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.     

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...     

Spatial and temporal variation of organic carbon in the northern South China Sea revealed by sedimentary records

Three sediment cores were taken from the Pearl River estuary and adjacent northern South China Sea (SCS). These sediment cores span the time interval 1900–2000 AD. The stratigraphy of the concentration, the ratio of total organic carbon (TOC) to total nitrogen (TN) and stable isotope (δ¹³C_org) of organic carbon (OC) from three high-resolution sediment cores were analyzed. The stratigraphic profiles of OC concentration, TOC/TN ratios and δ¹³C_org for the near past 100 yrs indicate that terrestrial organic matter decreases from 68.3% to 27.4% of the TOC in the Pearl River estuary, while Dapeng Bay (offshore east of Hong Kong) apparently had throughout little terrestrial organic matter input. The highest deposited OC occurs at the Humen River mouth and the OC concentrations are higher in the outer estuary than in the inner shelf of the northern SCS. The deposited OC at the River mouth increased with time, which could be caused by the high precipitation of land-derived organic matter and the high input of terrestrial organic matter, which is likely related to the rapid urbanization and industrial development in the Pearl River Delta since the 1970s. The OC concentrations did not exhibit an obvious increase with time in most areas of the Pear River estuary and adjacent inner shelf of the SCS, but the algal-derived OC concentration inferred from the δ¹³C_org values increased with time especially from 1980 to 2000 in the outer Pearl River estuary and Dapeng Bay. This increase is presumably caused by enhanced primary marine productivity supported by higher anthropogenic nutrient inputs.     

西江下游溶解无机碳含量的时空变异特征及其输出通量

选取西江下游干支流6个样点进行一个完整水文年度的观测分析,利用基本水文水化学参数来揭示河水溶解无机碳(DIC)含量的时空变异特征,并估算流域DIC输出通量.结果表明,西江下游干支流DIC含量受控于流域地质环境和水热条件,变化于0.74～2.40 mmol/L之间,存在明显的时空变异.干支流DIC含量季节变化模式基本一致,呈现汛期(不包括受洪水影响极强的时段)较高、非汛期较低而洪水期最低的变化特征,流域水热条件的季节变化是其根本原因;河水DIC含量的空间变异基本与流域碳酸盐岩空间分布格局一致,干流DIC含量明显高于支流,且向下游呈减小趋势.西江流域DIC输出通量约4.57×1012g/a,汛期和6月洪水贡献分别达84%和40%.全流域DIC侵蚀通量约12.95 g/(m2·a),在世界各流域中居中上水平.     

西江干流河水主要离子及锶同位素地球化学组成特征

水环境中锶（Sr）含量及其同位素组成特征的研究有助于认识区域水文地球化学特征及流域盆地岩石风化速率等地球化学行为,因此河流环境中Sr的地球化学行为是地球化学研究的重要课题之一。对中国南方西江干流及其支流河水主要阴阳离子及sr同位素组成进行了分析,发现其水化学组成主要以Ca^2＋、Mg^2＋、HCO3^-和SO4^2-离子为主,分别占阴阳离子组成的80％以上。郁江河水具有较高的Sr同位素比值（^87St／^86Sr=0．71049）和较低的Sr含量（0．0263mg／L）,而西江河水具有较低的Sr同位素比值以及较高的Sr含量,其Sr含量变化范围在0．0667．0．187mg／L之间,平均含量为0．136mg／L;Sr同位素比值变化范围在0．70856．0．70936之间,平均比值为0．70894。与世界主要河流水体中Sr含量平均值（0．078mg／L）及Sr同位素比值（^87Sr／^86Sr=0．7119）相比,西江干流水体具有较高的Sr含量及较低的Sr同位素比值。两条河流河水中主要离子及Sr的来源存在显著差异,西江干流河水中的主要溶解离子及Sr同位素主要源于碳酸盐岩（石灰岩和白云岩）的风化作用,主要受黔江及其上游红水河等化学组成所控制,而郁江则主要受碎屑岩风化作用的影响;同时,中上游地区的酸沉降及人类活动的输入可能导致西江干流水体受到一定程度的污染,而郁江受污染程度则相对较小。     

