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Post-GOE deep-water Fe-Si precipitates associated with volcanogenic massive sulfide deposits are an important feature of the Proterozoic rock record. Although it is clear that these enigmatic deposits formed in oxygen-deficient and hydrothermally influenced deep-water settings, the oxidation mechanism(s) resulting in their precipitation remain(s) unclear. Whilst existing genetic models typically couple direct and/or bacterially-mediated iron oxidation with abiotic silica precipitation, low temperature diffuse hydrothermal fluids offer a potential mechanistic alternative to explain the observed layering. Herein, via combination of petrographic observations with elemental and isotopic data (Fe, Si, and O), we explore the genesis of the primary mineral phases present within recent Fe-Si precipitates obtained from the Southwest Indian Ridge. Formation of ferrihydrite and opal-A in these precipitates provides insight into the genesis of widely invoked precursor minerals to post-GOE deep-water Fe-Si precipitates. Specifically, we find that the mineralogical layers that typify these Fe-Si precipitates may have originated via biologically mediated ferrihydrite precipitation and abiotic precipitation of opal-A from oversaturated fluids during diffuse flow. By analogy, we propose that diffuse hydrothermal fluid flow played an important role in the formation of post-GOE deep-water Fe-Si precipitates.

Sources and cycling of phosphorus in the sediment of inflow rivers (FL, TY and QY) along the eutrophic Chaohu lake, China were discussed by using the oxygen isotope compositions of phosphorus fract...

The 18O/16O (and 15N/14N) ratio of natural nitrate (NO3-) and nitrite (NO2-) can be used to extract valuable information about their source and fate as environmental contaminants, their metabolism as macronutrients in plants and animals, and their behavior in the N biogeochemical cycle. We developed an accurate, precise, sensitive (minimum sample size: 0.2 μg NO3--equivalent), and reliable (minimal oxygen exchange, loss, or gain) method to selectively isolate and purify nitrate and nitrite from natural water, soil, air, and plant materials by strong anion exchange (SAX) for low- to normal-salinity samples or strong cation exchange (SCX) for high-salinity samples, followed by quantitative conversion to their respective benzyl esters, which can be separated and individually analyzed for δ18O (and potentially δ15N) by gas chromatography (GC)/pyrolysis/GC/isotope-ratio mass spectrometry (IRMS). The method compares favorably with the currently popular bacterial denitrification and chemical reduction methods, in terms of sensitivity and reliability, and has the potential to simultaneously measure δ15N and δ18O of nitrate and nitrite from natural samples of various origins.

Information about plant photosynthetic carbon assimilation, physiology, and biochemistry is locked in the 18O/16O ratios of the individual positions of higher plants carbohydrates but is under-utilized, because of the difficulty of making these determinations. We report the extension of the wet chemistry approach we used to access the 18O/16O ratio of O-3 of glucose with a novel GC/Pyrolysis/IRMS-based method, to determine the 18O/16O ratios of O-4, O-5, and O-6. The O atoms (OH groups) at positions 1, 2, 5, and 6 of glucose were protected by acetonation (converting to 1,2;5,6-di-O-isopropylidene-glucofuranose, DAGF). The DAGF was then converted to 6-bromo-6-deoxy-1,2;3,5-di-O-isopropylidene-glucofuranose (6-bromoDAGF) with the simultaneous removal of O-6 with N-bromosuccinimide and triphenylphosphine. The DAGF was also methylated at O-3 with CH3I under the catalysis of NaH to 3-methylDAGF, which was then deacetonated to 1,2-O-isopropylidene-3-O-methyl-glucofuranose (3-methylMAGF). O-5 and O-6 were then removed as a whole from 3-methylMAGF by I2 oxidization under the catalysis of Ph3P and imidazole. Isotope mass balance was then applied to calculate the 18O/16O of O-5 and O-6 as a whole and O-6, respectively. Sampling at different stages of substrate conversion to product and applying a Rayleigh-type fractionation model were employed, when quantitative conversion of substrate was unachievable to calculate the δ18O of the converted substrate. Quantitative conversion of glucose with phenylhydrazine to phenylglucosazone also allowed for the calculation of δ18O2 by applying isotope mass balance between the two. A C4 starch-derived glucose intramolecular δ18O profile is now determined: O-3 is relatively enriched (by 12.16 mUr), O-4 is relatively depleted (by 20.40-31.11 mUr), and O-2 is marginally enriched (by 2.40 mUr) against the molecular average.

