太湖梅梁湾富营养化过程的同位素地球化学证据

以浅水湖泊太湖为研究对象,通过湖泊水体、水生生物同位素以及相应湖泊水体营养指标的比较分析,并根据梅梁湾钻孔沉积物TN,TP,TOC,C/N,δ15N,δ13C等多项指标记录,恢复了湖泊富营养化过程.研究结果表明,不同湖区植物碳、氮同位素值和水体NH4+的δ15N值变化反映了植物组成和营养水平的差异.梅梁湾水体NH4+的δ15N和水环境参数不同月份的变化反映了外部营养载荷的输入对湖泊环境有明显的影响.1950～1990年湖泊沉积物有机质碳、氮同位素同步变化的趋势说明湖泊初级生产力的增长和湖泊逐渐富营养化的过程,而1990年之后二者之间反相关关系的出现表明在富营养条件下,大量浮游植物生长对富15N的无机氮的吸收及表层沉积物有机质分解和反硝化作用,代表湖泊富营养化加剧.以同位素示踪,并结合元素地球化学指标变化,将太湖梅梁湾富营养化过程分为三阶段,以20世纪50年代和20世纪90年代为营养状态的转换时段,揭示了人类活动不断加强的影响,与近50年来的湖泊环境监测结果一致.     

滇东湖泊水生植物和浮游生物碳、氮稳定同位素与元素组成特征

稳定同位素示踪方法是研究生态系统组成与功能的重要手段,有助于认识湖泊食物网的基本组成与生物地球化学循环的主要过程.本研究选择了云南省东部地区营养水平不同的10个湖泊,开展了高等水生植物(沉水植物、漂浮植物)、浮游植物与浮游动物的空间调查,分析了不同生物在碳、氮稳定同位素信号与元素组成上的分布模式.在碳稳定同位素信号的分布上,漂浮植物在4种生物类型中最为偏负且变化幅度最小,为-28.99‰±0.86‰;浮游动物碳稳定同位素(-20.85‰±2.70‰)的分布特征与浮游植物(-21.88‰±2.97‰)显著相似;而沉水植物的碳稳定同位素显著偏正且变化范围较大,平均值为-12.04‰±4.57‰.结果表明,碳源及其传输途径的差异是导致湖泊生物体内碳同位素信号不同的主要驱动过程.在氮稳定同位素信号上,同为初级生产者的沉水植物(5.43‰±5.84‰)、漂浮植物(5.58‰±7.38‰)与浮游植物(7.26‰±3.83‰)较为相似,而浮游动物氮同位素信号(11.02‰±3.18‰)显著高于浮游植物且平均富集约3.46‰,反映了湖泊生物随着营养级的增加出现较为明显的同位素分馏效应.在空间分布上,湖泊生物碳同位素信号受到水温、水深等因素的明显影响,氮同位素信号则随湖泊营养水平的增加而逐渐偏正.与长江中下游等地区相比,云南湖泊生物的碳、氮元素含量总体偏高;同时,代表内源有机质组分的水生植物和浮游生物C/N质量比值都小于20.因此,本研究揭示的生物碳、氮同位素信号与元素组成特征可为评价高原湖泊食物网组成与生物地球化学循环提供重要的科学依据.     

若尔盖盆地兴措湖沉积记录揭示的近代气候与环境

依据湖泊沉积记录进行古气候环境要素定量的是过去全球变化研究的重要内容,本文通过若尔盖盆地兴措湖近代湖泊沉积特征、沉积物总有机碳及其同位素指标分析,并与器测气象资料进行比较,对兴措湖泊近代湖泊沉积物中有机碳及其同位素指标所代表的气候环境信息进行了定量研究,在此基础上,建立了兴措湖沉积物总有机碳及其同位素记录与对应的降水和气温间的函数关系,为定量恢复该区长尺度历史时期古气候环境特征提供了基础。     

