Sources and transports of polycyclic aromatic hydrocarbons in the Nanshan Underground River,China

Karst areas have much higher ecological vulnerability and are easy to be contaminated by polycyclic aromatic hydrocarbons (PAHs), which are introduced as health risk pollutants. PAHs ratios were used to understand the sources and transport behavior of PAHs conducted in the karst Nanshan Underground River, China. Water, sediments from the underground river and water, sediments, soil from the surface were collected monthly in 2011 and 2012. Abundant PAHs were found both in the underground river and in the surface system. The detected ΣPAHs concentrations varied from 353 to 13,203 ng L^?1 in the groundwaters and content from 169 to 12,038 ng g^?1 in the sediments of the underground river. The ratios of anthracene to anthracene, plus phenanthrene and fluoranthene to fluoranthene, plus pyrene indicated that PAHs were delivered in the groundwaters from combusted grass, wood, and coal, while in the sediments were a mixture of non-combusted petroleum, grass, wood, coal and combusted grass, wood, coal. The similarities in sources between an underground river and surface system indicated that farmlands play a major role for the transport of PAHs and contamination in the underground river. Karst features are liable for the transport behavior.     

Polychlorinated biphenyls in the Nanshan Underground River, China

Abstract Karst areas have much higher ecological vulnerability and are easy to be contaminated by polychlorinated biphenyls(PCBs) which are introduced as health risk pollutants.PCBs concentrations were used to understand the transport behavior of PCBs conducted in the karst Nanshan Underground River,China.Water and sediments from the underground river water,and sediments and soil from the surface of the corresponding watershed were collected monthly in 2011 and 2012 and PCBs were analyzed.Seasonal variations were found in concentrations of PCBs both in the waters and sediments.PCBs concentrations varied from 0.3 to 29.9 ng·L-1 in the groundwater,while from 0.1 to 366.1 ng·g-1 in the underground sediments.Correlations were found in concentrations of PCBs in waters and sediments between the underground river and surface systems which indicate that the surface systems play a major role for the transport of PCBs and contamination in the underground river systems.Karst features are liable for the transport behavior.The underground river waters transport PCBs at mean 3 g·day-1.     

Concentrations, potential sources and behavior of organochlorines and phenolic endocrine-disrupting chemicals in surficial sediment of the Shaying River, eastern China

Levels and distributions of organochlorine pesticides (OCPs) and phenolic endocrine-disrupting chemicals (EDCs) in surficial sediments of the Shaying River, the largest tributary of the Huaihe River in eastern China, were investigated to understand their relationship with the hydrodynamics. Concentrations of total hexachlorocyclohexane isomers (ΣHCHs) and dichlorodiphenyltrichloroethanes (ΣDDT) were in the range of 26.7–119 and 9.64–214 ng g^?1 with mean values of 104 and 80.7 ng g^?1, respectively. Residues of HCHs in sediments can be considered as originating from the application of both technical mixtures and lindane in the past. According to the spatial distribution of (DDD + DDE)/ΣDDT ratios, the influence of recent DDT inputs was dominant upstream, whereas DDD prevailed downstream, due to anaerobic degradation. Concentrations of total phenolic EDCs (ΣEDCs) including nonylphenol (NP), octylphenol (OP) and bisphenol A (BPA) ranged widely from 425 to 3,953 ng g^?1 with the highest level occurring in the middle reach. This accumulation could be attributed to the retransfer of surficial sediment from upstream, where the main sources are located. Spatial distribution of contaminants indicated that riverine hydrodynamics can significantly affect their behavior and fate in sediment. This evidence was further verified by multivariate statistical techniques such as Cluster Analysis (CA), Principle Component Analysis (PCA) and Discriminant Analysis (DA). The CA identified three distinct clusters reflecting the large complexity of river system like geography setting, hydrodynamic condition, etc. This finding was also confirmed by the DA. Furthermore, a PCA demonstrated that about 80.8 % of total spatial variance can be explained by the first three factors, which also indicated that contaminant spatial distributions are driven by local inputs, biodegradation and riverine hydrodynamics.     

