Sediment Total Organic Carbon Content Research Articles

Environmental controls on the distribution of metals in porewater and their diffusion fluxes at the sediment-water interface of the western Pacific

The intermountain basin of the western Pacific is rich in polymetallic nodules with commercial exploitation potentialities. Regarding the potential impacts of metals during deep sea mining operations, the regeneration process of metals with environmental controls and their diffusion fluxes at the sediment water interface (SWI) are of great importance. Our results demonstrated that the deep-sea environment in the western Pacific seafloor was characterized as organic carbon-starved sediments, with a total organic carbon content (TOC) between 0.2%–0.5%. Sedimentary Eh (SEH) ranged from 400 mV to 570 mV, indicating suboxidized to oxidized conditions. The vertical profiles of dissolved metals in porewater showed an enrichment of nodule-related metals and conservative metals (Mo, Li, Rb, Cs) in the uppermost suboxidized zone. They were related to desorption with labile particles, as well as remobilization by the reduction of Mn- and Fe-oxides under suboxidized condition. The diffusion fluxes of those nodule-related metals (Co, Ni, Mn, Pb, Zn) to the overlying water were low and fluctuated within the study area. The relatively high concentrations in the overlying water also confirmed a continuum with equivalent contributions to nodule formation from the bottom water as well as from the pore water. The principal components analysis (PCA) results further indicated that environmental gradients in Eh, TOC, δ13Corg, and mean grain size of sediment as well as spatial gradients in distance from the nearest sea mountain, latitude, and water depth posed a significant impact on the diffusion fluxes of different metals. Despite many uncertainties in sediment disturbance during nodule mining activities, this baseline information supports further estimation of the potential release of metals under sediment disturbance.

Mid-Holocene environmental change and human response at the Neolithic Wuguishan site in the Ningbo coastal lowland of East China

Coastal wetlands provided a favorable settling site for Neolithic people because of their highly exploitable biomass, but were vulnerable to marine hazards such as coastal flooding. The Chinese Hemudu culture persisted for ~2000 years (7200–5300 cal. year BP) in the Ningbo coastal lowland of East China. This study explores the Hemudu people’s survival strategy using sedimentological and chronological records, and organic and acetic-acid-leachable alkaline-earth (Ca, Sr, and Ba) chemistry on a well-dated profile from the coastal Wuguishan site in the Ningbo Plain. Analyses of alkaline-earth elements in surficial sediments collected from present-day alluvial plain, tidal river, and saltmarsh/tidal flat environments in the Ningbo Plain were also undertaken to explain sedimentary environmental changes and their linkage to Hemudu activity at the Wuguishan site. Results indicate high sediment acetic-acid-leachable Ca and Sr contents with high Sr/Ba ratios, and high sediment total inorganic carbon contents at the site during 6300–6000 cal. year BP, which coincided with a marine incursion at the nearby Neolithic Yushan site. However, the increasing sediment total organic carbon contents and decreasing δ13C values suggest that the Wuguishan site evolved from an upper tidal flat to a saltmarsh environment, attracting settlement by the prehistoric Hemudu people after ~6200 cal. year BP. Sr and Ca contents and Sr/Ba ratios decreased after ~6000 cal. year BP, indicating that the site developed into a low-salinity marsh in the supratidal environment after rapid accumulation caused by a storm event at ~6020 cal. year BP. Furthermore, the high Sr and Ba contents in the layers of Hemudu Culture Period III indicate the Hemudu people’s consumption of seafood and their adaption strategy for living in the vulnerable coastal wetland.

Distribution characteristics and ecological evaluation of chlorobenzene compounds in surface sediment of the Maowei Sea, Guangxi, China.

