Major Estuaries Research Articles

Distribution, sorption patterns, and outflows of riverine microplastics-affiliated linear alkylbenzenes and polycyclic aromatic hydrocarbons in a dynamic coastal zone.

Microplastics (MPs) pollution has emerged as a global concern. To mitigate the potential threats by MPs, particularly to coastal regions, it is crucial to comprehend the environmental behavior of MPs and their affiliated chemicals. In the present study, we collected floating MPs using a Manta net (0.33 mm mesh size) in a one-year sampling event in 2022 from the eight major estuaries in the Pearl River Delta, China, and also from five coastal sites in August and December in the same year. Nineteen linear alkylbenzenes (∑19LAB) and 16 polycyclic aromatic hydrocarbons (∑16PAH) affiliated with MPs were measured. The mean concentrations of MPs-affiliated ∑19LAB and ∑16PAH were 6710 (range: 3400-12300) and 5310 (range: 817-19,600) ng g-1, respectively, at the estuarine sites, and were 4920 (range: 2400-7600) and 2610 (range: 911-7890) ng g-1, respectively, at the coastal sites. Significant correlations were found between logarithmic MPs-water partition coefficients (log Kpw) and logarithmic suspended particulate matter-water partition coefficients (log Kd) values for LABs and PAHs, indicating analogous partitioning dynamics for MPs and suspended particulate matter with water. The annual riverine outflows were 1170 and 414 g for ∑19LAB and ∑16PAH, respectively. Although the riverine outflows of LABs and PAHs carried by MPs remain negligible compared to those by suspended particulate matter, an upward trend was identified between 2018 and 2022. Notably, the riverine input of LABs and PAHs carried by suspended particulate matter to the coastal ocean decreased from 2005/2006 to 2022, due to a combination of improved technological processes and energy structures.

Rare earth elements distribution in the Gulf of Cádiz (SW Spain): geogenic vs. anthropogenic influence

There is a current interest in the study of the geochemical behavior of the rare earth elements (REE) in aquatic systems since their identification as potential microcontaminants in natural waters. In this context, here we report the concentrations and patterns of dissolved REE (dREE) in the waters of the Gulf of Cádiz (GoC) and its major estuaries (Guadiana, Tinto-Odiel and Guadalquivir). Contamination in this area by metals has been extensively reported, linked to acid-mine inputs resulting from the mineralization of the Iberian Pyrite Belt, discharged mainly to the Tinto-Odiel river. However, the impact of these inputs on the concentrations and distribution of the dREE in the coastal waters of the GoC has not been addressed yet. Accordingly, elevated concentrations of dREE were obtained in the Tinto-Odiel estuary compared to the Guadiana and Guadalquivir, reflecting the impact of acid-mine drainage on this system. Only a significant fraction of anthropogenic gadolium (Gd) was observed in the Guadalquivir estuary, as a result of the input from major urban areas, where anthropogenic Gd fractions higher than 70% over the total dissolved pool were obtained for the freshwater end-member. Regarding the surface waters of the GoC, typical NE Atlantic distribution patterns of dREEs were obtained, but modified by two different end-members within this region. Accordingly, and despite the low water discharge of the Tinto-Odiel river, its elevated concentrations lead to an increase in the concentrations of dREEs in the nearshore waters of the GoC and producing a distinctive signature as observed for the MREE anomalies and HREE/LREE ratios. At the easternmost stations, close to the Strait of Gibraltar, these signals are also impacted by the inflow of Mediterranean waters and also by the discharge of the Guadalquivir river.