Chloride contamination in construction aggregates due to periodic saline water intrusion: a case study in the Kaluganga River Estuary, Sri Lanka

The Kaluganga River Estuary is one of the main sources of construction sand in Sri Lanka. Salt water intrusion along this estuary due to extensive sand mining has increased over the years. Thus, the focus of the current research is to understand the relationship between river sand mining, salt water intrusion, and the resultant effects on construction sand. Two surveys were conducted along the Kaluganga Estuary along an 11 km stretch from the river mouth at predetermined intervals to measure depth water quality profiles, and to collect sediment samples. These surveys were carried out during maximum spring tide; first in a dry period and then in a wet period, to understand hydrographic effects on the quality of river sands. Sand samples were analysed for absolute chloride content and grain size distribution. Results showed significant salt water intrusion during the dry period, averaging 2,307 μS cm^?1 in surface waters throughout the surveyed 11 km stretch along with 3,818 μS cm^?1 (average) in bottom waters up to 5.6 km upstream from the river mouth causing above normal chloride content in the bottom sandy sediments. The high chloride content in bottom sands was recorded up to 5.5 km from the river mouth making them unsuitable for construction purposes. However, during wet period, salt water intrusion levels in the bottom waters were insignificant (average 61 μS cm^?1) and the chloride content in bottom sediments was very low. This study highlighted the requirement for regulations on river estuary sandmining for construction purposes.     

重庆老龙洞地下河不同部位水体、表层沉积物有机氯农药含量及组成研究

为研究重庆老龙洞地下河不同部位水体、表层沉积物有机氯农药分布特征,用气相色谱-微池电子捕获检测器(GC-μECD)分析了样品中OCPs含量。结果表明:研究区水样、表层沉积物中OCPs检出率均为100 %,其浓度在时间上存在季节差异,水体中OCPs、DDTs、HCHs含量丰水期小于枯水期,而在表层沉积物中则表现为OCPs、HCHs丰水期大于枯水期,DDTs丰水期小于枯水期;在空间上则表现为水体中有机氯农药总体下游大于上游,而沉积物中则与之相反。通过对比可知,岩溶洞穴环境由于缺乏光照,空气流动缓慢,生物活动不频繁,使水体中的HCHs不易降解,沉积物中的HCHs不易重新释放而浓度高于洞外。枯水期由于洞内流速较小且变幅不大,水体中的DDTs大量沉积因而其浓度低于洞口,而丰水期洞口因受大量雨水的稀释作用DDTs反而低于洞内的含量;洞内沉积物中的DDTs则因洞内环境恒定不易重新释放和枯水期水体中的大量沉积而一直高于洞外。洞穴环境、不同污水汇入对水体中DDTs和表层沉积物中DDTs、HCHs的组成结构均有不同程度的影响,而对水体中HCHs的组成结构影响不大。此外,地下河不同部位污染源的输入对有机氯污染物的组成结构也有影响。与国内外水体及表层沉积物中HCHs、DDTs相比较,研究区水体、表层沉积物中HCHs、DDTs浓度分别处于中等和偏高水平。      

Distribution of polycyclic aromatic hydrocarbons in recent sediments of Sundarban mangrove wetland of India and Bangladesh: a comparative approach

The present work is the first attempt to compare the data of a comprehensive study of the origin and distribution of 16 priority pollutant polycyclic aromatic hydrocarbons (PAHs) in surface sediments (<63 μm) from 18 sampling stations, 9 from Sundarban of Bangladesh and 9 from Indian counterpart. Σ19PAHs concentration in sediments showed wide variations from 208.3 to 12,993.1 ng g^?1 dry weight in Indian Sundarban, whereas 208.4 to 4,687.9 ng g^?1 in the case of Bangladesh. Fluoranthene, pyrene, benzo(b)fluoranthene, benzo(a)pyrene and dibenzo(a,h)anthracene were predominant species for both the countries. The PAH diagnostic ratios indicated that the PAHs in sediments from both the countries were of mixed source of hydrocarbons of both petrogenic and pyrolytic origin. According to the numerical effect-based sediment quality guidelines, the levels of PAHs in the Sundarban wetland of Bangladesh and India should not exert adverse biological effects. The TEQ values calculated for samples from the Bangladesh and Indian Sundarban varied from 13.68 to 1,014.75 and 1.31 to 2,451 ng g^?1 d.w. with an average of 221.02 and 358.63 ng g^?1, respectively. The overall contamination status of PAH was higher in India than Bangladesh.     