To enhance our understanding on environmental conditions of the Maowei Sea in Guangxi province, China, the concentration and distribution of 22 chlorobenzene compounds (CBs) in the surface sediment were determined by gas chromatography-mass spectrometry (GC-MS). The relationship of the sediment between CBs and total organic carbon (TOC) was also investigated. The results showed that a total of eight kinds of CBs compounds were detected in the sediment samples which were collected from the coastal environment of the Maowei Sea, with an average concentration of 15.3ng·g-1 (the concentration range, 2.5-61.5ng·g-1). The rank of their average concentrations was as follows: 2,3,4,5,6-pentachlorotoluene > hexachlorobenzene, 2-chlorotoluene, 3-chlorotoluene and 2,3-dichlorotoluene > 2,4-dichlorotoluene > 4-chlorotoluene > pentachlorobenzene. Most CBs were distributed in sediments along the east coast of the Maowei Sea. For total TOC content in sediments, the concentration in the sampling locations was similar, with a mean concentration of 8.83g·kg-1 (the concentration range, 4.87-20.13g·kg-1). However, there was no significant correlation between the concentration of TOC and total CBs. Compared to the corresponding CBs in the sediment of other coastal areas in mainland China and other countries, the value of CBs in the Maowei Sea was low.

Historical record, source, and toxicity assessment of sedimentary organic matter using molecular composition of hydrocarbons in an urban lake, Wuhan, China

The historical record of the spatial distribution, source, occurrence, and ecotoxicology of organic matter deposited in the past 100 years was investigated in a sediment core from an urban lake, in central China by analyzing different organic targets. These targets included total organic carbon (TOC), n-alkanes, representative petroleum biomarkers of terpanes and steranes, non-alkylated polycyclic aromatic hydrocarbons (PAHs), and their alkylated congeners (APAHs). Three sediment cores were collected from East Lake (Wuhan, China) in September 2013. The freeze-dried samples were Soxhlet extracted and cleaned up/fractionated into saturated and aromatic fractions. Gas chromatography equipped with mass spectrometry (GC-MS) was used to analyze the specific target groups. The TOC content of sediment was determined by an elemental analyzer after the freeze-dried sediments were pre-treated with 1 mol L−1 HCl to remove carbonate. The impact of human activities has become more serious since the 1960s as determined by analyzing the historical records of the measured parameters, due to the isolation of the study water body from the Yangtze River and the development of the local social economy. Higher plant wax was the major source of the identified n-alkanes; non-alkylated PAHs were more abundant than their alkylated congeners over the past 100 years. The source identification of n-alkanes, petroleum biomarkers, and PAHs suggested that the mixed sources, including biogenic and petrogenic input, and the incomplete combustion of biomass/solid fossil fuel have contributed to the organic matter in the study lake. The toxicity assessment suggested the presence of PAHs would not cause potential toxicity to the benthic organisms. The historical record of organic matter with different molecular compositions reflects the hydrodynamic condition of the study lake and the development of the local social economy. The mixed biogenic, pyrogenic, and petrogenic sources have contributed to the lake sediments. The detected PAHs did not have negative impacts to benthic organics. This study will provide valuable information to control organic contamination and guide potential remediation technologies in the future.

Assessment of heavy metal pollution in surficial sediments from a tropical river-estuary-shelf system: A case study of Kelantan River, Malaysia

To understand the source-to-sink of pollutants in the Kelantan River estuary and the adjacent shelf area in Malaysia, a total of 42 surface sediment samples were collected in the Kelantan River-estuary-shelf system to analyze for grain size, total organic carbon (TOC) content, Al and heavy metals (Cr, Ni, Cu, Zn, Cd and Pb). The surficial sediments were mainly composed of clayey silt and the TOC content in sediments decreased from the river to the shelf. The surficial sediments experienced Pb pollution; Cr only showed a certain level of pollution in the coastal area of the estuary but not in other areas, and Ni, Cu, Zn, and Cd showed no pollution. The heavy metals mainly originated from natural weathering and erosion of rocks and soils in the catchment and enriched near the river mouth. Total organic carbon can promote the enrichment of heavy metals in sediments.

Open-water and under-ice seasonal variations in trace element content and physicochemical associations in fluvial bed sediment.

