Search

Under the steadily intensifying human activities in coastal areas, it is crucial to distinguish the sources of organic matter (OM) in sediments for better understanding of the environmental change. In this study, 25 surface sediments collected along the harbor and creeks areas off Karachi coast were used for total organic carbon (TOC), total nitrogen (TN), stable carbon (δ13C) and nitrogen (δ15N) isotopic compositions, phytoplankton biomarkers (brassicasterol, dinosterol and cholesterol) and glycerol dialkyl glycerol tetraethers (GDGTs) analyses, to trace the distribution of OM and identify its sources. TOC, TN, δ13C, and δ15N are in the range of 0.04% to 5.28%, 0.01% to 0.57%, − 17.55‰ to − 26.31‰, and 2.83‰ to 6.04‰, respectively. C/N values range from 4.24 to 21.04. The δ13C, δ15N, C/N, BIT (Branched Isoprenoid Tetraether) index together with phytoplankton biomarkers show both marine and terrestrial OM input to the creeks and Harbor stations. In contrast, the stations from Western Coast indicate a marine source predominance. A clearly impact of human activities is seen from sediments near river mouths. [ABSTRACT FROM AUTHOR]

A Gram stain-positive, non-spore-forming, non-motile, short-rod actinomyces strain GXQ1321T was isolated from maritime surface sediments in Beihai (21° 41′ 21.65″ N, 109° 05′ 76.56″ E), Guangxi Zhuang Autonomous Region, and a number of categorization studies were performed. Following a period of 72 h of incubation at a temperature of 30 °C within a modified actinomycete culture medium, the colony was light-yellow, circular, smooth, central bulge, convex, opaque, with a 1.2–2.3 mm diameter. Strain GXQ1321T had the ability to degrade cellulose. Chemotaxonomic studies revealed that the major methylnaphthoquinones in strain GXQ1321T was MK-8(H2). The most prevalent cellular fatty acids were anteiso-C19:0, anteiso-C15:0, anteiso-C17:0, and iso-C16:0. The whole-cell sugars of the strain GXQ1321T were identified rhamnose, xylose and glucose. Meso-diaminopimelic acid was found in the peptidoglycan hydrolysate, and the polar lipids were identified as diphosphatidylglycerol, three phosphoglycolipid, phosphatidylglycerol and two unknown glycolipid. This strain had 69.6% DNA G+C content. Strain GXQ1321T is classified as Brevibacterium based on its 16S rRNA gene sequence. It is closely related to Brevibacterium samyangense SST-8 T (96.8%) and Brevibacterium rongguiense 5221 T (96.3%). The average nucleotide identity (ANI) values of GXQ1321T and the above two type strains were 73.9–77.1%, and the digital DNA-DNA hybridisation (dDDH) values were 15.3–21.1%. Based on the phylogenetic, chemotaxonomic and physiological data, strain GXQ1321T was considered to be a novel species of the genus Brevibacterium, named Brevibacterium litoralis sp. nov, with the type strain GXQ1321T (= MCCC 1K08964T = KCTC 59167 T). [ABSTRACT FROM AUTHOR]

Lake Tanganyika, the second deepest lake in Africa, has a unique ecosystem that provides rich fish proteins for populations along the lake basin. With socioeconomic development and rapid population growth, Lake Tanganyika is threatened by environmental pollution. In this study, the concentrations of heavy metals, including Cr, Ni, Cu, Zn, Cd, Pb, Fe, and Mn, in the surface sediments of the inflow rivers in northeastern quadrant of Lake Tanganyika were characterized. The geoaccumulation index (Igeo) and enrichment factor (EF) were employed for heavy metal assessment. The results showed that heavy metal concentrations in the surface sediments of the inflow rivers in northeastern quadrant of Lake Tanganyika exhibited significant spatial variations. The concentration of heavy metals was the highest near urban areas, followed by the estuarine wetland and forest grassland. This indicated that heavy metal content was closely related to human activities. The concentrations of Zn, Cd, and Pb were defined as unpolluted, and the concentrations of Pb, and Fe were only slightly enriched. Principal component analysis and cluster analysis demonstrated that the heavy metals Cr, Zn, Cd, and Pb may originate from a mixture of natural sources and anthropogenic inputs, including agricultural and industrial inputs. Ni, Fe, and Mn were principally from natural sources, and Cu primarily originated from anthropogenic inputs such as vanadium iron ore mining and iron and steel smelting. These results are important for understanding the nonpoint sources of heavy metal pollution in the Lake Tanganyika Basin. [ABSTRACT FROM AUTHOR]

A total of 21 surface sediment samples collected from Arasalar River are subjected to sediment texture (sand-silt-clay ratio), trace elements, organic matter, and CaCO3 studies to understand the accumulation dynamics of sediments. To assess the impact of metal pollution in estuarine sediments, the essential parameters should be done by checking the sediment characteristics, spatial distribution of heavy metal sources, sediment dynamics, and geochemical analysis. To evaluate the contamination level of metal pollution, a basic standard reference is required to decipher the values ranging from natural to anthropogenic contribution. From this research analysis, it is observed that the study area predominantly comprises silty sand and sand silty nature. The calcium carbonate content in the sediment is found to be proportional to the presence of shell fragments, whereas the organic matter (OM) is derived from riverine and coastal input which acts as a primary source. The obtained results confessed the average contents (mg/g) for the following selected eight elements in the order of Fe (35249–49068) > Mn (286–519) > Ni (107–279) > Cu (78.30–155.70) > Cr (50–99) > Zn (38.70–91.90) > Pb (39.90–62.40), and Co (12.6–29.1) by using an atomic absorption spectrophotometer (AAS) are utilized for this analysis. Multivariate analysis of heavy metals affirms geogenic sources (weathering of parent rocks) for Fe, Mn, Cr, Co, and Zn, whereas Cu, Ni, and Pb originated from anthropogenic activities (urban and industrial activities). The pollution load index, sediment pollution index, Igeo index, and PERI are categorized as under polluted, low to moderate polluted, and low potential environmental risk variety. Constant inspection and guidance are needed to prevent effluences from various agriculture and industrial activities in the nearby regions. The findings from this research may support and help the government to follow the suitable remediation on the better management of river and coastal areas. [ABSTRACT FROM AUTHOR]

This study addresses the sources of aliphatic hydrocarbons (AHs) and polycyclic aromatic hydrocarbons (PAHs) in the surface sediments of the northwestern Persian Gulf and the muscle tissues of Jinga shrimp (Metapenaeus affinis), a commercially important aquatic species. In November 2018, 28 Jinga shrimp samples were systematically collected from four key fishing areas in Behrgan and Khormusi: Imam Khomeini Port (S1), Mahshahr Port (S2), Sejafi (S3), and Behrgan Wharf (S4). Additionally, sediment samples were collected from these locations, and AHs and PAHs concentrations were analyzed using gas chromatography-mass spectrometry (GC–MS). The average aliphatic concentration in Jinga shrimp was 4800.32 (μg g−1 DW), exceeding the sediment samples' 2496.69 (μg g−1 DW) estimate. Hydrocarbon component analysis revealed EPA priority list (PAH-16) and measured PAHs (PAH-29) concentrations in Jinga shrimp ranging from 1095.8 to 2698.3 (ng g−1 DW) and in sediments from 653.6 to 1019.5 (ng g−1 DW). Elevated AHs and PAHs in Jinga shrimp, compared to sediments, suggest a petrogenic source, notably at station S4 near Behrgansar and Nowruz oil fields. Low molecular weight (LMW) compounds dominated in both shrimp and sediment PAHs. Aliphatic composition profiles in shrimps closely mirrored sediment profiles, illustrating an even-to-odd carbon dominance gradient. Diagnostic ratio examinations of hydrocarbons indicated pervasive petroleum derivatives in the environment. This study establishes a direct correlation between hydrocarbon concentrations in shrimp and sediment samples and the corresponding aliphatic groups, PAH-16, and PAH-29. The findings underscore the potential of Jinga shrimp as a reliable indicator of hydrocarbon pollution in the northwestern Persian Gulf. [ABSTRACT FROM AUTHOR]