珠江三角洲经济区土壤碳储量及有机碳时空变化规律研究

土壤碳库是陆地碳库生态系统的主体,在全球碳平衡中具有重要的作用。通过开展珠江三角洲经济区多目标区域地球化学调查,获得了土壤全碳及有机碳数据,采用"单位土壤碳量"方法计算土壤碳储量,显示珠江三角洲经济区土壤有机碳总体分布:表层(0～0.2 m)土壤有机碳为9.71×107 t,碳密度为2271.34 t/km2;中层(0～1.0 m)土壤有机碳为3.71×108 t,碳密度为8666.05 t/km2;深层(0～1.8m)土壤有机碳为5.87×108 t,碳密度为13722.73 t/km2。对比其他地区,珠江三角洲土壤碳密度处于较低水平。分析了土壤、土地利用、地貌类型与成土母质对区域土壤碳库的影响程度,不同土壤单元有机碳储量分布特征。与第二次土壤普查比较,20年期间珠江三角洲表层土壤有机碳总体减少0.22×108 t,损失幅度达19.20%,仅惠州等地区有所增加。不同生态系统土壤有机碳减少程度不同。     

The variation of soil temperature and water content of seasonal frozen soil with different vegetation coverage in the headwater region of the Yellow River, China

The variation and distribution of temperature and water moisture in the seasonal frozen soil is an important factor in the study of both the soil water cycle and heat balance within the source region of the Yellow River, especially under the different conditions of vegetation coverage. In this study, the impact of various degrees of vegetation coverage on soil water content and temperature was assessed. Soil moisture (θ _v) and soil temperature (T _s) were monitored on a daily basis. Measurements were made under different vegetation coverage (95, 70–80, 40–50 and 10%) and on both thawed and frozen soils. Contour charts of T _s and θ _v as well as a θ _v–T _s coupling model were developed in order to account for the influence of vegetation cover and the interaction between T _s and θ _v. It was observed that soil water content affected both the overall range and trend in the soil temperature. The regression analysis of θ _v versus T _s plots indicated that the soil freezing and thawing processes were significantly affected by vegetation cover changes. Vegetation coverage changes also caused variations in the θ _v–T _s interaction. The effect of soil water content on soil temperature during the freezing period was larger than during the thawing period. Moreover, the soil with higher vegetation coverage retained more water than that with lower coverage. In the process of freezing, the higher vegetation coverage reduced the rate of the reduction in the soil temperature because the thermal capacity of water is higher than that of soil. Areas with higher vegetation coverage also functioned better for the purpose of heat-insulating. This phenomenon may thus play an important role in the environmental protection and effective uses of frozen soil.     

全新世年代框架约束下的东北地区土壤有机碳储库时空格局

土壤有机碳储库是全球碳循环的重要单元, 明确土壤有机碳储库的时空分布及其与气候的关系是有效发挥土壤碳封存作用的前提。本研究以东北地区半湿润-半干旱气候梯度带22个全新世实测土壤剖面为对象, 在AMS¹⁴C、OSL年代约束下, 以千年窗口碳密度为框架建立区域全新世土壤有机碳密度的时空分布模式, 从剖面序列和区域尺度分析全新世气候变化对土壤有机碳密度时空分布的影响。结果显示, 东北地区土壤有机碳密度自全新世以来明显增加, 12~9ka、9~6ka、6~3ka和3~0ka时段累积的土壤有机碳密度分别为2.21kg/m²、4.28kg/m²、6.92kg/m²和9.83kg/m²; 在空间上, 全新世土壤有机碳密度整体上自西南向东北呈增加趋势, 东北部高值区为35~50kg/m², 西部低值区为4~9kg/m²。无论在空间分布还是时间分布上, 东北地区全新世土壤有机碳密度均受气候要素(尤其湿度)控制。这表明, 全新世生物生产力较为稳定, 当气候偏冷湿时有利于土壤有机碳的积累, 这也意味着未来气候变暖不利于区域土壤有机碳的积累封存。

     

Temporal and spatial characteristics of dissolved organic carbon in the Wujiang River,Southwest China

River systems play an important role in the global carbon cycle. Rivers transport carbon to the ocean and also affect the carbon cycle in the coastal ocean. The flux from land to the ocean is thought to be a very important part of the land carbon budget. To investigate the effect of dam-building on dissolved organic carbon (DOC) in rivers, three reservoirs of different trophic states in the Wujiang basin, Guizhou Province, were sampled twice per month between May 2011 and May 2012. Temporal and spatial distributions of DOC in the reservoirs and their released waters were studied. It was found that different factors controlled DOC in river water, reservoir water, and released water. DOC in the rivers tended to be affected by primary production. For reservoirs, the main controlling factors of DOC concentration varied by trophic state. For the mesotrophic Hongjiadu Reservoir, the effect of primary production on DOC concentration was obvious. For the eutrophic Dongfengdu Reservoir and the hypereutrophic Wujiangdu Reservoir, primary production was not significant and DOC came instead from soil and plant litter.     

