富硫型水库沉积物AVS和SEM空间分布特征及重金属风险评价

随着湖库外源性污染的有效控制,沉积物污染特征成为影响湖库水环境质量的关键因素。本文以富硫型水库——汤河水库为研究对象,分析探讨水库沉积物的理化性质、重金属总量、酸可挥发性硫化物(acid volatile sulfide,AVS)和同步提取重金属(simultaneously extracted metals,SEM)的空间分布特征,采用沉积物基准法(sediment quality guidelines, SQGs)和AVS与SEM关系法对重金属可能诱发的生态风险和毒性效应进行评估。结果表明:汤河水库沉积物中AVS含量在0.03~51.75 μmol/g之间,并呈现坝前深水区>东支流库区>西支流库区的空间分布特征。根据Pearson相关性分析可知,汤河水库沉积物AVS含量与间隙水中SO₄^2-浓度、沉积物烧失量(LOI)含量呈显著正相关,与沉积物间隙水中NO₃^-浓度和沉积物pH呈现显著负相关。间隙水中SO₄^2-浓度和沉积物LOI含量是控制AVS产量的重要因素。水库沉积物中ΣSEM变化范围为0.52~2.75 μmol/g,呈现出东支流库区>坝前深水区>西支流库区的分布规律。水库沉积物中ΣSEM/AVS和ΣSEM-AVS的变化范围分别为0.06~22.73和-49.18~2.44 μmol/g,显示出水库坝前深水区表层0~10 cm沉积物不具有生态风险,而东、西支流库区沉积物中的SEM因为不能完全被AVS所固定而存在潜在生态风险。就单一重金属而言,汤河水库坝前深水区和东西支流中部区域沉积物Ni、Cu、Pb和Zn含量均介于临界效应含量(threshold effects level, TEL)值和可能效应含量(probable effect level, PEL)值之间,可产生低级风险毒性效应,但Ni的毒性效应风险接近中级,今后应予以重点关注。富硫型水库沉积物中容易出现高含量AVS,沉积物间隙水中SO₄^2-和NO₃^-的浓度是决定沉积物AVS净产量的重要因素。流域内重金属土壤背景值以及工业、采矿产业排放的废水类型直接影响着诱发生态风险的重金属种类。     

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.     

长江中下游湖泊群不同生活型水生植物分布的时空变化(1986—2020年)

不同生活型水生植物对水环境的影响和碳固持能力不同,开展大尺度范围内不同生活型水生植物的时空分布和动态变化研究,是全面掌握湖泊水生态环境变化趋势、准确核算水生生态系统碳源/碳汇的前提。以长江中下游10 km²以上(共131个)的湖泊为研究对象,基于野外调查和先验知识,通过光谱分析,研发了不同生活型水生植物遥感高精度机器学习识别算法,解析了长江中下游湖泊群不同生活型水生植物的时空变化规律。研究表明,长江中下游湖泊群不同生活型水生植物遥感监测精度为0.81,Kappa系数为0.74;1986—2020年长江中下游湖泊群水生植物面积为2541.58~4571.42 km²,占湖泊总面积的15.99%~28.77%,沉水植物是优势类型(Max_1995年=2649.21 km²,Min_2005年=921.38 km²),其次是挺水植物(Max_2005年=1779.44 km²,Min_2020年=569.05 km²)和浮叶植物(Max_2015年=685.68 km²,Min_2000年=293.04 km²);水生植物主要分布在长江干流流域湖泊群,其次是鄱阳湖流域、洞庭湖流域、太湖流域和汉江流域;变化趋势上,1986—2020年长江中下游湖泊群水生植物面积呈现先增长(1986—1995年)、后下降(1995—2010年)、再增加(2010年后)的趋势。本研究可为长江中下游湖泊群生态环境调查及水环境管理提供重要参考。     

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.     

