Silicon isotope compositions of dissolved silicon and suspended matter in the Yangtze River, China

Silicon isotope compositions of main channel samples of the Yangtze River were systematically investigated along with their chemical compositions. The concentration of suspended matter in the Yangtze River tends to decrease from the upper reaches to the lower reaches, corresponding to settling of the sediments in the lakes and reservoirs due to reduction of the velocity of water flow. The silica contents of suspended matter vary from 52.1% to 56.9% and their δ³⁰Si values vary from 0 to −0.7‰, both similar to those of shales. From the upper to lower reaches, the silica contents of suspended matter tend to increase, whilst their δ³⁰Si values tend to decrease. Both trends reflect the increase of clay minerals and decrease of carbonates in suspended matter.The concentrations of dissolved silicon vary from 97 to 121 μmol/L and their δ³⁰Si values vary over a wide range from 0.7 to 3.4‰. From the upper to lower reaches, dissolved silica concentrations tend to decrease and their δ³⁰Si values tend to increase. These trends mainly reflect the change of chemical and isotopic characteristics of the tributaries from the upper to lower reaches. The major factors responsible for these changes may be the high meteoric precipitation and significant silicon absorption by grass (in wetlands) and rice (in paddy fields) in drainage areas of the middle and lower reaches.There is no correlation between δ³⁰Si of dissolved silicon and that of suspended matter. The Δ³⁰Si_Diss-SPM values vary over a wide range of 1.0-3.7‰, indicating that (1) they are out of isotopic equilibrium, (2) dissolved silicon and the associated suspended matter do not belong to one physico-chemical system, and (3) isotopic exchange rate between them is very slow.The δ³⁰Si value of dissolved silicon output from the Yangtze River to the East Sea is estimated to be 3.0‰, much higher than the values reported for the Amazon and Congo rivers. This increases the δ³⁰Si range of dissolved silicon in the world’s rivers from 0.4-1.2%; to 0.4-3.4%.     

长江悬浮颗粒物中磷的赋存形态

2006年9~10月在长江采集悬浮颗粒物样品,应用改进后的SEDEX法对磷的赋存形态进行了分析.结果表明,自生磷灰石磷是长江悬浮颗粒物中磷的主要赋存形态.涪陵至万州江段,碎屑磷灰石磷的含量较高,弱吸附态磷和有机磷含量较低,磷的赋存形态主要受悬浮颗粒物含量的影响;香溪至葛洲坝下江段,弱吸附态磷和有机磷含量较高,碎屑磷灰石磷含量较低,磷的赋存形态主要受浮游植物生长及泥沙粒径的影响;城陵矶至大通江段,有机磷、碎屑磷灰石磷和铁结合态磷含量较高,弱吸附态磷含量较低,磷的赋存形态主要受泥沙粒径和洞庭湖输入的影响.长江悬浮颗粒物中生物可利用磷占颗粒态磷的45.6%,长江上游水体中生物可利用磷含量较低,下游含量较高.     

Fate of the Evros River suspended particulate matter in the northern Aegean Sea

Evros River is the most important river flowing into the North Aegean Sea (eastern Mediterranean) in terms of freshwater discharge, and the second largest one of Eastern Europe after the Danube River. Salinity and temperature measurements, together with suspended particulate matter concentrations were obtained in various depths at 14 stations in the adjacent Alexandroupolis Gulf during four seasons (June 1998, September 1998, February 1999 and March 2000) in order to investigate the particle dynamics and distributions in the northern Aegean Sea. Analysis of the collected data, together with particle observations under the scanning electron microscope and study of satellite images showed that, under certain circumstances driven by the hydrological and wind regime of the area, the Evros River particulate matter, with the associated pollutants, can be transferred far away from the estuary and implicitly comprise a hazardous factor for the environmental status of the northern Aegean Sea. This fact, combined with the future construction of the Burgas-Alexandroupolis pipeline, may cause a negative impact on the studied natural ecosystem.     

