experimental net was enclosed by a control small-mesh net in 70 hauls. Both contact and available-selection processes affecting the selectivity of the “boliche” were modelled by fitting two selection curves: the logistic (a retention curve) and the encounter-probability (probability that a fish contacts the net) models. The encounter-probability model gave the most appropriate results in terms of the deviance statistic and the lowest Akaike''s Information Criterion. Selectivity parameters were estimated for the main targeted fish species, highlighting differential avoidance reactions to the “boliche” for Eugerres plumieri (0.28), Diapterus rhombeus (0.24), Elops saurus (0.22), Micropogonias furnieri (0.13) and Cathorops spixii (0.16), but not Mugil incilis (all fish retained). To provide an overall (aggregated) effect of the “boliche” on the fish assemblage, the multi-species selection curve showed 61% retention at 15cm, indicating that 39% of the multi-specific component may avoid the “boliche”. [Copyright &y& Elsevier]

Abstract: Rare earth elements (REE from La to Lu), Al and Fe were analysed in 35 surface sediment samples from the Marabasco River-Estuary system, located in the active tectonic zone of Cocos Plate near the active Colima Volcano. The Peña Colorada iron mine is found in the Marabasco watershed and the river sediments are enriched by iron oxy-hydroxides. The average REE content is 86.9±26.8 mg·kg−1 and 95.5±50.3 mg·kg−1 for river and estuarine sediments respectively, which is low in comparison to other tropical coastal systems. The REE light/heavy content ratios (L/H) of Marabasco sediments are also low with averages of 5.2±0.8 (river) and 5.7±0.9 (estuary) due to the minor presence of LREE. The REE signature of the sediment by normalisation with chondrite indicated a slight negative anomaly of Europium and the absence of a Cerium anomaly. REE concentrations in the Marabasco sediments show a strong correlation with Al and Fe, with LREE having a greater affinity for Fe and HREE for Al. This antagonism is REE-ordered by their atomic number sequence in the river sediment case. This has not been previously observed in the environment and the presence of magnetite and the iron oxy-hydroxide enrichment may enhance it. This did not occur in the estuary of the Marabasco mine region where Al and Fe are both well correlated. [Copyright &y& Elsevier]

Abstract: Guanabara Bay (GB) is considered to be one of the most polluted environments of the southern Brazilian coastline. This typical estuarine system is impacted by the heavy discharge of both industrial and domestic waste from the Rio de Janeiro metropolitan area. The mollusc community structure and distribution was investigated between 2000 and 2001, using a three month sampling design of 38 stations, according to austral seasons. Species abundance was aggregated into progressively higher taxa matrices (genus, family, order) and were analysed using multivariate techniques. Mollusc distribution in GB varied significantly in space and time and was probably ruled by the organic enrichment effects of hypoxia and altered redox conditions coupled with prevailing patterns of circulation. Within the sectors of GB an increasing gradient in mollusc diversity and occurrence was observed, ranging from the azoic and impoverished stations in the inner sector to a well-structured community in terms of species composition and abundance inhabiting the outer sector. The non-metric multidimensional scaling (nMDS) and cluster analysis showed similar results when species were aggregated into genera and families, while greater difference occurred at coarser taxonomic identification (order). The literature about taxonomic sufficiency has demonstrated that faunal patterns at different taxonomic levels tend to become similar with increased pollution. In Guanabara Bay, an analysis carried out solely at family level is perfectly adequate to describe the eco-physiological stress. Further aggregation to order level changed the perceived patterns of differences. However, a different taxonomic resolution can be chosen depending on the type of ecological patterns investigated. [Copyright &y& Elsevier]

Abstract: The occurrence of Vibrio cholerae in water, sediment and copepods was studied over a wide range of salinity using conventional and polymerase chain reaction (PCR) techniques in the Cochin backwaters. V. cholerae occurred either as culturable or non-culturable form in this tropical estuary. During the pre monsoon period when high salinity prevailed (35.5psu) V. cholerae was associated with copepods only in non-culturable form, but with the onset of monsoon when lower salinity prevailed, copepod-associated-V. cholerae reverted back to culturable form. The optimum salinity range for culturability was found to be 15–20psu. This points to the fact that salinity is a major factor that which influences V. cholerae’s culturability and its association with copepods in Cochin backwaters. [Copyright &y& Elsevier]