喀斯特水库水化学特征及对无机碳沉积通量的指示

为探究筑坝后不同水库物理、化学、生物过程对水化学和碳循环的影响,本研究对贵州三岔河流域的平寨水库、普定水库以及猫跳河流域的红枫湖水库进行研究,于2018年3月2019年1月分别在入库河流和库区采集了分层水样和沉降颗粒物,并探究水中主要离子及颗粒物通量的时空变化特征及其控制因素.结果表明,水体主要离子的主要来源受碳酸盐溶解影响,并且离子浓度受光合作用控制.红枫湖水库水体水化学类型为Ca-Mg-HCO₃-SO₄型,普定水库、平寨水库水化学类型均为Ca-HCO₃-SO₄.夏季藻类光合作用诱导碳酸盐沉淀导致水体表层Ca²⁺、HCO₃^-及溶解态Si浓度降低,其降低幅度分别为20.87%~44.25%、33.12%~51.18%、48.55%~96.34%.此外,藻类光合作用也影响C、N、Si等生源要素间的化学计量关系.Mg²⁺/Ca²⁺比值在水体垂向剖面上主要受碳酸钙沉淀的控制,而在不同水库之间则主要受流域岩性的控制.根据沉积物捕获器通量计算的平寨水库、普定水库、红枫湖水库夏季颗粒无机碳沉积通量分别为0.74、1.36、0.27 t/（km²·d）,而根据水体Ca²⁺浓度降低计算的通量分别为0.31~0.64、0.35~0.99、0.09~0.29 t/（km²·d）,根据水体HCO₃^-浓度降低计算的通量分别为0.30~0.65、0.29~1.26、0.12~0.33 t/（km²·d）.其红枫湖水库无机碳沉降通量的实测值与计算值接近,而平寨、普定水库实际沉降通量高于计算值,这可能是有外源输入导致.因此,利用水化学分层数据能对喀斯特水库中的无机碳沉降通量进行合理估算,并且能够得到较好的估算结果,从而指示碳循环的过程.     

水位变化对干涸湖底沉积物有机碳矿化的影响

人为干扰和气候变化会改变湖泊水位状态,明确不同水位条件下湖泊沉积物有机碳矿化特征及其影响因素,对了解内陆水生态系统碳循环具有重要意义.为探究干旱区典型盐湖沉积物有机碳矿化速率对水位变化的响应,以巴里坤湖干涸湖底原状沉积物为研究对象,初步探究了0（T1）、-9（T2）、-23（T3）、-34（T4）和-45 cm（T5）水位处理对沉积物有机碳矿化速率的影响.结果表明,T1、T2和T3处理有机碳矿化速率在试验初期较高（0~10 d）,10 d后缓慢下降,T4和T5处理有机碳矿化速率呈先增加后降低趋势;T1（1.718 μmol/（m²·s））与T3（1.784 μmol/（m²·s））处理有机碳矿化速率不存在显著差异,T1处理有机碳矿化速率是T2、T4和T5处理的1.09、3.31和3.57倍,不同处理有机碳累积矿化量表现为T3 > T1 > T2 > T4 > T5.有机碳累积矿化量（C_t）占沉积物有机碳（C₀）的比例（C_t/C₀）介于0.012~0.044之间,沉积物有机碳潜在排放量（C_i）占C₀的比例（C_i/C₀）介于0.018~0.045之间;水位降低,沉积物有机碳矿化常数（k值）减小,T1处理k值最大（0.137 d）,T4处理最小（0.032 d）.线性方程C_r=0.008x+0.488能较好地模拟有机碳矿化速率（C_r）与水位（x）的关系;不同水位处理有机碳矿化速率与模拟柱中沉积物5 cm温度呈显著的指数函数关系,T4、T5处理有机碳矿化温度敏感系数（Q₁₀）显著高于T1、T2和T3处理,即水位降低增加了巴里坤湖干涸湖底沉积物Q₁₀.因此,就巴里坤湖干涸湖底沉积物而言,水位从0 cm降至-45 cm时有机碳矿化速率降低,Q₁₀增加;反之水位上升则会促进有机碳矿化分解,Q₁₀降低.水位持续下降抑制有机碳矿化可能是维持干旱区盐湖沉积物碳库稳定的机制之一.     