Seasonality, distribution, and harvest trends of Crevalle Jack in Texas

AbstractObjectiveCrevalle Jack Caranx hippos are important coastal predators and support an increasingly popular catch‐and‐release sport fishery. However, population declines have recently been perceived by stakeholders in parts of the species' range. Here, we aimed to provide distribution and harvest trends for Crevalle Jack in the northwestern Gulf of Mexico.MethodsLong‐term fishery‐independent and fishery‐dependent data were collected by the Texas Parks and Wildlife Department from 1983 to 2021. Bag seine, bay trawl, and gill‐net samples were collected in conjunction with angler creel surveys. Crevalle Jack that were observed in fishery‐independent sampling were used to assess patterns in both juvenile and adult relative abundance, distribution, and seasonality. In addition, boosted regression tree models were used to highlight important predictors of Crevalle Jack presence. Crevalle Jack harvest observed during angler surveys was used to describe the fishery, including differences in inshore and offshore catch patterns. Relative abundance of both juveniles and adults was variable across years but displayed no trend throughout the time series.ResultCrevalle Jack of all sizes were found within inshore waters, with subadults and large adults particularly reliant on estuarine systems. Recruitment peaked in early summer, with juveniles occupying all major estuaries along the coast. Shifts in recruitment were evident in bag seines, as the mean date of catch trended almost 2 weeks earlier over the study period. The Crevalle Jack fishery was spread across inshore and offshore waters, with significantly larger fish harvested offshore during summer. The majority of anglers who harvested Crevalle Jack stated that they were specifically targeting other species, thus supporting the notion that the targeted fishery is mainly catch and release.ConclusionAs Crevalle Jack declines have been noted elsewhere in the species' range, these results could help to inform future management decisions in Texas.

Trace element geochemistry of sediments in the Pearl River Estuary and its implication for provenance

The Pearl River system is China’s third longest river and the Pearl River Estuary is a major estuary in China. In the paper, a sediment core collected from the coastal zone in the Pearl River Estuary was analyzed for trace element concentrations and grain size to identify provenance during the past decades. In addition, the tectonic framework of the study area has also been studied using reliable geochemical tracers, including rare earth elements (REEs) and trace elements. The results reveal a significant contribution of reworked sediment from multiple sources. Discrimination diagrams suggest that the sediments display felsic characteristics with recycled components, and therefore, the source rock types of the sediments are presumed to be granitic rocks. The REE patterns observed in the samples primarily reflect the influence of an ancient continental crust that contains felsic materials on the sediments with an LREE/HREE ratio of 7.94–9.56 (mean 8.46) and a δ Eu value of 0.61–0.70 (mean 0.65). The sediments are plotted into a zone of continental island arcs, which was formed during the late Mesozoic subduction of the ancient Pacific. The study on the source of sediment cores shows that the main source of sediments in this area excludes the possibility of the upper middle river from the Pearl River Watered, which reflects the importance of the lower Pearl River Basin, especially the Dongjiang River, for material transport in the study area. Our results demonstrate that the geochemical characteristics of trace elements in sediment could provide an efficient approach to identify sediment provenance in estuaries worldwide.

Quantification, characterization and risk assessment of microplastics from five major estuaries along the northern Bay of Bengal coast

Microplastics (MPs) as hazardous contaminants has drawn the rapid attention of the general public due to their omnipresence and adverse impacts on ecosystems and human health. Despite this, understanding of MPs contamination levels in the estuarine ecosystems along the Bay of Bengal coast remains very limited. This research focused on the presence, spatial distribution, morpho-chemical characteristics and ecological implications of MPs in water and sediment from five key estuaries (Meghna, Karnaphuli, Matamuhuri, Bakkhali, and Naf rivers) within the Bengal delta. Out of the five estuaries, the Meghna exhibited the least amount of MPs in both surface water (150.00 ± 65.62 items/m3) and sediment (30.56 ± 9.34 items/kg). In contrast, the highest occurrence of MPs was recorded in Karnaphuli river water (350.00 ± 69.22 items/m3) and Matamuhuri river sediment (118.33 ± 26.81 items/kg). ANOVA indicated a statistically significant distinction (p < 0.01) among the examined estuaries. Most identified MPs were fibers and < 0.5 mm in size in both water and sediment samples. Transparent MPs were dominant in both water (42.28%) and sediment (45.22%). Besides violet, red, blue, pink and green colored MPs were also observed. Various polymer types, including PE, PP, PET, PS, Nylon, EVA, and ABS, were detected, with PE being the dominant one. Based on the polymer risk index (PHI), the estuaries were classified as hazard level V, signifying a severe level of MP contamination. However, the potential ecological hazardous index (PHI), potential ecological risk index (RI), and pollution load index (PLI) indicated moderate pollution levels. This study offers initial insights into the pollution caused by MPs in major estuaries of Bengal delta, which policymakers can utilize to implement suitable management strategies.