湖泊沉积有机碳同位素与环境变化的研究进展

湖泊沉积有机质稳定碳同位素（δ^13Corg)在区域气候与环境变化方面的应用近年来发展迅速,成果令人瞩目,保存在各类湖泊岩芯中的δ^13Corg记录揭示了晚更新世以来大气CO2浓度的变化、湖泊水位波动、湖区生态与植被的变迁以及气温变化等重要环境信息,由于造成δ^13Corg值变化的影响因素较多,确定个湖与环境变化有关的主导因素时常有赖于其它证据的帮助,诸如地球化学、古湖沼学、孢粉学、分子同位素地层学等等,前人通过研究来自不同类型湖泊、具不同曲线形态特征的δ^13Corg记录,提出了多种环境解释模型,本文对此作了归纳和评述。鉴别和澄清湖泊沉积有机质的源物质以及有机物源随环境变化而发生过的变化,是研究δ^13Corg记录环境意义至关重要的基础性工作,由于有机质含量、碳氮比值、氢指数、生物残留物鉴别等常能提供有关有关湖泊有机质来源、产率、成岩作用等方面的有用信息,这方面的研究结果应该尽可能一并提供,以利于恰当地应用现有的环境解释模型,或者建立个湖新模型,单体生物标志化合物鉴别通常也能为区分湖积有机质中陆生、水生、细菌生等不同碳的来源提供有用信息,特定化合物同位素分析技术近年来成功地应用于建立单体生物标志化合物碳同位素地层学,为湖积有机碳同位素在生态环境演变研究方面的应用提供了思路,我国许多湖泊的湖底沉积岩芯尚未钻取,那些对过去全球变化研究有价值的δ^13Corg记录有待我们去获取和研究。     

1860年以来博斯腾湖碳沉积过程演变

选取博斯腾湖3个不同点位岩芯,在²¹⁰Pb和¹³⁷Cs年代序列基础上,利用沉积物中的各理化指标,分析了该湖碳沉积的时空变化特征,结合各指标的相关性、沉积速率、C/N、同位素特征等,探讨了该湖1860年以来碳沉积环境的变化过程,为干旱区湖泊碳埋藏研究提供了依据.结果表明：1860-1910年,沉积速率相对较小,受人类活动影响较小,磁化率、中值粒径、总无机碳（TIC）较为稳定,总有机碳（TOC）含量相对较低,此时该湖有较多陆源有机质的输入;1910-1950年,湖泊西部浅水域沉积速率明显高于东部深水区,西北湖区水域有大量外源物质的输入,而湖泊初级生产力较低,内源贡献相对较小;1950-1980年,全湖TOC、TIC含量均呈现升高的趋势,尤其是西北近黄水沟水域升高最快,湖泊内源贡献在增加,陆源组分的输入相对前一阶段要少;1980-2002年,沉积速率快速升高,尤其湖泊东部水域最为明显,TOC含量均呈现升高的趋势,湖泊西部水域初级生产力要高于东部深水区,湖面蒸发较强,气候比较温暖;2002年以来,全湖沉积速率相对较高,外源有机质贡献较小.过去150年博斯腾湖沉积物碳累积速率整体上呈现出升高的趋势,尤其是近50年来快速升高,东部湖区碳累积速率比西部湖区高.     

南四湖沉积剖面中色素与有机碳同位素特征的古环境意义

湖泊沉积物中的色素含量与种类是研究湖泊初始生产力的湖泊环境的有效手段之一。而有机碳同位素比值反映了沉积有机物来源信息。本文在对南四湖沉积剖面中总有机含量分析的基础上,测定了有机碳的同位素比值,同时通过剖面中色素指标的分析,揭示该湖泊环境演化历史。研究表明,南四湖成湖时代为２．４５ｋａＢ．Ｐ．,成湖水体主要来自黄河泛滥;其次,南四湖东西沉积环境差异较大,西部（微山湖）主要受黄河泛滥影响,东部（独山湖     

南四湖沉积剖面中色素与有机碳同位素特征的古环境意义

湖泊沉积物中的色素含量与种类是研究湖泊初始生产力和湖泊环境的有效手段之一．而有机碳同位素比值反映了沉积有机物来源信息．本文在对南四湖沉积剖面中总有机碳含量分析的基础上,测定了有机碳的同位素比值,同时通过剖面中色素指标的分析,揭示该湖泊环境演化历史．研究表明,南四湖成湖时代为2．45kaB．P,成期水体主要来自黄河泛滥;其次,南四湖东西沉积环境差异较大,西部（微山湖）主要受黄河泛滥影响,东部（独山湖）则为山麓碎屑沉积;近代南四湖中蓝藻大量繁盛,湖泊具有逐步向富营养化发展的趋势．     

洱海悬浮颗粒物和表层沉积物有机碳氮同位素来源特征及水质指示意义

为探究湖泊水体悬浮颗粒物和沉积物有机碳、氮来源及水质指示意义,分析了2013-2014年洱海悬浮颗粒物和表层沉积物有机碳同位素(δ13C)、氮同位素(δ15N)和C/N比值时空变化特征及与水质的关系.结果 表明:①洱海悬浮颗粒物δ13C、C/N、δ15N在旱、雨季差异显著(P＜0.05),旱季变化范围分别为-31.75...     

