Geochemical distribution,bioavailability and potential toxicity of some trace metals in a complex micro-tidal estuary,Southwest India

The spatial and temporal variations of some trace metals in the surface sediments of Cochin Estuary were analyzed along with their geochemical associations to identify the possible sources, bioavailability and the health risks posed by them. The dominance of kaolinite and suggested that clay minerals distribution is influenced by sediment sorting. Total metal analysis revealed enrichment for Cd, Pb and Zn due to anthropogenic activities. The speciation analysis established that notwithstanding the large availability, carbonate as well as organic and sulfides bound fractions showed negligible associations with most of the metals. Hydrous Fe–Mn oxides appeared to play a major role in controlling the fate and transport of these metals in the sediments of Cochin Estuary. Lower contribution of the residual fractions for Cd (21%–26%), Pb (<60%) and Zn (24%–42%) indicated an obvious increase of other geochemical fractions. Risk assessment analysis revealed that regardless of total concentration, none of the analyzed metals were at safe levels in the estuary as appreciable percentages were found to be associated with mobile geochemical forms. The speciation study conspicuously established that the metals originating from non-geogenic sources are largely associated with the labile fractions and hence are more detrimental to the aquatic biota.     

Mercury in surface waters of a macrotidal urban estuary (River Adour, south-west France)

Surface waters were collected in the River Adour estuary (south-western France) during different sampling periods from 1998 to 2001 in order to investigate the phase distribution and speciation of methylmercury (MeHg⁺). Although a high variability is observed, significant higher average concentrations of total MeHg⁺ (dissolved and particulate) are measured during the warm seasons, at 4.40±8.18 pM and 3.90±1.87 pM for July 1998 and September 1999, compared with the winter seasons, with concentrations at 0.99±2.85 pM and 1.00±1.75 pM for February 1998 and February 2001, respectively (one-tailed t-test, P=0.01). The seasonal variations are explained with enhanced bacterial activity during summer and sedimentation/resuspension phenomena. Additionally, signi-ficant longitudinal variations of the MeHg⁺ concentrations are observed. The highest levels in both dissolved and particulate fractions are found within the downstream urban estuarine area. This can be explained by the high methylation potential of the sediments, but direct anthropogenic inputs of MeHg⁺ from specific discharge points cannot be neglected. Biogeochemical factors like phytoplankton biomass and salinity also show a relationship with MeHg⁺ partitioning in the surface waters of the Adour estuary.     

Geochemical index of trace metals in the surficial sediments from the western continental shelf of India, Arabian Sea

The present study focuses on the determination and abundance of trace metals (viz. Cu, Ni, Zn, Cr, Co, Cd, Mn and Fe) in the surficial sediments of west coast of Arabian Sea along the Indian subcontinent. Sediment samples were collected from three transects along the western continental shelf of Arabian Sea. The enrichment of Fe and Mn in coastal oxic-sediments indicates the precipitation of these redox sensitive elements as Fe- and Mn-hydroxides and oxides, whereas the low Fe and Mn concentrations in the oxygen deficient sediments of deeper stations reflects the dissolution of their hydroxides and oxides. Concentrations of fairly redox insensitive trace metals like Cu, Ni, Zn, Cr and Cd (with the exceptions of Cr) showed higher values at nearshore sediments, then it decreased towards seaward and again showed a slight increase at oxygen minimum stations in all the three transects. This geochemical variability in their distributional characteristics is mainly associated with the extent to which the precipitation or dissolution of Fe- and Mn-oxides/hydroxides occur since the scavenging or releasing effects of Fe- and Mn-oxides/hydroxides act as significant ‘sinks’ or ‘sources’ of heavy metals. The change in wind pattern, coastal upwelling and increased productivity are also the reported factors which influence the biogeochemical cycling of trace metals in the surface sediments of west coast of India. Enrichment factor generally showed a high gradient accumulation from nearshore to shelf.     