不同营养水平湖泊浮游植物吸收和比吸收系数变化特征

利用太湖和博斯腾湖8月份、天目湖6 8月份的采样数据,开展不同营养状态下浮游植物吸收和比吸收系数的变化规律研究,并探讨其影响因素.利用综合营养指数法,太湖8月42个采样点中20个点为重度富营养,标记为太湖TⅠ,22个点为中度富营养,标记为太湖TⅡ,天目湖夏季、博斯腾湖8月的富营养水平分别为轻度富营养和中营养.440 nm处浮游植物吸收系数a_ph(440)按照营养水平从高到低由重度富营养到中营养分别为1.02±0.51、0.69±0.40、0.78±0.24和0.20±0.04 m^-1,相应地675 nm处浮游植物吸收系数a_ph(675)分别为0.59±0.32、0.38±0.23、0.41±0.13和0.08±0.02 m^-1.统计检验显示,重、中度富营养的太湖以及轻度富营养的天目湖浮游植物吸收系数显著高于中营养的博斯腾湖.440 nm处浮游植物比吸收系数a_ph^*(440)分别为0.013±0.006、0.012±0.004、0.038±0.008和0.051±0.013 m²/mg Chl.a.统计检验显示,重度、中度富营养的太湖浮游植物比吸收系数显著小于轻度富营养的天目湖,而天目湖浮游植物比吸收系数又显著小于中营养的博斯腾湖.另由400~700 nm浮游植物的光谱曲线可以明显看出不同营养状态浮游植物吸收系数的变化情况,表现为:重度富营养太湖TⅠ>轻度富营养的天目湖>中度富营养的太湖TⅡ>中营养的博斯腾湖.太湖和天目湖属于富营养化湖泊,浮游植物吸收系数明显高于中营养的博斯腾湖,这充分反映了随营养程度增加,浮游植物吸收逐渐增加.天目湖浮游植物略高于太湖TⅡ是因为太湖非藻类悬浮颗粒物含量高,所以吸收系数偏小.比吸收系数的变化情况与吸收系数的变化情况恰好相反,随着营养程度的增加依次递减.随营养程度增加浮游植物吸收逐渐增加是由于水体营养盐增加促进浮游植物生长,浮游植物生物量逐渐增加所致,而比吸收系数逐渐降低则由于色素包裹效应所致.     

蓝藻碎屑堆积对湖泊沉积物矿化特征的影响

蓝藻水华暴发形成的大量有机碎屑,沉降到沉积物表面,影响沉积物有机质矿化,进而影响碳氮磷循环.本实验选择于桥水库湖心区作为沉积物采样点,通过设置不同密度藻屑添加组（×1倍组和×20倍组）及空白对照组,研究藻屑堆积对沉积物矿化特征的影响及其环境效应,为蓝藻水华影响下的饮用水环境修复和科学管理提供一定的理论依据.结果表明：（1）藻屑添加降低了上覆水pH值,改变了沉积物生物酶活性.藻屑添加密度越大,上覆水pH值越低、波动越大,反映了培养过程异养微生物活性的变化.×1倍组的转化酶活性较高;×20倍组蛋白酶活性和碱性磷酸酶活性较高.（2）藻屑添加对沉积物的矿化途径和沉积物产物的释放速率产生了显著影响.藻屑添加密度越大,有机质矿化速率越大.其中,×1倍组主要增强好氧矿化,释放CO₂;×20倍组主要增强厌氧产甲烷矿化,释放CH₄.（3）不同密度的藻屑添加组,其氮磷扩散、释放通量存在明显差别.×1倍组以沉积物吸附为主,其上覆水NH₄⁺和PO₄^3-平均释放速率与对照组差异较小;×20倍组的NH₄⁺在第0~10天以沉积物吸附为主,之后和PO₄^3-均以向上覆水中释放为主,其NH₄⁺和PO₄^3-平均释放速率（分别为0.223）和0.075 mg/（L·d））明显大于其他实验组.因此,大量蓝藻堆积明显促进沉积物的碳氮磷矿化,释放大量CO₂、CH₄和氮磷营养盐至上覆水中,对湖泊水环境造成污染,为蓝藻的生长繁殖作贡献.     