乌梁素海悬浮颗粒物和沉积物有机碳同位素特征及来源

悬浮颗粒物和沉积物是湖泊有机污染物的主要承载物质,其稳定同位素研究对有效识别有机质污染导致的湖泊富营养化具有重要意义.本研究选取乌梁素海为研究区,于2019年4月（融冰期）、7月（夏灌期）和10月（秋灌期）对湖区及入湖渠道的表层沉积物和悬浮颗粒物中有机碳的δ¹³C、C/N比及总有机碳（TOC、POC）和总氮（TON、PON）含量进行测定分析,联合采用δ¹³C、C/N及同位素多元混合模型研究湖泊有机碳来源及其贡献率.结果表明,乌梁素海悬浮颗粒物有机碳δ¹³C_POC的变化范围为-23.29‰~-29.75‰,呈现10月>4月>7月、入湖渠道>湖区的趋势,悬浮颗粒物POC/PON比变化范围为4.10~21.35,呈现出4月<7月<10月的时间变化,悬浮颗粒有机质主要来源于浮游植物（51.59%）、入湖渠道泥沙（34.60%）和大型水生植物（13.76%）.沉积物有机碳δ¹³C_TOC变化范围为-27.58‰~-22.68‰,呈现4月<10月<7月的变化,沉积物TOC/TON比变化范围为3.06~23.77,时空变化明显,沉积物有机质则主要源于入湖渠道挟带的泥沙,贡献达72.79%以上,而浮游植物与大型水生植物的贡献率相差较小,分别为11.85%和15.36%.本研究可以初步判定受入湖渠道影响的富营养化湖泊中悬浮颗粒物和沉积物有机碳来源,为改善湖泊有机污染和研究有机碳来源提供更多理解.     

呼伦湖东露天矿剖面有机碳的总量及其稳定碳同位素和古环境演化

湖泊沉积物中有机碳的总量（TOC）取决于湖泊的初始生产力及有机质沉积后的保存能力,而有机碳的稳定同位素（δ~(13)C）值则反映了不同来源有机质的组成以及流域古植被状况。本文通过对内蒙呼伦湖东露天煤矿剖面TOC及δ~(13)C值的垂直分布的研究,结合剖面的沉积特征及孢粉、硅藻分析结果,讨论了呼伦湖地区末次冰期以来古气候古环境演化过程。结果表明有机碳的总量及其稳定碳同位素可作为分析古气候环境的一种有效的代用指标。     

Changes in sediment transport in the Kuye River in the Loess Plateau in China

In this paper, the changes in sediment transport over 51 years from 1955 to 2006 in the Kuye River in the Loess Plateau in China are assessed. Key factors affecting sediment yield and sediment transport, such as precipitation depth, discharge, and human activities are studied. To investigate the changes in sediment yield in this watershed, a trend analysis on sediment concentration, precipitation depth, and discharge is conducted. Precipitation depths at 2 Climate Stations （CSs）, as well as discharge and sediment transport at 3 Gauging Stations （GSs） are used to assess the features of sediment transport in the Kuye River. The rtmoff modulus （defined as the annual average discharge per unit area, L/（s·km^2）） and the sediment transport modulus （defined as the annual suspended sediment transport per unit area, t/（yr km^2）） are introduced in this study to assess the changes in runoff and sediment yield for this watershed. The results show that the highest average monthly discharge during the study period in the Kuye River is 66.23 m^3/s in August with an average monthly sediment concentration of 88.9 kg/m^3. However, the highest average monthly sediment concentration during the study period in the Kuye River is 125.34 kg/m^3 and occurs in July, which has an average discharge of 42.6 m^3/s that is much less than the average monthly discharge in August. It is found that both the runoff modulus and sediment transport modulus at Wenjiachuan GS on the Kuye River has a clear downward trend. During the summer season from July to August, the sediment transport modulus at Wenjiachuan GS is much higher than those at Toudaoguai and Longmen GSs on the Yellow River. The easily erodible loess in the Kuye River watershed and the sparse vegetation are responsible for the extremely high sediment yield from the Kuye River watershed. The analyses of the grain size distribution of suspended load in the Kuye River are presented. The average monthly median grain size of suspended load in the Kuye River is largest in February and then decreases until June. In July, the average monthly median grain size of suspended load approaches another peak and decreases until September. Then, the median grain size of suspended load starts to increase until February of the following year. However, the average monthly median grain size of suspended load in the Yellow River at Toudaoguai and Longmen GSs is the smallest between early summer and late fall The median grain size in the Yellow River starts to increase in November and approaches the largest size in January.     