Amino acid nitrogen isotopic fractionation patterns as indicators of heterotrophy in plankton, particulate, and dissolved organic matter

Bulk nitrogen (N) isotope signatures have long been used to investigate organic N source and food web structure in aquatic ecosystems. This paper explores the use of compound-specific δ¹⁵N patterns of amino acids (δ¹⁵N-AA) as a new tool to examine source and processing history in non-living marine organic matter. We measured δ¹⁵N-AA distributions in plankton tows, sinking particulate organic matter (POM), and ultrafiltered dissolved organic matter (UDOM) in the central Pacific Ocean. δ¹⁵N-AA patterns in eukaryotic algae and mixed plankton tows closely resemble those previously reported in culture. δ¹⁵N differences between individual amino acids (AA) strongly suggest that the sharply divergent δ¹⁵N enrichment for different AA with trophic transfer, as first reported by [McClelland, J.W. and Montoya, J.P. (2002) Trophic relationships and the nitrogen isotopic composition of amino acids. Ecology83, 2173-2180], is a general phenomenon. In addition, differences in δ¹⁵N of individual AA indicative of trophic transfers are clearly preserved in sinking POM, along with additional changes that may indicate subsequent microbial reworking after incorporation into particles.We propose two internally normalized δ¹⁵N proxies that track heterotrophic processes in detrital organic matter. Both are based on isotopic signatures in multiple AA, chosen to minimize potential problems associated with any single compound in degraded materials. A trophic level indicator (ΔTr) is derived from the δ¹⁵N difference between selected groups of AA based on their relative enrichment with trophic transfer. We propose that a corresponding measure of the variance within a sub-group of AA (designated ΣV) may indicate total AA resynthesis, and be strongly tied to heterotrophic microbial reworking in detrital materials. Together, we hypothesize that ΔTr and ΣV define a two dimensional trophic “space”, which may simultaneously express relative extent of eukaryotic and bacterial heterotrophic processing.In the equatorial Pacific, ΔTr indicates an average of 1.5-2 trophic transfers between phytoplankton and sinking POM at all depths and locations. The ΣV parameter suggests that substantial variation may exist in bacterial heterotrophic processing between differing regions and time periods. In dissolved material δ¹⁵N-AA patterns appear unrelated to those in POM. In contrast to POM, δ¹⁵N-AA signatures in UDOM show no clear changes with depth, and suggest that dissolved AA preserved throughout the oceanic water column have undergone few, if any, trophic transfers. Together these data suggest a sharp divide between processing histories, and possibly sources, of particulate vs. dissolved AA.     

黄河口有机碳的时空输运特征及其影响因素分析

通过2004年4月,2004年9月,2005年9月,2006年4月4个航次,结合2003年8月对河道感潮带的连续同步观测,对低流量下黄河口有机碳的输运特征进行了考察。结果发现:黄河输入至河口的悬浮物中颗粒有机碳(POC)含量约为0.51%,主要以陆源输入为主,几乎不受季节变化影响,由于大量POC含量低的陆源泥沙的稀释作用,浮游植物对总颗粒有机碳的贡献只有在悬浮物含量(TSS)<200mg/L时才能显现出来;黄河口TSS超过455mg/L时,有机碳入海以颗粒有机碳为主;反之,以溶解有机碳为主。黄河口悬浮物在低盐度区沉降作用前后的中值粒径降低,Φ>16μm的悬浮物的沉降作用比Φ<16μm的悬浮物更为剧烈,POC含量随悬浮物粒径的降低而升高,黄河携带的颗粒有机碳80%以上集中在Φ<16μm的TSS中;低流量下,黄河口最大混浊带对POC的过滤效率为65%,混浊带对POC的过滤效应能造成黄河口POC的有效通量被高估;由于受黄河口沉积物向水体解析DOC的影响,在盐度小于10时,DOC几乎不受海水稀释作用的影响,但在盐度大于10的区域DOC与盐度表现出良好的负相关关系,黄河口枯、丰水期淡水端溶解有机碳的有效浓度分别高于实测最高值20%和10%左右,从而造成黄河口DOC有效通量被低估。     