Mapping Suspended Sediment Changes in the Western Pacific Coasts

The Western Pacific Coasts (WPC) are the outlets of many large Asian rivers. In recent years, the interplay of climate changes and human activities has persistently altered the suspended sediment concentrations (SSC) in the WPC, triggering substantial shifts in coastal ecosystems. However, the scarcity of coastal observation stations hampered comprehensive investigations at large scales. This study employed three representative SSC retrieval models and utilized Landsat images acquired from 1990 to 2020 to estimate the SSC in the WPC with a focused endeavor to dissect the intricate spatial and temporal variability of SSC in the region. The findings revealed the following insights: (1) The outcomes derived from the three distinct SSC models consistently manifested a discernible decreasing pattern in SSC changes over the past three decades across all six major estuaries (Liao River Estuary, Yellow River Estuary, Yangtze River Estuary, Hangzhou Bay, Pearl River Estuary, and Mekong River Estuary). (2) The seasonal attributes of the six major estuaries differed, primarily due to distinct dominant influencing factors like precipitation, upstream sediment load, wind, and tides. (3) Collectively, SSC tends to be relatively higher in the Yangtze River Estuary, Hangzhou Bay, and Yellow River Estuary, while the Pearl River and Mekong River Estuaries exhibit relatively lower levels. Notably, the SSC exhibited distinct spatial traits along the coastlines of different estuaries. (4) SSC in the non-estuarine regions along the WPC, a similar significant declining trend in SSC is observed as in the estuaries, albeit the rate of decline generally appeared to be less pronounced. Furthermore, regions with faster rates of SSC reduction are typically concentrated near major estuaries in the northern part of the Coasts. The decline in estuarine SSC plays an important role in the overall decrease in SSC across the WPC. These study outcomes held substantial significance for advancing the stability and sustainable evolution of the WPC.

Distinct patterns of distribution, community assembly and cross-domain co-occurrence of planktonic archaea in four major estuaries of China

BackgroundArchaea are key mediators of estuarine biogeochemical cycles, but comprehensive studies comparing archaeal communities among multiple estuaries with unified experimental protocols during the same sampling periods are scarce. Here, we investigated the distribution, community assembly, and cross-domain microbial co-occurrence of archaea in surface waters across four major estuaries (Yellow River, Yangtze River, Qiantang River, and Pearl River) of China cross climatic zones (~ 1,800 km) during the winter and summer cruises.ResultsThe relative abundance of archaea in the prokaryotic community and archaeal community composition varied with estuaries, seasons, and stations (reflecting local environmental changes such as salinity). Archaeal communities in four estuaries were overall predominated by ammonia-oxidizing archaea (AOA) (aka. Marine Group (MG) I; primarily Nitrosopumilus), while the genus Poseidonia of Poseidoniales (aka. MGII) was occasionally predominant in Pearl River estuary. The cross-estuary dispersal of archaea was largely limited and the assembly mechanism of archaea varied with estuaries in the winter cruise, while selection governed archaeal assembly in all estuaries in the summer cruise. Although the majority of archaea taxa in microbial networks were peripherals and/or connectors, extensive and distinct cross-domain associations of archaea with bacteria were found across the estuaries, with AOA as the most crucial archaeal group. Furthermore, the expanded associations of MGII taxa with heterotrophic bacteria were observed, speculatively indicating the endogenous demand for co-processing high amount and diversity of organic matters in the estuarine ecosystem highly impacted by terrestrial/anthropogenic input, which is worthy of further study.ConclusionsOur results highlight the lack of common patterns in the dynamics of estuarine archaeal communities along the geographic gradient, expanding the understanding of roles of archaea in microbial networks of this highly dynamic ecosystem.