A 200-kHz circular split-beam echosounder (BioSonics, DT6000) was placed in the center of a macrotidal mangrove channel in north Brazil to study the movement patterns of tidal migrating fish. Vertical beaming gave high signal-to-noise ratios (21dB) during neap tides in the dry season 2002. Despite low Secchi depths, a diel change in the vertical target distribution was apparent when fish inhabited the water column only during the night flooding. Moreover, responses in vertical distribution occurred at dusk and dawn. The multispecies population simultaneously caught with a tidal trap consisted of juveniles and adults of small species, and juveniles of larger species (mean total length of fish: 14cm), being reflected in target strength values ranging from -60 to -40dB. Nekton organisms usually traveled with the tide. At low water fish concentrated in the subtidal channel sections, swam slowly and meandered in different directions. At first flood rise—the strongest ambient change—the entire fish population ‘rode the tide’ to immigrate into the intertidal zone, indicated by fast, linear, upstream tracks throughout the water column. At slack high water fish milled around (likely Cetengraulis edentulus and Anchovia clupeoides at night and epibenthic fish in daytime). When sampling the spatiotemporal distribution of fish in intertidal environments, the 3D spatial heterogeneity versus time should be considered. A net upstream longitudinal current together with a regular first flood rise likely promoted retention of fish in this mangrove nursery from one tide to the next. In well-mixed shallow-water environments with a dominant epibenthic fish population, horizontal and vertical beaming should be combined since deeper sections may serve as a refuge for the fish. [Copyright &y& Elsevier]

The distribution of petroleum hydrocarbons and their effects on the periphytic algal biomass using in situ microcosms were investigated in Ponggol estuary located on the northeastern coast of Singapore. Dissolved or dispersed petroleum hydrocarbon (DDPH) concentrations in the surface and bottom waters and absorbed or adsorbed petroleum hydrocarbon (AAPH) concentrations in sediments were monitored from July 1999 to June 2000. Results showed concentrations ranging from 4.42 to 248.94 μg l−1, from 0.35 to 1099.65 μg l−1, and from 20.55 to 541.01 mg kg−1 for DDPH in surface and bottom waters and AAPH in sediments, respectively. Accidental spillages of fuel from dredgers operating in the estuary, fuel and engine oil from recreational boats, shipping operations in the adjacent strait, and runoff monsoon drains in the vicinity were some of the possible sources of petroleum hydrocarbons in the estuary. An assessment of environmentally realistic concentrations of petroleum hydrocarbons on periphytic algal biomass using in situ microcosms revealed signs of acute toxicity. A reduction in periphytic algal biomass (with respect to controls) of 68–93% was observed for various treatments exposed to diesel. [Copyright &y& Elsevier]

Sediments from Guanabara Bay, sampled as short-cores (50–60 cm) from eight stations, were analysed for the elemental (C and N), isotopic (δ13C and δ15N) and molecular composition (steroids) of the organic matter. The objective of this study was to examine whether there are changes in the sources of sedimentary organic matter pool due to increasing N, P and particulate loads to the bay over the last 100 years. On average, we found a 10-fold increase in the flux of organic matter to the sediments with a maximum of 41.7 mol C m−2 year−1. C/N and δ13C time–space distribution and mass balance calculations indicate that the organic material results from a mixture of marine, terrestrial and estuarine sources, with a growing predominance of autochthonous inputs in recent years. Dinosterol was predominant in most samples (>50% of all measured sterols). Concentrations of dinosterol increased significantly in the last two decades and reached values as high as 150 μg g−1 dry sediment. Net increases in concentration were estimated using the first-order decay rate constants derived from experimental data. There are strong indications that an increase in carbon storage occurred in response to growing eutrophic conditions. In spite of the high respiration rates occurring in the water column, fast sedimentation rates result in the transfer of a significant carbon fraction to the anoxic sediments. Further decomposition proceeds only in the first 10 cm of sediment as indicated by the decay rates. [Copyright &y& Elsevier]

