Bhaskar Deb Bhattacharya

A comparison of sediment quality guidelines for toxicity assessment in the Sunderban wetlands (Bay of Bengal, India).

The aim of this paper was to obtain the first screening ecotoxicological risk evaluation in the Sunderban wetlands, the largest prograding delta in the estuarine phase of the River Ganges. The characterization of exposure was conducted by means of an extensive survey of several persistent organic pollutants (PAHs, PCBs, DDTs, PBDEs, HCHs, HCB) measured in seven core sediments from the Sunderban wetlands, obtaining a dataset with more than 2200 analyses. The pollutant effects were assessed by the use of three different sediment quality guidelines (SQGs) previously developed in the literature to evaluate toxicity induced in sediment-dwelling organisms. The three different approaches chosen for risk assessment of the Sunderban were the consensus SQGs obtained by TEC (threshold effect concentration), PEC (probable effect concentration) and EEC (extreme effect concentration), the threshold/probable effect level (TEL/PEL) approach and, finally, the ERL-ERM guidelines, including the m-ERM-Q (mean ERM quotient). The evaluation of the toxicity induced by a mixture of the target pollutants indicated the importance of gamma-HCH contamination in the Sunderban sediments despite the very low concentrations measured in core sediments. A different sensitivity for toxicity assessment due to quality guidelines was obtained, as the consensus SQGs based on TEC were less conservative and protective than the TEL and ERL approaches, while the use of m-ERM-Q seems to be the most powerful tool to predict the toxicity related to a contaminant mixture.

Commonness and rarity in the marine biosphere

Significance Tests of biodiversity theory have been controversial partly because alternative formulations of the same theory seemingly yield different conclusions. This has been a particular challenge for neutral theory, which has dominated tests of biodiversity theory over the last decade. Neutral theory attributes differences in species abundances to chance variation in individuals’ fates, rather than differences in species traits. By identifying common features of different neutral models, we conduct a uniquely robust test of neutral theory across a global dataset of marine assemblages. Consistently, abundances vary more among species than neutral theory predicts, challenging the hypothesis that community dynamics are approximately neutral, and implicating species differences as a key driver of community structure in nature. Explaining patterns of commonness and rarity is fundamental for understanding and managing biodiversity. Consequently, a key test of biodiversity theory has been how well ecological models reproduce empirical distributions of species abundances. However, ecological models with very different assumptions can predict similar species abundance distributions, whereas models with similar assumptions may generate very different predictions. This complicates inferring processes driving community structure from model fits to data. Here, we use an approximation that captures common features of “neutral” biodiversity models—which assume ecological equivalence of species—to test whether neutrality is consistent with patterns of commonness and rarity in the marine biosphere. We do this by analyzing 1,185 species abundance distributions from 14 marine ecosystems ranging from intertidal habitats to abyssal depths, and from the tropics to polar regions. Neutrality performs substantially worse than a classical nonneutral alternative: empirical data consistently show greater heterogeneity of species abundances than expected under neutrality. Poor performance of neutral theory is driven by its consistent inability to capture the dominance of the communities’ most-abundant species. Previous tests showing poor performance of a neutral model for a particular system often have been followed by controversy about whether an alternative formulation of neutral theory could explain the data after all. However, our approach focuses on common features of neutral models, revealing discrepancies with a broad range of empirical abundance distributions. These findings highlight the need for biodiversity theory in which ecological differences among species, such as niche differences and demographic trade-offs, play a central role.

Geochemical fractionation of trace elements in sediments of Hugli River (Ganges) and Sundarban wetland (West Bengal, India)

A sequential extraction procedure was carried out to determinate the concentrations of 11 elements (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) in different geochemical phases of sediments collected along the Hugli (Ganges) River Estuary and in the Sundarban mangrove wetland, eastern coastal part of India. The chemical speciation of elements was determined using the three-step sequential extraction procedure described by the European Community Bureau of Reference. Total metal concentration was determined using a microwave-assisted acid digestion procedure. Metal concentrations were near the background level except for As for which a moderate pollution can be hypothesized. The mobility order of the metals was: Cd > Mn > Cu > Zn > As > Co > Pb > Ni > Fe > Cr > Al. The highest percentage of Cd (>60%) was found in the most labile phase. Residual fraction was prevailing for Fe, Cr and Al, while Pb was mainly associated with the reducible fraction. Data were compared with Sediment Quality Guidelines to estimate the relationship between element concentrations and adverse biological effects on benthic community, finding the possibility of some toxic effects due to the presence of As in the entire studied area and Cd, only in Calcutta.