This study assessed the accumulation levels and ecological risks associated with seven heavy metals (As, Pb, Cd, Hg, Cu, Cr, Zn) in the surface sediments of the Bong Mieu River in Quang Nam Province, Vietnam. The sampling encompassed 10 locations (S1–S10), considering areas both impacted and less impacted by gold mining activities. The findings revealed elevated levels of heavy metal pollution and associated ecological risks attributable to gold mining. Heavy metal content varied within specific ranges: As (70.6–341.2 mg/kg), Pb (216.3–504.1 mg/kg), Hg (0.138–0.252 mg/kg), Cd (0.91–1.51mg/kg), Cu (18.3–45.5 mg/kg), Cr (10.5–19.1 mg/kg), and Zn (49.3–84.1 mg/kg). Among these elements, Hg, Cu, Cr, Zn, and Cd adhered to the acceptable limits of VNTR 43:2017/MONRE (VNTR 43:2017/MONRE: National Technical Regulation/Ministry of Natural Resources and Environment of Vietnam). However, As and Pb content at all locations exceeded these limits significantly, with As being 4.1–20 times higher and Pb 2.3–5.5 times higher. The pollution of Pb and As was attributed to waste discharge from gold mining activities, which carry substantial amounts of these metals in various forms. The Igeo indicated heavy pollution of As and Pb in the sediments. Ecological risk factors were ranked as follows: E r i (As) > E r i (Pb) > E r i (Hg) > E r i (Cd) > E r i (Cu) > E r i (Cr) > E r i (Zn). The potential ecological risk (RI) due to combined heavy metal impact varied across locations, with S2 > S8 > S9 > S6 > S7 > S10 > S1 > S3 > S4 > S5, exhibiting low to moderate risk (RI values ranging from 73.4 to 252.8). The study area demonstrated high contamination levels for As and Pb, coupled with low to moderate potential ecological risks. [ABSTRACT FROM AUTHOR]

This study aimed to understand the occurrence of mercury in the water environment of typical cold and arid lakes and the regulating environmental factors. Water and surface sediment samples were collected from July to August, 2022 in the Wuliangsuhai Lake region for the analysis of total mercury (THg) and total methylmercury (TMeHg). Lake water THg and TMeHg ranged between 19.20 ~ 668.10 and 0.10 ~ 11.40 ng/L, respectively, exceeding China's environmental quality standards and contents of other lakes and reservoirs in China and other areas. Surface sediments showed lower mean THg and TMeHg of 261.85 and 0.18 μg/kg, respectively, with the former significantly exceeding the background value of Inner Mongolia and unpolluted natural lakes but lower than those of lakes affected by human factors, such as aquaculture. Sediments showed relatively low methylation and TMeHg (0.01–0.21%) concentrations. Correlation analysis identified salinity, total dissolved solids, conductivity, and redox potential as important factors affecting mercury speciation in water, whereas those in surface sediments were organic matter, pH, and total iron content. This study conducted preliminary research on the different species of Hg in Wuliangsuhai Lake water environment, which can provide scientific evidence for the specific treatment of Hg pollution in agriculture, or industry and other related fields. Our results suggest that upstream and downstream regulatory agencies should strengthen the regulation of agricultural and industrial production, moderately reduce human activities, and reduce the use of mercury-rich substances such as pesticides. [ABSTRACT FROM AUTHOR]

Rivers in deserts present unique geographical features owing to aeolian-fluvial interactions. In this study, 510 surface sediment samples were gathered from eight watersheds to systematically examine the major element characteristics of riparian sand dunes in northern China deserts. The findings revealed that these dunes could be categorized into three primary zones: Type I, comprising Keriya, Tora, Heihe, and Langqu rivers in the west; Type II, featuring the Maquan River in the Tibetan Plateau; and Type III, including Mu Bulag, Kuye, and Xar Moron rivers in the east. Specifically, the Type III region is characterized by a limited fresh material supply, a relatively high Chemical Index of Alteration (CIA), and the influence of nearby rivers on the provenance of riparian dunes, leading to a higher degree of chemical weathering than that of Type I in the west. Notably, Type II is marked by weak-moderate chemical weathering degree and a comparatively higher CIA value. These classifications and their difference of degree of chemical weathering are possibly governed by the type of parent rock and the availability of material. This research offers new insights into the classification of riparian dunes impacted by aeolian-fluvial interactions in arid regions of the northern China deserts. Furthermore, it provides valuable implications for studies focusing on the provenance of sediments. [ABSTRACT FROM AUTHOR]

Nitrogen (N) in sediments was a key element of lake eutrophication. The spatial distribution characteristics of four parts N in surface sediments were investigated by sequential extraction method, including free nitrogen (FN), exchangeable nitrogen (EN), hydrolyzable nitrogen (HN), and residual nitrogen (RN). Modified models were utilized to describe the adsorption isotherms of ammonia nitrogen (NH4+-N) in sediments and thus predict the risk of N release. The correlation between environmental factors and N concentration was discussed, as well as the migration or transformation and release risk of N between different mediums. The results showed that spatial variations characteristics of N fractions were influenced by the lake topography and surrounding human activities. The content of total nitrogen (TN) in the sediments was 933.4 ~ 3006.8 mg/kg, with an average of 1835 mg/kg. The HN, RN, FN, and EN in sediments accounted for 66.85%, 21.35%, 6.82%, and 4.92% of TN, respectively. There was a significant correlation between each fraction of N and TN and also between different fractions of N (p < 0.01). Fitting by modified Langmuir model indicated that the adsorbed amounts of N in the sediments at maximum (Qmax) was, from greatest to least, southeast lake (2905.3 mg/kg) > southwest lake (1415.4 mg/kg) ≈ north lake (1424.6 mg/kg). Environmental parameters (pH, DO, C/N, etc.) affected the occurrence fraction of nitrogen, which could cause the persistent and increased risk of sustained release of high concentrations of endogenous N. N pollution in sediment and interstitial water is severe, and the risk of endogenous N release will gradually increase in the future. [ABSTRACT FROM AUTHOR]

The horizontal distributions of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) in the surface sediments where complex aquaculture is conducted in Shido Bay, Seto Inland Sea, Japan, were determined to investigate the impact of fish and oyster farming. We also determined five fractions of phosphorus in the surface sediments. Relatively high phosphorus contents (P/C ratios) were observed in fish farming areas, likely due to the waste feed and fecal matter. Moreover, relatively high abundances of the Ca-bound P (Ca-P) and detrital P (Ref-P) fractions were observed in fish farming areas, likely due to bones of small fish used as feed. Our results strongly suggest that the P/C ratio and the Ca-P and Ref-P fractions in the surface sediments are good indicators of the effects of fish farming and allow its characterization, and are particularly valuable in the area of complex aquaculture. [ABSTRACT FROM AUTHOR]

The study of diatoms in the surface sediments of Academy Bay (Sea of Okhotsk) revealed a rich diatom flora (187 species and intraspecific taxa), represented mostly by marine and brackish water species. The predominance of benthic-planktonic and benthic species indicates a significant role of microphytobenthos in Academy Bay. The diatom assemblages distinguished with the use of cluster analysis are homogeneous in their taxonomic composition, but differ in ecological structure, which is mainly determined by water salinity. The concentration of diatoms in the sediments in the open part of Academy Bay and in the apex of Ulban Bay depends on a high productivity of waters and the lithological composition of sediments. A relatively low content of diatoms in the sediments is associated with the severe climatic conditions of the region that is close to the Arctic. [ABSTRACT FROM AUTHOR]

Urmia Lake, in the northwest of Iran, is the largest body of saline water in the Middle East, which has been desiccated in recent decades. To investigate the pollution status and ecological-health risks of heavy metals and metalloids in the surface sediments of this lake, 26 sediment samples were collected along the salt marshes of the lake and were analyzed for heavy metals and metalloid concentrations. The potential ecological risk assessment was carried out using enrichment factor (EF), geo-accumulation index (Igeo), contamination factor (CF), and potential ecological risk (Eri) standard indices. The average concentrations (mg kg−1) of heavy metals and metalloids were as follows: Fe (11,714) > Sr (320.8) > Mn (274.3) > V (28.5) > Cu (24.7) > Zn (21.2) > As (17.3) > Ni (14.8) > Cr (12.6) > Pb (11) > Co (4.0) > U (1.7), Hg (0.6) > Mo (0.36). The concentrations of As, Hg, and Sr in lake sediments were higher than geochemical background values. The non-carcinogenic risks caused by heavy metals and metalloids were insignificant regarding health risks. Levels of carcinogenic risk for metal(loid)s were in the acceptable ranges (10−6–10−4). The ecological risk was low, except for As, Sr, and Hg which showed moderate to significant EF, Igeo, and CF values. Arsenic and Sr were enriched in the surface sediments in desiccated parts of the lake due to complete lake water evaporation. It seems that further drying of the lake increases the potential ecological risk of heavy metals and metalloids in the surface sediments of Urmia Lake. [ABSTRACT FROM AUTHOR]