Across the circumpolar world, intensive anthropogenic activities in the southern reaches of many large, northward-flowing rivers can cause sediment contamination in the downstream depositional environment. The influence of ice cover on concentrations of inorganic contaminants in bed sediment (i.e., sediment quality) is unknown in these rivers, where winter is the dominant season. A geomorphic response unit approach was used to select hydraulically diverse sampling sites across a northern test-case system, the Slave River and delta (Northwest Territories, Canada). Surface sediment samples (top 1 cm) were collected from 6 predefined geomorphic response units (12 sites) to assess the relationships between bed sediment physicochemistry (particle size distribution and total organic carbon content) and trace element content (mercury and 18 other trace elements) during open-water conditions. A subset of sites was resampled under-ice to assess the influence of season on these relationships and on total trace element content. Concentrations of the majority of trace elements were strongly correlated with percent fines and proxies for grain size (aluminum and iron), with similar trace element grain size/grain size proxy relationships between seasons. However, finer materials were deposited under ice with associated increases in sediment total organic carbon content and the concentrations of most trace elements investigated. The geomorphic response unit approach was effective at identifying diverse hydrological environments for sampling prior to field operations. Our data demonstrate the need for under-ice sampling to confirm year-round consistency in trace element-geochemical relationships in fluvial systems and to define the upper extremes of these relationships. Whether contaminated or not, under-ice bed sediment can represent a "worst-case" scenario in terms of trace element concentrations and exposure for sediment-associated organisms in northern fluvial systems. Environ Toxicol Chem 2017;36:2916-2924. © 2017 SETAC.

Pharmaceutical chemicals, steroids and xenoestrogens in water, sediments and fish from the tidal freshwater Potomac River (Virginia, USA)

ABSTRACTSelected pharmaceutical chemicals, steroids and xenoestrogens (PCSXs) consisting of 29 endocrine modulators, therapeutic drugs, pesticides, detergents, plastics, and active ingredients in household products were measured in water, riverbed sediments and fish collected in a tributary embayment of the Potomac River (Hunting Creek, Alexandria, VA, USA) in the vicinity of wastewater discharge. A total of 17 PCSXs were found in the Hunting Creek samples, with steroid hormones (e.g., progesterone and 17α-ethinylestradiol), triclosan, dextromethorphan and bisphenol A being the most prominent micropollutants detected.The geospatial distribution of the PCSXs in Hunting Creek indicated that the steroids correlated with wastewater treatment plant discharge in all matrices, but such an association is tentative in Hunting Creek given the complex nature of urban sources of PCSXs and hydrodynamics in an urban tidal river. The sediment PCSX concentrations correlated with sediment total organic carbon content at all sampling sites. For the most part, the PCSXs showed an enrichment in fish tissue relative to sediments when concentrations were normalized to lipids and sediment organic carbon contents, but the influence of endogenous steroids is also an important consideration for these chemicals.

Occurrence, spatial distribution, and ecological risks of typical hydroxylated polybrominated diphenyl ethers in surface sediments from a large freshwater lake of China.

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) have been frequently observed in marine aquatic environments; however, little information is available on the occurrence of these compounds in freshwater aquatic environments, including freshwater lakes. In this study, we investigated the occurrence and spatial distribution of typical OH-PBDEs, including 2'-OH-BDE-68, 3-OH-BDE-47, 5-OH-BDE-47, and 6-OH-BDE-47 in surface sediments of Taihu Lake. 3-OH-BDE-47 was the predominant congener, followed by 5-OH-BDE-47, 2'-OH-BDE-68, and 6-OH-BDE-47. Distributions of these compounds are drastically different between sampling site which may be a result of differences in nearby point sources, such as the discharge of industrial wastewater and e-waste leachate. The positive correlation between ∑OH-PBDEs and total organic carbon (TOC) was moderate (r=0.485, p<0.05), and site S3 and S15 were excluded due to point source pollution, suggesting that OH-PBDEs concentrations were controlled by sediment TOC content, as well as other factors. The pairwise correlations between the concentrations of these compounds suggest that these compounds may have similar input sources and environmental behavior. The target compounds in the sediments of Lake Taihu pose low risks to aquatic organisms. Results show that OH-PBDEs in Lake Taihu are largely dependent on pollution sources. Because of bioaccumulation and subsequent harmful effects on aquatic organisms, the concentrations of OH-PBDEs in freshwater ecosystems are of environmental concern.

