G. N. Nayak

Sedimentary and Geochemical Signatures of Depositional Environment of Sediments in Mudflats from a Microtidal Kalinadi Estuary, Central West Coast of India

Abstract A detailed study of sediment components and selected metals has been carried out in two mudflat cores collected from the creeks of Kalinadi Estuary, India, in order to assess the variations in distribution of sediment components, metals, and the controlling processes, including early diagenetic movements, if any. Grain size analyses reveal the possibilities of three episodes of deposition in a highly varying depositional environment with overall fining up of the cores. Organic carbon (OC) is comparatively high in muddy Core KM, which was collected from a more sheltered creek with a narrow mouth in the estuarine interior, than sandy Core KH, which was collected from a creek with a wide mouth nearer to the sea. Geochemical data show an upper zone of marked enrichment of all trace metals, including Fe and Mn, in both the cores. The variations in sediment components as well as associated metals between the two cores reveal variations in controlling factors including the morphology setup. The distribution of trace metals in Core KH are controlled by the proportions of finer fraction of sediments, degradation of organic carbon, and redox-sensitive Fe and Mn oxides, while the distribution of trace metals in Core KM are probably controlled by the finer sediments as well as by redox-sensitive Fe and Mn oxides.

Heavy metals contamination in mudflat and mangrove sediments (Mumbai, India)

The focus of this study, carried out on mudflat and mangrove sediments of Ulhas Estuary and Thane Creek in Mumbai, India, documents how sediment analysis in different ecosystems can help in understanding metal behaviour and pollution status of the region. Based on the the geoaccumulation index (I geo ), the study shows that the estuarine and creek regions, being recipients of industrial and domestic wastes, display moderate pollution. Ulhas Estuary with higher clay and organic matter contents, exhibits higher amounts of metals than Thane Creek. Furthermore, using correlation and cluster analyses, the creek projects stable subenvironments with similar types of metal associations, with Fe and total organic carbon as the dominant metal carriers. By contrast, in the estuarine subenvironments, the metal associations do not reveal any distinct trend, which may be attributed to the disturbance caused by dredging activities routinely carried out in the region. Factor analysis carried out on I geo data in both regions further helped in identifying polluted metal groups.

Distribution of Sediment Parameters and Depositional Environment of Mudflats of Mandovi Estuary, Goa, India

Abstract Tidal flats are being used to understand sea level changes, pollution history, and depositional environment. From the part of the long-term study, distribution of sediment components, organic carbon, total phosphorus, and selected elements (Fe, Mn, and Cr) are used in this paper to understand diagenetic processes and hydrodynamic processes involved during the deposition of sediment. The present study revealed that the sediment components, organic carbon, and phosphorus play an important role in controlling the distribution and concentration of elements. Importance of the oxic–anoxic layer in the distribution and concentration of metals are discussed. Hydrodynamic conditions of the sediments deposited are delineated using triangular diagram.

Geochemistry and bioavailability of mudflats and mangrove sediments and their effect on bioaccumulation in selected organisms within a tropical (Zuari) estuary, Goa, India.

Metals are non-degradable in the aquatic environment and play a vital role in estuarine biogeochemistry but could also be detrimental to associated biota. A comparative evaluation of the trace metal concentrations (Fe, Mn, Zn, Cu, Ni, and Co) was carried out in the Zuari estuary, Goa during the post-monsoon season of 2013 at six locations, each representing three mangrove and three mudflat regions. In addition, fractionation of trace metals in sediments was performed to provide information on the mobility, distribution, bioavailability and toxicity. Special attention was paid to the marine mollusks viz. bivalves and gastropods that are extensively used as bio-indicators in coastal pollution. Considering the percentage of metals in the sequentially extracted fractions, the order of mobility from most to least bioavailable forms was Mn > Zn > Cu > Ni > Co > Fe. Mn maintained high bioavailability (average around 60%) in Fe-Mn oxide and carbonate bound forms indicating that Mn is readily available for biota uptake. The bioavailability of Fe was on an average of around 6% whereas other metals like Cu, Zn, Ni and Co were around 19% to 34%. When the bioavailable values were compared with standard Screening Quick Reference Table (SQUIRT), Zn showed higher toxicity level and bioavailability in the lower estuary. On the basis of calculated Bio Sediment Accumulation Factors (BSAFs), overall trend in bioaccumulation was in the order of Cu > Zn > Mn > Ni > Co > Fe. Metal Pollution Index (MPI) computed was higher for gastropods than bivalves.

Geochemical Assessment in a Creek Environment in Mumbai, West Coast of India

To understand the status of metal pollution, various sediment parameters such as organic matter, sediment composition and heavy metal concentrations were analyzed at the head and mouth end of a creek in western Mumbai, India. High metal concentrations were observed at the inner creek-(head)-end, characterized by the presence of finer sediments and higher organic matter as compared to near the mouth of the creek. Geochemical indices employed to determine the pollution status of the region, showed that the creek is moderately polluted with Cu and Pb. Increase of Pollution Load Index (PLI) in the upper portions of both the cores, representing recently settled sediments, supports the influence of external discrete anthropogenic sources like agricultural runoff, industrial and atmospheric inputs. The mean concentrations of most elements exceed the threshold effect level (TEL), probable effect level (PEL) and effects range low (ERL) values indicating that, there may be ecotoxicological risk to sediment dwelling organisms.