冰封期乌梁素海沉积物-水界面氨氮的交换特征

为揭示冰封期氨氮（NH₄⁺-N）在沉积物-水界面的迁移机制及内源性营养盐对全湖污染的贡献,于2018年2月初在乌梁素海湖区7个采样点采集了上覆水体与沉积物样品,得到了冰封期上覆水体与沉积物间隙水中的NH₄⁺-N浓度,估算了沉积物-水界面NH₄⁺-N的扩散通量.结果显示,上覆水体中NH₄⁺-N浓度变化范围为0.55~1.60 mg/L,平均值为1.05 mg/L,0~5 cm表层沉积物间隙水中NH₄⁺-N浓度是上覆水体中的10倍以上,其变化范围为6.64~18.63 mg/L,平均值为11.92 mg/L.估算沉积物间隙水NH₄⁺-N向上覆水体的扩散通量为1.282~4.269 mg/（m²·d）,表明在湖水冻结过程中,底泥沉积物接纳了大量的可溶性污染物成为内源污染源,会在冰封稳定期、融冰期和融冰后的一段时间内成为湖水的主要污染源.     

城市湖泊不同水生植被区水体温室气体溶存浓度及其影响因素

为了解城市湖泊不同水生植被区水体温室气体的溶存浓度及其影响因素,于2015年4-11月按每月2次的频率采用顶空平衡法对聊城市铃铛湖典型植被区——菹草区、莲藕区和睡莲区表层水中CO₂、CH₄和N₂O的溶存浓度进行监测,计算水中温室气体的饱和度和排放通量,并测定水温（T）、pH、溶解氧（DO）、叶绿素a及营养盐浓度等理化指标,以探究水体环境因子对温室气体溶存浓度的影响.结果表明,铃铛湖各植被区水体温室气体均处于过饱和状态,是大气温室气体的"源";莲藕区CH₄浓度、饱和度和排放通量均显著高于菹草区,而各植被区N₂O和CO₂均无显著性差异;不同植被区湖水中DO、总氮（TN）、总磷（TP）和硝态氮（NO₃^--N）浓度具有显著差异,其中DO、TN和NO₃^--N浓度均表现为菹草区最高,莲藕区最低,而TP浓度则正好相反;各植被区温室气体浓度和水环境参数间的相关分析和多元回归分析的结果表明,水生植物可通过影响水体的理化性质对温室气体的产生和排放产生显著差异影响,在菹草区亚硝态氮（NO₂^--N）、NO₃^--N、T和DO是控制水体温室气体浓度的主要因子;睡莲区为TP和pH;莲藕区则为pH、NO₂^--N和DO.     

Spatiotemporal patterns of carbon sequestration in a large shallow lake,Chaohu Lake: Evidence from multiple-core records

Lake sediment can sequestrate large amounts of carbon and this issue has become a research hotspot. However, most of research on carbon burial in lakes is based on a single (or a few) sediment core records and so may underestimate the variability of carbon burial features within a single lake. In this study, therefore, Chaohu Lake, a typical large shallow lake in the middle and lower reaches of the Yangtze River, was selected to conduct multiple, high resolution sediment core studies to elucidate that variability. Overall 18 sediment cores are analyzed according to paleolimnological proxies (including ²¹⁰Pb/¹³⁷Cs for 3 master cores); sediment accumulation rate, total organic carbon, grain size and loss of ignition is measured or estimated for most cores. The spatiotemporal variations of organic carbon burial rate (OCBR), carbon storage and their driving factors were examined. Results show: 1) There was a clear temporal difference in carbon burial during the past 150 years, with OCBR varying from 1.1 g C/m²/y to 25.6 g C/m²/y (mean 9.8 g C/m²/y). OCBR began to increase after around 1900, a rapid increase followed after 1950s and a downward trend after 1970s. Total carbon burial amount (OCBA) in the lake since the 1850s is 1.11 x 10¹⁰ g. 2) The average OCBR of six sediment cores in the northwest lake area is 13.4 g C/m²/y, significantly higher than that for sediment cores in other areas (9.6 g C/m²/y). 3) TOC, OCBR, OCBA in all 18 cores exhibited similar temporal patterns (i.e. marked increase since 1950s in most of the cores) but with significant differences in several lake locations. 4) During the last 150 years, carbon burial in Chaohu Lake appears to be greatly affected by changes in regional temperature and population size, according to their significant correlations. OCBR also has a significant correlation with the average lake level in the past 50 years, indicating human activity (notably dam building). This has imposed an important impact on OCBR in Chaohu Lake. This multi-sediment core study reveals the spatiotemporal characteristics of carbon burial in the lake and provides an important basis for increasing the accuracy of calculating carbon storage in large shallow lakes.     