Variations in trace gas concentrations in different environments in India

Observations of trace gases (SO₂, NH₃, NO₂ and O₃) were made during the period 1981 to 1984 at 6 different locations representative of urban industrial, urban, nonurban, thermal power plant and marine environment. Diurnal variations of the trace gases were studied in an urban environment. Except in the urban industrial environment, the concentration of NH₃ was found in the range of background values. Also, the average concentrations of NO₂ and O₃ at the different environments were in the order of background values. However, the concentrations of SO₂ were substantially higher by about 7 times, in urban industrial and thermal power plant environments. The diurnal variations of SO₂, NH₃ and NO₂ showed anitphase relationship with surface temperature at the urban environment station which is relatively free of industrial pollution. Discussion is centred on trace gas variations in different environments in India together with the values reported for various countries in the world.     

TritiogenicHe in groundwater in Takaoka

³He/⁴He ratios up to 3.5 times the ratio of atmospheric He were found in groundwater samples. The³He enrichment can be attributed to radiogenic³He produced by in-situ beta-decay of³H. This shows that tritiogenic³He is accumulating in confined waters. From tritiogenic³He and³H concentrations, ages of groundwaters can be calculated. Detection of tritiogenic³He gives a tool to trace a tritium contamination which occurred in the past and cannot be assessed only by the³H counting method.     

Projected changes in flood indices in selected catchments in Poland in the 21st century

The aim of this study is to estimate likely changes in flood indices under a future climate and to assess the uncertainty in these estimates for selected catchments in Poland. Precipitation and temperature time series from climate simulations from the EURO-CORDEX initiative for the periods 1971–2000, 2021–2050 and 2071–2100 following the RCP4.5 and RCP8.5 emission scenarios have been used to produce hydrological simulations based on the HBV hydrological model. As the climate model outputs for Poland are highly biased, post processing in the form of bias correction was first performed so that the climate time series could be applied in hydrological simulations at a catchment-scale. The results indicate that bias correction significantly improves flow simulations and estimated flood indices based on comparisons with simulations from observed climate data for the control period. The estimated changes in the mean annual flood and in flood quantiles under a future climate indicate a large spread in the estimates both within and between the catchments. An ANOVA analysis was used to assess the relative contributions of the 2 emission scenarios, the 7 climate models and the 4 bias correction methods to the total spread in the projected changes in extreme river flow indices for each catchment. The analysis indicates that the differences between climate models generally make the largest contribution to the spread in the ensemble of the three factors considered. The results for bias corrected data show small differences between the four bias correction methods considered, and, in contrast with the results for uncorrected simulations, project increases in flood indices for most catchments under a future climate.     

Changes in thermal extremes in Poland

Changes in thermal extremes of the climate of Poland in 1951–2010 are examined. Warm extremes have become more frequent, while cold extremes have become less frequent. In the warming climate of Poland, the increase in the number of extremely warm days in a year and the decrease in the number of extremely cold days in a year have been observed. Also the increase of the maximum number of consecutive hot days in a year and the decrease of the maximum number of consecutive very cold and extremely cold days in a year have been observed. However, the trends are not of ubiquitous statistic significance, as the natural variability is strong.     

Copper in natural waters in Transbaikalia

Cu concentrations in surface (river and lake) and subsurface waters are determined. The geographic pattern of Cu distribution in natural water is identified. This pattern is controlled by the difference between its concentrations in drained rocks and soils and the geochemical redox conditions of its migration. Territories with low, medium, and elevated Cu concentrations in natural waters are identified. The concentrations of Cu in natural waters of the region are found to be generally lower than the Clarke values.     

Hydrological changes in the Ganges system in Bangladesh in the post-Farakka period

Abstract

The basin area of the Ganges River in Bangladesh is extremely dependent on a regular water supply from upstream to meet requirements for agriculture, fisheries, navigation, salinity control, and domestic and industrial sectors. In 1975, India commissioned a barrage on the Ganges River at Farakka to divert a significant portion of the dry season flow in order to make the Calcutta Port navigable. Statistical analyses of discharge and water level data have been carried out to determine if significant changes have occurred in the hydrology of the Ganges system in Bangladesh in the post-Farakka period. Siltation of the Gorai River (an offtake of the Ganges River) has also been examined using the stage-discharge relationship and regression analysis. The analyses show that the diversion has caused considerable hydrological changes in the Ganges system in Bangladesh. The water supply in the dry season has been reduced substantially, while siltation of the Gorai River has increased significantly.