The COVID-19 lockdown significantly improved the global environmental quality by restricted anthropogenic activities. We aimed to understand the response of Indian coastal environmental quality and an estuarine (Zuari estuary, central west coast of India) water quality to the lockdown using satellite-derived data sets and in-situ measurements, respectively. The in-situ study was carried out for two weeks (during August and September 2020) to measure chlorophyll- a and macro-nutrients. Recent 5-years (2015–2019; March–August) data sets of aerosol optical depth (AOD), rainfall, air temperature, sea surface temperature (SST), chlorophyll- a , particulate inorganic carbon (PIC) and particulate organic carbon (POC) were compared with lockdown period (2020). The AOD was decreased during the lockdown period (23 ± 11%) as compared with recent 5-years shows the significant impact of lockdown on industrial, transport and urbanization activities. The water quality parameters and chlorophyll- a biomass have remained similar to the past data sets, indicating the insignificant effect of lockdown on these parameters. The results of the case study were compared with the previous reports, which showed a decrease in the concentration of nitrate, phosphate and silicate and comparable concentration of chlorophyll- a. Recent studies show significant impacts of lockdown on the atmospheric parameters and water quality parameters, however the present study did not observe any significant variations in the in- situ and satellite derived data sets of water quality and chlorophyll- a. We have discussed the possible reasons underlying in the less/undetectable response of the chlorophyll- a and water quality of the Indian coastal waters and estuaries during the lockdown. • The satellite derived environmental quality parameters during lockdown (2020) were compared with recent 5-years. • In-situ measurements (nutrients and chlorophyll-a) were compared with past studies. • Aerosol optical depth along the coast was significantly decreased during lockdown. • Nutrients brought by terrestrial runoff neutralize the lockdown impacts on nutrients/pollutants input to the estuary. • There was no significant change in the in- situ and satellite derived chlorophyll- a due to short period of lockdown. [ABSTRACT FROM AUTHOR]

The Serinhaém River estuary is located in the Environmental Protection Area (EPA) of Pratigi, in the State of Bahia, Brazil, which is recognized for being a relatively well-preserved environment. In this work, the levels of aluminum (Al), arsenic (As), barium (Ba), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn) were determined to evaluate the behavior of these chemical elements through geochemical parameters. Eighty-one sediment samples were collected in five sediment cores along the estuarine region. The results of the composition of the Serinhaém river basin showed high levels of Fe, Al, and Mn in the sediment samples. By using Principal Component Analysis, it was observed that 55.8% of the elements have a significant correlation with Fe, Al, and Mn, which may have the same origin or be associated with Fe and Mn oxy-hydroxides, and aluminosilicates. Although Cr, As, and V are correlated with Fe, Mn, and Al, their concentrations are above those established by NOAA, suggesting adverse effects on biota. Barium concentrations increased toward the outfall, where it meets the Camamu Bay, which is naturally enriched with this element. It was also possible to observe that along with the vertical profile, there were no variations in the concentrations of the elements, while along the estuary, it was possible to verify that the cores differ from each other. The estuary of the Serinhaém River can be considered to be influenced relatively little by human activities, and its concentrations can be considered as a base level for this coastal region. Unlabelled Image • The chemical elements in sediment cores do not vary with depth. • Organic carbon did not correlate with all chemical elements. • Most elements have the same origin as Fe, Al, and Mn. • The chemical elements did not correlate with the granulometry of the sediment. • The location of the points is more important than the depth of the estuary. [ABSTRACT FROM AUTHOR]

