不同出露时间下洞庭湖洲滩土壤及生态系统呼吸特征

于2015年1月洞庭湖枯水期,针对不同出露时间下的洲滩,调查其土壤理化性质,并利用LI-8100便携式二氧化碳气体分析仪监测其生态系统呼吸.结果表明：在洞庭湖枯水期,洲滩出露后,洲滩土壤有机质、硝态氮、铵态氮和全氮含量随出露时间增长而先升高后降低.土壤溶解性有机碳含量是影响洞庭湖枯水期洲滩生态系统呼吸强度的最重要影响因子.溶解性有机碳含量随出露时间增长而提高,洲滩生态系统呼吸强度随之提高,并在洲滩出露约60天后达到最高值.出露洲滩生态系统呼吸通量均值为0.72±0.55 μmol/（m²·s）,超过杨树林地、芦苇地和农田地,成为洞庭湖区冬季CO₂排放最活跃的区域.     

1500 years of lake sedimentation due to fire,earthquakes, floods and land clearance in the Oregon Coast Range: geomorphic sensitivity to floods during timber harvest period

Sediment cores retrieved from landslide‐dammed Loon Lake recorded events back to the 5th century AD in a forested, mountainous catchment, thereby providing an opportunity to compare the impacts of known recent perturbations, including floods and timber harvesting with those of an early period in the cores, floods, fires, and earthquakes. High‐resolution multi‐parameter (grain size, %TC, %TN, and magnetic susceptibility) data allowed the core stratigraphy to be classified as background sedimentation and events. ¹³⁷Cs and radiocarbon dating, as well as a varved record in the last 75 years provided age control. Mean mass accumulation rate from 1939 to 1978 AD, the time of peak timber harvest and a cool wet phase of the Pacific Decadal Oscillation, was 0.79 (0.74–0.92, 95% C.L.) g cm^‐2 y^‐1, significantly higher than mean rates of both the more recent contemporary period (coincident with the passing of the legislation that regulated harvesting practices in the region), 1979–2012 AD, at 0.58 (0.48‐0.70) and the entire early period, 0.44 (0.41–0.46). Several event deposits are coeval with independently estimated ages of eight Cascadia subduction zone earthquakes in the early period, including the 1700 AD Mw 9.0 event. These deposits are predominantly formed by hyperpycnal flows, as are the known event deposits in the contemporary period. The high mass accumulation rate and greater frequency of thick event deposits during the early contemporary period point to the extraordinary role of timber harvesting in priming the landscape for subsequent sedimentary delivery during floods. Copyright © 2017 John Wiley & Sons, Ltd.     

When to conduct an isotopic survey for lake water balance evaluation in highly seasonal climates

One‐time or short‐term lake water isotopic surveys are often employed to evaluate regional lake water balance. However, it can be difficult to determine the optimal time‐window for sampling to obtain a representative long‐term perspective of lake water balance in settings influenced by seasonal variations in precipitation, evaporative loss, glacial/snow meltwater, and larger seasonal shifts in isotopic composition of precipitation. This is especially true for areas of the Tibetan Plateau that are influenced by the summer Indian monsoon. Although high‐frequency sampling is always preferred as the most rigorous approach to characterize the water budget of lakes or watersheds, this may be impractical in remote regions and over large spatial scales. To assess the potential sensitivity of isotope balance characterization to seasonal variability, we used a weekly lake water isotope data set acquired over a period of 3 years on the Tibetan Plateau to evaluate the potential inaccuracies that might have arisen from using isotopic data collected during narrower time‐windows. For this assessment, we use weekly isotopic data collected during the study and assume that these sampling events were stand‐alone one‐time surveys. We then demonstrate the sensitivity of the isotope balance method in this setting, particularly for the rainy season that significantly underestimated the evaporation/inflow. In contrast, isotopic composition of the lake water was found to be more representative of long‐term conditions when sampled in October on the Tibetan Plateau. To broaden our evaluation of seasonality effects over a range of climatic zones, published high‐frequency isotopic data were also compiled, and a similar assessment was carried out for selected regions of the world. The synthesized data and model outputs, which confirm pronounced variations in lake water isotopic composition and evaporation/inflow across a range of seasonal climates, were used to determine optimal sampling windows for these specific regions.     