洞穴溶解有机质组分和循环过程的季节变化特征

溶解有机质（DOM）是岩溶碳汇的关键部分和重要的碳源,但是对于DOM在岩溶含水层中的性质和代谢过程的研究仍然有限。本研究以重庆雪玉洞地下河为例,对洞穴有机碳的来源、组成以及微生物作用对季节补给源变化的响应进行探讨,为进一步了解微生物介导的有机碳转化过程提供研究基础。运用三维荧光EEM研究水体有色溶解有机质（CDOM）的性质和组分并反演地下河水中有机质的来源和组成,结合地下河水水化学特征和16S rDNA细菌群落及功能多样性的季节变化特征,以了解季节性补给源的变化对洞穴地下水DOM输入和性质的影响。结果发现,雪玉洞地下河水以微生物内源有机质为主（61%~77%）,降雨是引起岩溶给地下河水中CDOM光谱特征变化的最重要因素,雨季外源有机质输入增加,地下河水中外源有机碳组分含量和芳香性、腐殖酸类物质增加,细菌群落多样性和代谢功能基因随之变化,洞穴中向外输出的外源有机碳增加;旱季地下河水滞留时间和蒸发作用增强,因而微生物对有机质的代谢降解过程更加充分,向洞外输出的有机碳以内源为主。本研究有助于增加对岩溶洞穴地下水系统中微生物对有机碳转化过程的理解。     

Distribution and composition of suspended particulate matter in the Atlantic Ocean: Direct measurements and satellite data

The main purpose of this work is to study the real distribution and spatial–temporal variations of suspended particulate matter and its main components in surface waters of the Atlantic Ocean on the basis of direct and satellite measurements for development of new and perfection of available algorithms for converting satellite data. The distribution fields of suspended particulate matter were calculated and plotted for the entire Atlantic Ocean. It is established that its distribution in the open ocean is subordinate to the latitudinal climatic zonality. The areas with maximum concentrations form latitudinal belts corresponding to high-productivity eutrophic and mesotrophic waters of the northern and southern temperate humid belts and with the equatorial humid zone. Phytoplankton, the productivity of which depends primarily on the climatic zonality, is the main producer of suspended particulate matter in the surface water layer.     

Natural isotopic composition of nitrogen as a tracer of origin for suspended organic matter in the Scheldt estuary

The natural isotopic composition of suspended particulate organic nitrogen was determined in the Southern Bight of the North Sea and in the Scheldt estuary. These data show that δ¹⁵N constitutes a convenient tracer of the origin of the suspended matter.In the winter, in the absence of intensive primary production, the suspended organic matter of the Scheldt estuary is a mixture of two components: a continental detrital component characterized by a low δ value of 1.5%. and a marine component with a mean δ value of 8%..During the phytoplankton flowering period, lasting from early May to October, intensive primary production occurs throughout the estuary giving rise to a third source of organic matter. This material is characterized by high δ values reflecting the isotopic composition of ammonia, the nitrogenous nutrient assimilated by phytoplankton in the estuary.The nitrification process occuring in the mixing area of the Scheldt estuary leads to higher downstream δ values of ammonia (>20%.) which permits the distinction between estuarine from fresh-water phytoplankton. Simple isotopic budget calculations show that, both in the upstream part and in the downstream part, autochthonous phytoplanktonic material contributes a major part of the total suspended matter in the Scheldt estuary during summer.     