Identical carbon isotope trends of carbonate and organic carbon and their environmental significance from the Changhsingian (end-Permian), Meishan,South China

High resolution carbon isotope analyses of carbonate and organic carbon from Meishan, South China showed that the variation of δ13Ccarb is marked by three large positive excursions during the Changhsingian (end-Permian). Carbon isotope stratigraphy during this stage shows three cyclic intervals in δ13Ccarb, with two cycles corresponding to the lower (Paleofusulinid minima Zone) and one corresponding to the upper Changhsingian (P. sinensis Zone). The large positive δ13Ccarb excursions indicate episodes of enhanced burial of isotopically light or-ganic carbon, presumably in response to deep-water anoxia episodically extending into shallow water with the rise of sea level. The organic carbon during the Changhsingian is distinguished into two groups, and the δ13Corg of each group parallels (separately) the more detailed profile of δ13Ccarb, strongly showing that the values of fractionation Δ13Ccab-org remain relatively constant, with only two intervals with anomaly. The enhanced fractionation Δ13Ccab-org with large negative δ13Corg excursions apparently indicates significant inputs from sulfide-oxidizing bacteria and green sulfur bacteria, notably at bed 24 just predating mass extinction. Our evidence appears to support that the ex-tended euxinic water is possible for the main pulse of mass extinction at the end-Permian.     

南海区域海气热通量的变化特征分析

应用由卫星SSM/I(Special Sensor Microwave/Imager)和AVHRR(Advanced Very High Resolution Radiometer)遥感资料,使用先进的海气通量计算方法(TAGA COARE3.0),计算出南海1987年7月至2004年12月共200个月的海气界面的感热和潜热通量(0.25°×0.25°),其结果与实测结果比较发现,由卫星反演的海气热通量与实测结果非常一致.与GSSTF2的结果相比,其时空分布变化特征基本一致.由此说明,利用卫星遥感获得的热通量可以用来进行中国近海海气相互作用的研究以及作为我国气候预测研究的重要依据.由多年南海海气热通量的分析表明,南海区域热通量的变化具有显著的年变化和年际变化特征,其周期分别是0.5a、1a、准3a和6～11a.其中准3a和6～11a周期与中国旱涝的周期一致.因此,可以认为南海区域热通量的年际变化对中国的旱涝分布将起着不可低估的作用.     

Sedimentary record of black carbon in the Pearl River estuary and adjacent northern South China Sea

The concentrations of black carbon (BC) and δ¹³C_BC were determined in sediments of three dated cores from the Pearl River estuary (core PR-3) and adjacent northern South China Sea (cores SS-30, E2). For comparison, the total organic C (TOC) contents and δ¹³C_TOC in the sediments were also measured. Relatively higher concentrations and fluxes of BC were found in sedimentary core PR-3, taken in the Pearl River estuary. The BC concentration profiles or fluxes correlated well with fossil-fuel usage in the Pearl River Delta. Maximum BC fluxes occurred in the late 1970s to early 1980s as recorded in core PR-3, and in the 1950s (core SS-30), reflecting the maximum BC emission in the Pearl River Delta and Hong Kong region, respectively. After the 1980s, a rapid decrease of BC fluxes and a light δ¹³C_BC excursion were presumably due to improvements in combustion and pollution-control technologies and a shift of energy structure from biomass and coal to a mixture of coal, gas, oil and biomass. The fossil BC that contributed to total BC in core PR-3 increased from 20–30% to 70–80% during the last five decades. The study also shows that BC correlates well with terrestrial organic matter and that the ratio of BC to TOC is a good pollution indicator in relation to anthropogenic activities.     