Environmental DNA compliments traditional sampling for monitoring fish communities in a Texas estuary

AbstractObjectiveEnvironmental DNA (eDNA) metabarcoding has become an important method for inventorying and monitoring biota in aquatic systems. The Texas Parks and Wildlife Department conducts regular fishery‐independent sampling of biotic communities using traditional sampling gears, such as gill nets and bag seines, in all of the major estuaries of adjacent to the Gulf of Mexico in Texas. Previous studies have shown that eDNA approaches can complement traditional sampling methods.MethodsWe compared fish community structure data in the Cedar Lakes estuary system obtained with traditional sampling gears with data obtained using eDNA sampling using a small sequence of mitochondrial 12S ribosomal RNA gene and a validated taxonomic reference file.ResultFor spring and fall of 2022, eDNA metabarcoding detected a larger number of species than either bag seines or gill nets. Species richness detected via eDNA in two seasons in a single year was comparable with the species richness of agency’s historical record based on traditional gears for Cedar Lakes.ConclusionSeasonal and spatial variation in species richness was similar between traditional and eDNA sampling; however, eDNA metabarcoding allowed detection of several species that would be difficult or impossible to capture with either bag seines or gill nets. We observed two limitations of eDNA metabarcoding. Read depth was not a good index of relative abundance, which limits our ability to infer relative biomass using single samples. Secondly, we observed detection bias in our eDNA results. Specifically, eDNA failed to detect two species of elasmobranchs present when water sampling was performed and eDNA also performed poorly compared to traditional sampling gears for some species of bony fishes. Despite these limitations, eDNA metabarcoding proved to be an efficient and cost‐effective alternative and compliment to traditional fisheries sampling gears for fishery‐independent monitoring of community structure and composition in estuaries of the Gulf of Mexico.

Recent Foraminifera From the Mahanadi River Estuary, East Coast of India

The Mahanadi River estuary (Figure 1) is one of the major estuaries in India and the largest one in the Odisha State. It is situated within latitudes 190 47? and 200 30? N and longitudes 850 33? and 860 49? E. It originates from Amarakantak region of Madhya Pradesh and flows through Madhya Pradesh and Odisha States over a length of 890 kms having a drainage basin of about 1,41,600 sq. kms with a large catchment area. It opens into the Bay of Bengal at Pardeep in Cuttack district. It has a wide opening into the sea at its northeastern end. The tidal stretch extends up to 32 kms from the mouth. The entire area is full of mangrove vegetation together with mud flats traversed by a network of tidal creeks except some portions such as Paradeep and Astaranga mouth regions which are sandy shorelines. The studies on Recent foraminifera in relation to the prevailing ecological parameters such as salinity, temperature, dissolved oxygen, and pH, and sediment characteristics and organic matter content of the sediments have been carried out in the present investigations. These studies can be used to delineate the palaeo-environments which serve as useful tools in the exploration for petroleum. 10 sediment and 10 water samples were collected from the estuary for the study of foraminifera and sediment characters, and water analysis respectively. The foraminifera of the estuary were identified. 12 abundant species which are Ammobaculities exiguus, Ammonia beccarii, Ammonia beccarii tepida, Elphidium advenum, Elphidium hispidulum, Milliamina fusca, Nonion depressulus, Pararotalia nipponica, Pararotalia cf. globosa, Quinqueloquelina lamarckina, Quinqueloculina seminulum and Rosalina globularis and are related to the prevailing ecological parameters and the substrate characteristics including the organic matter content.

Variation of mercury in 4 major estuaries in the Gulf of Thailand during wet season