Hydrogeochemistry and dissolved inorganic carbon isotopic composition on karst groundwater in Maolan, southwest China

The forest ecosystem in the Maolan karst forest, southwest China is the only concentrated, intact, and relatively stable karst forest ecosystem which has survived in the area at the same latitude in the world, and is a valuable karst forest plant resource as well. Groundwater samples from Maolan karst forest were collected from wells and springs during summer; and concentrations of major ions and dissolved inorganic carbon (DIC) isotopic compositions were measured. The pH values range from 7.2 to 8.3 results from the dissolution of carbonate, HCO₃ ⁻ is the dominant species of DIC in groundwater. Calcium and HCO₃ ⁻, followed by Mg²⁺ and SO₄ ²⁻ dominate the chemical composition of major ions in the groundwaters. Groundwater samples have δ¹³C values in the range from −8.1‰ to −16.6‰, which are lower than that of the other karst city groundwaters in the southwest China. Combining δ¹³C_DIC ratios with measurements of HCO₃ ⁻ and pH clearly distinguishes the principal processes underlying the geochemical evolution of groundwater in Carboniferous carbonate aquifers, where processes can be both degradation of organic matters in the soil and the carbonate dissolution.     

Iron isotope fractionation during biogeochemical cycle: Information from suspended particulate matter (SPM) in Aha Lake and its tributaries,Guizhou, China

Iron isotope compositions of suspended particulate matters (SPM) collected from the Aha Lake, an artificial lake in the karst area of Yun-Gui Plateau, and its tributaries in summer and winter were investigated for our understanding of the behavior of Fe isotopes during iron biogeochemical cycling in lake. δ⁵⁶Fe values of SPM display statistically negative shift relative to IRMM-014. Samples from the lake display a range from ?1.36‰ to ?0.10‰ in summer and from ?0.30‰ to ?0.07‰ in winter, while river samples vary from ?0.88‰ to 0.07‰ in summer and from ?0.35‰ to ?0.03‰ in winter. The average iron isotope composition of aerosol samples is + 0.10‰, which is very similar to that of igneous rocks (0.09‰). The SPM in most rivers and water column showed seasonal variation in δ⁵⁶Fe value: the δ⁵⁶Fe values of SPM in summer were lower than in winter. The seasonal variation in δ⁵⁶Fe value of the riverine SPM should be ascribed to the change in source of particulate Fe and geochemical process in the watershed: More particulate Fe was leached from soil and produced by weathering of pyrite widely distributed in coal-containing strata. It is suggested that both allochthonous inputs and the redox iron cycling control the variations of δ⁵⁶Fe values for SPM in lake.During summer stratification, an Fe cycle named “ferrous wheel” is established near the redox boundary where the upwardly diffusing Fe(II) is oxidized and the reactive Fe oxides formed will continuously sink back into the reduction zone to complete the cycle. The δ⁵⁶Fe values for SPM reach the minima, ?0.88‰ for DB station and ?1.36‰ for LJK station, just near the redox boundary as a result of the Fe cycling, where a rough 45% to 76% of Fe in these particles was produced by the repetitive cycle. Due to random transportation and diffusion, δ⁵⁶Fe values of the particles near the redox zone distributed into approximately a Gaussian shape. The good negative correlation existed between δ⁵⁶Fe values and Fe/Al ratios for DB station, suggesting that they together can be used as good indicators of the redox-driven Fe transformations.     

Microscopic morphology and elemental composition of size distributed atmospheric particulate matter in Urumqi, China