It is of great significance to study the distribution characteristics and transport of heavy metals in complex sedimentary environments and areas with intensive human activities. This study analyzed sediment size, heavy metal contents (Cu, Zn, Cd, Cr, and Pb), organic carbon content, and sulfide content in surface sediments collected from 27 sites in Chengbei Sea. The main controlling factors of the distribution and transport of heavy metals were discussed from the perspective of sediment dynamics. The concentrations of Cu, Zn, Cd, Cr, and Pb in surface sediments were 7.9–20.5 mg/kg, 33.8–94.6 mg/kg, 0.08–0.26 mg/kg, 6.3–62.3 mg/kg, and 3–13.4 mg/kg, respectively. According to the geoaccumulation index, the study area was not polluted by the heavy metals, except for Cd, which did not pollute only areas with relatively coarse-grained sediments. Combining the results of correlation analysis, tidal residual current analysis, sediment transport trend analysis, and principal component analysis confirmed that Cu, Zn, and Cd originate from natural sources, and their distribution characteristics are mainly controlled by the grain size of surface sediments. Cr and Pb could be attributed to human activities, such as oil exploration, and their distribution characteristics were affected by sediment transport and tidal residual current. Zonation of the sedimentary dynamic environment also provided reference for the relationship between the distribution of heavy metals in surface sediments and sedimentary environments. [ABSTRACT FROM AUTHOR]

Interest in the study of microplanktonic organisms in the Arctic has increased owing to their direct participation in the process of sedimentation and sensitive response to changes in environmental and climatic factors. This study presents new data on the taxonomic diversity and content of radiolarian skeletons and agglutinated tintinnid ciliate loricae in the Upper Holocene sediments of the Laptev Sea, East Siberian Sea, and the adjacent part of the Arctic Ocean. We traced the spatial distribution of representative microfauna of these groups in surface sediments and sediment cores. Radiolarian skeletons were found in the surface sediments of the continental slope of the Laptev Sea and adjacent parts of the Arctic Ocean. These belong to the following six species: Stylatractus (?) sp., Actinomma leptoderma leptoderma, Actinomma leptoderma longispina, Streblacantha circumtexta, Spongotrochus glacialis, and Cycladophora davisiana. The radiolarian fauna detected was in deep sea and close to the fauna of the Nansen Basin (Central Arctic). Furthermore, we found tintinnid ciliate loricae belonging to the following seven species: Tintinnopsis ventricosoides, Tintinnopsis fimbriata, Tintinnopsis turbo, Tintinnopsis nitida, Tintinnopsis sp. cf. fusus (?), Tintinnopsis sp., and Stenosemella nivalis. In the study area, the tintinnid ciliate loricae of these species were discovered for the first time and traced mainly in the coastal shelf zone, which can be explained by their ecology. The only exception is that of T. nitida, which was found only on the continental slope of the Laptev Sea. Our findings advance knowledge on the biodiversity of Arctic seas and can be used to monitor ecological and paleoceanographic changes in the Arctic region. [ABSTRACT FROM AUTHOR]

Our research was motivated by significant warming in the Arctic in recent decades and the influence of this warming on diatoms, which are the main producers in the seas of the Eastern Arctic. For this purpose, we studied the qualitative concentrations and quantitative ratio of diatoms from the surface sediments of the Laptev Sea (LS), the East Siberian (ESS) and Chukchi seas (ChS), and the Arctic Ocean (AO), obtained by box corers in 2016 and 2018. The ecological structure of the diatom assemblages of these sediments, reflecting the current environmental conditions, was also analyzed. Compared with the end of the last century, there were significant changes in species composition and quantitative ratio of the diatom assemblages in the sediments from the AO and the LS and ESS. In contrast, the diatom assemblages in the sediments from the ChS had not significantly changed in terms of species composition or quantitative ratio over the same three decades. The observed transformations in the diatom assemblages of the surface sediments were associated with substantial changes in water temperature, current flow, salinity, ice melting, and prolonged ice-free periods associated with global warming in the Northern Hemisphere in recent decades. The foregoing processes have clearly had strong impacts on the environment and the biota of the Arctic region. [ABSTRACT FROM AUTHOR]

The epicontinental seas to the east of China have become highly anthropogenically impacted due to rapid economic development in recent decades, resulting in various environmental problems, including heavy metal pollution. The Bohai Strait, as a key junction connecting the material-energy exchange between the Bohai and Yellow Seas, is extremely critical in regional pollution prevention and control. To ascertain the spatial distribution and contamination levels of heavy metals in the surface sediments of the northern Bohai Strait, a systematic investigation was conducted. Geochemical analysis revealed that the concentrations (in ppm) of heavy metal elements in surface sediments vary in the range of 4.19–77.6 for As, 0.04–0.21 for Cd, 5.1–65.7 for Pb, 0.30–39.40 for Cu, 7.77–46.50 for Ni, 1.50–86.60 for Cr, 11.70–91.80 for Zn, and 0.005–0.038 for Hg. Ecological statistics indicate that the northern Bohai Strait suffers from prominent heavy metal pollution primarily induced by As, Cd, and Pb, accompanied by relatively weak pollution of Cu and Ni. Sediments collected from the submarine depressions and the southeast region exhibit higher heavy metal concentrations, and as a consequence, more serious ecological risk. Correlation analysis indicated that the accumulations of Hg, Cr, and Zn were associated with the deposition of organic matter. Preliminary provenance discrimination suggested that the pollutants were mainly derived from the eastern parts of the North Yellow Sea, rather than the Bohai region. [ABSTRACT FROM AUTHOR]

Paleolimnological records from temperate South-Central Chilean lakes revealed a recent and marked increase in the relative abundances of the key-planktonic diatom species Asterionella formosa and Aulacoseira distans. To better understand these changes, we studied the ecological niches of planktonic diatoms in 42 temperate Chilean lakes (36–43°S). We used morphological analysis of spring and early summer diatom communities, as well as sub-fossil sedimentary assemblages along gradients in mixing regime, light climate, and water chemistry. For Asterionella formosa and the species belonging to the genus Aulacoseira, morphology based enumerations were combined with molecular phylogenies using the 18S rDNA and rbcL genes to determine their taxonomic position and explore potential hidden diversity. Analysis of extant and sub-fossil communities revealed similar patterns, with small Discostella species (D. mascarenica and D. pseudostelligera) and Urosolenia eriensis being characteristic for large, well-mixed lakes, whereas Aulacoseira pusilla (previously erroneously identified as A. distans in Chile) is more dominant in smaller, warmer, and stratified water bodies. This suggests that recent increases in the latter taxon might be related to changes in the physical lake properties in the region, rather than a recent increase in nutrient concentrations. By contrast, Asterionella formosa occurred in lakes with a high Si concentration. Phylogenetic data of the most common species belonging to the genera Aulacoseira and Asterionella showed little evidence for hidden diversity in most of the taxa, except for the Aulacoseira granulata complex. This indicates that the Chilean strains are closely related to populations in the Northern Hemisphere. The results of this study will allow for more accurate diatom-based reconstructions of limnological changes in South-Central Chilean lakes. This is crucial to better understand climate dynamics in the region, as these lakes are known to be sensitive to alterations in windiness and precipitation in response to changes in the intensity and latitudinal position of the Southern Hemisphere Westerlies and the El Niño-Southern Oscillation. [ABSTRACT FROM AUTHOR]

Heavy metals contamination in sediments may endanger ecosystems and human health via the food chain. In fact, there is little to no understanding about heavy metal accumulation in surface sediment of one of the most economically important marine bodies for Vietnam, the Thai Binh Coast, where five large rivers co-discharge into the Gulf of Tonkin. Twenty-seven surface sediment samples were collected from the intertidal regions and analyzed for: arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), nickel (Ni), and zinc (Zn) using inductively coupled plasma mass spectroscopy (ICP-MS). The studied area exhibited a large spatial variation in the concentration of heavy metals, e.g., the dry sediment concentration of Cd was the least (0.05–0.49 mg.kg−1), whereas that of Zn was the greatest (45.4–252 mg.kg−1). Based on the geoaccumulation index ( I geo ), most of the studied heavy metals were accumulated at low pollution levels, except four locations exhibited moderately and highly polluted levels of Hg with I geo Hg values from 1.92 to 2.66. However, the high contamination factor value implicated that not only Hg but also all other detected heavy metals in this area resulted from anthropogenic activities along the coast and the river upstream. This implied the need for quick action from the government. In addition, numerous analytical methods were used to see the association between metals, total organic carbon (TOC), and particle size distribution, including Pearson correlation coefficient (P) and principal component analysis (PCA). Hg demonstrates lowest connection with TOC (PHg-TOC ~ 0) but individual heavy metal correlations are largely positive, with many reaching 1.0 (e.g., PNi-Cr = 0.89, PCd-As = 0.72, PNi-Cu = 0.76, and PCu-Cr = 0.72). From the PCA diagram, we can observe that those sampling points in the positive direction of PC1 were expected to have a high concentration of Cu, Zn, As, Ni while having extremely little sand content. [ABSTRACT FROM AUTHOR]