The Red River sediment budget in the Yinggehai and Qiongdongnan basins,northwestern South China Sea,and its tectonic implications

ABSTRACT

The rapid uplift of the Tibetan plateau, the intense movement of the Ailao Shan-Red River Shear Zone (ARSZ), and the related climate change during the Cenozoic Indo-Asian collision have been widely studied; however, their timings varied considerably due to different data and methods used. As these events have been documented in the Red River sediment that came from the eastern Tibetan plateau and the Red River region and eventually deposited in the offshore Yinggehai and Qiongdongnan basins, here these events can be explored by calculating and analysing the Red River sediment budget, especially in the Qiongdongnan basin based on dense seismic profiles and wells. Results show that the Red River sediment mainly accumulated in the Yinggehai basin and the west part of the Qiongdongnan basin, and there are three sedimentary accumulation peaks in the Red River sediment budget during ~29.5–21, ~15.5–10.5, and ~5.5–0 Ma. By further comparing with previous studies on the timings of these events, it is inferred that the first sedimentary peak, prior to the onset of the monsoon intensification (~22 Ma), was probably driven by an intense left-lateral movement of the ARSZ in ~29.5–21 Ma. The second peak (~15.5–10.5 Ma), however, reflects a rapid uplift of the Tibetan plateau after the cessation of the left-lateral strike slip of the ARSZ. The third peak (~5.5–0 Ma) is most likely linked with a right-lateral movement of the ARSZ and the related climate change. Overall, the Red River sediment budget from the offshore Yinggehai and Qiongdongnan basins provides an important constraint on the timings of these tectonic events as well as the related climate change during the Cenozoic Indo-Asian collision.     

A decade of variation of COD in the Changjiang River （Yangtze River） and its variation trend analysis

The average annual value of COD (chemical oxygen demand) fluxes of the Changjiang River (Yangtze River) and its main tributaries in the past decade (i.e., 1991–2000), has been evaluated. Based on the data from the Datong Hydrological Station (DHS), it was found that the Dongting Lake drainage basin contributed the greatest water discharge (35.8%) and COD flux (48.3%) among the main tributary drainage basins, followed by the Poyang Lake drainage basin with the contributions of 15.4% and 19.3%,respectively. By the end of the year of 2000, COD flux in the Changjiang River rose by almost 45% relative to that in the year of 1991, reaching about 1941000 ton/a at DHS. Statistical analysis revealed that industrial wastewater discharge, as well as COD in it, was found decreasing in the same period, due to the gradual reinforcement of environmental management. Moreover, correlation analysis indicated that non-point pollution from agriculture and increasing discharge of domestic sewages caused by rapid growth of population along the Changjiang River drainage valley should be responsible for the high COD. Furthermore, with the current trend of population growth and agricultural development in this basin, water quality of the Changjiang River, in terms of COD level, is going to deteriorate in the near future. Thus, the rational applications of fertilizers and pesticides in agriculture and the proper treatment of domestic sewages before they are discharged would be the most concerned controlling parameters.     

An organic carbon budget for the Mississippi River turbidity plume and plume contributions to air-sea CO2 fluxes and bottom water hypoxia

We investigated seasonal variability in organic carbon (OC) budgets using a physical-biological model for the Mississippi River turbidity plume. Plume volume was calculated from mixed layer depth and area in each of four salinity subregions based on an extensive set of cruise data and satellite-derived suspended sediment distributions. These physical measurements were coupled with an existing food web model to determine seasonally dependent budgets for labile (reactive on time scales of days to weeks) OC in each salinity subregion. Autochthonous gross primary production (GPP) equaled 1.3×10¹² g C yr⁻¹ and dominated labile OC inputs (88% of the budget) because riverine OC was assumed mostly refractory (nonreactive). For perspective, riverine OC inputs amounted to 3.9×10¹² g C yr⁻¹, such that physical inputs were 3 times greater than biological inputs to the plume. Annually, microbial respiration (R) accounted for 65% of labile OC losses and net metabolism (GPP—R) for the entire plume was, autotrophic, equaling 5.1×10¹¹ g C yr⁻¹. Smaller losses of labile OC occurred via sedimentation (20%), advection (10%), and export to higher trophic levels (5%). In our present model, annual losses of labile OC are 10% higher than inputs, indicating future improvements are required. Application of our model to estimate air-sea carbon dioxide (CO₂) fluxes indicated the plume was a net sink of 2.0×10⁹ mol CO₂ yr⁻¹, of which 90% of the total drawdown was from biotic factors. In all seasons, low salinity waters were a source of CO₂ (pCO₂=560–890 μatm), and intermediate to high salinity waters were a sink of CO₂ (pCO₂=200–370 μatm). Our model was also used to calculate O₂ demand for the development, of regional hypoxia, and our spring and early summer budgets indicated that sedimentation of autochthonous OC from the immediate plume contributed 23% of the O₂ demand necessary for establishment of hypoxia in the region.     