Speciation of heavy metals in sediments from the Scheldt estuary,Belgium

A simple three-step sequential extraction procedure was applied to study the speciation of heavy metals in sediment from Scheldt estuary, and their relationship to sediment grain size and organic matter content. The sedimentary metal content was fractionated into carbonate and exchangeable, metals bound to organic matter and residual fractions. Sedimentary total metal content was also determined using an industrial microwave (ETHOS 900) HF/HNO₃ extraction method. The extracts were analysed for metals using inductively coupled plasma atomic emission spectrometry. The bioavailable fraction (exchangeable and metals bound to organic matter) comprised less than the other forms. Residue metals were the dominant form of metals in almost all studied sites. The average total metal content for the studied sites decreased in the order Fe>Cr>Cu>Co>Zn>Pb>Cd. Based on average values for the studied sites, the highest bioavailable metals in sediments were Cd (38%) from Westkapelle, Zn (17%) from Yerseke, Co (12%) from Domburg, Cr (9%) from Vlissingen, Fe and Pb each (2%) from Yerseke, and Cu (1%) from Domburg. Metal recovery was good, with<10% difference between the total metal recovered through the extractant steps and the total metal determined using HF/HNO₃ extract.     

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.     

Seasonal and tidal impact on the organic compounds and nutrients distribution in tropical mangroves,Kerala, India

Seasonal changes in the concentration of nutrients and various organic compounds were studied in the waters surrounding mangroves and in the marshy areas of mangroves. Higher amounts of nutrients and organic compounds were observed during low tide. This is due to the remineralisation of plant detritus in this area. High concentration of carbohydrates, proteins, chlorophyll and phosphate were observed during monsoon, which can be attributed to the leaching of plant detritus as well as the land run-off. During pre-monsoon and post-monsoon high tannin and lignin concentration was noted. A 24-hour sampling was also done to study the tidal impact on the concentrations of various organic compounds and nutrients in this ecosystem. Even though a tidal impact was observed, a clear picture was not reported in this study.     

Seasonal and tidal impact on the organic compounds and nutrients distribution in tropical mangroves, Kerala, India

Seasonal changes in the concentration of nutrients and various organic compounds were studied in the waters surrounding mangroves and in the marshy areas of mangroves. Higher amounts of nutrients and organic compounds were observed during low tide. This is due to the remineralisation of plant detritus in this area. High concentration of carbohydrates, proteins, chlorophyll and phosphate were observed during monsoon, which can be attributed to the leaching of plant detritus as well as the land run-off. During pre-monsoon and post-monsoon high tannin and lignin concentration was noted. A 24-hour sampling was also done to study the tidal impact on the concentrations of various organic compounds and nutrients in this ecosystem. Even though a tidal impact was observed, a clear picture was not reported in this study.     

Aerobic heterotrophic bacterial diversity in sediments of Rajakkamangalam estuary, south west coast of India

The abundance of aerobic heterotrophic bacterial population in the sediment sample of six experimental stations (S1 to S6) at Rajakkamangalam estuary was studied for a period of one year from March, 1998 to February, 1999. The important bacterial genera encountered were Pseudomonas, Bacillus, Vibrio, Escherichia, Micrococcus, Enterobacter, Salmonella, Aeromonas, Shigella, Klebsiella, Proteus, Alkaligenes, Staphylococcus, Citrobacter and Flavobacterium. The bacterial population based on numerical counts showed wide fluctuations in their distribution at different stations. Among the bacterial genera Pseuaomonas was found to be the dominant genus during the experimental period. The qualitative and quantitative distribution of microflora in the sediment samples are discussed.     

春、夏季长江口海水、沉积物及生物体中重金属含量及其评价

根据2009年5月（春季）、8月（夏季）长江口海域的环境调查资料,分析了长江口及其临近海域水相、表层沉积物及生物体内的6种重金属含量及分布特征,利用单因子指数法对污染状况进行了评价,并就污染来源进行了探讨。结果表明：研究海域春季表层水体中以Cu和Hg污染为主,超标率均为30%,而底层则主要为Hg污染,超标率为35%,Zn和Pb除个别站位超标外,其它站位状况良好;夏季表、底层水体中重金属污染以Cu、Zn和Hg污染较为严重,各重金属质量浓度约为春季水体中的2倍。研究海域春季表层沉积物中重金属污染状况由大到小依次为Cd、As、Cu、Zn、Pb、Hg,夏季表层沉积物中重金属污染状况由大到小依次为Cd、Cu、As、Hg、Zn、Pb,春、夏季沉积物中各重金属质量分数有所差异,总体表现为春季高于夏季。生物体内重金属质量分数状况较好,均符合各类食品安全标准。春、夏季沉积物对重金属的富集能力有所不同;但总体表现为春季富集能力高于夏季,这可能与泥沙再悬浮造成的重金属重新释放有关;鱼类和甲壳类对不同重金属的富集能力有所差异,鱼类对重金属的富集能力由大到小依次为Cd、Pb、Cu、Zn、Hg、As,而甲壳类对重金属的富集能力由大到小依次为Pb、Cd、Hg、Zn、Cu、As。     