Seismic peak amplitude as a predictor of TOC content in shallow marine sediments

Acoustic remote sensing is a highly effective tool for exploring the seafloor of both deep and shallow marine settings. Indeed, the acoustic response depends on several physicochemical factors such as sediment grain size, bulk density, water content, and mineralogy. The objective of the present study is to assess the suitability of seismic peak amplitude as a predictor of total organic carbon (TOC) content in shallow marine sediments, based on data collected in the Cabo Frio mud belt in an upwelling zone off southeastern Brazil. These comprise records of P-wave velocity (V P) along 680 km of high-resolution single-channel seismic surveys, combined with analyses of grain size, wet bulk density, absolute water content and TOC content for four piston-cores. TOC contents of sediments from 13 box-cores served to validate the methodology. The results show well-defined positive correlations between TOC content and mean grain size (phi scale) as well as absolute water content, and negative correlations with V P, wet bulk density, and acoustic impedance. These relationships yield a regression equation by which TOC content can be satisfactorily predicted on the basis of acoustic impedance for this region: y = − 4.84 ln(x) + 40.04. Indeed, the derived TOC contents differ by only 5% from those determined by geochemical analysis. After appropriate calibration, acoustic impedance can thus be conveniently used as a predictor of large-scale spatial distributions of organic carbon enrichment in marine sediments. This not only contributes to optimizing scientific project objectives, but also enhances the cost-effectiveness of marine surveys by greatly reducing the ship time commonly required for grid sampling.

Microbial bioavailability of 2,2′,4,4′-Tetrabromodiphenyl ether (BDE-47) in natural sediments from major rivers of China

Microbial degradation plays a crucial role in eliminating polybrominated diphenyl ethers (PBDEs) in environments. However, the microbial bioavailability of PBDEs in aquatic sediments is not well understood. In this work, the bioavailability of 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47), a typical PBDE congener, to PBDE-degrading microorganisms in natural sediments from six Chinese rivers under anaerobic conditions was investigated. The contents of black carbon (BC) and total organic carbon (TOC) in the six sediment samples were in the range of 0.025%–0.30% and 0.03%–3.38%, respectively. BDE-47 desorption from various sediments was fitted well with the first-order three-compartment desorption model. The desorbing fraction of sediment-associated BDE-47 at each desorption time interval exhibited a significant negative correlation with the BC content (p < 0.01). In the sediments, the anaerobic debromination of BDE-47 by microorganisms underwent a stepwise debromination pathway generating mainly three lower brominated congeners (BDE-28, -17 and −4). The microbial debromination ratio of BDE-47 ranged from 4.21% to 7.89% in various sediments after 120 d incubation anaerobically, and it negatively correlated with the content of sediment BC significantly (p < 0.01). However, the desorbing fraction and microbial debromination ratio of BDE-47 only showed weak correlations with the TOC content in sediments (p > 0.05). Furthermore, there was a significant positive correlation of desorbing fraction of BDE-47 from sediments with its microbial debromination ratio (p < 0.01) as well as with the level of its three lower brominated products (p < 0.05) after the first 20 d incubation. This study suggests that the BDE-47 bioavailability to microorganisms in anaerobic river sediments is mainly influenced by the content of sediment BC which controls the desorbing fraction of sediment-associated BDE-47.

Predicted effectiveness of in-situ activated carbon amendment for field sediment sites with variable site- and compound-specific characteristics

A growing body of evidence shows that the effectiveness of in-situ activated carbon (AC) amendment to treat hydrophobic organic contaminants (HOCs) in sediments can be reliably predicted using a mass transfer modeling approach. This study analyzes available field data for characterizing AC-sediment distribution after mechanical mixing of AC into sediment. Those distributions are used to develop an HOC mass transfer model that accounts for plausible heterogeneities resulting from mixing of AC into sediment. The model is applied to ten field sites in the U.S. and Europe with 2–3 representative HOCs from each site using site- and HOC-specific model parameters collected from the literature. The model predicts that the AC amendment reduces the pore-water HOC concentrations by more than 95% fifteen years after AC deployment for 18 of the 25 total simulated cases when the AC is applied at doses of 1.5 times sediment total organic carbon content with an upper limit of 5 dry wt%. The predicted effectiveness shows negative correlation with the HOC octanol–water partitioning coefficients and the sediment-water distribution coefficients, and positive correlation with the effectiveness calculated based on equilibrium coefficients of sediment and AC, suggesting the possibility for use of the values for screening-level assessments.