A survey of 60 high mountain lakes of Colombia's Eastern Range was performed to evaluate the response of surface-sediment diatoms to environmental variables. In each one of these lakes, water samples were taken for physical and chemical characterization, and diatoms were collected from the superficial bottom sediment at the deepest part. Multivariate statistical analyses were made to determine the relationships between environmental and biological data, specifically which environmental variables explain the diatom distribution. For each of these significant environmental variables, optima and ecological tolerances were calculated using the weighted-average method, which allowed for the classification of the species according to their environmental preferences. The lakes showed a wide range of environmental gradients in variables such as pH, alkalinity, and nutrients. In addition, the depth of the lakes was a direct determinant of the light environment of the water column. A total of 339 diatom taxa were identified belonging mainly to the genera Eunotia and Pinnularia. Variables related to pH-alkalinity gradient, trophic condition (nitrates and phosphorus), and physical factors (radiation at the bottom) had a significant effect on diatom composition. Despite the fact that the total organic carbon environmental range was high, the effect of this variable on diatom species composition was not significant. In conclusion, the diatoms of the studied lakes showed a significant ecological relationship with environmental variables which are potentially important in environmental reconstruction. Diatoms in the study sites can provide useful and independent quantitative information to investigate the recent impacts of global change on tropical high mountain ecosystems. [ABSTRACT FROM AUTHOR]

Hydrothermal venting has a profound effect on the chemical and biological properties of local and distal seawater and sediments. In this study, lipid biomarkers were analyzed to examine the potential influence of hydrothermal activity on the fate of organic matter (OM) in surface sediments around Tianxiu Hydrothermal Field in the Carlsberg Ridge (CR), Northwest Indian Ocean. By comparing the biomarker distributions of the samples with that of other typical hydrothermal sediments in the mid ocean ridge, it is shown that the location of the samples is not affected by the hydrothermal activity. The relatively low abundances of terrestrial n-alkyl lipids and riverine 1,15-C32 diol suggested a minor contribution of terrigenous OM to the study area. The bacteria contributed predominantly to sedimentary marine OM; however, other marine source organisms, e.g., eukaryotes (i.e., phytoplankton and fungi) could not be completely neglected. The marine-originated biomarkers showed significantly variable distributions between the two sediments, suggesting different dynamic physical and biogeochemical processes controlling the fate of marine OM. This study identified various diagnostic biomarkers (5,5-diethyl alkanes, diols and β-OH FAs), which may have significant environmental implications for future works in this region. [ABSTRACT FROM AUTHOR]

The study aimed to determine the level of mercury (Hg) and its labile and stable forms in the surface sediments of the Baltic Sea. The work considers the impact of current and historical sources of Hg on sediment pollution, together with the influence of different environmental parameters, including water inflows from the North Sea. Surface sediments (top 5 cm) were collected in 2016–2017 at 91 stations located in different areas of the Baltic Sea, including Belt Sea, Arkona Basin, Bornholm Basin, Gdańsk Basin, West Gotland Basin, East Gotland Basin, and the Bothnian Sea. Besides, the particulate matter suspended in the surface and near-bottom water was also collected. The analysis of total Hg concentration and individual Hg forms in collected samples was carried out using a 5-step thermodesorption method. This method allows for the identification of three labile and thus biologically available, fractions of Hg, which are mercury halides, organic Hg, mercury oxide and sulphate. Two stable fractions, mercury sulphide and residual Hg, were also determined. The highest Hg concentrations, reaching 341 ng g−1, were measured in the highly industrialised Kiel Bay, which was additionally a munition dumping site during and after World War II. High Hg level, ranging from 228 to 255 ng g−1, was also recorded in the surface sediments of the Arkona Basin, which was a result of the cumulative effect of several factors, such as deposition of Hg-rich riverine matter, favourable hydrodynamic conditions and military activities in the past. The relatively elevated Hg concentrations, varying from 60 to 264 ng g−1, were found in the Gdańsk Basin, a region under strong anthropopressure and dominated by soft sediments. The sum of labile Hg in sediments was high and averaged 67% (with the domination of organic Hg compounds), which means that a large part of Hg can be released to the water column. It was found that the water inflows from the North Sea intensify the remobilisation of Hg and its transformation into bioavailable labile forms. As a consequence, the load of Hg introduced into the trophic chain can increase. Despite the significant reduction of Hg emission into the Baltic in the last decades, surface sediments can be an important secondary Hg source in the marine ecosystem. This is especially dangerous in the case of the western Baltic Sea. [ABSTRACT FROM AUTHOR]

Purpose: Though the process and players of nitrification are important in the ecology and biogeochemistry of Arctic fjords; there are very limited studies available on the ecology of ammonia oxidizers. Hence, we studied the abundance, diversity, and niche separation of ammonia oxidizers in the surface sediment of two high Arctic fjords (Kongsfjorden and Krossfjorden) to explore their ecology in the Arctic system. Materials and methods: Surface sediment samples were collected from eight stations (four stations from each fjord). The diversity and abundance of ammonia-oxidizing bacteria (AOB) and archaea (AOA) were analyzed using ammonia monooxygenase A (amoA) gene from the sediment metagenome. Environmental variables including bottom temperature and salinity, and sediment characteristics such as total carbon (TC), total nitrogen (TN), total sulfur (TS), and total organic carbon (TOC), were measured. Results and discussion: AOA were more abundant than AOB in most of the samples and AOA/AOB ratios ranged from 0.63 to 17.11. AOA were dominated by Nitrosopumilus lineage (67.5%), followed by Nitrososphaera lineage (32.2%). Most of the AOB were affiliated with Nitrosospira lineage (82.2%), and comparatively lesser contribution (18.2%) was observed for Nitrosomonas. We could not observe comammox bacteria in our samples. The distribution of ammonia oxidizers had a significant influence with the total nitrogen and total organic carbon content. Conclusions: Both AOA and AOB showed spatial variations in community composition within the fjords and between the fjords with a domination of freshwater/soil communities in the inner fjord stations. Freshwater and soil influx from glacial melt had a significant influence in controlling the environmental variables in the fjords which in turn regulated the distribution and niche selection of ammonia oxidizers. [ABSTRACT FROM AUTHOR]

The distribution and origins of Ni and V were assigned in the surficial sediments from 160 stations in Shadegan international wetlands with 537,700 ha. The findings showed that the mean total content of Ni and V in the surface sediments were 45.08 ± 12.09 and 25.25 ± 20.8 μg g−1 dw, respectively. According to the analysis chemical speciation, the Ni and V residual fraction in the surface sediments were calculated for > 80% of the total level of metals, indicating that the metals may be an indicator for the input of natural resources. The analysis of the interpolation maps according to their chemical fractionation manifested that the Ni and V pollution hotspots have been happened in the northern, southern, and western points. Interpolation maps also highlighted that Ni and V are often controlled by natural factors like parent material; however, anthropogenic inputs have also caused the accumulation of these metals in the sediment. [ABSTRACT FROM AUTHOR]