Distribution and source of organochlorine pesticides (OCPs) in the sediments of Poyang Lake

The concentrations of typical organochlorine pesticides (OCPs) (DDTs, HCHs, PCP-Na, and HCB) were measured to understand distribution and source of OCPs in surface and columnar sediments of Poyang Lake in 2006. And OCPS concentrations in surface sediment in 2017 were made a comparison with those in 2006 at several same sampling sites. OCPs showed higher concentrations in main stream than in river mouths (entrance of river flow into lake) of the lake. The average concentrations of HCHs and DDTs were 4.63 ± 3.86 and 20.15 ± 26.86 ng/g in surface sediments in 2006, respectively. Concentrations of OCPs in 2017 were lower than in 2006, such as HCHs average 1.98 ± 2.04 ng/g and DDTs average 4.87 ± 1.48 ng/g in 2017, indicating historical residual and degradation. The primary isomers of HCHs and DDTs in the lake were α-HCH, γ-HCH and p,p′-DDD, respectively. HCHs were from historical residual and lindane application. DDTs were from historical residual. PCP-Na total concentrations in surface sediment were 77.36 ng/g in 2006 and 44.04 ng/g in 2017. The concentration of HCB residues in surface sediment was 0.92 ± 0.90 ng/g in 2006 and 0.42 ± 0.38 ng/g in 2017. The concentrations of OCPs in columnar sediments showed annual variations, and the peak concentrations occurred in 1953, 1961, 1974, 1982, and 1995, showing close relations with onset of production OCPs pesticide in 1950s and its later prohibition in 1980s and a large number agricultural cultivated land decrease in 1990s in China. The concentrations of HCB in columnar sediments were average 2.33 ± 1.26 ng/g. OCPs of columnar sediments were from historical residues and lindane input. The main contamination of OCPs was PCP-Na and p,p′-DDD in Poyang Lake. On the whole, the combination of surface samples (0–5 cm in depth) and columnar samples (0–38 cm in depth) in a single study would give insight into OCPs pollution levels in different years (temporal resolution) and in different regions (spatial resolution) in Poyang Lake.     

岩溶水系统对大气CO2的潜在影响——基于热力学的研究

认识不同条件下岩溶水释放或吸收CO2的反应过程是研究碳酸盐岩对碳循环响应的前提和基础。本文从吉布斯自由能的热力学原理出发,对全球不同岩溶地区162组岩溶水(河水、溪水、湖水等)进行了热力学研究,结果显示:1)河水、溪水、湖水和洞穴滴水等岩溶水所处的环境因方解石矿物沉积而释放CO2成为大气CO2一个潜在的源;2)地下水在所处的环境下由于方解石的溶解而吸收CO2,成为大气CO2一个潜在的汇;3)少数出露点的泉水所处的环境既可发生方解石的溶解而吸收CO2,成为大气CO2的潜在汇,也可发生方解石的沉积而释放CO2,成为大气CO2的潜在源;4)在洪水期,泉水的水化学特征变化并未导致对大气CO2潜在贡献在源汇之间的跨跃性转变。162组岩溶水数据中,所有河水与溪水皆无一例外地在释放CO2。结果表明,从吉布斯自由能的热力学原理出发,研究岩溶水系统对大气CO2潜在源汇的贡献,没有条件约束,是一种较好的途径。     

Transport of particulate organic carbon by the Mississippi River and its fate in the Gulf of Mexico

This study was designed to determine the amount of particulate organic carbon (POC) introduced to the Gulf of Mexico by the Mississippi River and assess the influence of POC inputs on the development of hypoxia and burial of organic carbon on the Louisiana continental shelf. Samples of suspended sediment and supporting hydrographic data were collected from the river and >50 sites on the adjacent shelf. Suspended particles collected in the river averaged 1.8±0.3% organic carbon. Because of this uniformity, POC values (in μmol l^?1) correlated well with concentrations of total suspended matter. Net transport of total organic carbon by the Mississippi-Atchafalaya River system averaged 0.48×10¹² moles y^?1 with 66% of the total organic carbon carried as POC. Concentrations of POC decreased from as high as 600 μmol l^?1 in the river to <0.8 μmol l^?1 in offshore waters. In contrast, the organic carbon fraction of the suspended matter increased from <2% of the total mass in the river to >35% along the shelf at ≥10 km from the river mouth. River flow was a dominant factor in controlling particle and POC distributions; however, time-series data showed that tides and weather fronts can influence particle movement and POC concentrations. Values for apparent oxygen utilization (AOU) increased from ～60 μmol l^?1 to >200 μmol l^?1 along the shelf on approach to the region of chronic hypoxia. Short-term increases in AOU were related to transport of more particle-rich waters. Sediments buried on the shelf contained less organic carbon than incoming river particles. Orgamic carbon and δ¹³C values for shelf sediments indicated 3 that large amounts of both terrigenous and marine organic carbon are being decomposed in shelf waters and sediments to fuel observed hypoxia.     