Humid Little Ice Age in arid central Asia documented by Bosten Lake, Xinjiang, China

Short sediment cores retrieved from Bosten Lake, the largest inland freshwater lake in China, were used to explore humidity and precipitation variations in arid central Asia during the past millennium. The chronology of the cores was established using 137Cs, 210Pb and AMS 14C dating re- sults. Multi-proxy high-resolution analysis, including pollen ratios of Artemisia and Chenopodiaceae (A/C), carbonate content and grain size, indicates that the climate during the past millennium can be divided into three stages: a dry climate between 1000―1500 AD, a humid climate during the Little Ice Age (LIA) (c. 1500―1900 AD), and a warm dry period after 1900 AD. On centennial timescales, the climate change in northwestern China during the past 1000 years is characterized by oscillations between warm-dry and cold-humid climate conditions. All the proxies changed significantly and indi- cate increased precipitation during the LIA, including increased pollen A/C ratios and pollen concen- trations, decreased carbonate content and increased grain size. The humid period during the LIA re- corded by the Bosten Lake sediments is representative of arid central Asia and is supported by nu- merous records from other sites. During the LIA, the water runoff into the Keriya River and Tarim River in the Tarim Basin increased, while the ice accumulation in the Guliya ice core increased. Additionally, the lake levels of the Aral and Caspian Sea also rose, while tree-ring analysis indicates that precipita- tion increased. We hypothesize that both the lower temperature within China and the negative anomalies of North Atlantic Oscillation (NAO) during this period may have contributed to the humid climate within this area during LIA.     

Sudden enhancement of sedimentation flux of <Superscript>210</Superscript>Pb<Subscript>ex</Subscript> as an indicator of lake productivity as exemplified by Lake Chenghai

The fundamental assumption of ²¹⁰Pb sediment dating is the stable flux of ²¹⁰Pb_ex, which was derived from atmosphere and then transferred into sediments via lake water. When the sedimentation rate is relatively constant, the ²¹⁰Pb_ex activity in sediments will be exponentially reduced with sedimentation age. ²¹⁰Pb_ex in lake water is incorporated into sediments mainly via organic particulates. If the sedimentation flux of organic matter in lake water is suddenly increased, ²¹⁰Pb_ex will be significantly deposited and then transferred into sediments. On the one hand such sudden purification effect is obviously unfit for the fundamental assumption of ²¹⁰Pb dating; on the other hand, the sudden enhancement of ²¹⁰Pb_ex flux would be indicative of the conspicuous variation of primary productivity of lake water. This problem will be discussed in accordance with the variation trend of ²¹⁰Pb_ex in the vertical profile of recent sediments of Lake Chenghai, Yunnan Province. The sediment core was collected from the deep-water area of Lake Chenghai in June 1997. The vertical profile of ¹³⁷Cs activity is characterized by a tree-peak pattern. This profile gave reliable ages, and also showed the stability of sediment accumulation in the recent ten years. The vertical profile of ²¹⁰Pb_ex activity displays a specific distribution of peaks, and is similar to the vertical profile of C_org. This phenomenon seems to be related to the mechanism of constraining the transfer of ²¹⁰Pb_ex into lake sediments. The average atomic ratios of H_org/C_org and C_org/N_org in Lake Chenghai sediments are 5.51 and 7.04, respectively, indicating that the organic matter was predominantly derived from the remains of endogenic algae. In terms of the three-stage evolutionary characteristics of organic matter in sediments, i.e., “deposition-de-composition-accumulation”, the sedimentation fluxes (F(C_org)) of organic carbon (C_org) since 1970 were calculated by modeling. The sedimentation fluxes of ²¹⁰Pb_ex (F(²¹⁰Pb_ex)) in different years display good synchronous relations with the sedimentation flux of organic carbon (F(C_org)), especially in the years of 1972–1974 and 1986–1989. The variation of F(C_org) led to the variation of F(²¹⁰Pb_ex); the variation of F(²¹⁰Pb_ex) reflects, to some extent, the historical variation of lake productivity.     