The Mae Klong River (MK), Tha Chin River (TC), Chao Phraya River (CP), and Bang Pakong River (BPK) are recognized as critical conveyors of terrestrial substances, including pollutants, into the Inner Gulf of Thailand (Inner GOT). This study sought to explore the presence of mercury (Hg), a highly toxic and bioavailable pollutant, in both water and surface sediment at the mouths of the four rivers in pre- and post-wet season (WS). The results revealed that the total mercury (T-Hg) concentrations in the water ranged from 10 ng/L (TC) to 125 ng/L (CP) in pre-WS and 17 ng/L (MK) to 1011 ng/L (TC) in post-WS. Notably, the post-WS concentrations of T-Hg were relatively higher than the pre-WS, with an average concentration of particulate Hg (P–Hg) increasing by approximately 3–5 times. Consequently, the average P–Hg proportion to T-Hg of each estuary in the post-WS was comprised of greater than 67%. Moreover, a correlation was observed among salinity, total suspended solid (TSS) and particulate Hg (P–Hg). Similarly, the estuarine sediment, excluding MK, exhibited a higher average concentration of T-Hg during the post-WS period. The average T-Hg concentration in sediment ranged from 17 (BPK) to 119 (MK) μg/kg in pre-WS and 15 (MK) to 140 (CP) μg/kg in post-WS. The presence of organic matter (total organic carbon or TOC content), and clay-sized particles were identified as potential factors influencing the concentration of T-Hg in the sediment. In addition, a higher positive correlation was observed between T-Hg and silt-sized particles in BPK. In this study, both T-Hg in the water column and T-Hg in sediment increased during the post-WS period, suggesting that Hg transportation from sources to river mouths during WS were intensified. Furthermore, the correlation between T-Hg and fine-grained particle, as well as the greater T-Hg levels in the estuarine sediment, indicates that Hg may be transported from rivers to the offshore marine environment via the fine-grained fraction.

Integrated Zoning and Spatial Heterogeneity of Coastal Watershed-Nearshore Waters

Integrated land-sea development and protection are important for the sustainable development of coastal areas. To promote the transition from separate land-sea management to integrated land-sea governance, the scientific delineation of the integrated spatial zoning units of coastal watershed-nearshore waters is an important tool for integrated land-sea management. From the perspective of physical geography, this study uses digital hydrological analysis based on DEM data to determine the coastal basin range and generate multilevel watersheds and river networks using different thresholds, and establishes spatial correspondence among physical geospatial spaces, such as watershed zones, coastlines, and nearshore waters, after considering the boundaries of major estuaries and bays. On this basis, the coastal zone is divided into several integrated spatial zoning units of coastal watershed-nearshore waters, and a physical geography-based integrated spatial zoning method is developed to form a physical geography-based land-sea integrated spatial zoning scheme. This study conducted spatial heterogeneity research of the integrated spatial zoning units, from the perspectives of topography analysis, land use analysis, socioeconomic analysis of the watershed, sea use analysis, seawater quality analysis of the nearshore waters, and load pressure analysis of the watershed-nearshore waters. The elemental differences of zoning units are studied in detail, which can provide a data reference for establishing the relationship between watersheds and nearshore waters. Applying this research method to the Guangxi Zhuang Autonomous Region in China, where the land-sea linkage pattern is forming, can provide a spatial reference and scientific basis for land-sea integrated management for ecological protection and sustainable resource utilization in the coastal zone.

Seasonal variability of modern benthic foraminifera assemblages in a mangrove ecosystem from northeast coastal Bay of Bengal

Benthic foraminifera assemblages, nutrient dynamics of surface and porewater from 10 intertidal sites spanning over two years (2019–2020) covering two major estuaries in Sundarbans mangrove were evaluated to understand role of seasonal precipitation and primary production (driven by eddy nutrients) with a focus on standing crop. Benthic foraminifera abundance ranged between 280 individuals/10 cc in pre-monsoon (2019), 415 individuals/10 cc in post-monsoon 2019 and 630 individuals/10 cc in post-monsoon (2020). Standing crop was highest in post-monsoon coinciding with eddy nutrients driven stoichiometry and increase in abundance of large diatom cells. Calcareous and agglutinated foraminifer taxa Ammonia sp.1, Quinqueloculina seminulum, Entzia macrescens and Textularia sp. respectively were frequent. Entzia macrescens was found in dense mangrove vegetation sites; exhibited strong relationship with sediment texture and pore water total organic carbon. One of the major findings is mangroves with pneumatophores improves oxygen availability in sediment and leads to an increase in standing crop.

The Interaction of Seasons and Biogeochemical Properties of Water Regulate the Air-Water CO2 Exchanges in Two Major Tropical Estuaries, Bay of Bengal (India).