Mobility of trace elements between the river water,the sediments,and the pore water of Las Catonas Stream,Buenos Aires Province,Argentina

The composition of river water, sediments, and pore waters (down to 30 cm below the bed) of Las Catonas Stream was studied to analyze the distribution of trace elements in a peri-urban site. The Las Catonas Stream is one of the main tributaries of Reconquista River, a highly polluted water course in the Buenos Aires Province, Argentina. The semi-consolidated Quaternary sediments of the Luján Formation are the main source of sediments for Las Catonas Stream. The coarse-grained fraction in the sediments is mainly composed of tosca (calcretes), intraclasts, bone fragments, glass shards, quartz, and aggregates of fine-grained sediments together with considerably amounts of vegetal remains. The clay minerals are illite, illite–smectite, smectite, and kaolinite. For the clay-sized fraction, the external surface area values are mostly between 70 and 110 m²g^?1, although the fraction at 15 cm below the bottom of the river shows a lower surface area of 12 m²g^?1. The N₂ adsorption–desorption isotherms at 77 K for this sample display a behavior indicative of non-porous or macroporous material, whereas the samples above and below present a typical behavior of mesoporous materials with pores between parallel plates (slit-shaped). As, Cr, Cu, and Cd concentrations increase down to 15 cm depth in the sediments, where the highest trace element and total organic carbon (TOC) concentrations were found, and then decrease toward the bottom of the core. Except for As, the levels of the other heavy metals show higher concentration in surficial waters than in pore waters. Distribution coefficients between the sediments, pore water, and surficial water phases indicate that As is released from the sediments to the pore and surficial waters. Cu content strongly correlates with TOC (mainly from vegetal remains), suggesting that this element is mainly bound to the organic phase.     

The distribution, sources and toxicity risks of polycyclic aromatic hydrocarbons and n-alkanes in riverine and estuarine core sediments from the Daliao River watershed

The burial characteristics and toxicity risks associated with n-alkanes and polycyclic aromatic hydrocarbons (PAHs) in the riverine and estuarine sediments of the Daliao River watershed were investigated based on three sediment cores. The sum of the n-alkane and PAH concentrations, normalized to organic carbon (OC), ranged from 0.27 to 63.09 μg g^?1OC^?1 and 6.60 to 366.20 μg g^?1OC^?1, respectively. The features and the history of industrial activities, such as the oil and chemical industries and port activities near the river and estuary, resulted in different distributions and sources of hydrocarbons. The sources of pollution were identified based on n-alkane indexes and on diagnostic ratios of PAHs. The diagnostic ratios indicated that the n-alkanes were derived from both biogenic and petrogenic sources in different proportions and that the PAHs were derived primarily from petrogenic combustion sources. A hierarchical cluster analysis grouped the core samples into two clusters. The first cluster, river sediments, corresponded to industrial activities; the second cluster, estuarine sediments, corresponded to port shipping activities. The toxic potency of the PAHs in the cores was assessed in terms of toxic equivalents (TEQs) of dibenzo[a,h]anthracene and benzo[a]pyrene. The top layer of the sediment in the cores had a relatively high toxicity. The TEQ values for benzo(a)pyrene (TEQ_BaP) and dioxins (TEQ_TCDD) furnished a consistent assessment of the PAHs in the sediment cores.     