Highlights • Three distinct types of carbonates exist in cold seeps in the Okinawa Trough. • Carbonate forms between lower part of SMTZ and upper part of methanogenic zone. • Hydrothermal has the potential to foster Fe-AOM in cold seep sediment. • Metal-AOM might have an influence on early Earth's methane flux and metal cycle. Abstract Anaerobic oxidation of methane (AOM) is an important process that regulates methane budget in the global carbon cycle. Sulfate is traditionally regarded as the most important electron acceptor for AOM. However, recent studies reveal that reactive metal reduction-driven AOM (metal-AOM) may also present on natural environments. Partitioning the methane-C sink from anaerobic oxidation between sulfate reduction-driven AOM (sulfate-AOM) and metal-AOM is thus becoming a scientific challenge to be addressed. This study aimed to show that metal-AOM has a potential to complement sulfate-AOM, especially when methane seeps met sediments enriched in iron and manganese oxides supplied by hydrothermal plumes. Samples of authigenic carbonate were collected from the cold seeps on the western slope of the Okinawa Trough (OT), a semi-enclosed back-arc basin with cold seeps and hydrothermal activities coexist spatially. Petrologic and mineralogical observations provided faithful evidence of a close genetic relationship between goethite and authigenic carbonates, likely indicating the presence of metal-AOM although some contributions of organoclastic Fe reduction cannot be ruled out. The most possible place of metal-AOM was between the lower part of the sulfate–methane transition zone (SMTZ) and the immediate upper part of the methanogenic zone. The characteristics of δ13Ccarb [−53.7‰ to −3.3‰ Vienna-PeeDee Belemnite (VPDB)] also point to our carbonate samples as the products of AOM. These authigenic carbonates was further identified as three possible types of carbonate of different sources: sulfate-AOM, metal-AOM, and hydrothermal carbonates, depending on the correlations among concentrations of carbonate-associated sulfate (CAS), δ13Ccarb, and δ18Ocarb. Based on these findings, we tentatively suggested that the reduction of reactive metals carried by hydrothermal plumes might drive the methane oxidation in the adjacent cold seep areas, resulting in the precipitation of unique carbonates and enhancement the efficiency of “the benthic methane filter”. This study reported the coupling or interaction between the two extreme submarine environments by metal-AOM for the first time, which might help in understanding and improving the global carbon and metal cycles now and in the past. Previous article in issue

The spread of millet agriculture to southeast (SE) China is critical to understanding the region's economic pattern and its potential impact on the proposed initial expansion of proto-Austronesians. In this study, we present new multidisciplinary evidence for the development of millet agriculture from three Neolithic sites in Fujian Province, China: Hulushan, Pingfengshan and Huangguashan. The carbonized seeds from Hulushan indicate the existence of millet agriculture around 3842-3649 cal. BP. Meanwhile, we tested stable carbon and nitrogen isotope ratios of faunal remains (n = 22) from Pingfengshan and Huangguashan shell midden sites in a coastal area of Fujian. The stable isotope results for pigs (δ15N values range from 4.9 to 11.2‰, and δ13C values range from −24.1 to −11.2‰) show significant variations, suggesting that these pigs were fed different foods, including C3 plants, C4 plants and marine resources. Specifically, two samples of pig collagen with strong millet signals were directly dated to about 4000-3600 cal. BP. These new findings provide substantial evidence for a new understanding of the development of millet agriculture in SE China.