Spatio-temporal distribution patterns of the epibenthic community in the coastal waters of Suriname

This study aimed to characterize the spatio-temporal patterns of the epibenthic community in the coastal waters of Suriname. Data were collected on a (bi)monthly basis in 2012–2013 at 15 locations in the shallow (<40m) coastal area, revealing three spatially distinct species assemblages, related to clear gradients in some environmental parameters. A species-poor coastal assemblage was discerned within the muddy, turbid-water zone (6–20m depth), dominated by Atlantic seabob shrimp Xiphopenaeus kroyeri (Crustacea: Penaeoidea). Near the 30m isobath, sediments were much coarser (median grain size on average 345±103µm vs. 128±53µm in the coastal assemblage) and water transparency was much higher (on average 7.6±3.5m vs. 2.4±2.1m in the coastal assemblage). In this zone, a diverse offshore assemblage was found, characterized by brittle stars (mainly Ophioderma brevispina and Ophiolepis elegans) and a variety of crabs, sea stars and hermit crabs. In between both zones, a transition assemblage was noted, with epibenthic species typically found in either the coastal or offshore assemblages, but mainly characterized by the absence of X. kroyeri. Although the epibenthic community was primarily structured in an on-offshore gradient related to depth, sediment grain size and sediment total organic carbon content, a longitudinal (west-east) gradient was apparent as well. The zones in the eastern part of the Suriname coastal shelf seemed to be more widely stretched along the on-offshore gradient. Although clear seasonal differences were noted in the environmental characteristics (e.g. dry vs. rainy season), this was not reflected in the epibenthic community structure. X. kroyeri reached very high densities (up to 1383ind1000m−²) in the shallow coastal waters of Suriname. As X. kroyeri is increasingly exploited throughout its range, the current study provides the ecological context for its presence and abundance, which is crucial for an ecosystem approach and the sustainable management of this commercially important species and its habitat.