Heavy metals associated with reduced sulfur in sediments from different deposition environments in the Pearl River estuary, China

Distribution of acid volatile sulfur (AVS) and the simultaneously extracted metals (SEM: Cu, Pb, Zn, Cd, Ni) in sediment profiles has been studied at five sites in Pearl River estuary, China. Of the five sampling locations, Nos.1 and 2 are in the middle shoal, Nos.3 and 4 in the west shoal and No. 5 locates to the south of the estuary. The AVS content in the sediments of the middle shoal varies in a small range (0.25–4.06 μmol g⁻¹), while that of west shoal increases with depth from 0 to ultimately 26.09 μmol g⁻¹. The SEM concentration in the sediment profiles at location Nos. 1, 2 and 5 is generally in the range of 0.95±0.2 μmol g⁻¹ with a slight upward increase, while that in the sediment of west shallows are much higher (1.43–2.42 μmol g⁻¹) with a significant upward increase, especially in the upper layer of ca. 15 cm. The observed upward increase of SEM content at all the sites implies that heavy metal contamination of sediment in the Pearl River estuary is increasing. Calculations of the excess heavy metal content which is defined by SEM-AVS molar difference suggests that the upper sediment in the Pearl River estuary, especially on the west shallows, could be a source of heavy metal contaminants and may cause toxicity to the benthos. The site-specific distribution patterns in the AVS and SEM profiles were interpreted according to the hydrogeochemistry of deposition environments.     

Seasonal variations in physico-chemical parameters and heavy metals in water and sediments of Uppanar estuary, Nagapattinam, India

The present study was carried out to determine the physico-chemical characteristics and heavy metals in water and sediments in Uppanar Estuary, Nagapattinam, Southeast coast of India during January to December 2007. The minimum and maximum values of atmospheric and surface water temperatures (degrees C), salinity (per thousand), pH and dissolved oxygen (ml l(-1)) were: 26.0-35.0; 25.0-33.5; 8.0-35.0; 7.2-8.2 and 2.8-5.5 respectively. The ranges of nitrate, nitrite, phosphate and silicate were: 7.05-24.23; 0.82-3.15; 0.31-2.18 and 40.0-198.0 (microM) respectively. The ranges of heavy metals in water (microg 1(-1)) and sediment (microg g(-1)) copper zinc, cadmium and mercury were: 2.45-18.25; 26.43-101.24; 1.23-24.35 and 0.01-0.22 and 5.02-81.27; 22.47-75.42; 2.25-10.06 and 0.01-0.16 respectively.     

Seasonal variations of organic-carbon and nutrient transport through a tropical estuary (Tsengwen) in southwestern Taiwan