With the population growth, urbanization and industrialization, China has become a hotspot of atmospheric deposition nitrogen (ADN), which is a threat to ecosystem and food safety. However, the impacts of increased ADN on rice growth and grain metal content are little studied. Based on previous long-term ADN studies, greenhouse experiment was conducted with four simulated ADN rates of 0, 30, 60 and 90 kg N ha−1 yr−1 (CK, N1, N2 and N3 as δ15N, respectively) to assess rice growth and metal uptake in a red soil ecosystem of southeast China during 2016–2017. Results showed that simulated ADN could promote rice growth and increase yields by 15.68–24.41% (except N2) and accumulations of cadmium (Cd) or copper (Cu) in organs. However, there was no linear relationship between ADN rate and rice growth or Cd or Cu uptake. The 15N-ADN was mainly accumulated in roots (21.31–67.86%) and grains (25.26–49.35%), while Cd and Cu were primarily accumulated in roots (78.86–93.44% and 90.00–96.24%, respectively). 15N-ADN and Cd accumulations in roots were significantly different between the two growing seasons (p

Hyperspectral image (HSI) classification has been long envisioned in the remote sensing community. Many methods have been proposed for HSI classification. Among them, the method of fusing spatial features has been widely used and achieved good performance. Aiming at the problem of spatial feature extraction in spectral-spatial HSI classification, we proposed a guided filter-based method. We attempted two fusion methods for spectral and spatial features. In order to optimize the classification results, we also adopted a guided filter to obtain better results. We apply the support vector machine (SVM) to classify the HSI. Experiments show that our proposed methods can obtain very competitive results than compared methods on all the three popular datasets. More importantly, our methods are fast and easy to implement.

The typhoon process has a significant influence on the distribution of heavy metals in sediments. Based on the heavy metal (V, Cr, Co, Ni, Cu, Zn, Pb, and Mn) contents in surface sediments collected under normal conditions and post-typhoon Matmo in Quanzhou Bay in 2014, the distributions, sources, and impacts of typhoon processes on heavy metals and pollution conditions were studied and discussed. The results showed that the heavy metals can be divided into two categories: Class I metals (Cu, Zn, Pb, and Mn) were mainly distributed in the estuary and significantly increased after the typhoon, and Class II metals (V, Cr, Co, and Ni) were distributed in the coastal intertidal zone and estuary and remained unchanged or decreased after the typhoon. The heavy metal assessment showed that heavy metal pollution in Quanzhou Bay was serious and tended to increase after the typhoon. The increased metal supply and enhanced riverine and tidal hydrodynamics after the typhoon may be the main factors influencing the variations in heavy metal content and distribution. This study provided a basis for the accurate evaluation and scientific management of heavy metal pollution caused by typhoon processes in Quanzhou Bay.

Recent studies have highlighted the valuable role played by mangrove forests in carbon sequestration and storage. Although Indonesia accounts for a large proportion of global mangrove area, knowledge on the carbon stock and sources in the Indonesian mangrove is still limited. In this study, we quantified the ecosystem organic carbon (OC) stock and its spatial variation at an oceanic mangrove in Wori, North Sulawesi, Indonesia. The sources of soil OC were also investigated. The results showed that the mangrove soil had a substantial OC stock containing 15.4 kg/m2 (calculated by carbon) in the top 50 cm soil, and represented the majority of the ecosystem OC stock at the Wori mangrove. The mangrove biomass and ecosystem OC stock were 8.3 kg/m2 and 23.7 kg/m2, respectively. There was no significantly difference in the soil OC stock among the stations with difference distances offshore, while the highest mangrove biomass OC stock was found at the seaward station. Isotope mixing calculations showed that the rich OC in mangrove soils was attributed to the accumulated autochthonous mangrove source while the suspended organic matter in tidal water and the mangrove-adjacent seagrass contributed less than 20% to the soil OC. The results further demonstrated the importances of the oceanic mangrove in carbon storage and the mangrove plants in contributing OC to their soils.