互花米草生物量变化对盐沼沉积物有机碳的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 互花米草生物量变化对盐沼沉积物有机碳的影响 DOI: 10.5846/stxb201404090685 作者: 作者单位: 南京大学,南京大学,南京大学,南京大学,盐城工学院 环境科学与工程学院,青岛海洋地质研究所 作者简介: 通讯作者: 中图分类号: 基金项目: 江苏省自然科学基金重点研究专项(BK2011012); 海洋公益性行业科研专项经费项目(2010418006); 海洋沉积与环境地质国家海洋局重点实验室开放基金(MASEG201205); 国土资源部海洋油气资源和环境地质重点实验室基金项目(MRE201408) The response of organic carbon content to biomass dynamics in Spartina alterniflora marsh Author: Affiliation: Nanjing University,Nanjing University,Nanjing University,Nanjing University,School of Environmental Science and Engineering, Yancheng Institute of Technology, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以江苏王港典型互花米草(Spartina alterniflora)盐沼湿地为研究对象,分析光滩及互花米草滩沉积物中有机碳的水平和垂向分布特征,了解互花米草生物量的季节动态变化,探讨二者之间的相互关系,在此基础上研究互花米草生物量分布和季节变化对沉积物中有机碳(TOC)含量的影响。结果表明,互花米草枯落物中的有机碳数量在两个月内衰减了40%,而表层沉积物中TOC含量及其中互花米草来源TOC所占比例的变化,均与互花米草地表枯落物量的季节变化存在两个月的"相位差",这与枯落物快速分解时间大致吻合,说明枯落物是表层沉积物中TOC的重要来源。高达60%的互花米草地下生物量分布在0-20cm深度内,该深度范围内沉积物中TOC含量较高,且TOC主要来源于互花米草。此外,不同深度TOC含量与地下生物量之间存在良好的正相关关系,说明地下生物量是影响沉积物TOC含量的重要因子。研究区互花米草年固碳能力为2274g m-2 a-1,盐沼沉积物中TOC埋藏速率达到了470 g m-2 a-1,是地表一个重要的碳汇;同时研究区每年向近岸水域输出大量的TOC,是近岸海域生态系统的一个重要碳源。 Abstract:Spartina alterniflora (C4) was introduced to the coastal region of Jiangsu Province as an exotic species in 1982. This perennial grass then gradually invaded regions previously occupied by native C3 plants. Much research has focused on variation of the ecosystem carbon cycle and has demonstrated that this S. alterniflora invasion has increased the carbon accumulation rate. However, the impact of plant biomass (both aboveground and belowground) on the organic carbon content of salt marsh sediments requires further study. To explore the response of organic carbon content to the biomass dynamics in an S. alterniflora marsh, the contents of total organic carbon (TOC), total nitrogen (TN), and stable carbon isotope composition (δ13C) of sediments, in an S. alterniflora marsh as well as the bare flat, were investigated by analysis of coral and surface sediments, together with the biomass variations of S. alterniflora. The sediment water content, grain size, and δ13C of coastal water and S. alterniflora were also determined. The Litterbag method was used to measure the S. alterniflora litter decomposition rate. The results indicate that the organic carbon of newer litter rapidly decomposed in the first 2 months, and then remained stable. The seasonal variation of the TOC content of surface sediments in the S. alterniflora marsh was significant, and a 2-month phase shift was not only observed in the TOC content variations and surface litter mass but was also recorded for the proportion of organic carbon derived from S. alterniflora and surface litter mass. However, this phase-shift phenomenon did not exist on the bare flat, indicating that the litter is a dominant source of the organic carbon in surface sediments. The results show that 60% and 33% of belowground biomass was observed in the top 20 cm and at 20-40 cm depths, respectively. Compared with the bare flat, the vertical changes of TOC content in the S. alterniflora marsh showed a different distribution pattern. That is to say, the TOC content of sediments at depths < 20 cm was significantly higher than those at depths > 20 cm, and had an increasing trend from depth 20 cm to the surface. A similar variation was observed for the proportion of organic carbon derived from S. alterniflora in the top 20 cm of sediments. Furthermore, there was a remarkably positive relationship between the belowground biomass of S. alterniflora and TOC content. This suggests that belowground biomass plays an important role in TOC variation along the profiles. The greatest and least plant organic carbon storages in the S. alterniflora marsh were observed in October and April, respectively. The average carbon fixation of S. alterniflora, with quantity 2274 g·m-2·a-1, was 460% that of terrestrial vegetation in China. Similarly, the burial rate of organic carbon of S. alterniflora marsh sediments, with quantity 470 g·m-2·a-1, was significantly greater than the average value of coastal salt marshes in China. Thus, the S. alterniflora salt marsh fixed large amounts of carbon dioxide from the air, and enhanced the organic carbon accumulation of the sediment. 参考文献 相似文献 引证文献

Relationship between total organic carbon content and sedimentation rate in ancient lacustrine sediments, a case study of Erlian basin, northern China

Relationship between total organic carbon content (TOC) and sedimentation rate (SR) had been studied mainly in marine sediments, which is generally thought to be positive or negative correlation. Based on the data sets of sediment intervals from 111 exploration wells of 8 subbasins in Erlian lacustrine basin, northern China, the relationship between TOC and SR in ancient lacustrine sediments has been studied. The result points out that accompanied with increasing SR, TOC tends to increase and then decrease. The turning point of SR in all subbasins approximates 5cm/ka. Based on the research on biomarker and carbon isotope data, it has been found that the relationship between TOC and SR is controlled by the redox conditions when SR is lower than 5cm/ka, while SR is higher than 5cm/ka, the relationship is controlled by the paleoproductivity. When SR is lower than 5cm/ka, TOC tends to increase with increasing SR in all subbasins, indicating that it is the degradation that controls the TOC. Under the oxidation conditions, the degradation is intense, higher SR gets bigger TOC growth, while in reduction conditions, the degradation is weak, higher SR gets smaller TOC growth. When SR is higher than 5cm/ka, TOC tends to decrease with increasing SR in all subbasins, indicating that clastic dilution, instead of degradation, is the key factor controlling the TOC. The dilution effect is more significant in low palaeoproductivity environment than in high palaeoproductivity environment. Higher SR gets bigger reduction in low palaeoproductivity environment while it gets smaller TOC reduction in high palaeoproductivity environment.