Microscopic morphology and elemental composition of atmospheric particulate matter (PM) in 13 different size fractions from 0.01 to 10 μm were studied using a Field Emission Scanning Electron Microscope with Energy-Dispersive Spectrometer (FESEM–EDX). The relative mass fractions exhibited a bimodal distribution with a major mode in the fine range (0.18–1 μm) and a minor mode in the coarse range (>1 μm), suggesting that the major pollution of PM is fine particles in this area of Urumqi atmosphere. The PM could be classified as follows: aluminosilicate/silica mineral, Si–Al rich fly ash, Fe oxide particle, Ti dominant particle, sulfate/carbonate crystal, carbonaceous aerosols (including soot, organic carbon, tar ball and irregularly shaped carbon). The soot and organic carbon with anthropogenic sources are dominant types in fine range samples (<1 μm). The natural source minerals and secondary synthesized sulfate/carbonate crystals were accumulated in the coarse range (>1 μm). Elemental composition of various types of particles (0.056–5.6 μm) was also analyzed by EDX. C, S, O, N, Si, Al, Fe, Ca, Na, K, Mg, Cl, F, Hg were detected in most samples. Si, Al and Ca accumulated in coarse fractions, while S and Hg mainly accumulated in fine fractions. Concentrations of 15 metallic elements in size range from 0.1 μm to 5.6 μm were divided into three groups based on their possible sources. (1) The crustal elements (Al, Mg, Fe, Mn and V), mainly present in coarse particles (>1 μm); and (2) the anthropogenic source elements (Ca, Ni, As, Cu, Pb, Cd and Hg). The concentrations of Ca and Ni increased with increasing particle size, while As, Cu, Pb, Cd and Hg showed opposite trends. As, Cu, Pb, Cd and Hg accumulated mainly in fine fraction (<1 μm). (3) The multi sources elements (Cr, Co and Se) possibly come from both natural and anthropogenic sources. High levels of heavy metals, especially Hg in nanosize particles, may pose great risk to human health.     

Rare earth elements (REE) of dissolved and suspended loads in the Xijiang River, South China

The Xijiang River is the main channel of the Zhujiang (Pearl River), the second largest river in China in terms of water discharge, and flows through one of the largest carbonate provinces in the world. The rare earth element (REE) concentrations of the dissolved load and the suspended particulate matter (SPM) load were measured in the Xijiang River system during the high-flow season. The low dissolved REE concentration in the Xijiang River is attributed to the interaction of high pH and low DOC concentration. The PAAS-normalized REE patterns for the dissolved load show some common features: negative Ce anomaly, progressively heavy REE (HREE) enrichment relative to light REE (LREE). Similar to the world’s major rivers the absolute concentration of the dissolved REE in the Xijiang River are mainly pH controlled. The degree of REE partitioning between the dissolved load and SPM load is also strongly pH dependent. The negative Ce anomaly is progressively developed with increasing pH, being consistent with the oxidation of Ce (III) to Ce (IV) in the alkaline river waters, and the lack of Ce anomalies in several DOC-rich waters is presumably due to both Ce (III) and Ce (IV) being strongly bound by organic matter. The PAAS-normalized REE patterns for the dissolved load and the SPM load in rivers draining the carbonate rock area exhibit middle REE (MREE) enrichment and a distinct maximum at Eu, indicating the preferential dissolution of phosphatic minerals during weathering of host lithologies. Compared to the Xijiang River waters, the MREE enrichment with a maximum at Eu disappeared and light REE were more depleted in the South China Sea (SCS) waters, suggesting that the REE sourced from the Xijiang River must be further fractionated and modified on entering the SCS. The river fluxes of individual dissolved REE introduced by the Xijiang River into the SCS vary from 0.04 to 4.36 × 10⁴ mol a⁻¹.     

Organic geochemistry of suspended and settling particulate matter in Lake Michigan

Organic matter contained in particulate matter in Lake Michigan waters and sediments has been characterized by $\text{C}\text{N}$ ratios and by distributions of biomarker fatty acids, alkanols, sterols, and aliphatic hydrocarbons. Differences in organic constituents of particulate matter from various depths and distances from shore indicate a complex interaction of production, transformation, and destruction of the organic matter contained in sinking particles. Near-surface material contains important contributions of landderived organic matter, presumably of eolian input. Midwater particles have predominantly aquatic organic material of algal origin. At the sediment-water interface, selective suspension of the finer fractions of surficial sediments enriches bottom nepheloid layers with these sediment size classes. As a result, near-bottom particulate matter has an aquatic biomarker character. Organic matter associated with sinking particles undergoes substantial degradation during passage to the bottom of Lake Michigan, and aquatic components are selectively destroyed relative to terrigenous components.     