The exchange of CO2 between the air–water interfaces of estuaries is crucial from the perspective of the global carbon cycle and climate change feedback. In this regard, we evaluated the air–water CO2 exchanges in two major estuaries—the Mahanadi estuary (ME) and the Dhamra estuary (DE) in the northern part of the Bay of Bengal, India. Biogeochemical properties of these estuarine waters were quantified in three distinct seasons, namely, pre-monsoon (March to May), monsoon (June to October), and post-monsoon (November to February). The significant properties of water, such as the water temperature, pH, salinity, nutrients, dissolved oxygen, chlorophyll-a (chl a), and photosynthetic pigment fluorescence of phytoplankton, were estimated and correlated with CO2 fluxes. We found that the ME acted as a source of CO2 fluxes in the monsoon and post-monsoon, while DE acted as a sink during the monsoon. The stepwise regression model showed that the fluxes were primarily driven by water temperature, pH, and salinity, and they correlated well with the phytoplankton characteristics. The chl a content, fluorescence yield, and phycobilisomes-to-photosystem II fluorescence ratios were major drivers of the fluxes. Therefore, for predicting air–water CO2 exchanges precisely in a large area over a seasonal and annual scale in the estuaries of the Bay of Bengal, India, critical key parameters such as water temperature, pH, salinity, chl a, and fluorescence yield of phytoplankton should be taken into consideration. However, the responses of phytoplankton, both in terms of production and CO2 capture, are critical research areas for a better understanding of air–water CO2 exchanges in coastal ecology under climate change scenarios.

Assessment of vertical and horizontal distribution of meiobenthos along a salinity gradient in the Tana and Sabaki Estuaries, north coast Kenya

Meiobenthos respond to variability in salinity gradients in estuarine habitats and are thus suitable organisms for ecological studies. The vertical and horizontal distribution of the meiofauna community structure of two major estuaries (Sabaki and Tana) on the north coast of Kenya were compared. The aim was to draw a meiofaunal dataset inventory of the two estuaries and to examine how salinity gradient, seasonality and sediment characteristics influence their structure. Replicate samples were collected from three sampling stations along the salinity gradient of each river estuary. A total of 3,556 individuals belonging to 26 taxa were recorded. Based on seasons and across stations, the upper surface (0-5 cm) layer recorded the highest meiobenthic density (90 ± 42 ind.10 cm-2), followed by 46 ± 23 ind.10 cm-2 (5-10 cm) and 30 ± 8 ind.10 cm-2 in the deepest sediment layer (10-15 cm) studied. The southeast monsoon season recorded the highest mean density (160 ± 22 ind.10 cm-2) compared to the northeast monsoon season (22 ± 12 ind.10 cm-2) for both estuaries. Results of the non-Metric Multidimensional Scaling technique revealed distinct seasonal composition in meiobenthos but not between the estuaries. Results of the 2-way ANOSIM test confirmed no significant differences in meiobenthic composition between the estuaries (p = 0.712). However, seasonal difference was significant (p = 0.001) with higher densities for nematoda (166 ± 99 ind.10 cm-2 and 56 ± 29 ind.10 cm-2) recorded in Tana and Sabaki, respectively during the southeast monsoon season. At least 7 taxa out of a total of 26 were present in both estuaries. Salinity gradient, season and sediment depth were found to influence the meiobenthic densities and taxa composition.

Organochlorine pesticides in marine sediments and seawater from Cirebon coastal water, West Java, Indonesia: Concentration, spatial distribution, potential sources, and ecological risk assessment

Organochlorine pesticides (OCPs) were investigated in surface sediments and seawater from three major estuaries at Cirebon coastal water, West Java Province, Indonesia. Total concentrations of OCPs in seawater and sediment varied from 10 to 120 ng/L (32 ± 36 ng/L) and 1.5 to 17 ng/g dw (mean of 7.4 ± 4.0 ng/g dw), respectively. OCPs concentrations in Sukalila estuary were higher than those detected in Bondet and Kejawan estuaries. The drins group was the predominant OCPs contaminant in seawater and sediment samples. Historical application of DDT, recent use of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), and application of technical hexachlorocyclohexanes (HCHs) are significant sources of DDTs and HCHs, respectively. The concentrations of γ-HCH and heptachlor epoxide in marine sediment elevated the value of Threshold Effect Limit (TEL) in 48% of the total study stations but lowered the value of Probable Effect Limit (PEL), suggesting that they ocassionally trigger adverse effects on benthic organisms.