新疆博斯腾湖浮游细菌丰度对富营养化及咸化的响应

本文以地处干旱地区我国最大的内陆淡水湖——博斯腾湖为研究对象,于2010年6月,在博斯腾湖大小湖区共选取23个采样点,采用表面荧光显微镜直接计数法( FDC)研究了水体中浮游细菌丰度的空间分布规律及其与环境因子的关系.结果表明:博斯腾湖水体中总氮(TN)浓度在0.26-1.45 mg/L之间变动(均值0.91 mg/L...     

利用210Pb、137Cs和241Am计年法测算云南抚仙湖现代沉积速率

通过对云南抚仙湖沉积物柱芯样品的210Pb、137Cs和241Am测试表明,柱芯剖面上有明显的1963年和1986年137Cs蓄积峰,验证了1975年次级蓄积峰存在的可能性,这些峰形完好的蓄积峰对抚仙湖的现代沉积环境有明显的时标意义。利用137Cs计年法得到抚仙湖沉积物自1963年、1975年及1986年以来到2007年的平均沉积速率分别为0.063g/(cm2·a)、0.052g/(cm2·a)和0.039g/(cm2·a),说明了过去近五十年抚仙湖沉积速率整体上经历了一个由快到慢的过程。借助于241Am 的1963年蓄积峰可以提高137Cs计年的准确性。根据210PbCRS计年模式,计算出每个样品深度所对应的年代,与137Cs计年法比较存在一定的偏差,分析了两种计年方法存在差异性的原因。通过质量深度和年代分析,抚仙湖的沉积速率变化幅度比较大,表明抚仙湖近129年来的沉积环境不稳定,可能与相应历史时期的人类活动有密切的关系。     

Micro-hole and multigrain quartz luminescence dating of Paleodeltas at Lake Fryxell,McMurdo Dry Valleys (Antarctica), and relevance for lake history

Relict (perched) lacustrine deltas around the perennially ice-covered lakes in the Taylor Valley, Antarctica, imply that these lakes were up to 40 times larger in area than at present since the last glacial maximum (LGM). These deltas have been used to constrain ice-margin positions in Taylor Valley, and the boundaries of the proposed LGM ice-damned Glacial Lake Washburn. The timing of these high lake levels has depended on ¹⁴C chronologies of algal layers within relict lacustrine deltas. To provide additional geochronometric data for the post-LGM lake-level history, we applied photon-stimulated-luminescence (PSL) sediment dating to polymineral fine silt and sand-size quartz from 7 perched-delta and 3 active-delta sites of different elevations along 3 major meltwater streams entering Lake Fryxell. Our PSL dating of 4 quartz-sand samples from core tops in the seasonal ice-free moat of Lake Fryxell (elevation ∼18 m a.s.l.) and two core-top moat samples from the seasonal moat of Lake Vanda in nearby Wright Valley establish that adequate PSL clock zeroing (by daylight) occurs in regional, modern shoreline deposits. Minimum-age micro-hole PSL results from the moats are consistently near 100 a. Minimum-age micro-hole age estimates for the deltas range from ∼50 to 100 a near the present lake level up to 13.4 ± 1.3 ka at 240 m. These are systematically younger than the comparable, reservoir-uncorrected, ¹⁴C ages that range from 7 ka (cal yr BP) to 13 ka (cal yr BP) near lake level up to 20 ka (cal yr BP) at 220–240 m elevation. Our results indicate the occurrence of a dramatic discrepancy between PSL minimum-age and ¹⁴C age estimates that is presently unresolved.     