Baseline assessment of heavy metal concentrations in surficial sediment from Kachemak Bay, Alaska.

Heavy metal inputs to coastal Alaska ecosystems are driven by sediment loads from glacial meltwater and river outflows. This study characterized the spatial distribution of 16 major and trace metals in five strata in Kachemak Bay, as well as sediment total organic carbon content and grain size. Homer Harbor, a shallow harbor within the study area, contained elevated metal concentrations compared to the other strata. Outside the harbor, several metals, including Cr, Ni, Pb, and Zn, were significantly higher in the eastern strata than in the western portions of the bay. The opposite was true for a few other metals, such as Hg. However, most metal concentrations were below the National Oceanic and Atmospheric Administration's sediment quality guidelines for sediment toxicity to benthic communities.

Spatial variations in recent ostracode assemblages and bottom environments in Trincomalee Bay, northeast coast of Sri Lanka

Trincomalee Bay is situated on the northeast coast of Sri Lanka. This is the first study to report the recent ostracode assemblages in this bay. As a result, at least 36 ostracode taxa were identified from surface sediments in the bay. Many of them are typical tropical-water species that have been reported from inner bays and shallow marine areas around the coast of the Indo-Pacific region. We compared the species composition of ostracodes in the study area with that in adjacent seas. The result clearly showed that ostracode assemblages from Sri Lanka have strong connection with those along the coast of the Indian subcontinent. Moreover we evaluated the bottom environment in Trincomalee Bay on the basis of statistical analyses of ostracode assemblages combined with grain size, and total organic carbon (TOC) and total nitrogen (TN) contents. The results showed that the TOC content is related to grain size and is relatively high in the inner part of Inner Harbor and Koddiyar Bay, where fine-grained sediments are distributed. Four biofacies were recognized based on Q-mode cluster analysis using ostracode data for 36 taxa. Biofacies I is consistent with distributions of fine-grained sediments with moderate TOC contents (0.30%–0.49 %). Biofacies II is collected from relatively deep water areas with sediments of low TOC contents (0.22%–0.41 %) in InnerHarbor. Biofacies III and IVare characterized by euryhaline species and are influenced by fresh water and shallow depth with low TOC contents (0.14%–0.37%) in sediments. The ostracode distribution in Trincomalee Bay is depend on natural environmental factors such as water depth, grain-size, TOC contents of sediments, and water salinity.

Levels and distribution of tetrabromobisphenol A and hexabromocyclododecane in Taihu Lake, China

The occurrence and distribution characteristics of tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD) in water and sediments from Taihu Lake, China, were investigated. The analytes were quantified by reversed-phase liquid chromatography coupled to electrospray ionization mass spectrometry. The TBBPA levels in water ranged from below the limit of detection (LOD) to 1.12 ng/L, whereas levels in sediments were between 0.056 ng/g dry weight and 2.15 ng/g dry weight. Regarding HBCD, concentrations were from below the LOD to 0.37 ng/L for water samples and from 0.046 ng/g dry weight to 2.56 ng/g dry weight for sediments. No correlation was found between sediment total organic carbon content and TBBPA/HBCDs, while significant positive correlations (r2 = 0.63, p < 0.005) were observed between TBBPA concentrations and HBCD concentrations in sediments. The highest TBBPA (2.15 ng/g dry wt) and total HBCD concentration (2.56 ng/g dry wt) was found at sampling site 1 (S1), while total HBCD levels fell dramatically with increasing distance from S1, suggesting that the estuary inputs around Taihu Lake were important sources of TBBPA and HBCDs. Compared with the pollution levels in the other regions of the world, the concentrations of TBBPA and HBCDs in Taihu Lake were at a moderate or low level. Further study on the sources of TBBPA and HBCDs is required for both assessment of their potential risks and better pollution management in Taihu Lake.