This paper reports the fluvial fluxes and estuarine transport of organic carbon and nutrients from a tropical river (Tsengwen River), southwestern Taiwan. Riverine fluxes of organic carbon and nutrients were highly variable temporally, due primarily to temporal variations in river discharge and suspended load. The sediment yield of the drainage basin during the study period (1995–1996, 616 tonne km^–2 year^–1) was ca. 15 times lower than that of the long-term (1960–1998) average (9379 tonne km² year^–1), resulting mainly from the damming effect and historically low record of river water discharge (5.02 m³ s^–1) in 1995. The flushing time of river water in the estuary varied from 5 months in the dry season to >4.5 days in the wet season and about 1 day in the flood period. Consequently, distributions of nutrients, dissolved organic carbon (DOC) and particulate organic carbon (POC) were of highly seasonal variability in the estuary. Nutrients and POC behaved nonconservatively but DOC behaved conservatively in the estuary. DOC fluxes were generally greater than POC fluxes with the exception that POC fluxes considerably exceeded DOC fluxes during the flood period. Degradation of DOC and POC within the span of flushing time was insignificant and may contribute little amount of CO₂ to the estuary during the wet season and flood period. Net estuarine fluxes of nutrients were determined by riverine fluxes and estuarine removals (or additions) of nutrients. The magnitude of estuarine removal or addition for a nutrient was also seasonally variable, and these processes must be considered for net flux estimates from the river to the sea. As a result, nonconservative fluxes of dissolved inorganic phosphorus (DIP) from the estuary are –0.002, –0.09 and –0.59 mmol m^–2 day^–1, respectively, for dry season, wet season and flood period, indicating internal sinks of DIP during all seasons. Due to high turbidity and short flushing time of estuarine water, DIP in the flood period may be derived largely from geochemical processes rather than biological removal, and this DIP should not be included in an annual estimate of carbon budget. The internal sink of phosphorus corresponds to a net organic carbon production (photosynthesis–respiration, p–r) during dry (0.21 mmol m^–2 day^–1) and wet (9.5 mmol m^–2 day^–1) seasons. The magnitude of net production (p–r) is 1.5 mol m^–2 year^–1, indicating that the estuary is autotrophic in 1995. However, there is a net nitrogen loss (nitrogen fixation–denitrification < 0) in 1995, but the magnitude is small (–0.17 mol m^–2 year^–1).     

Distribution and behaviour of polycyclic aromatic hydrocarbons in subtropical river estuary,Okinawa, Japan

Surface water samples were collected along the salinity gradient of Manko estuary in Okinawa, Japan, between January and November 2012, to examine spatial and temporal variability in the distribution, composition, behaviour, and sources of particulate polycyclic aromatic hydrocarbons (PAHs). Concentrations of total particulate PAHs ranged from 169.7?ng?g^?1 at riverine station (N1) in November 2012 to 922?ng?g^?1 at another riverine station (K3) in May 2012. Based on observed environmental behaviour, particularly relationships to organic matter, the PAHs appear divisible into two groups: group I (low molecular weight) PAHs were characterised by low particles affinity and strong correlations with a pool of autochthonous organic matter (e.g. high concentrations of polyunsaturated fatty acids), reflecting processes controlling their delivery to the estuary; and, in contrast, group II (high molecular weight) PAHs were characterised by high particles affinity and exhibited estuarine distribution primarily controlled by suspended solid load and inputs from terrigenous sources through river inflows. This relationship, coupled with isomer ratios indicative of combined mixed sources from petroleum and petroleum combustions, indicates that terrestrial run-off is the dominant mode of delivery of particulate PAHs in the estuary. The relationships between distinct groups of PAHs and lipid biomarkers demonstrated in this study suggest that very specific pools of particulate organic matter, as opposed to concentrations of particulate organic carbon alone, can be important in the transport and fate of hydrophobic contaminants.     

Diversity of soft-bottom benthos in a tropical estuary: Gulf of Nicoya,Costa Rica

The community structure of soft-bottom infauna is described for the Gulf of Nicoya, Costa Rica, Central America, with special reference to the relationship between diversity and a tropical estuary. Of the 205 species of invertebrates collected in July, 1980, polychaetes comprised 58.6% by number of species and 68.1% by number of individuals. Density ranged from zero to 8 744 m^-2 with a mean of 1 269 m^-2 per station, and biomass ranged from zero to 10.986 g m^-2 with a mean of 2.010 g m^-2. Numerical analysis indicated considerable faunal homogeneity, characterized by polychaetes. Five major polychaete feeding guilds were recognized. From measures of diversity we concluded that the soft-bottom community of the Gulf of Nicoya was not rich for a tropical estuary. Physical processes (riverine runoff and frontal systems) mainly influenced community structure and function in the lower Gulf whereas biological processes (predation) seemed to prevail in the upper Gulf.Southern California Ocean Studies Consortium Contribution No. 23     