Characterizing metal levels and their speciation in intertidal sediments along Mumbai coast, India

The present study investigated the concentration, distribution and speciation of metals (Fe, Mn, Cu, Pb, Co, Zn and Cr) in sediments of Mumbai region. Pearsons correlation matrix and cluster analyses showed good association of metals with grain size and organic matter. Factor analysis applied to the speciation data helped to identify the role of different sediment fractions in metal retention. The environmental risks of metals, evaluated by sediment quality guidelines, revealed some contamination in the region. However, the Individual and Global Contamination Factors and the Risk Assessment Code, suggested low risk to the aquatic environment, except of Mn in the creek sediments.

Geochemical Evidence of Anthropogenic Impacts in Sediment Cores from Mudflats of a Tropical Estuary, Central West Coast of India

The concentration of trace metals (Co, Cr, Zn, Cu, and Pb), major elements (Al, Mn, Fe, Ca, Mg, and K), along with the percentage of sediment components (sand, silt, clay, and organic carbon), was determined in three sediment cores, collected from intertidal regions of the Zuari estuary (ZA and ZR) and Cumbharjua canal (CB). The Cores CB and ZR, collected from the upper middle estuarine environment, showed higher values of finer fractions and total organic carbon as well as metals (except of Ca) than Core ZA, which was sampled from the lower estuarine environment. The concentration of trace metals including Mn and Fe was found to be largely dependent on the proximity to mining areas, with Core ZR and Core CB representing the highest metal concentrations (Mn, Fe, Cr, and Zn). Absence of a significant early diagenetic remobilization might have preserved the metal loadings due to mining and industrial activities in Cores ZR and CB. In Core ZA, all the elements except Cu showed significant enrichment in the upper portion. Enrichment factor computed in all the cores was found to be above 2 for all the studied metals except Zn, which suggests a high degree of metal contamination. All these observations indicate that the present study area is under the strong influence of anthropogenic activities, especially in recent years.

Assessment of metal enrichment and their bioavailability in sediment and bioaccumulation by mangrove plant pneumatophores in a tropical (Zuari) estuary, west coast of India.

Sediment collected from the estuarine mangroves of the Zuari estuary and Cumbharjua canal were analyzed to assess the concentration, contamination and bioavailability of metals. Mangrove pneumatophores were also analyzed to understand the metal bioaccumulation in mangrove plants. The results indicated the variation of metal concentrations in sediment along the estuary was attributed to changing hydrodynamic conditions, type of sediment and metal sources. Further, speciation studies revealed that Fe, Cr, Co, Ni, Cu and Zn were mainly of lithogenic origin and less bioavailable while high Mn content in the sediment raised concerns over its potential mobility, bioavailability and subsequent toxicity. The mangrove plants exhibited difference in metal accumulation due to variations in sediment parameters and metal availability, in addition to difference in plant species and tissue physiology that affect metal uptake. Moreover, the mangrove plants reflected the quality of the underlying sediment and can be used as a potential bio-indicator tool.

Role of sediment size in the distribution and abundance of metals in a tropical (Sharavati) estuary, west coast of India

Two sediment cores representing adjacent mudflat and mangrove sub-environments from the middle region of Sharavati estuary were analyzed for sand, silt, clay and organic carbon at 2-cm interval. Metal concentration was also analyzed for all bulk sediment samples and selected samples for different sediment size fractions (sand (4Ø), medium silt (6Ø) and clay (8Ø) of both the cores for Aluminium (Al), Iron (Fe), Manganese (Mn), Nickel (Ni), Zinc (Zn), Copper (Cu), Cobalt (Co), and Chromium (Cr). The sediments of mudflat environment are found to be enriched with metals, organic carbon (OC) associated with finer sediments. However, the core collected from the mangrove environment showed higher coarser material. The association and degradation of organic matter played important role in distribution of metals in silt and clay fractions in mudflat core. The paper also discusses on source of sediments and process involved with time. Higher enrichment factor (EF) values of Zn in silt and clay fraction and Co in sand and silt fraction are observed in the mangrove core as compared to mudflat core, whereas, Cu is enriched in the silt and clay fraction of mudflat core. However, Cr was enriched in all the fractions of both the cores. Pollution load index (PLI) indicated higher metal enrichment in the clay fraction of both the cores.

Processes and factors regulating the distribution of metals in mudflat sedimentary environment within tropical estuaries, India

The present study investigates processes and factors which determine the distribution of grain size, organic carbon and metals in mudflat sediment cores collected from lower regions of three tropical estuaries, viz., Mandovi, Sharavathi and Gurupur. The three rivers are similar in terms of monsoonal characteristics and discharge pattern, but are different in tidal range, catchment area geology and anthropogenic activities. The data revealed increase in finer sediments, organic carbon and metals in the recent years in Mandovi and Sharavathi estuaries, while the data revealed decrease in the Gurupur estuary. The increase in finer sediments in Mandovi and Sharavathi estuaries was attributed to catchment area activities, rainfall and runoff and mixing behaviour within estuaries. The change in the morphology of the Mangalore spit led to an increase in coarser sediments in the recent years in the Gurupur estuary. The similarity in distribution pattern of metals to that of finer sediments and organic carbon in three estuaries indicated the role of finer sediments and organic carbon in distribution of metals. In addition, correlation, factor and cluster analyses suggested the role of Fe and/or Mn oxide in adsorption of metals onto sediments. However, the factors regulating distribution of metals varied among the three estuaries, which are attributed to variations in rock types in their basins, in addition to changes in response to natural forces and human activities.