Perfluorinated compounds in surficial sediments of the Ganges River and adjacent Sundarban mangrove wetland, India

This study reports the first evidence of the quantification of two dominant perfluorinated compounds (PFCs), namely perfluorooctanesulfate (PFOS) and perfluorooctannoate (PFOA), in surface sediment samples (0-5 cm; n=13) from the Ganges (Hugli) River including Sundarban wetland, India using HPLC-MS/MS. The concentrations of PFOA exhibited a wide range of concentrations from <0.5 to 14.09 ng/g dry wt, whereas the concentration of PFOS was always below the detection limit of <0.5 ng/g dry wt. A consistent enrichment of PFOA was recorded in all the five sites of Sundarban (mean value 11.61±1.86) whereas it was of moderate concentration or below the detection level in the seven sites along with the lower stretch of the Ganges (Hugli) River estuary (mean value 5.96 ng/g dry wt±5.36). Wastewater and untreated effluents are likely the major causes of accumulation of PFCs in sediments. The present paper could be used as baseline study to assess future monitoring programs of the ecosystem.

Distribution and Ecosystem Risk Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) in Core Sediments of Sundarban Mangrove Wetland, India

The origin and distribution of 19 priority pollutant polycyclic aromatic hydrocarbons (PAHs) in core sediments (<63 μm) from the Sundarban mangrove wetland, northeastern part of Bay of Bengal, India, were investigated by gas-chromatography/mass spectrometry (GC/MS). Sedimentary organic carbon and textural properties were also analyzed in order to assess the role of geochemistry on PAH distribution. ∑19PAHs concentration in sediments showed wide variations from 9.4–4222.8 ng/g dry weight, with an overall increase of the high molecular PAHs in the deeper depth profiles. Fluoranthene, chrysene, and pyrene were the most abundant hydrocarbons in sediments and it can be explained by active inputs of soil materials due to frequent strong rainfalls in this tropical climatic zone. A rather exceptional prevalence of high molecular weight PAHs was substantiated: nearly 80% of ∑19PAHs include fluoranthene (18–20%), chrysene (14–16%), and pyrene (10–11%). Carcinogenic compounds were present in moderately high (DBA, BkF, BbF) or negligible and low concentrations (BaP, InP) in a majority of cases. The PAH diagnostic ratios indicated that the PAHs in sediment cores were of pyrolytic origin, and that atmospheric deposition and land runoff may serve as the important pathways for PAHs input to the sediments. The total PAH levels were expressed as the benzo (a) pyrene toxicity equivalents (TEQcarc) making this compound a potential marker for PAH pollution. The baseline data can be used for regular ecological monitoring, considering the industrial and agricultural growth around this important estuarine environment. The results indicated that the PAHs in sediments of Sundarban wetland resulted in low to moderate ecosystem risk.

Congener profiles of polychlorinated biphenyls in core sediments of Sunderban mangrove wetland (N.E. India) and their ecotoxicological significance

The paper presents the first comprehensive survey of congener profiles of polychlorinated biphenyls (PCBs) in core sediment samples (<63 μm particle size) covering seven sites in Sunderban mangrove Wetland, north-eastern part of the Bay of Bengal. Results pointed out a non-homogenous contamination of the wetland with Σ23PCB values ranging from 0.5 to 26.9 ng g-1 dry weight, reflecting very low to moderate contamination closely in conformity to other Asian coastal environment. The general decreasing order of the dominant congeners to the total load was: CB138 > 153 > 149 > 101, indicating the predominance of hexa-chlorinated congeners. The spatial distribution revealed significant differences in concentration related to local urbanization with industrial and land-based sources. No uniform temporal trend on PCB levels was recorded probably due to particular hydrological characteristics of the wetland and/or non-homogenous inputs from point sources. Strong positive correlations between the seven dominant congeners suggest their common sources and similar environmental behaviors. These results were also used for a risk assessment evaluation in the Sunderban wetland, showing that the present PCB levels were exceeding in few cases the lower limit of sediment quality guidelines of Environmental Protection Agency and Canadian Council of Ministers of the Environment.

Bioaccumulation of trace elements in dominant mesozooplankton group inhabiting in the coastal regions of Indian Sundarban mangrove wetland.

Mesozooplankton (Body size 20-200 μm) along with the surface water were collected from coastal regions of Sundarban, northeastern part of Bay of Bengal considering three seasons, namely premonsoon, monsoon and postmonsoon. Samples were analyzed for community structure and the dominant copepod species were further analyzed for trace metal concentration. In total, 50 copepods were identified (22 families and 43 genera). The dominant mesozooplankton species included 9 copepods and an epipelagic chaetognath, exhibited both spatial and seasonal variations. Metal concentration exhibited considerable inter-specific variations for the copepods and the mean concentrations were: Fe, 1350.2-51118.3 μg/g; Al, 647.2-73019.1 μg/g; Ni, 32.4-110.3 μg/g; Mn, 122.8-1066.5 μg/g; Pb, 0.04-97.5 μg/g; Pb, 10.6-97.5 μg/g; Cd, 4.2-21.6 μg/g; Cu, 17.4-145.1 μg/g; Zn, 225.7-1670.9 μg/g; Cr, 21.7-194.3 μg/g; Co, 1.32-111.1 μg/g. Metal concentrations showed the following order: Sagitta bedoti>Coryceas danae>Oithona sp.>Eucalanus subcrassus>Labidocera euchaeta>Paracalanus parvus>Acartiella tortaniformis>Acartia spinicauda>Pseudocalanus serricaudatus.