Analyses of living (L) and dead (D) foraminifera assemblages associated to environmental parameters were applied at the Almada River Estuary, aiming for assessments concerning local biodiversity, hydrodynamic sector and environmental quality. A total of 27 species were identified in the living assemblage and 35 in the dead, with the predominance of Ammonia tepida and Cribroelphium excavatum. A DCA for the living fauna demonstrated that C. excavatum Adelosina milletti, Elphidium discoidade, Rosalina bradyi and Triloculina oblonga were associated to shallow areas with muddy sediment and under marine influence in the estuary. Laryngosigma lactea and Pyrgo oblonga were associated to deep areas with sandy sediment under marine influence. All agglutinated species and the calcareous D. nitida and Miliolinella subrotunda were associated with organic matter and high chlorophyll levels from mangrove areas. A cluster analysis performed for L and D revealed five estuary regions: I - composed predominantly by D transported from the inner shelf; II - composed by L marine species; III - composed by D transported from region II and the inner shelf; IV - composed by living agglutinated species that delimit the beginning of the upper estuary area; and V - composed by transported agglutinated foraminifera and some calcareous species transported during storm episodes The present study was efficient in the environmental characterization of the Almada River Estuary and can be used as a baseline to understand natural or anthropic impacts in this ecosystem. • Evaluation of environmental and ecological conditions in the Almada River Estuary. • Characterization of impacted areas with few or none foraminiferal specimens. • Recognition of bioindicators species of organic matter accumulation. • Identification of pollution and hydrodynamic bioindicator assemblages. [ABSTRACT FROM AUTHOR]

Estuaries receive the anthropogenic pollutants of their watershed area. Dhamra estuary, on the east coast of India, is such an estuary that receives a huge amount of pollutants, and it will eventually pose a threat to the ecological sensitive areas in its vicinity. Therefore, a study was carried out on physico-chemical parameters and chlorophyll- a to delineate the sources of variation during pre-monsoon and post-monsoon seasons. Surface water sampling was carried out from 12 stations in the estuarine and coastal area. Factor analysis and cluster analysis were applied to seasonal data to understand the sources of variation. From the study, it was observed that the chemical parameters are severely affected by anthropogenic influences such as sediment dredging, aquaculture effluent, and waste from industry and sewage from upstream. In the long run, this will affect the nearby nesting ground of vulnerable Olive Ridley turtles, high bio-diverse mangrove forests, and saltwater crocodile habitat. • Nutrient spikes during non-monsoon seasons indicate anthropogenic sources. • The water quality is influenced by aquaculture effluents and dredging activities. • Anthropogenic influence on the coastal water will affect nearby protected areas. [ABSTRACT FROM AUTHOR]

Benthic indices are a potential measure of a system's ecological quality status. It is vital for an efficient index to distinguish the anthropogenic effects from the natural stress associated with seasonality, especially in complex ecosystems such as the tropical monsoonal estuaries. AZTI's Marine Biotic Index (AMBI), one of the most successful indices, relies on the distribution of soft-bottom macrobenthic communities into five different ecological groups (EGs) according to their sensitivity to stress. The AMBI was employed in the anthropized Ulhas estuary (India) to test its vulnerability to seasonality. Also it was endeavored in this study to test whether data transformations enhanced the efficiency of AMBI. AMBI values obtained during monsoon failed to distinguish between differently impacted stations in the major stretch of the estuary due to the uniformly dominant occurrence of Namalycastis ouanaryensis, an EG IV species with affinity for low salinity. The AMBI successfully evaluated the status of the estuary during the non-monsoonal seasons whereas it failed to perform well during the monsoon as it either underestimated or overestimated the ecological quality status of >55% of the stations. The results obtained by averaging the AMBI scores of the non-monsoonal seasons gave an accurate ecological status of the estuary. A good level of agreement between all the applied transformations implied that the data transformations did not improve the AMBI efficiency. Conversely, AMBI based on untransformed data indicated a stronger correlation with the contamination proxies than those derived from various data transformations. Image 1 • Effect of seasonality and transformations on AMBI was studied in tropical estuary. • Monsoonal AMBI failed to discriminate between differently impacted stations. • AMBI successfully evaluated the status of the estuary during non-monsoonal seasons. • Data transformations did not influence the performance of AMBI. [ABSTRACT FROM AUTHOR]