The dispersing process of hydrothermal plumes could be documented in the hydrothermal sediments beneath the plume trajectory. Here we report the results of mineralogical and geochemical analyses of eight surficial distal plume sediment samples recovered from the flank of Endeavour Segment, Juan de Fuca Ridge (JdFR). The geochemical analysis based on selective leaching showed that hydrothermal fluids contribute a proportion of Fe-Mn oxides (4.51–7.17 wt% of bulk sediments) to the plume sediments along with obviously enriched hydrothermally-sourced Al, Ca and some trace elements. The contents of reactive Fe in the sediments had no distinct relationship with the distance to the vents. We propose that the early mineralization of abundant organic matters in the distal plume sediments causes reactive Fe oxyhydroxide to undergo dissimilatory iron reduction (DIR) and thus overprints or even eradicates the original hydrothermal signal. Furthermore, the contents of some elements (P, V, U and Cr), which are traditionally believed to be closely associated with reactive Fe, had no correlation with the Fe content here. However, it was found that, within a distance of 2–15 km, the two-endmember mixing between seawater and hydrothermal fluid could be fingerprinted by the Sr-Nd isotopic ratio associated with the reactive Fe-Mn oxyhydroxides. In addition, reactive Mn content also provides a faithful record of the hydrothermal process. We also show that the decoupling behaviors between active Fe and Mn during precipitation and subsequent early diagenesis in the distal plume sediments provide valuable implications for future studies about the fates and oceanic budgets of various associated scavenging-prone elements.

Nitrate (NO

The

Fifty-seven riverine samples in three typical regions, namely, upper mountainous (zone 1), middle hilly (zone 2), and lower plain (zone 3) regions, were collected in May (low flow) and August (high flow) of 2016, and chemical parameters and isotopes were analyzed to enrich the knowledge of riverine nitrate sources and transformations in the Taizi River basin. Results showed that NO3- concentrations in zone 3 were the highest, followed by zones 2 and 1. NO3-/Cl- molar ratios and nitrate dual isotopes indicated that NO3- was mainly from chemical fertilizer (CF) in zones 1 (57.0%) and 2 (43.1%) according to a Bayesian mixing model (SIAR) and mixed sources of CF, nitrification of soil organic nitrogen (SON), and manure and sewage (M&S) in zone 3 (92.8%), during the high-flow season. NO3- was mainly from CF and SON in zones 1 (76.7%) and 2 (74.0%), during the low-flow season. NO3-sources were different in the three rivers of zone 3 mainly due to various urban inputs. Contributions of CF, SON, and M&S increased by 13%, 8.3%, and 7.5% in zones 1, 2, and 3, respectively, from the low-flow to the high-flow season. NO3- in the Taizi River was mainly influenced by nitrification in soils, while no significant denitrification was found in the three zones. Measures for reducing NO3- inputs to rivers should be considered by improving effectively utilizing rate of chemical fertilizer and inhibit nitrification.

The concentrations of Cr, Ni, Cu, Zn, As, Cd, Pb, and Al in suspended particles were measured, and temperature, salinity, flow velocity and direction during a tidal cycle were observed before and after Typhoon Fung-wong at six stations in Quanzhou Bay, respectively. The comparison results show that, after the typhoon, the salinity in Quanzhou Bay decreased, whereas the concentrations of heavy metals increased by a factor of between 2 and 10, and the high heavy metal concentration corresponded to the low value of ratio between heavy metals and Al (HMs/Al), suggesting that these increased heavy metals were mainly from natural sources. Instantaneous unit width flux calculations for heavy metals at different stations indicate that sediments are an important source of heavy metals in suspended particles under the influence of typhoon, which has significantly contribution to understanding the impact of typhoons on the heavy metal pollution in the coastal area.