Assessment of the ultra-trace mercury levels in selected desert plants

Conventional methods that assessed the mercury (Hg) levels were not only an outcome of atmospheric pollution, but also the possibility of Hg contamination from the sample collection to laboratory analyses. Our studies used the direct mercury analyzer that measured Hg rapidly and precisely at ultra-trace concentrations with detection limit of 0.0015 ng g^?1 on six favored desert plants and their surrounding soil in Kuwait. Analysis revealed elevated Hg concentrations in Tamarix chinensis Lour., and Salsola imbricate Forssk., among the chosen desert plants, especially during summer than in winter, thus labeling the qualities of a bio-indicator to Hg pollution. The overall parts-wise analysis on the six selected plants showed the elevated mean Hg concentrations in the leaves (0.89 ng g^?1) followed by root (0.51 ng g^?1) and stem (0.39 ng g^?1) in the desert plants. Reasons attribute to the capability of these plant parts to absorb, accumulate, and assimilate Hg at varying concentrations. The overall mean Hg concentration was high in soil (2.24 ng g^?1) in comparison with the mean Hg concentrations in the desert plants (0.60 ng g^?1) irrespective of the two seasons. Translocation and bioaccumulation factors indicated low uptake of Hg translocation in the plant parts from the soil. Furthermore, the mean Hg concentration was found high in samples collected from Governorates (GIII) in comparison with the samples collected from other Governorates indicating the effect of pollution from various sources. The present study characterizes the selected plants as bio-indicators and also validates the impact of regional and seasonal variations to Hg pollution at ultra-trace levels in the arid ecosystem.     

Occurrence of synthetic musk compounds in surface,underground, waste and processed water samples in Belgrade,Serbia

This study assessed the state of waters in Belgrade regarding pollution with musk compounds as the target contaminants. Eleven of these compounds were alicyclic, two were macrocyclic, and one was polycyclic. Solid-phase microextraction was used for the isolation of these compounds from waste, surface and underground waters and from processed water prepared for drinking, while comprehensive orthogonal two-dimensional gas chromatography with mass spectrometry was used as the final analytical method. In wastewater samples, galaxolide was detected in concentrations of 1.13 and 0.40 μg/L, while in the Sava River and underground water its concentrations were 0.09 and 0.038 μg/L. The lowest concentrations of the investigated musk compounds were detected in underground water samples, indicating that this is the cleanest water of all the analyzed sources with respect to musk compounds. Comparing the results of musk compound concentrations determined in surface river water samples and clean river water samples utilized for drinking, a lower concentration of these compounds was detected in the clean river water samples. The majority of musk compounds were found in waters utilized for drinking. Based on the concentration values, we conclude that the analyzed waters are moderately polluted with these compounds.     

Characteristics and distributions of atmospheric mercury emitted from anthropogenic sources in Guiyang,southwestern China

Continuous measurements of speciated atmospheric mercury (Hg), including gaseous elemental mercury (GEM), particulate mercury (PHg), and reactive gaseous mercury (RGM) were conducted in Guizhou Province, southwestern China. Guiyang Power Plant (GPP), Guiyang Wujiang Cement Plant, Guizhou Aluminum Plant (GAP), and Guiyang Forest Park (GFP) in Guiyang were selected as study sites. Automatic Atmospheric Mercury Speciation Analyzers (Tekran 2537A) were used for GEM analysis. PHg and RGM were simultaneously collected by a manual sampling system, including elutriator, coupler/impactor, KCl-coated annular denuder, and a filter holder. Results show that different emission sources dominate different species of Hg. The highest average GEM value was 22.2 ± 28.3 ng·m^?3 and the lowest 6.1 ± 3.9 ng·m^?3, from samples collected at GPP and GAP, respectively. The maximum average PHg was 1984.9 pg·m^?3 and the minimum average 55.9 pg·m^?3, also from GPP and GAP, respectively. Similarly, the highest average RGM of 68.8 pg·m^?3 was measured at GPP, and the lowest level of 20.5 pg·m^?3 was found at GAP. We conclude that coal combustion sources are still playing a key role in GEM; traffic contributes significantly to PHg; and domestic pollution dominates RGM.     