1850年以来呼伦湖沉积物无机碳埋藏时空变化

湖泊沉积物碳埋藏及其驱动机制是陆地生态系统碳循环及全球变化研究的热点问题之一,但以往湖泊碳循环的研究大多局限于有机碳,较少考虑无机碳的地位和作用.我国干旱-半干旱地区湖泊众多、无机碳储量丰富,在区域碳循环过程中的作用日益突出,因此探讨这些地区湖泊沉积物无机碳埋藏变化对深入理解区域碳循环具有重要意义.本研究通过对内蒙古高原呼伦湖15个沉积岩芯样品无机碳含量(TIC)的测定,结合沉积岩芯210Pb、137Cs年代标尺,分析了1850年以来呼伦湖无机碳埋藏速率时空变化,并揭示了影响呼伦湖无机碳埋藏的主要因素.结果表明,1980s之前,呼伦湖无机碳含量总体维持在相对稳定的低值,1980s之后开始快速增加,且近百年来呼伦湖平均无机碳含量在不同湖区差异不显著.1850年以来呼伦湖无机碳埋藏速率变化范围约为7.10～74.29 g/(m2·a),平均值约为36.15 g/(m2·a),且大体上可分为3个阶段,即1900s以前相对稳定的低值阶段、1900s-1950s期间的快速增加阶段以及1950s以来的波动增加阶段,各阶段无机碳埋藏速率平均值分别约为10.40、26.29和41.00 g/(m2·a).空间上,呼伦湖无机碳埋藏速率整体表现为中部高、南北两端低的分布格局,这可能与湖心水动力条件相对稳定,有利于碳酸盐沉积有关.此外,呼伦湖无机碳埋藏速率与湖区温度变化呈显著正相关,而与周边人类活动影响关系不明显,表明在未来全球变暖背景下,呼伦湖无机碳埋藏速率将进一步增加,湖泊在区域碳循环中的作用将更加显著.     

Potential for accurate and precise radiocarbon ages in deglacial-age lacustrine carbonates

Lacustrine carbonate deposits (tufa) record variations in terrestrial hydrology and are preserved in many now-arid regions of the world, but are challenging to date with precision and accuracy. Many contain detritus and/or unsupported thorium (Th) that degrades or prevents the measurement of precise uranium-series (U-series) ages, and radiocarbon ages are frequently affected by both the reservoir (hard-water) effect and contamination with younger atmospheric carbon. The usual method of testing the accuracy of carbonate ¹⁴C measurements, comparison with U/Th ages or organic carbon dates, does not separate the reservoir and modern contamination effects, allowing for only relatively imprecise age estimates in samples undatable by U/Th.We have separated the modern contamination problem and the reservoir effect using a step dissolution technique on a variety of carbonate materials from Mono Lake, California, a long-lived closed-basin lake sensitive to regional precipitation variability. New dissolution experiments focus on the deglacial sediments of the Wilson Creek Formation, which preserve ostracodes and fans and mounds of thinolite, a cold-water, hydrated calcium carbonate (CaCO₃.6H₂O). Stepped-dissolution ages of thinolite crystals and dense calcites increased by 500–1000 years over the bulk age, and produced a plateau of analytically indistinguishable ages, indicating nearly complete removal of modern carbon. Repeated experiments on ostracodes from a single sample showed an increase of >3500 years over the bulk age and >6500 years from first to last step, but ages increased up to the last ∼5% of the CO₂ evolved, without forming a plateau. This may be due to the extremely large surface area-to-volume ratio of ostracodes, and inhomogeneous dissolution of the hundreds of individual shells required for the experiments. Further experiments are planned to test the effects of modern carbon on tufa, gastropods, and other shells, with the goal of systematically testing the precision and reliability of chronologies for dramatic changes in lake level in arid regions of the world.     

白洋淀湿地不同植物群落区表层沉积物碳氮磷化学计量特征

白洋淀是雄安新区的核心生态功能区.为探究白洋淀不同植物群落区表层沉积物碳(C)氮(N)磷(P)化学计量特征,采集了96组表层沉积物样品开展对比分析.研究表明:白洋淀湿地表层沉积物总有机碳(TOC)含量均值为39.64 g/kg,范围为14.4～ 136.82 g/kg,总氮(TN)和总磷(TP)均值分别为2.62和0....