The mineral composition of the heavy subfraction from surface sediments of the Sea of Okhotsk has been studied using two detailed profiles (the Magadan-Kuril Islands and the Shantar Islands-Central part of the Sea of Okhotsk) and data from the Sakhalin Gulf. The obtained data have been analyzed by the methods of multivariate statistics, which allowed us to identify the main associations of heavy minerals that show regional differences in the mineral complexes of marine sediments. A significant effect of the solid discharge of the Amur River on sedimentation processes has been recorded. Two large regional sources of clastic material, the Amur-Sakhalin and Kuril-Kamchatka supplying provinces, had a major influence on the formation of the mineral composition of the sediments. [ABSTRACT FROM AUTHOR]

n-Alkanes are biomarkers that are widely used as paleoenvironmental reconstruction proxies in lacustrine sediments. However, studies on their sedimentation and factors affecting sedimentation in large lakes remain relatively scarce. In this study, 120 surface sediments collected from Selin Co, central Tibetan Plateau, were used to analyze the spatial distribution of n-alkanes in a modern sedimentary system, and the factors controlling this distribution were further discussed. The sedimentary n-alkanes of Selin Co were mainly long- and middle-chain components with single or double peaks, belonging to the mixed-type input of terrestrial and aquatic plants. Leaf waxes derived from terrestrial plants in the catchment of Selin Co were the main source followed by aquatic plants, while planktonic algae living in the lake water column was a minor source, as demonstrated by their low concentration. The distribution of aquatic and terrigenous n-alkanes in the surface sediments showed a significant spatial heterogeneity; this was controlled by different factors and sedimentary processes. The distribution of terrigenous n-alkanes was mainly controlled by underwater topography; high concentrations in the sedimentary center of the east lake basin and the sub-basin in the northwest were evident. Aquatic n-alkanes were found in substantially higher concentrations in the western estuary of Zhagen River and Ali River, as well as in the southern sub-basin, Yagen Co. These distributions might be influenced by differences of geographical environment in the watershed of these main inflow rivers, as well as the intensity of sunlight, itself intensity controlled by the transparency of the water column. Although n-alkanes from the center of a lake could represent an integration of catchments in most cases, their spatial heterogeneity in large lakes like Selin Co would introduce uncertainty to paleoenvironmental reconstructions. Consequently, it is very important to investigate thoroughly the spatial distribution and controlling factors of n-alkanes in modern lake environments. It is inferred that these findings will have broad significance in large lakes similar to Selin Co, and that they will benefit studies that use n-alkanes as proxies to reconstruct past environmental changes. [ABSTRACT FROM AUTHOR]

Purpose: Variations in hydrocarbon composition and concentration are essential for the assessment of its source and environmental health in estuarine environments. This study aims to reveal the spatial and temporal distribution of multiple hydrocarbons in surface sediments of the Pearl River Estuary, and to further determine various sources of these hydrocarbons. Materials and methods: Surface sediments were taken monthly from four sites along a spatial transect from the Pearl River Estuary in a whole year by using a gravitational bottom sampler. A series of bulk parameters including the grain size, total organic carbon content, and total nitrogen content were measured. Hydrocarbons in sediments were extracted and analyzed by the gas chromatography-mass spectrometry. Results and discussion: The abundances of higher plants and phytoplankton-derived n-alkanes, petrogenically derived pristane, phytane, hopanes, and steranes with geological configuration, and anthropogenically derived hydrocarbons, including linear alkylbenzenes and polycyclic aromatic hydrocarbons all showed decreasing trends towards the coastal ocean. In contrast, the diatom-derived C25 highly branched isoprenoids increased towards saline sites. Monthly fluctuations of aliphatic and aromatic hydrocarbons at the estuarine mouth were smaller than the upstream freshwater sites, where high monthly variation (up to fivefold) was observed for most of the hydrocarbons detected. Conclusions: This study showed substantial monthly and spatial variations of hydrocarbons in the surface sediments of the Pearl River Estuary. Distribution and composition of sedimentary hydrocarbons indicate mainly anthropogenic inputs (e.g., petroleum residues and synthetic detergents) and terrestrially higher plants, followed by aquatic inputs. [ABSTRACT FROM AUTHOR]

Forty-three surface sediment samples were collected in September 2019 from Tasaul Lake (Black Sea coast, Romania) to examine the metal distribution patterns, assess the level of metal contamination, and identify the pollutant sources. The determined mean metal concentrations were as follows: Al 49,772 mg/kg, Zn 84.40 mg/kg, Cr 83.70 mg/kg, V 76.45 mg/kg, Ni 42.53 mg/kg, Cu 34.27 mg/kg, Pb 26.30 mg/kg, As 12.49 mg/kg, and Hg 0.06 mg/kg. The metals in the surface sediments of Tasaul Lake displayed moderate spatial variation, with higher metal concentrations mainly occurring in the south and southeast (As, Pb, and Hg), southwest (Cu and Zn), and west of the lake (Cr, Ni, and V). Heavy metal contamination in sediments is assessed using pollution indices such as enrichment factor, contamination factor, and pollution load index. The highest CFs and EFs were determined for As (moderate to high pollution), followed by Pb (low to moderate pollution). The Cu, Zn, and Hg pollution indices showed values corresponding to low pollution levels, while Ni, Cr, and V presented the lowest indices, suggesting unpolluted sediments. Multivariate statistical analyses were performed to identify the origin of the analyzed heavy metals. Cr was predominantly sourced from lithogenic components, Ni and V originated from both natural and anthropogenic sources, and As, Cu, Zn, Pb, and Hg showed mainly anthropogenic sources such as agricultural runoff, domestic and industrial wastewater discharges, and quarrying activities. [ABSTRACT FROM AUTHOR]

The sediment acts as not only sink but also source of heavy metals in aquatic environment, which may cause the endogenous pollution in drinking water reservoirs. In this work, we collected the surface sediments from Qingcaosha Reservoir, the largest river-embedded reservoir in China, and investigated the spatial distribution, risk, and sources of heavy metals in four seasons. Significant spatial and seasonal heterogeneity could be found in the distribution of five heavy metals (Cr, Cu, Mn, Zn, and Ni) in the surface sediments. The highest concentrations of the five metals were detected in the sediments from the reservoir downstream, especially in summer and next spring. The geo-accumulation index (Igeo) and enrichment factor (EF) suggest that the sediment pollution caused by single metal was heavier in summer than in other seasons. Also, the Nemerow pollution index (PIN) manifests that the synergetic pollution induced by five metals was most serious in summer, followed by next spring. However, the potential ecological risk index (PERI) indicates that none of these metals caused potential ecological risk in four seasons. Comprehensive analysis demonstrates that the sediment pollution gradually increased from autumn to winter and then to next spring. Principal component analysis shows that the main pollution source of five heavy metals may come from industrial wastewater and domestic sewage, which was almost independent of seasons. This work can provide data support for the subsequent seasonal optimization of drinking water quality and reservoir management. [ABSTRACT FROM AUTHOR]

During the last few decades, sedimentary carbons gain great concerns of research interest among the scientific committee worldwide due to their adverse impact on aquatic chemistry, ecology, and hence human health along with global climate change. In the present study, we investigated the spatial distribution of mass concentration of sedimentary carbon (viz. black carbon: BC, and its components, char and soot) along with their burial fluxes in the surface sediments of the South Yellow Sea (SYS). The concentration of sedimentary carbon is measured by using an emerging method of thermal/optical reflectance. The observed BC concentration is found in the range of 0.02–1.02 mg g−1 with a mean value of 0.49 ± 0.26 mg g−1. The mean burial fluxes of BC, char, and soot also have a similar spatial variation to their concentration with the mean value along with relative standard deviation (in bracket) 22.43 ± 12.49 (~ 56%), 5.90 ± 3.99 (~ 68%), and 16.53 ± 10.67 (65%), respectively. Relatively lower value of char/soot ratio, i.e., 0.48 ± 0.22, indicates the dominance of soot in surface sediments that could be mainly derived from the fossil fuel combustion which is further confirmed from emission inventory data suggesting maximum contribution, i.e., ~ 66–80%, of the total BC emission emitted from residential and industrial emission sources. The back trajectories analysis revealed a significant impact of long-range transportation on BC concentration in the surface sediments of SYS. Further study of BC concentrations in sea sediments and their interaction with other organic/inorganic compounds in continental shelves is highly needed for a better understanding of the global carbon cycle. [ABSTRACT FROM AUTHOR]

Abstract—The distribution of Sc, Co, Hf, Cr, Th, and rare-earth elements in samples of surface sediments collected during cruises 67th and 68th of the R/V Akademik Mstislav Keldysh in the Barents Sea and in its bays is analyzed. The results obtained suggest that the predominant part of the bottom sediments of the Barents Sea is composed of thin-grained siliciclastics that was supplied with suspended particulate matter of the North Cape (Atlantic) Current through the erosion of the northwestern Scandinavian coasts and some seafloor areas. Some sediments in the northern part of the sea were formed through the erosion of rocks of the Novaya Zemlya and Franz Josef Land. A certain role in their formation was probably played by material from Svalbard as well as by the Pechora River suspended particulate matter. The established isotopic characteristics (εNd, 207Pb/206Pb and 87Sr/86Sr) of surface sediments suggest that the main contribution to the formation of bottom sediments of the central Barents Sea was made by rocks of the mainland part affected by the North Cape Current. The comparison of the 87Sr/86Sr values ​​in the surface sediments of the central part of the Barents Sea and in the ice-rafted sediments carried by the Transpolar Drift showed their significant difference. This suggests a reatively small contribution of ice-rafted material to the formation of surface sediments of the Barents Sea. [ABSTRACT FROM AUTHOR]