RATIONALE Quantitatively relating 13 C/12 C, 2 H/1 H and 18 O/16 O ratios of plant α-cellulose and 2 H/1 H of n-alkanes to environmental conditions and metabolic status should ideally be based on the leaf, the plant organ most sensitive to environmental change. The fact that leaf organic matter is composed of isotopically different heterotrophic and autotrophic components means that it is imperative that one be able to disentangle the relative heterotrophic and autotrophic contributions to leaf organic matter. METHODS We tackled this issue by two-dimensional sampling of leaf water and α-cellulose, and specific n-alkanes from greenhouse-grown immature and mature and field-grown mature banana leaves, taking advantage of their large areas and thick waxy layers. Leaf water, α-cellulose and n-alkane isotope ratios were then characterized using elemental analysis isotope ratio mass spectrometry (IRMS) or gas chromatography IRMS. A three-member (heterotrophy, autotrophy and photoheterotrophy) conceptual linear mixing model was then proposed for disentangling the relative contributions of the three trophic modes. RESULTS We discovered distinct spatial leaf water, α-cellulose and n-alkane isotope ratio patterns that varied with leaf developmental stages. We inferred from the conceptual model that, averaged over the leaf blade, only 20% of α-cellulose in banana leaf is autotrophically laid down in both greenhouse-grown and field-grown banana leaves, while approximately 60% and 100% of n-alkanes are produced autotrophically in greenhouse-grown and field-grown banana leaves, respectively. There exist distinct lateral (edge to midrib) gradients in autotrophic contributions of α-cellulose and n-alkanes. CONCLUSIONS Efforts to establish quantitative isotope-environment relationships should take into account the fact that the evaporative leaf water 18 O and 2 H enrichment signal recorded in autotrophically laid down α-cellulose is significantly diluted by the heterotrophically formed α-cellulose. The δ2 H value of field-grown mature banana leaf n-alkanes is much more sensitive than α-cellulose as a recorder of the growth environment. Quantitative isotope-environment relationship based on greenhouse-grown n-alkane δ2 H values may not be reliable.

Information about plant photosynthetic carbon assimilation, physiology, and biochemistry is locked in the

RATIONALE Although the 2 H/1 H ratio of the carbon-bound hydrogens (C-Hs) in α-cellulose extracted from higher plants has long been used successfully for climate, environmental and metabolic studies, the assumption that bleaching with acidified NaClO2 to remove lignin before pure α-cellulose can be obtained does not alter the 2 H/1 H ratio of α-cellulose C-Hs has nonetheless not been tested. METHODS For reliable application of the 2 H/1 H ratio of α-cellulose C-H, we processed plant materials representing different phytochemistries and photosynthetic carbon assimilation modes in isotopically contrasting bleaching media (with an isotopic difference of 273 mUr). All the isotope ratios were measured by elemental analyzer/isotope ratio mass spectrometry (EA/IRMS). RESULTS Our results show that H from the bleaching medium does appear in the final pure α-cellulose product, although the isotopic alteration to the C-H in α-cellulose due to the incorporation of processing H from the medium is small if isotopically "natural" water is used to prepare the processing medium. However, under prolonged bleaching such an isotope effect can be significant, implying that standardizing the bleaching process is necessary for reliable 2 H/1 H measurement. CONCLUSIONS The currently adopted method for removing lignin for α-cellulose extraction from higher plant materials with acidified NaClO2 bleaching is considered acceptable in terms of preserving the isotopic fidelity if isotopically "natural" water is used to prepare the bleaching solution.

The 18O/16O ratio at both molecular and positional levels in the carbohydrates of higher plants is a reliable proxy for the plant growth environment, and a potential indicator of the plant photosynthetic carbon assimilation mode, and its physiological, biochemical and metabolic status. The lack of exploitable nuclear resonance in 18O and 16O and the extremely low 17O abundance make the NMR-based PSIA (position-specific isotopic analysis) a significant challenge. In this Article, an alternative three-step wet chemistry based method for accessing the 18O/16O of glucose O-3 is presented. The O atoms (OH groups) at positions 1, 2, 5, and 6 were first protected by acetonation (converting glucose to 1,2;5,6-di-O-isopropylidene-glucofuranose). The protected glucose was then esterified at O-3 by thionoformylation. Subsequent Barton–McCombie deoxygenation quantitatively removed the O-3 from the protected sugar. Mass balance was then applied to calculate the 18O/16O of O-3 using the isotopic values of the protected...