Fractionation and chlorination of organic carbon in water from Yinluan River, Tianjin, China

Total organic carbon in unpolluted water from Yinluan River, Tianjin, China was fractionated into five operational defined fractions of particulate organic carbon, hydrophobic compounds, humic substances, non-humic anions, and other hydrophilic compounds using a multi-step filtration and adsorption scheme. The organic carbon contents and the trihalomethane formation potential of these fractions were determined. It was demonstrated that about half of the dissolved organic carbon in the sample is humic substances which is quite active in term of chlorination reaction. Particulate organic carbon is also an important precursor of the volatile halogenated hydrocarbons. All other fractions, which account for another half of the dissolved organic carbon, contribute to a relatively small percentage of the trihalomethanes produced during the chlorination experiment. It was concluded that humic substances, dissolved or suspended, are the most important precursor of halogenated hydrocarbons during chlorination, owing to their high abundance and trihalomethane formation potential.This study was supported by the National Excellent Young Scientist Fund of China.     

Metabolism and organic carbon fluxes in the tidal freshwater Hudson River

We summarize rates of metabolism and major sources and sinks of organic carbon in the 148-k long, tidally influenced, freshwater Hudson River. The river is strongly heterotrophic, with respiration exceeding gross primary production (GPP). The P:R ration averages 0.57 (defined as the ratio of GPP to total ecosystem respiration) if only the aquatic portion of the ecosystem is considered and 0.70 if the emergent marshes are also included. Gross primary production (GPP) by photoplankton averages approximately 300 g C m^?2 yr^?1 and is an order of magnitude greater than that by submersed macrophytes. However, the river is deep, well mixed, and turbid, and phytoplankton spend a majority of their time in the dark. As a result, respiration by living phytoplankton is extremely high and net primary production (NPP) by phytoplankton is estimated to be only some 6% of GPP. NPP by phytoplankton and submersed macrophytes are roughly equal (approximately 20 g C m^?2 yr^?1 each) when averaged over the river. Emergent marshes are quite productive, but probably less than 16 g C m^?2 yr^?1 enters the aquatic portion of the ecosystem from these marshes. Heterotrophic respiration and secondary production in the river are driven primarily by allochthonous inputs of organic matter from terrestrial sources. Rates of metabolism vary along the river, with depth being a critical controlling factor. The P:R ratio for the aquatic portion of the ecosystem varies from 1 in the mid-river to 0.2 in the deeper waters. NPP is actually negative in the downstream waters where average depths are greater since phytoplankton respiration exceeds GPP there; the positive rates of NPP occurring upriver support a downstream advection of phytoplankton to the deeper waters where this C is largely respired away by the algae themselves. This autotrophic respiration contributes significantly to oxygen depletion in the deeper waters of the Hudson. The tidally influenced freshwater Hudson largely fits the patterns predicted by the river continuum model for larger rivers. However, we suggest that the continuum model needs to more clearly distinguish between GPP and NPP and should include the importance of autotrophic respiration by phytoplankton that are advected along a river. The organic carbon budget for the tidally influenced freshwater Hudson is balanced to within a few percent. Respiration (54%) and downstream advection into the saline estuary (41%) are the major losses of organic carbon from the ecosystem. Allochthonous inputs from nonpoint sources on land (61%) and GPP by phytoplankton (28%) are the major sources to the system. Agricultural erosion is the major source of allochthonous inputs. Since agricultural land use increased dramatically in the last century, and has fallen in this century, the carbon cycle of the tidally influenced freshwater Hudson River has probably changed markedly over time. Before human disturbance, the Hudson was probably a less heterotrophic system and may even have been autotrophic, with gross primary production exceeding ecosystem respiration.