Heavy metals (Sc, Cr, Co, Ni, Cu, Ga, Ge, Nb, Mo, Cd, In, Hf, Ta, W, Tl, Pb, Bi, Th, and U) in the surface sediments of the Ganges-Brahmaputra-Meghna (GBM) river system of the Bengal Basin (BB) were measured to evaluate the heavy metal contamination and anthropogenic influence. The average concentration levels of most of the heavy metals (except Mo and Tl) were above the average crustal and shale values. Contamination indices, including the contamination factor, pollution load index, enrichment factor, and geo-accumulation index, and multivariate statistical analyses indicated that the GBM is slightly polluted by heavy metals with some considerable pollution from Bi, Th, Ta, Cd, Nb, Pb, In, and U. Among the four individual rivers, the Brahmaputra River and Ganges-Brahmaputra (GB) confluence river sediments contain higher heavy metal concentrations than do the Ganges and Meghna Rivers, which may be caused by the effects of local municipal discharge, industrial or urban wastes, and ferry crossing activities. [ABSTRACT FROM AUTHOR]

At present, the understanding of the dynamics of denitrifiers at different dissolved oxygen (DO) layers under organic carbon consumption within the surface sediments remains inadequate. In this study, high-throughput sequencing and quantitative PCR targeting nirS gene were used to analyze the denitrifier abundance dynamics, community composition, and structure for aerobic (DO 0.5–6.9 mg/L), hypoxic-anoxic (DO 0–0.5 mg/L), and anoxic (DO 0 mg/L) layers in surface sediments under organic carbon consumption. Based on the analysis of nirS gene abundance, the values of denitrifying bacteria decreased with organic carbon consumption at different DO layers. When the bacterial species abundance at the genus level were compared between the high-carbon and low-carbon sediments, there was significant increase in 6 out of 36, 7 out of 36 and 6 out of 36 genera respectively for the aerobic, hypoxic-anoxic and anoxic layers. On the other hand, 14 out of 36, 9 out of 36 and 15 out of 36 genera showed significant decrease in bacterial species abundance respectively for the aerobic, hypoxic-anoxic and anoxic layers. Additionally, 14 out of 36, 20 out of 36, and 15 out of 36 genera had no change in bacterial species abundance respectively for the aerobic, hypoxic-anoxic, and anoxic layers. This indicates that the carbon utilization ability of different denitrifiers on each DO layers was generally different from each other. Diversity of denitrifying bacteria also presented significant differences in different DO layers between the high- and low-carbon content sediment layers. Moreover, under the high-carbon and low-carbon content, the abundance of nirS gene showed a high peak within the hypoxic-anoxic regions, suggesting that this region might be the main distribution area for the denitrifying bacteria within the surface sediments. Furthermore, community of unique denitrifiers occurred in different DO layers and the adaptive changes of the denitrifier community followed the organic carbon consumption. [ABSTRACT FROM AUTHOR]

Based on a monthly field survey in 2011 of the Pearl River Estuary, the dynamics of polycyclic aromatic hydrocarbons (PAHs) in surface sediments (depth < 5 cm) were explored. The seasonal variations in PAH level and composition were investigated in this study, as well as their environmental behaviors, the role of particles, and source apportionment. The concentration of the sum of 16 priority PAHs (defined as ∑16PAHs) ranged from 0.32 to 1.10 μg/g, while that of the sum of 62 PAHs (defined as ∑tPAHs) varied from 0.83 to 2.75 μg/g. The levels of both the ∑16PAHs and ∑tPAHs peaked in February, although the minimum levels appeared in different months—December and August, respectively. The seasonal difference in the ∑tPAHs was significant (flood season, 7.69 μg/g; dry season, 10.51 μg/g). The 5-ring PAH compound (e.g., perylene) was the most abundant and was responsible for 35% of the total, which implied a terrestrial input source via the Pearl River. Sediment particles were predominantly composed of clayed sand, and sediment PAHs showed a greater tendency to be adsorbed onto the large-sized particles rather than the fine fractions. Total organic carbon (TOC) could considerably facilitate the sediment PAHs. Principal component analysis revealed that vehicle emission sources, petroleum sources, and combustion sources were the major anthropogenic contamination sources. The diagnostic ratios of various individual PAHs were also explored. These findings are particularly useful for understanding the geochemistry of organic pollutants in the complex estuarine environment. [ABSTRACT FROM AUTHOR]

Surface sediment samples from the East Siberian and Chukchi seas have been analyzed for the quantitative distribution, taxonomic composition, and ecological structure of diatom and dinoflagellate cyst assemblages. According to the results, the diatom and dinocyst distribution in surface sediments indicates the distribution of different water masses in the region. [ABSTRACT FROM AUTHOR]

In order to further explore the relationship between water body eutrophication of some reaches of Yellow River and phosphorus species in sediments, and evaluate phosphorus release potential from sediments to overlying water, we investigated the distribution of P species and their release risk in the surface sediments from different reaches along Yellow River, as well as the influence of artificial dam on phosphorus cycle in Yellow River. The results show that the content of calcium phosphorus (PCa) is higher than the content of bioavailable phosphorus (BP) (BP = Pex + PFe; in the formula, Pex means exchangeable phosphorus and PFe means iron phosphorus) in the surface sediments from Yellow River. Among all the surface sediment samples from 21 stations, only Dayudu section (H15) has a ratio of W (BP)/W (PCa) higher than 0.5; the results show that the intensity of phosphorus release from H15 is high, and there is a potential risk of eutrophication in water, while the phosphorus release level of water sediment in other reaches of Yellow River is low. The content of BP and total phosphorus (∑P) in surface sediments along the Yellow River is in descending order: middle reaches of Yellow River > upper reaches of Yellow River > Yellow River downstream, while the content order of total phosphorus (TP) in the overlying water is as follows: Yellow river downstream > middle reaches of Yellow River > upper reaches of Yellow River (except the H7 station), indicating that extensive artificial corresponding damming in Yellow River basin makes the concentration of TP increasing significantly in overlying from upstream to downstream. The establishment of Haibowan water conservancy project in Yellow River makes the total particulate matter (TPM) concentration in the water to reduce to very low lever in Wuhai H7 section, and the phosphorus concentration in the overlying water reaches 0.136 mg L−1. [ABSTRACT FROM AUTHOR]

In order to depict the distribution of diatom fossils in surface sediments and to establish a reliable reference data for further paleoenvironmental study in the Changjiang (Yangtze) River estuary and its adjacent waters, the diatom fossils from 34 surface sediment samples and their relationship with environmental variables were analyzed by principal component analysis and redundancy correspondence analysis. The diversity and abundance of diatom fossils were analyzed. Some annual average parameters of the overlying water (salinity, temperature, turbidity, dissolved oxygen, depth, dissolved inorganic nitrogen, dissolved inorganic phosphate and dissolved inorganic silicate) were measured at each sampling site. A total of 113 diatom taxa and one silicoflagellate species were identified in the investigation area. Diatom fossils were better preserved in fine sediments. The absolute abundance of diatom fossils did not significantly differ between inshore and offshore areas, the species diversity decreased from inshore to offshore. This may be because high nutrients and low salinity promoted the growth of more brackish species in coastal waters. The diatom taxa were divided into three groups, on the basis of their response and indication to environmental changes. For example, Actinocyclus ehrenbergii and Cyclotella stylorum were dominant in coastal waters (Group 1 and Group 3) with high nutrients and low salinity; the relative abundances of Paralia sulcata and Podosira stelliger were significantly higher in offshore sites (Group 2, average 39.5%), which were characterized by high salinity and deep water. Four environmental variables (salinity, dissolved inorganic nitrogen, temperature and water depth) explained the composition and distribution of diatom taxa independently (P< 0.05), this finding can be applied in further paleoenvironmental reconstruction research in this area. [ABSTRACT FROM AUTHOR]

Compared to larger lakes, ponds have rarely been the focus of palaeoecological studies. A common feature of ponds, especially those subject to eutrophication, is mass surface coverings of lemnoid Araceae (duckweed) which have severe implications for ecological processes in small waterbodies, in particular lowered oxygen content. To help understand the implications of duckweed dominance for the long-term ecology of ponds, and to determine the potential for palaeoecological studies in ponds more generally, we develop a new diatom-based Lemna-indicator metric. Recent studies of diatom host-plant relationships have shown significant associations between duckweed and the epiphytes Lemnicola hungarica and Sellaphora saugerresii (formally known as Sellaphora seminulum). To determine the potential of these species as palaeo-indicators of long-term duckweed dynamics in ponds, we investigated the diatom composition of surface sediment assemblages in sets of duckweed and non-duckweed-dominated ponds in Norfolk, eastern England. In addition, we undertook diatom analysis of two cores from a small farmland pond (Bodham Rail Pit) subject to a known duckweed dominance event (1999-2005). Both L. hungarica and S. saugerresii were significant predictors of past Lemna dominance in the surface sediments. Further, in the core study, both diatom species accurately and closely tracked the documented “on-off” duckweed cycle. Our study suggests huge potential for using ponds in palaeoecological studies and for diatom-based investigations of floating plant histories. [ABSTRACT FROM AUTHOR]