重庆典型岩溶区地下河水体有机氯农药污染初步研究

利用GC-ECD对重庆典型岩溶区地下河水体中有机氯农药(OCPs)进行检测,结果表明,地下河水中OCPs浓度为3.41～51.34ng/L,均值为13.23ng/L;滴滴涕(DDTs)浓度为0.07～2.37ng/L,均值为0.72ng/L;六六六(HCHs)浓度为1.16～39.82ng/L,均值为7.89ng/L。南川湾滩地下河水体有机氯农药污染最为严重,其上游纸厂排放废水是影响该地下河有机氯农药污染的主要原因。与国内外其它河流相比较,研究区地下河水体有机氯农药含量处于中低水平。由于岩溶区特殊的二元结构,地表水体一旦受到污染,将直接影响到地下水体。因此,对岩溶地下河进行有机污染物的调查研究具有重要的现实意义      

大气干湿沉降: 地下河多环芳烃的重要来源——以广西清水泉地下河为例

为证实大气干湿沉降物是岩溶地下河中多环芳烃(PAHs)的来源,研究选择了某城市典型的岩溶地下河水源地作为研究地点,采用大气干湿采样器、聚氨酯泡沫(PUF)大气被动采样器分别采集大气及其干湿沉降物样品,同时采集地下河水样和分层采集流域土壤,利用气相色谱-质谱联用仪(GC-MS)测定了16种PAHs优先控制污染物。结果表明,地下河流域大气干湿沉降中PAHs的干湿沉降通量为147.26 ng·(m2·d)-1,流域PAHs沉降量为1943.8 g;大气中的PAHs浓度为45.33 ng·m-3;地下河水中PAHs浓度平均值为220.98 ng·L-1;土壤中PAHs浓度为38.72 ng·g-1;大气、降雨和土壤中PAHs组成以2~3环的萘、芴、菲、荧蒽、芘5种为主,地下河水中以芴、菲、荧蒽、芘、苯并[a]蒽、苯并[a]芘6种为主。利用地下河多介质中的16种PAHs成分谱、特征比值结合它们的物理化学性质进行PAHs的源解析,研究显示大气干湿沉降是岩溶地下河水中多环芳烃的主要污染源之一,这归因于岩溶地区防污性能的脆弱性。     

Hydrochemical,isotopic, and reservoir characterization of the Pasinler (Erzurum) geothermal field,eastern Turkey

The reservoir temperature and conceptual model of the Pasinler geothermal area, which is one of the most important geothermal areas in Eastern Anatolia, are determined by considering its hydrogeochemical and isotope properties. The geothermal waters have a temperature of 51 °C in the geothermal wells and are of Na–Cl–HCO₃ type. The isotope contents of geothermal waters indicate that they are of meteoric origin and that they recharge on higher elevations than cold waters. The geothermal waters are of immature water class and their reservoir temperatures are calculated as 122–155 °C, and their cold water mixture rate is calculated as 32%. According to the δ¹³C_VPDB values, the carbon in the geothermal waters originated from the dissolved carbon in the groundwaters and mantle-based CO₂ gases. According to the δ³⁴S_CDT values, the sources of sulfur in the geothermal waters are volcanic sulfur, oil and coal, and limestones. The sources of the major ions (Na⁺, Ca²⁺, Mg²⁺, Cl^?, and HCO₃ ^?) in the geothermal waters are ion exchange and plagioclase and silicate weathering. It is determined that the volcanic rocks in the area have effects on the water chemistry and elements like Zn, Rb, Sr, and Ba originated from the rhyolite, rhyolitic tuff, and basalts. The rare earth element (REE) content of the geothermal waters is low, and according to the normalized REE diagrams, the light REE are getting depleted and heavy REE are getting enriched. The positive Eu and negative Ce anomalies of waters indicate oxygen-rich environments.     

Analyses of the Compositional Characteristics and Sources of the Organochlorine Pesticides in the Surface Sediments of Guanghai Bay,Taishan City,Guangdong Province