Total organic carbon (TOC), total nitrogen (TN), δ13Corg, δ15N, and grain size were measured in two sediment cores from reserves adjacent to Dongshan Bay, China. The aims were to identify organic matter (OM) sources and to evaluate the combined impact of human activity and natural environmental processes over the last ∼100 yr. In a coral reserve far from the estuary of Zhangjiang River, the average sediment accumulation rate (SAR) was 0.51 cm/yr from ca. 1839–2015, and the values of δ13Corg and C/N (atomic ratio of TOC to total N) ranged from −21.9‰ to −23.7‰ and from 5.7 to 8.1, respectively. In a mangrove forest reserve near the estuary, SAR averaged 0.49 cm/yr from ca. 1891–1985 and 2.41 cm/yr from ca. 1985–2015, and the δ13Corg and C/N values ranged from −22.7‰ to −26.3‰ and from 9.3 to 21.7, respectively. By combining a comparison plot of C/N and δ13Corg and a binary mixing model (based on δ13Corg and Norg/Corg, respectively), the major OM sources were assigned and their sedimentary contributions estimated. The sedimentary OM in the coral reserve had mainly an offshore marine authigenic signature with an average terrigenous contribution of 56%. While input from the Zhangjiang River declined from the 1980 s, urban development, deforestation and land reclamation contributed to an overall increase in the total mass accumulation rate (MAR). The coral was also severely damaged by the advent of poaching around the same time. These two factors collectively resulted in a rapid decrease in OM content and OC accumulation rate (CARorg) of the sediments until the establishment of the coral reserve in 1997. Changes in terrain and climate and the construction of water conservancy facilities were traditionally the primary factors responsible for changes in the sedimentary environment of the mangrove forest reserve. Since the 1980s, however, the expansion of the mangrove forest along with human activity has led to rapid increases in MAR and CARorg; while, protective measures and a favorable climate have also promoted the growth of the mangrove forest.

Coastal embayments play a vital role in the global carbon cycle either as sources of organic matter to open sea or as carbon sinks due to the accumulation of organic matter in sediments. This paper describes a study of Luoyuan Bay, a typical semi-enclosed embayment with a total area of approximately 227 km 2 in a strong tidal environment. The analysed results indicate that the particulate organic carbon (POC) concentration in suspended particulate matter (SPM) varies from 0.57 mg/L to 1.33 mg/L at the bottom layer (0.5 MAB, meters above bed) and from 0.54 mg/L to 1.25 mg/L at the surface layer (0.5 MBS, meters below surface). The δ 13 C‰ ranges from −25.52‰ to −23.54‰ and exhibits different variations at the surface and bottom layers in spring and neap tides. The POC content in deposited particulate matter (DPM) varies from 0.62% to 2.95%, increasing from spring to neap tide, and the δ 13 C and C/N molar ratio are −25.29‰ ∼ −21.41‰ and 4.18–8.53, respectively. The settling fluxes of POC obtained by sediment trap decrease from 2.25 g/m 2 ·tide during the spring tide to 0.55 g/m 2 ·tide during the neap tide with a mean value of 1.41 g/m 2 ·tide during the observation, whereas the settling flux of SPM decreases from 456.76 g/m 2 ·tide during the spring tide to 37.12 g/m 2 ·tide during the neap tide. Combining the δ 13 C and C/N molar ratio, three end-members are recognized, i.e., freshwater algae and phytoplankton, marine algae and phytoplankton, and kelp-derived detritus. The mean contribution to POC from these three sources is 57.2%, 31.8% and 11.0% in SPM, and 39.9%, 35.0% and 25.1% in DPM, respectively. The POC from freshwater algae, phytoplankton and kelp-derived detritus is controlled by sediment dynamic processes.

In order to mitigate investments, stock price forecasting has attracted more attention in recent years. Aiming at the discreteness, non-normality, high-noise in high-frequency data, a support vector machine regression (SVR) algorithm is introduced in this paper. However, the characteristics in different periods of the same stock, or the same periods of different stocks are significantly different. So, SVR with fixed parameters is difficult to satisfy with the constantly changing data flow. To tackle this problem, an adaptive SVR was proposed for stock data at three different time scales, including daily data, 30-min data, and 5-min data. Experiments show that the improved SVR with dynamic optimization of learning parameters by particle swarm optimization can get a better result than compared methods including SVR and back-propagation neural network.