The effect of bacterial activity of surface sediment layer on nutrient regeneration and release from bottom sediment should be an important factor in estimating nutrient fluxes. In this study, core incubation experiments were conducted to investigate the bacterial activity in a shallow coastal area, Shido Bay, the Seto Inland Sea, from May to September 2016. High nutrient upward fluxes were observed in a high temperature period. Sodium azide (NaN3) was added to the overlying water of the core incubation experiment system to inhibit bacterial activity. The results of adding NaN3 showed that the bacteria could not only regenerate nutrients but also assimilate nutrients in the bottom sediments. Moreover, bacteria in the superficial layer, the top 2-3 mm layer of surface sediment (SL), markedly assimilated NH4 and PO4, although they did not assimilate Si(OH)4. Judging from these results, we concluded that the upward nutrient fluxes were fundamentally regulated by temperature, which affected the physicochemical processes and bacterial activity, because our previous study showed that the nutrient fluxes were scarcely affected by the activities of microphytobenthos, which were active only during winter when sufficient light penetrated to the seafloor. [ABSTRACT FROM AUTHOR]

Surface sediments can integrate a wide variety of information of seawater in marginal seas, e.g., the Quaternary sedimentary shelf such as the East China Sea (ECS) and Yellow Sea (YS). The Tessier and BCR sequential extraction procedures (SEPs) have been widely applied for extraction of various geochemical phases from sediments. To choose a suitable SEP for phase extraction of sediments from the above Quaternary sedimentary shelf, efficiency and selectivity experiments were conducted on typical individual minerals and the applicability of each SEP was assessed for natural sediments (the natural sediment standard GSD-9 and three surface sediment samples). The geochemical represented elements (Ca, Fe, Mn, Al, and Ti) were measured using both SEPs. Both SEPs have good dissolution efficiency and selectivity for the targeted geochemical phases; the optimized extractant volume for each fraction was determined. The Tessier SEP is particularly recommended for the study of adsorption-desorption process. The application of the Tessier SEP to surface sediments can furnish valuable information, including the productivity conditions (via the reducible fraction Mn) and sedimentary environments (via the carbonate fraction Ca). These results confirm that the Tessier SEP is suitable for elemental fractionation in sediments from the Chinese continental shelf. [ABSTRACT FROM AUTHOR]

Surface sediments from Reloncaví Fjord and the Chiloé inner sea in Chilean Patagonia were extracted and analyzed to estimate deltamethrin and diflubenzuron levels. These antiparasitary pesticides have been used for decades in the salmon industry. Relationships were determined between pesticide concentrations and organic carbon percent in sediments. Deltamethrin (0.39–1.05 µg g−1 dw) was found at all sampling sites but diflubenzuron (0.06–0.09 µg g−1 dw) at only five. Diflubenzuron levels were similar for sediments from other fjord areas. However, deltamethrin concentration was 2–3 fold higher than other studies on this area. The organic carbon percent was correlated positively and significantly with diflubenzuron, but not with deltamethrin. Our results suggest that the high deltamethrin concentrations in sediments are due to the increased use of pyrethroids around salmon farming areas. But, the diflubenzuron levels can be explained by degradation processes. [ABSTRACT FROM AUTHOR]

A superficial sediment layer (SL) is the top 2-3 mm layer of surface sediment that may contribute to high upward nutrient flux. To study the characteristics and the biogeochemical processes in the superficial layer, the seasonal variation in the total phytopigments (chlorophyll a and pheo-pigments), total organic carbon (TOC), and total nitrogen (TN) of the surface sediments in a shallow coastal area, Shido Bay, were measured, and the influence of the superficial sediment layer on nutrient flux at the sediment-water interface was investigated. TOC and TN content were relatively constant for the SL and subsurface layers (0-1 and 1-2 cm) during the study period. In contrast, total phytopigments content was higher in the SL layer than in the subsurface layers. The results of upward nutrient flux experiments showed higher nutrient release within the whole sediment core (SL remaining) than the SL-less (SL removed) core. Moreover, high nutrient fluxes were observed during the high temperature season, indicating that seasonal variation in nutrient flux was regulated by temperature. Moreover, in the low temperature season, the SL seemed to absorb nutrients, probably because of microphytobenthos photosynthesis that took up the nutrients under the sufficient light penetration to the sea floor. [ABSTRACT FROM AUTHOR]

Our objective was to evaluate distribution and accumulation of trace elements (TEs) in surface sediments along the Hooghly (Ganges) River Estuary, India, and to assess the potential risk with view to human health. The TE concentrations (mg kg dry weight) exhibited a wide range in the following order: Al (31.801 ± 15.943) > Fe (23.337 ± 7584) > Mn (461 ± 147) > S (381 ± 235) > Zn (54 ± 18) > V (43 ± 14) > Cr (39 ± 15) > As (34 ± 15) > Cu (27 ± 11) > Ni (24 ± 9) > Se (17 ± 8) > Co (11 ± 3) > Mo (10 ± 2) > Hg (0.02 ± 0.01). Clay, silt, iron, manganese and sulphur were important for the accumulation of TE in the sediments as confirmed by factor analysis and Pearson correlation. The accumulation and dispersal of TEs were most likely to be governed by both tide-induced processes and anthropogenic inputs from point and non-point sources. Enrichment factor analysis and geoaccumulation index revealed serious contamination of the sediments with Se and As, while comparing the consensus-based sediment quality guidelines (SQGs), adverse biological effects to benthic fauna might be caused by As, Cu, Ni and Cr. This investigation may serve as a model study and recommends continuous monitoring of As, Se, Cu, Ni and Cr to ascertain that SQGs with respect to acceptable levels of TEs to safeguard geochemical health and ecology in the vicinity of this estuary. [ABSTRACT FROM AUTHOR]

This research focuses on the fractionation and distribution patterns of heavy metals (Zn, Cu, and Fe) in surficial sediments collected from Shadegan Wildlife Refuge, the biggest wetland in southern part of Iran, to provide an overall classification for the sources of metals in the study area using a sequential extraction method. For this purpose, a four-step sequential extraction technique was applied to define the partitioning of the metals into different geochemical phases of the sediment. The results illustrated that the average total level of Zn, Cu, and Fe in surface sediments were 55.20 ± 16.04, 22.86 ± 5.68, and 25,979.01 ± 6917.91 μg/g dw, respectively. On the average, the chemical partitioning of all metals in most stations was in the order of residual >oxidizable-organic > acid-reducible > exchangeable. In the same way, the results of calculated geochemical indices revealed that Cu, Zn, and Fe concentrations are mainly influenced by lithogenic origins. Compared with consensus-based SQGs, Cu was likely to result in occasionally harmful biological effects on the biota. [ABSTRACT FROM AUTHOR]

The content of organic carbon (OC) normalized to the specific surface area (SSA) of sediment is widely used to trace variations in OC loading (OC/SSA). This study presents observations of OC/SSA of surface sediments collected in the Chukchi Sea, a typical Arctic marginal sea. Shelf sediments exhibit much higher OC/SSA values than slope sediments in the study area. Compared with OC/SSA values reported from the East Siberian Shelf and Mackenzie River, the slope sediments possess lower OC loading. This abrupt decrease in OC/SSA is mostly related to the lower primary production on slope as well as possible oxidization processes. The results of linear regression analysis between OC and SSA indicate a sedimentary source rock for the OC in the Chukchi Sea sediments. Moreover, shelf sediments with low SSA possess a larger rock OC fraction than slope sediments do. The dataset of the present study enables a more thorough understanding of regional OC cycling in the Chukchi Sea. [ABSTRACT FROM AUTHOR]