Assessment of ecological quality status of Küçükçekmece Bay (Marmara Sea) by applying BENTIX, AMBI, BOPA and BO2A biotic indexes

This study was carried out to explore the effectiveness of different biotic indexes in the Marmara Sea. The assessment of ecological quality status (EQS) was performed by applying the biotic indexes BENTIX, AMBI, BOPA, BO2A and Shannon-Wienerdiversity, in combination with the estimation of total organic carbon (TOC) content of sediments. BOPA and BO2A indexes tended to overestimate the EQS of the stations. BENTIX was the most efficient index as it demonstrated conceivable EQS results with respect to TOC load and successfuly determined “acceptable” or “not acceptable” status of the stations. TOC content of sediment, which significantly correlated with several benthic measures (S, N, AMBI, BENTIX), proved to be a valuable proxy measure in evaluating the likelihood of benthic impairment. When overall EQS of northern Marmara Sea was discussed, the region was designated as ecologically disturbed with only 25.7% of the stations in acceptable status.

Hydrogen sulfide and organic carbon at the sediment–water interface in coastal brackish Lake Nakaumi, SW Japan

The relationship among H2S, total organic carbon (TOC), total sulfur (TS) and total nitrogen contents of surface sediments (0–1 cm) was examined to quantify the relationship between H2S concentrations and TOC content at the sediment water interface in a coastal brackish lake, Nakaumi, southwest Japan. In this lake, bottom water becomes anoxic during summer due to a strong halocline. Lake water has ample dissolved SO4 2− and the surface sediments are rich in planktic organic matter (C/N 7–9), which is highly reactive in terms of sulfate reduction. In this setting the amount of TOC should be a critical factor regulating the activity of sulfate reduction and H2S production. In portions of the lake where sediment TOC content is less than 3.5 %, H2S was very low or absent in both bottom and pore waters. However, in areas with TOC >3.5 %, H2S was correlated with TOC content (pore water H2S (ppm) = 13.9 × TOC (%) − 52.1, correlation coefficient: 0.72). H2S was also present in areas with sediment TS above 1.2 % (present as iron sulfide), which suggests that iron sulfide formation is tied to the amount of TOC. Based on this relationship, H2S production has progressively increased after the initiation of land reclamation projects in Lake Nakaumi, as the area of sapropel sediments has significantly increased. This TOC–H2S relationship at sediment–water interface might be used to infer H2S production in brackish–lagoonal systems similar to Lake Nakaumi, with readily available SO4 2− and reactive organic matter.

Carbon burial by shallow lakes on the Yangtze floodplain and its relevance to regional carbon sequestration

AbstractFloodplain lakes may play an important role in the cycling of organic matter at the landscape scale. For those lakes on the middle and lower reaches of the Yangtze (MLY) floodplain which are subjected to intense anthropogenic disturbance, carbon burial rates should, theoretically, be substantial due to the high nutrient input, increased primary production and high sediment accumulation rates. There are more than 600 lakes &gt;1 km2 on the Yangtze floodplain including 18 lakes &gt;100 km2 and most are shallow and eutrophic. 210Pb‐dated cores were combined with total organic carbon (TOC) analyses to determine annual C accumulation rates (C AR; g C m−2 yr−1) and the total C stock (since ~1850). The sediment TOC content is relatively low with an average &lt;2% in most lakes. C AR ranged from ~5 to 373 g C m−2 yr−1, resulting in C standing stocks of 0.60–15.3 kg C m−2 (mean: ~5 kg C m−2) since ~1850. A multicore study of Chaohu lake (770 km2) indicated that spatial variability of C burial was not a significant problem for regional upscaling. The possible effect of changes in lake size and catchment land use on C burial was examined at Taibai lake and indicated that lake shrinkage and declining arable agriculture had limited effects on C AR. The organic C standing stock in individual lakes is, however, significantly dependent on lake size, allowing a simple linear scaling for all the MLY lakes. Total regional C sequestration was ~80 Tg C since ~1850, equivalent to ~11% of C sequestration by soils, but in ~3% of the land area. Shallow lakes from MLY are a substantial regional C sink, although strong mineralization occurs due to their shallow nature and their role as C sinks is threatened due to lake drainage.