The settling of particulate organic carbon is significant for the vertical transfer and burial of organic carbon. Using time-series sediment traps, we collected settling particulate matter in the near-bottom layer (8 mab [meters above bed]) over eight continuous days in the continental shelf waters of the northern Taiwan Strait and analyzed the particulate organic carbon content. The observational results indicated that the deposition flux in the continental shelf waters during the summer in the north-eastern Taiwan Strait is 0.86 g/m 2 ·d ∼10.68 g/m 2 ·d; the corrected deposition flux is lower than the measured value by approximately 4.5%–30.6%. The particulate organic carbon (POC) content and δ 13 C org ‰ value are 0.589%–0.741% and −20.74‰∼−22.61‰. The δ 13 C org ‰ indicated that the settling particulate matter was primarily from marine sources at a contribution rate of 70%–88%. Settling particulate matter primarily came from the re-suspension of bottom sediment which accounted for 65%–85% of settling particulate matter. The rising thermocline and halocline near the bottom can strengthen the contribution of re-suspension to the settling particulate organic carbon.

The sulfate reduction process plays an important role in the early diagenesis of organic matter in the estuarine and coastal sediments. In this study, the sulfate reduction rates (SRR) were determined by the 35SO42− radioactive tracer method, and the SO42−, CH4, Cl− of sediment porewater and total organic carbon (TOC), temperature, and redox potential (Eh) of sediment were determined simultaneously at three stations (QA, HQ, and GS) in different sedimentary environments of the Pearl River Estuary to study the sulfate reduction process and its important role in organic matter mineralization. The results show that SRR was mainly controlled by the content and availability of organic matter in sediments of the Pearl River Estuary. The consumption of sulfate mainly included the organic matter mineralization on the upper sediments and the anaerobic oxidation of methane (AOM) driven by sulfate in the sulfate-methane transition zone (SMT), which formed two peaks in the SRR profile, respectively (stations HQ and GS). Affected by physical disturbance, there was only one SRR peak formed above the SMT at station QA. The results of flux calculations for AOM and sulfate reduction show that the contributions of AOM to total sulfate reduction were 7.04 %, 5.46 %, and 42.0 % at stations QA, HQ, and GS, respectively, which were also controlled by the content and availability of organic matter in sediments. The depths of SMT in sediments of stations QA, HQ, and GS were 25, 30, and 213 cm, respectively, which were controlled by the input of organic matter and sulfate concentration in sediments. The calculation results show that total fluxes of sulfate reduction were 22.7, 35.3, and 3.9 mmol m−2 d-l at stations QA, HQ, and GS, respectively, and the rates of organic carbon mineralization by sulfate reduction were 45.4, 70.6, and 7.8 mmol m−2 d-l. In the estuarine mouth (station GS) with relatively weak hydrodynamic force and deep water, the burying efficiency of organic matter in sediment was higher than that in the brackish coast (station HQ); whereas the burial efficiency of organic matter in sediment cannot be comprehensively estimate in the upper estuary (station QA) due to the existence of the fluid mud layer. These findings contribute to a comprehensive understanding of the biogeochemical cycling process of sulfate and methane in sediments of the Pearl River Estuary.

With sea level rise in the early Holocene, the warm and low-salinity sea water from the Java Sea was transported into the eastern Indian Ocean after the opening of the Sunda Strait. However, the impact of this process on sediment provenance and paleoproductivity is rarely known. In this study, we analyzed the grain size, Sr-Nd-Pb isotopic compositions and biogenic elements of core CJ01-185 (1538 m water depth) in the eastern Indian Ocean off the Sunda Strait. Our new results reveal a large volcanic eruption in the west of Java at 2.1 ka, and the Krakatau eruption at 1883 CE. On the basis of the Pb isotopic compositions, 87 Sr/ 86 Sr ratios, and e Nd values, we infer that sediments from core CJ01-185 were derived primarily from Java Island. There is a distinct change in Sr-Nd-Pb isotopic compositions of the sediments from the last glacial period to the Holocene, indicating less radiogenic Nd isotopes from the Java Sea into the eastern Indian Ocean after the opening of the Sunda Strait at ∼10 ka. Moreover, the sedimentation rate increased significantly from 6.5 cm kyr −1 during the last glacial period to 20 cm kyr −1 in the Holocene. The input of additional terrigenous nutrients from the Java Sea induced paleoproductivity with higher TOC and TN concentrations after the opening of the Sunda Strait. Our results thus suggest that the paleoproductivity was mainly influenced by terrigenous materials input in the Holocene, other than southeast monsoon or upwelling in the last glacial period.