Plastic pollution in an estuary: A preliminary study on the Rupsha river in southwestern Bangladesh

Plastic pollution is one of the major threats to the biodiversity of coastal mangrove forest Sundarbans. The current research focused on the preliminary assessment of plastics load to benthic biodiversity in a major estuary, the Rupsha in southwestern Bangladesh. Visual studies were conducted at five different sampling sites based on human activities, viz Kalibari ghat (S1), Rupsha ferry ghat (S2), Lobonchora ghat (S3), Rupsha bridge ghat (S4) and Putimari ghat (S5 as reference site). Thirteen (13) different plastic types under three categories were identified from the five-study sites. These categories belong to (i) fishing related debris: net, line, buoy, other fishing materials (ii) domestic useable plastics: bottle, bucket, bag/film, foamed polystyrene and polythene, and (iii) category of other types including packet, rope, pipe and shoes. Among all types, packet and polythene were the most abundant in number and both of them were the highest in number in Rupsha ferry ghat (8.67±3.79 for polythene and 9.33±5.86 for packet) whereas lowest in S5 (0.67±0.58 for polythene). Overall, the highest number of plastics (individual items) was identified in S2 station (36±12.5) following to S4 station (24.33±1.53) and lowest at S5 (3.33±0.58). Biodiversity index were also calculated where higher species richness (D) and Shannon index (H) were observed to be higher in S5 compared to other sampling sites.

Substantial submarine groundwater discharge in the estuaries of the east coast of India and its impact on marine strontium budget

The concentration and isotopic compositions of dissolved Sr (87Sr/86Sr) were measured in four major estuaries of the east coast of India, including those of the Ganga (Hooghly), Mahanadi, Godavari, and the Krishna during their peak discharge period, July-September 2013, along with particulate matters in some of them. Dissolved Sr displays strong conservative behaviour in all four estuaries within the analytical uncertainties, emphasizing simple mixing between river water and seawater. Sr isotopic composition, however, behaved non-conservatively in all four estuaries. Dissolved 87Sr/86Sr of many samples in these estuaries deviate significantly from the theoretical mixing line defined by seawater and river water, indicating some additional sources of radiogenic Sr in all four estuaries. Such deviation in the Ganga estuary could result from a minor dissolution of suspended material with very radiogenic Sr in the turbid zone of the estuary. However, several lines of evidence support submarine groundwater discharge as an important source of Sr in these estuaries. We used an inverse modelling approach to characterize the significance of submarine groundwater discharge and quantified its fluxes from the four estuaries based on 87Sr/86Sr in this study, highlighting its potential to estimate groundwater contribution to the water budget in estuaries. The fluxes of submarine groundwater discharge from the estuaries of the east coast of India is estimated to be ∼ 11000 ± 900 m3s−1, dominated by the Ganga-Brahmaputra system, and delivers ∼ 1.1 ± 0.06 × 109 moles of Sr annually with quite radiogenic 87Sr/86Sr, 0.7228, comparable to their riverine fluxes. These estuaries contribute 0.3 – 0.7% to the global submarine groundwater discharge derived Sr. This study reveals a large supply of radiogenic Sr from submarine groundwater discharge which further increases the requirement of less radiogenic Sr to balance the continental radiogenic Sr in the global marine Sr budget.