Organochlorine pesticides (OCPs) are a class of toxic and harmful persistent organic pollutants widely found in environment. Hexachlorocyclohexane (HCHs) and DDTs are two of the most widely used OCPs (Qiu et al., 2004), so it is important to find out their compositional characteristics and sources in surface sediments. Guanghai Bay is located in the south of Guanghai Bay Industrial Park in Taishan City, Guangdong Province. It borders Huangmaohai to the east and Zhenhai Bay to the west, covering an area of about 236 square kilometers. In this study, surface sediments were collected at 16 sites in Guanghai Bay (Fig. 1). After the surface sediments were pretreated, GC‐MS was used to analyze OCPs. A total of 14 OCPs were detected and their content was shown in Table 1. The concentration of ΣOCPs ranged between 0.507～0.860ng·g‐1, with an average of 0.680 ng?g‐1. In general, the content of ΣOCPs was the highest at No. A12 site. The concentrations of these 14 detected OCPs ordered as dieldrin > epoxy heptachlor > P, P'‐DDD > γ‐HCH >endrin >aldrin > P, P'‐DDE >mirex >hexachlorobenzene >P, P'‐DDT > α‐HCH > δ‐HCH >β‐HCH > heptachlor.     

Loading, Transformation, and Retention of Nitrogen and Phosphorus in the Tidal Freshwater James River (Virginia)

A nutrient mass balance for the tidal freshwater segment of the James River was used to assess sources of nutrients supporting phytoplankton production and the importance of the tidal freshwater zone in mitigating nutrient transport to marine waters. Monthly mass balances for 2007–2010 were based on riverine inputs, local point sources (including sewer overflow events), ungauged inputs, riverine outputs, and tidal exchange. The tidal freshwater James River received exceptionally high areal loads (446 mg TN m^?2 day^?1 and 55 mg TP m^?2 day^?1) compared to other estuaries in the region and elsewhere. P inputs were principally from riverine sources (84 %) whereas point sources contributed appreciably (54 %) to high N loads. Despite high loading rates and short water residence time, areal mass retention was high (143 mg TN m^?2 day^?1 and 33 mg TP m^?2 day^?1). Retention of particulate fractions occurred during high discharge, whereas dissolved inorganic fractions were retained during low discharge when chlorophyll-a concentrations were high. On an annualized basis, P was retained more effectively (59 %) than N (32 %). P was retained by abiotic mechanisms via trapping of particulate forms, whereas N was retained through biological assimilation of dissolved inorganic forms. Results from a limited suite of stable isotope determinations suggest that DIN from point sources was preferentially retained. Combined inputs from diffuse and point sources accounted for only 20 % and 36 % (respectively) of estimated algal N and P demand, indicating that internal nutrient recycling was important to sustaining high rates of phytoplankton production in the tidal freshwater zone.     

Anaerobic Carbon Mineralisation Through Sulphate Reduction in the Inner Shelf Sediments of Eastern Arabian Sea

Monsoon-induced coastal upwelling, land run-off, benthic and atmospheric inputs make the western Indian shelf waters biologically productive that is expected to lead to high rates of mineralisation of organic matter (OM) in the sediments. Dissimilatory sulphate reduction (SR) is a major pathway of OM mineralisation in near-shore marine sediments owing to depletion of other energetically more profitable electron acceptors (O₂, NO₃ ^?, Mn and Fe oxides) within few millimetres of the sediment-water interface. We carried out first ever study to quantify SR rates in the inner shelf sediments off Goa (central west coast of India) using the ³⁵S radiotracer technique. The highest rates were recorded in the upper 10 cm of the sediment cores and decreased gradually thereafter below detection. Despite significant SR activity in the upper ～12 to 21 cm at most of the sites, pore water sulphate concentrations generally did not show much variation with depth. The depth integrated SR rate (0.066–0.46 mol m^?2 year^?1) decreased with increasing water depth. Free sulphide was present in low concentrations (0–3 μM) in pore waters at shallow stations (depth <30 m). However, high build-up of sulphide (100–600 μM) in pore waters was observed at two deeper stations (depths 39 and 48 m), 7–11 cm below the sediment-water interface. The total iron content of the sediment decreased from ～7 to 5 % from the shallowest to the deepest station. The high pyrite content indicates that the shelf sediments act as a sink for sulphide accounting for the low free sulphide levels in pore water. In the moderately organic rich (2–3.5 %) sediments off Goa, the measured SR rates are much lower than those reported from other upwelling areas, especially off Namibia and Peru. The amount of organic carbon remineralised via sulphate reduction was ～0.52 mol m^?2 year^?1. With an estimated average organic carbon accumulation rate of ～5.6 (±0.5) mol m^?2 year^?1, it appears that the bulk of organic matter gets preserved in sediments in the study region.