Concentrations of heavy metals, aluminium (Al), chromium (Cr), copper (Cu), iron (Fe), nickel (Ni), vanadium (V) and zinc (Zn) were analysed in the tissues of two estuarine fish species; Tilapia ( Sarotherodon melanotheron) and silver catfish ( Chrysichthys nigrodigitatus) and also in the surface sediments from Okrika estuary in the Niger Delta area of Nigeria. The sampling was conveyed in two seasons, October/November, 2015 and January/February, 2016, representing the climax of both wet and dry seasons, respectively. The levels of the metals in the fish species and surface sediments were analysed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The sequence of the metal accumulations in Tilapia was; Fe > Al > Zn > Cu > Cr > V > Ni, in silver catfish; Fe > Al > Zn > Cu > Cr > Ni > V and for sediment; Al > Fe > Zn > Cr > V > Ni > Cu. Levels of the metals in the fish species and sediment were higher than the international permissible limits based on the criteria or application of relevant pollution indices and standards. This indicates that the two fish species were not fit for human consumption. A two-way analysis of variance was used to test the difference in metal concentrations in the fish tissues and sediment. Mean differences were separated by the use of t test. Although, some degree of pollution was found in the reference or control site because Niger-Delta is strongly localised and congested with oil-refining and other industrial activities thereby making it difficult to get a clean estuary. In comparison to the metal accumulations in the tissues of the fish species from oil-impacted creeks (Ekerekana, Okari and Ogoloma) and less oil-impacted counterpart (control site), higher levels ( p < 0.05) of the metals were observed in the impacted than the less impacted creek. For most of the metals, S. melanotheron had higher concentrations than the C. nigrodigitatus. Seasonal variations reflected that there was higher accumulation of the metals in the two fish species in the rainy season than the dry season. For sediment, there was significant difference for most of the metals between these two creeks except for Al. The multivariate tools of principal component analysis, Pearson correlation analysis and the use of vanadium/nickel ratio were used to confirm the possible source of the metals in the environmental matrices from oil pollution. Therefore, it is mandatory and expedient to ensure regular monitoring of the trace element loadings in these creeks and to take appropriate measures to alleviate the incident to safeguard the health of the public. [ABSTRACT FROM AUTHOR]

Twenty-two organochlorine pesticides (OCPs) were investigated in Anhui reach of Huaihe river, China. Seventeen out of 22 OCPs were detected by GC-MS. The mean concentrations of OCPs followed the order: HCHs > DDTs > HCB > chlordanes > endosulfans. Levels of total HCHs and total DDTs ranged from 2.54 to 13.91 ng g (mean = 7.52 ng g) and 0.016 to 2.54 ng g (mean = 0.45 ng g), respectively. The concentrations of DDTs were lower than those of HCHs. Compared with the other rivers in China, DDTs and HCHs were relatively lower or similar. Statistical analysis indicated that the OCPs concentration differences were not insignificant between upstream, midstream and downstream. The compound compositions suggested that historical usage of lindane and fresh DDT were the main sources. The regression analysis indicated that TOC has influence on the levels of HCHs and little influence on the levels of DDTs in the sediments. [ABSTRACT FROM AUTHOR]

The distribution of diatoms from surface sediments of the West Philippine Basin was analyzed, with 68 species and varieties of diatoms from 26 genera identified. Diatom abundance varied spatially, with the absolute abundance of diatoms ranging from 0 to 3.4×10 frustules/g. The seven tropical pelagic diatoms were Alveus marinus, Azpeitia africana, Azpeitia nodulifera, Hemidiscus cuneiformis, Hemidiscus cuneiformis var. ventricosus, Roperia tesselata and Rhizosolenia bergonii. The relative abundance of these species was greater than 20%, and their distribution pattern in the sediments was overlaid by the flow of the Kuroshio Current. Ethmodiscus rex was present at 159 stations, formed the most abundant and dominant species in the diatomaceous ooze, and thus referred to as Ethmodiscus ooze. Ethmodiscus rex was also a major contributor to primary production in the region. A principal component analysis was employed to explain the relationship between samples and variations in diatom species from the WPB. Four diatom assemblages were distinguished, representing different oceanographic conditions; their spatial distributions were closely related with the North Equatorial Current and Kuroshio Current patterns in the region. These diatom assemblages can therefore be useful in deciphering late Quaternary palaeoceanographic reconstructions of the West Philippine Basin. [ABSTRACT FROM AUTHOR]

In order to identify contaminating trace metals and their sources, studies on trace metals are often included in routine environmental monitoring programs. Twenty-five near-shore bottom sediment samples from the inner shelf region (near Cuddalore) of the Bay of Bengal were analysed for sediment texture, organic matter, carbonate (CaCO) concentrations and total trace metal concentrations (TTMs) (Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn and Cd) in order to evaluate geochemical processes such as enrichment and their origin. The presence of carbonates (2.5-5.8 %) indicates the dominance of calcareous shells in the region. A relatively high percentage of organic matter (0.2-3.9 %) is attributed to the predominance of finer sediments entering through the minor rivers. High concentrations of TTMs in fine and organic-rich sediments are influenced by municipal and industrial sources, which contention is well supported by correlations of TTMs concentrations with Fe-Mn fractions. Geoaccumulation index ( I ) calculations indicate that Cr, Cu, Ni, Pb and Cd concentrations are above the values expected from their presence in the discharge of effluents from the industrial zones bordering the shoreline. Comparing the findings of the present study with those from different parts of the World, Cr, Cu, Ni, Pb appear to be enriched in the sediments of the region. [ABSTRACT FROM AUTHOR]

Identifying the provenance of sediments carried by modern rivers can provide information on earth surface processes and help us to interpret geological history more clearly. The types and distribution patterns of surface sediments deposited in river systems are determined mainly by the fluvial flux and weathering of the proximal source rocks. In this paper, analysis of the heavy mineral content of 99 surface sediment samples was used to identify the source of the sediments carried by the Dan River in China. The objectives of this study are to: (1) determine the characteristics and distribution of the sediments, and (2) identify and classify the various depositional areas according to their differing source areas. The Dan River is divided into the lower, middle, and upper reaches to investigate the spatial distribution of heavy minerals. The main minerals detected were amphiboles, pyroxene, epidote, garnet, tourmaline, zircon, apatite, rutile, sphene, anatase, pyrite, and ilmenite. Generally, ilmenite (0.7% to 69.1%), amphibole (0% to 93.6%), epidote (0% to 53.3%), garnet (0% to 36.7%) and pyroxene (0% to 42.0%) were the most frequent detrital heavy minerals in the studied river sections. The Dan River and its tributaries are characterized with respect to their heavy mineral assemblages and heavy mineral indexes. Six depositional areas are distinguished and classified as Depositional area A (the Laoguan, Qi, and Xian rivers), Depositional area B (the Qingyou and Wuguan rivers), Depositional area C (the Laojun River), Depositional area D (the upper reaches of the Dan River), Depositional area E (the Yinhua River), and Depositional area F (the Tao River). The provenance study indicated that the sediments were derived mainly from the proximal exposed rocks. Sediments in the middle reaches of the Dan River were derived from Depositional areas B, C, and E, whereas sediments in the lower reaches were derived mainly from the local rocks along the river. Similar heavy mineral assemblages were obtained from Danjiangkou Reservoir and Depositional area A, especially for the Laoguan River, indicating the significant influence of Depositional area A on the reservoir. [ABSTRACT FROM AUTHOR]

The present study investigates the quality of surface sediments from the Bizerte lagoon (North Tunisia) using an integrated approach including chemical contaminant analysis, bioassays and sediment quality guidelines (SQGs). Sediment samples were collected at 9 sites and analyzed for eight heavy metals (Hg, Cd, Cr, Cu, Pb, Zn, Ni, Fe and Mn). PAHs, PCBs, OCPs were measured previously in the same sediment samples. Our results indicated that the highest concentrations of metals were found near urban areas due to the municipial and industrial wastewater discharges. Sediment pollution assessment was carried out using geoaccumulation index and enrichment factor, which indicate a widespread pollution by Cd, Pb, Ni and Zn in the studied sediments. For bioassays, aqueous and organic extracts were used to assess toxicity and genotoxicity in sediments by using Microtox and SOS Chromotest, respectively. Toxicity levels were compared to metallic and organic pollutants contents. Our results highlight differences in the pattern of responses between the different assays and show no correlation with all the studied contaminants, emphasizing the influence of other contaminants not analyzed in the present study. Based on SQGs, the results of toxicity assessment indicated that adverse effects caused by Ni and Zn would be expected frequently. Nickel was found to have the highest predicted acute toxicity, followed by Zn, Pb, Cd, Cu and Cr. There was no significant relationship between sediment toxicity calculated from heavy metal concentrations (SQG approach) and those measured with bioassays. These findings support the use of integrated approachs for evaluating the environmental risks of sediments. [ABSTRACT FROM AUTHOR]