长江干流颗粒有机碳及其同位素组成的季节性输送特征

2007年夏季和冬季对长江干流悬浮物进行了季节性采样,系统分析了悬浮物颗粒有机碳含量及稳定碳同位素的组成,研究了其空间分布以及季节变化特征。结果显示,长江干流夏季颗粒有机碳含量在0．4％～1．3％,冬季含量在0．7%-2．2％。冬季和夏季颗粒有机碳平均δ^13C值分别为-24．74‰和～24．83‰,季节性差异不大,在...     

Nature of particulate organic matter in the River Indus,Pakistan

Suspended sediments from the Indus River collected during 1981 through 1983 were analyzed for POC and its constituent fractions including amino acids, amino sugars and sugars. Percentage of POC decreased with increasing suspended matter concentrations, which suggested dilution of organic matter by mineral matter.The concentrations of amino acids, amino sugars and sugars varied, respectively, between 180 and 2000 μg/l, 5 and 125 μg/l, and 60 and 1100 μg/l. Their contributions to POC varied between 2 and 60% for amino acids and amino sugars, and between 2 and 15% for sugars. They were high during low sediment discharge (February to June), and low during high sediment discharge (August and September). Suspended sediments associated with high sediment discharge periods were characterized by low ratios of:

• 1.(i) aspartic acid:β-alanine
• 2.(ii) glutamic acid:γ-aminobutyric acid
• 3.(iii) amino acids:amino sugars
• 4.(iv) hexoses:pentoses. These and the relative distribution pattern of the monosaccharides such as galactose, arabinose, mannose and xylose indicated that, not only dilution, but also differences in the sources and processes affect the POC transport in the Indus River. These result in transport of biodegraded organic matter during high sediment discharge periods: this appears to be common to other major rivers of the region, with depositional centers in deep sea areas. These rivers, with their high sediment loads, could contribute up to 8 to 11% of the global annual organic carbon burial in marine sediments.

     

黄河水及其悬浮物硅同位素组成的变化特征及其地质环境意义

2005年7月沿黄河干流及4条主要支流系统采集了28个水样,对水及悬浮物的化学组成、矿物组成、水化学成分和硅同位素组成进行了综合分析.黄河水中悬浮物在不同站点的浓度差异悬殊,由8.8～302120mg/L不等,与黄河两岸人类活动(水库、牧场、农田)和自然环境变化(流域岩性、植被覆盖程度)关系密切.悬浮物中SiO2含量介...     

Iron isotope composition of the suspended matter along depth and lateral profiles in the Amazon River and its tributaries

Samples of suspended matter were collected at different locations, seasons, depths and lateral profiles in the Amazon River and three of its main tributaries, the Madeira, the Solimões and the Negro rivers. Their iron isotope compositions were studied in order to understand the iron cycle and investigate the level of isotopic homogeneity at the river cross-section scale. Samples from four depth profiles and three lateral profiles analyzed show suspended matter δ⁵⁷Fe values (relative to IRMM-14) between −0.501 ± 0.075‰ and 0.196 ± 0.083‰ (2SE). Samples from the Negro River, a blackwater river, yield the negative values. Samples from other stations (whitewater rivers, the Madeira, the Solimões and the Amazon) show positive values, which are indistinguishable from the average composition of the continental crust (δ⁵⁷Fe_IRMM-14 ∼ 0.1‰). Individual analyses of the depth and lateral profiles show no significant variation in iron isotope signatures, indicating that, in contrast to certain chemical or other isotopic tracers, one individual subsurface sample is representative of river deeper waters. This also suggests that, instead of providing detailed information on the riverine iron cycling, iron isotopes of particulate matter in rivers will rather yield a general picture of the iron sources.