Distribution and Dynamics of Radiatively Active Gas (RAG) Emissions From Major Estuaries of the Sundarbans Mangrove, India

The world’s largest mangroves ecosystem, the Sundarbans, being highly productive and a place for extensive organic matter cycling, is considered to be the hotspot for biogeochemical studies in the tropical estuarine environment. Hence, the spatial and temporal dynamics of the biogenic gases (CO2, CH4, and N2O), also known as radiatively active gases, were measured in mangrove-dominated estuaries of the system. In addition to spatial and seasonal observation, three full tidal cycles were observed at one site. Results showed that the air/water gas saturations were widely distributed and highly variable along the stretch. The gas saturations showed varying responses to salinity and tidal fluctuations. This indicated that localized biogeochemical processes may be more influential than simple mixing and dilution processes in controlling the variability of these gases. The surface waters were always supersaturated with CH4 (Up to 13,133%) relative to the atmosphere. However, N2O ranged from 8 to 1,286% and CO2 from 30 to 2075%. N2O fluxes were ∼4.8 times higher in the pre-monsoon than the post-monsoon. CH4 fluxes were ∼3.6 times higher in the pre-monsoon than both the monsoon and the post-monsoon. CO2 fluxes were ∼10 times higher in the monsoon than both the pre-monsoon and the post-monsoon. The seasonality in the gas saturation could be linked more to the availability of substrates than physicochemical parameters. Overall, air/water CH4 fluxes varied maximally (0.4–18.4 μmol m−2 d−1), followed by CO2 fluxes (−0.6–10.9 mmol m−2 d−1), and N2O fluxes varied the least of all (−0.6–5.4 μmol m−2 d−1). Interestingly, CH4 and N2O fluxes were positively correlated to each other (p &amp;lt; 0.05), suggesting organic matter decomposition as the key factor in the production of these two gases. Finally, these water–air CO2, CH4, and N2O flux estimates show that the estuaries are a modest source of CH4 but fluctuate between sources and sinks for CO2 and N2O gases.

Seasonal Changes of Macrophytes in Major Estuaries of Gujarat, India

Gulf of Khambhat is the biggest gulf of Western India, having four major rivers i.e., Sabarmati, Mahi, Narmada and Tapi. These estuaries, rich in macrophytes were studied for understanding the change of vegetation pattern across different seasons. Vegetation composition at Sabarmati, Mahi, Narmada and Tapi estuaries was dominated by halophytes Avicennia marina, Acanthus ilicifolius, Aeluropus lagopoides and Suaeda maritima species. The halophyte diversity was predominating over hydrophytes in all the estuaries. There is narrow ecological transition between aquatic and terrestrial species. Avicennia marina showed maximum frequency of occurrence at Sabarmati estuary. Phytosociological analysis was done in order to understand the change in the vegetation pattern wherein at Narmada estuary the abundance of Proteresia coarctata was decreasing from winter to monsoon season while Acanthus ilicifolius and Sonneratia alba were recorded at Tapi estuary only. Maximum value of Shannon's index diversity (SHID) was &gt; 2 to 4 and Simpson diversity index (SIDI) was 0.87 to 0.97 in different seasons across four estuaries. GIS mapping and heterogeneity in the vegetation patches were studied by FRAGSTATS software. Maximum heterogeneity was recorded at Narmada estuary.

Occurrence and abundance of young mullet Mugil liza (Teleostei: Mugilidae) in the surf zone along the southern coast of Brazil

The southern population of Mugil liza is distributed from Argentina (47°S) to the state of São Paulo, Brazil (23°S). Young mullets use the estuaries as nursery grounds, and prior to recruitment into estuaries they use the surf zone as a temporary habitat. Based on 12 consecutive months of sampling, this study used generalized linear models (GLM) to analyse the relationships between environmental variables and the presence and relative abundance of young mullets in the surf zone adjacent to six major estuaries in southern Brazil (between 29°S and 33°S). Young mullets were present in all seasons over the sampling period, but the probability of occurrence was higher in winter and was associated with low temperatures. The water temperature alone explained more than half of the total deviance of the GLM models for presence (23%) and abundance (21%) of young mullets in the surf zone. Site 2 (Rio Grande) had lower temperatures in the colder months, the highest probability of occurrence of all collection sites and the greatest abundance (n=3402) of young M. liza, which represented 52% of the total of individuals (n=6493) caught among the six sites sampled.