The geochemical compositions of sediments in the Dongshan Bay, a semi-enclosed bay on the southeast coast of China, were obtained to identify pollutant sources and evaluate the anthropogenic impacts over the last 100 years. The results indicated that the metal flux had been increasing since the 1980s. Enrichment factor values (Pb, Zn and Cu) suggested only slight enrichment. The proportion of anthropogenic Pb changed from 9% to 15% during 2000-2014. Coal combustion might be an important contamination source in the Dongshan Bay. The historical variation in the metal flux reflected the economic development and urbanization in the Zhangjiang drainage area in the past 30 years. According to the Landsat satellite remote sensing data, the urbanization area expanded approximately three times from 1995 to 2010. The δ13C values (-21‰ to -23‰) of the organic matter (OM) in the sediments indicated that the OM was primarily sourced from aquatic, terrigenous and marsh C3 plants. Nitrogen was mainly derived from aquatic plants and terrigenous erosion before the 1980s. However, the total organic carbon (TOC) contents, total nitrogen (TN) contents and δ15N had been increasing since the 1980s, which suggested that the sources of nitrogen were soil erosion, fertilizer and sewage. In addition, the TOC and TN fluxes in the Dongshan Bay had significantly increased since the 1980s, which reflected the use of N fertilizer. However, the TOC and TN fluxes significantly decreased in the past decade because environmental awareness increased and environmental protection policies were implemented.

Near-bed suspended sediment concentration (SSC) was measured at the margin and in the interior of a Spartina alterniflora marsh in Luoyuan Bay, a semi-enclosed embayment sheltered from the East China Sea, in January and July 2008. Variations in SSC at the two stations correlated to the tidal cycle: high SSC occurred in the early stage of the flood tide and the later stage of the ebb tide, while SSC was significantly lower at all other times. The SSC increased from the neap tide to the spring tide in both winter and summer. The high SSC in winter was primarily a result of stronger hydrodynamic processes, whereas the high SSC in summer was primarily attributable to biological activity. The particulate organic carbon (POC) in the S. alterniflora marsh of Luoyuan Bay primarily originates from freshwater and marine algae and phytoplankton, while the contribution of marsh detritus is limited. The contribution of POC to near-bed SSC is less than 5% in both winter and summer. During winter, the near-bed SSC was closely related to the bottom shear stress; therefore, variations in SSC were controlled by hydrodynamic processes. However, the correlation between bottom shear stress and near-bed SSC was poor in summer because of the interference of burrowing organisms during the late stage of the ebb tide. The maximum estimated contribution of turbid water flowing out of caves due to the biological activity of burrowing organisms was approximately 30.3 mg L−1 or 20.2 to 50.5% with a mean value of 34.9% of total SSC at the late stage of the ebb tide. Our findings also suggest that the relative importance of hydrodynamic processes and biological activity can vary considerably between seasons.

The chemical linkage between α-cellulose and lignin in plant cell walls has long been a controversial topic and crucial to devising effective strategies for sustainable biomass and bioenergy utilization. In this new contribution, we surveyed 80 Poaceae (Gramineae) species grown in tropical Hainan Island (China) to test the hypothesis that the presence of oxygen-containing chemical linkage in Poaceae species is widespread. Our innovative natural abundance oxygen isotopic analysis allowed us to infer that more than 1/3 of the species investigated has chemical (ether) linkages between α-cellulose and lignin in their leaf cell walls, with a species-specific 2–89 oxygen-containing bonds for every 1000 glucose units. However, the presence of such linkage appears to be phylogeny-dependent. On average, species of C3 photosynthetic mode are found to have more extensive oxygen-containing linkages than those of C4 photosynthetic mode. Our finding challenges the conventional view that no chemical bonds between α-cell...