黄河口潮间带表层沉积物重金属和营养元素的分布特征

于2010年5月采集了5个断面的黄河口潮间带高、中和低潮滩的表层沉积物样品,对沉积物的理化性质、重金属和营养元素的空间分布特征进行了研究,并采用单因子污染指数法和综合潜在生态风险指数法,参考加拿大安大略省环境和能源部关于沉积物质量指南,对黄河口潮间带沉积物质量进行了评价。结果表明,除Cu和Pb外,其它重金属和营养元素质量分数均表现为河口北侧高于南侧;除Hg外,高、中和低潮滩的表层沉积物重金属和营养元素质量分数无显著差异,没有表现出成熟潮滩明显的垂岸分带特征。Pb质量分数高于渤海表层沉积物的高值,是该区域的首要污染因子;Hg在河口北侧近河口的两个站位低潮滩质量分数达到海洋沉积物质量一类标准的1.7和1.8倍,存在一定的潜在生态风险;TN和TOC质量分数范围在安全级别,TP质量分数在20%的站位超过最低安全级别,存在一定的安全风险。与国内其它潮滩相比,黄河口潮间带重金属Zn、Cd、Hg和As的质量分数处于较低水平,Cu和Pb质量分数处于中等水平,TOC和TP质量分数与长江口潮间带相当,TN质量分数较低。研究结果将为黄河三角洲地区生态保护、环境管理和污染治理提供基础数据。     

It's a dirty job but someone has to do it: The role of marine benthic macrofauna in organic matter turnover and nutrient recycling to the water column

Benthic macrofaunal populations through their feeding, bioturbation, burrow construction and sediment irrigation activities have profound influences on organic matter inputs to marine sediments (biodeposition) and on the vertical distribution of deposited organic matter within the sediment. These effects in turn influence the rates and pathways of organic matter mineralisation, and element cycles. Similarly, bioturbation, burrow construction and burrow irrigation are major determinants of sediment-water column fluxes of oxygen and nutrients.

In this review, I discuss the influences of the different benthic macrofaunal feeding (functional) groups on mineralisation processes and sediment-water column fluxes of particulate and dissolved nutrients. How these effects influence diagenic processes, the balance between aerobic and anaerobic processes, and the redox status of the surficial sediments. Finally, I discuss some of the limitations of the predominantly laboratory techniques which have been used to study “macrofaunal effects” and how this hinders the inclusion of the effects in quantitative sediment biogeochemical models.     

It's a dirty job but someone has to do it: The role of marine benthic macrofauna in organic matter turnover and nutrient recycling to the water column

Benthic macrofaunal populations through their feeding, bioturbation, burrow construction and sediment irrigation activities have profound influences on organic matter inputs to marine sediments (biodeposition) and on the vertical distribution of deposited organic matter within the sediment. These effects in turn influence the rates and pathways of organic matter mineralisation, and element cycles. Similarly, bioturbation, burrow construction and burrow irrigation are major determinants of sediment-water column fluxes of oxygen and nutrients.

In this review, I discuss the influences of the different benthic macrofaunal feeding (functional) groups on mineralisation processes and sediment-water column fluxes of particulate and dissolved nutrients. How these effects influence diagenic processes, the balance between aerobic and anaerobic processes, and the redox status of the surficial sediments. Finally, I discuss some of the limitations of the predominantly laboratory techniques which have been used to study “macrofaunal effects” and how this hinders the inclusion of the effects in quantitative sediment biogeochemical models.     

Assessment of petroleum hydrocarbon in a tropical brackish water lagoon: Chilika,India

Assessment of petroleum hydrocarbon (PHC) in the Chilika Lagoon, India, revealed a significant spatio-temporal variation in surface water (analysis of variance: n?=?120, p?相似文献   

Diets of piscivorous fishes in a tropical Australian estuary,with special reference to predation on penaeid prawns

The diets of fish from the tropical Embley Estuary in the eastern Gulf of Carpentaria, Australia, were analysed with particular reference to piscivory and predation on juveniles of commercially important penaeid prawns from October 1986 until July 1988. Of the 77 species caught, 52 were piscivorous, and of these 37 ate penaeid prawns. The most numerous piscivores wereScomberoides commersonianus, Arius proximus, Lates calcarifer, Polydactylus sheridani andRhizoprionodon acutus, the first four of which accounted for over 90% of all prawns eaten. Twenty species are commercially important species of prawns. The proportions of penaeids in the diets varied seasonally, according to the density of penaeids in the estuary. The proportion was highest during the pre-wet period (November) and lowest during the dry period (July–August). Predation on prawns was highest in the lower and middle reaches of the river. Estimates of the rates of predation on the two most common juvenile commercial prawns,Penaeus merguiensis andP. semisulcatus, are presented and discussed.