Mercury Concentration in Sediment Cores from Sundarban Mangrove Wetland, India

The work presents an extended database (n = 123) of total mercury (THg) in fine-grained sediment fraction (<63 μm) of core samples in 10 sampling stations of the Sundarban mangrove wetland, India, formed at the estuarine realm of the Hugli (Ganga) River. Results revealed a wide range of spatial, seasonal, and intertidal flat variations of THg (7.3 to 93.3 ng/g) with a definite enhancement level at the lower stretch of the estuary, which has extreme mangrove vegetation. An overall enrichment of THg in surface/subsurface layers of the core is tentatively explained by remobilization and resuspension of the metal from deeper sediments (36–40 cm). A strong positive correlation was observed between the Hg and clay fraction content of the sediments, while correlations of Hg with organic carbon was poor. Based on the index of geoaccumulation (Igeo), enrichment factor (EF), and anthropogenic factor (AF) values, it is suggested that the sediments of Sundarban were found to be less polluted with respect to total mercury. The data reported are a useful baseline for THg in Sundarban and would be of importance in future sediment quality studies.

Impact of silver nanoparticles on benthic prokaryotes in heavy metal-contaminated estuarine sediments in a tropical environment.

Little knowledge is available about the potential impact of commercial silver nanoparticles (Ag-NPs) on estuarine microbial communities. The Hugli river estuary, India, is susceptible to heavy metals pollution through boat traffic, and there is the potential for Ag-NP exposure via effluent discharged from ongoing municipal and industrial activities located in close proximity. This study investigated the effects of commercial Ag-NPs on native microbial communities in estuarine sediments collected from five stations, using terminal restriction fragment length polymorphism (T-RFLP) technique. An increase in the number of bacteria in consortium in sediments was observed following exposure to Ag-NPs. In general microbial communities may be resistant in estuarine systems to the antimicrobial effects of commercial Ag-NPs, but key microorganisms, such as Pelobacter propionicus, disappeared following exposure to Ag-NPs. In conclusion, the T-RFLP analysis indicated that Ag-NPs have the potential to shape estuarine sediment bacterial community structure.

Fluvial geomorphology of the Kupa River drainage basin, Croatia: A perspective of its application in river management and pollution studies

Summary. This paper aims to describe for the first time the geomorphology, tectonic setting, lithological framework and granulometric properties of the transboundary Kupa River basin of Croatia, Slovenia and Bosnia and Herzegovina, situated at the very south of the Danube River basin. The generally meandering, east to west running course of the Kupa River starts from a karstic spring in the mountainous region and flows down to the plains with braided channels, particularly at points of outfall of a large number of tributaries joining both from the north and the south. Belonging to the seismically active terrain and Adriatic carbonate platform, the geomorphic aspects of the river catchments, channel patterns and deposition-erosion processes are significantly controlled by seismicity related faults and thick carbonate succession of karst in Dinarides. The river borne materials vary widely in size from boulders to fine sand, the mineral compositions of which are derived from the metamorphic and sedimentary rocks. The gravelly marginal bars and channel bars are quite common at the upper reach of the river whereas, sandy point bars characterize some locations of inner meander bends. The gravelly channel-lag deposits and exposed bed rocks often hinder the streamline flow of the river during the low water level in the summer months. Flow separations together with very sluggish back flow against bed rock barriers cause distinctive differences in flow patterns and flow velocities in many places along the course of the river. The calculated grain size parameters were used to evaluate the model of Mc Laren (1981). It was found to be in agreement with our results, that sediments became finer and more positively skewed in the direction of transport. During the summer months, this potentially resourceful river is getting locally moribund and arrested within its course due to fall of river level and extremely uneven bed level configuration along both transverse and longitudinal profiles of the river. Influx of pollutants and their restricted circulation in many places have led to severe eutrophication with macroalgal blooms and generation of marsh vegetation,. Human interference by construction of weirs for hydroelectrical power plants, construction of embankments for bank protections together with stacking of rock boulders on river bed for angling, dredging and mining of river bed in some places has further caused modifications to the morphology, morphodynamics and grain size characteristics of the river channel. Contamination from barite mine tailings, agriculture, industries and sewage waters has attained an alarming state on some stretches. The authors have suggested the need for systematic monitoring of the Kupa drainage basin, especially in terms of its channel patterns, tectonic geomorphology and hydro-meteorological control, in addition to pollutants in sediments and waters, and thus to understand past environment and future changes.