柴达木盆地尕斯库勒盐湖区成盐物质的来源与水力迁移作用

水动力条件是盐湖成盐成矿的必要条件之一.利用研究区各类水体的理化参数(pH、氧化还原电位、电导率和总溶解性固体)、水化学特征、元素比值等参数识别尕斯库勒盐湖成盐元素的来源及水力迁移作用.结果表明:尕斯库勒盐湖成盐元素主要来源于蚀源区岩石风化,其中冰川融水、硅酸盐风化、碳酸盐风化和蒸发盐风化分别占0.04%、0.15%、63.89%和35.92%,在祁漫塔格山前一带,受到深部补给作用.高山区到平原区,水动力条件总体上逐渐降低;而在垂向上随着深度的增大含水层Ⅰ~Ⅱ之间水动力条件逐渐减弱,含水层Ⅲ~Ⅴ之间水动力条件变充足.河流与溢出带水体之间存在局部水流系统,与平原区含水层之间存在区域水流系统.水动力条件和水力联系对元素的迁移和富集具有明显的相关性,二者控制着元素的迁移速度以及元素在空间上的富集规律并影响着水化学类型.     

基于主客观赋权模糊综合评价法的湖泊水生态系统健康评价

运用湖泊营养状态指数判断湖泊的富营养化状态,并根据湖泊的水质、沉积物和水生生物群落的现状和特点,运用主观赋权法中的层次分析法和客观赋权法中的熵权法结合模糊综合评价法,对长江中游地区江汉湖群37个湖泊的水生态系统进行健康状态评价.对湖泊富营养化的调查结果表明,海口湖处于中营养状态,18个湖泊处于富营养化状态,18个湖泊处于超富营养化状态.湖泊生态系统健康评价的研究结果表明,37个湖泊中,处于健康状况"优"的湖泊只有海口湖,处于健康状况"良"的湖泊有5个,分别为东西汊湖、花马湖、梁子湖、童家湖和涨渡湖,其余31个湖泊均处于健康状况"差"的状态.经过与湖泊营养状态指数的对照,本研究结果表明,由主观赋权的专家评分的层次分析法结合模糊综合评价法对江汉湖群湖泊水生态健康状态的评价效果相比客观赋权的熵权模糊综合评价法更贴合实际.     

A REVIEW OF MOUNTAIN-BASIN COUPLING OF JIANGHAN AND DONGTING BASINS WITH THEIR SURROUNDING MOUNTAINS

Sedimentary basin and orogenic belt are two important components of continental structure with internal genetic links. The study of the basin-mountain coupling can reconstruct and restore the coupling relationships between the deep lithosphere process, near-surface structure and climate change over time. The Jianghan-Dongting Basin locates in the middle reaches of the Yangtze River, presenting a clear basin and mountain boundary with the Qinling-Dabie Shan to the north, the Mufu Shan to the southeast, the Wuling Shan to the southwest, and the E'xi Mountain to the west, respectively. The Meso-Cenozoic Jianghan-Dongting Basin was affected by the subduction and collision of the Pacific plate and the Indian Ocean plate on the Eurasian continent, resulting in multiple tectonic evolution processes. There are some big rivers pouring into the Jianghan-Dongting Basin, such as the Yangtze River, Hanjiang River, Ba River, Xiangjiang River, and Yuanjiang River, etc. to serve as the material transport belts linking between the orogenic belt denudation and basin deposition. Therefore, the Jianghan-Dongting Basin has become a multi-source sedimentary basin, which makes it a natural laboratory to explore the geological processes from source to sink. Because the low-temperature thermochronology(e.g. fission-track and(U-Th)/He)can record the recent uplift time of mountains, they are widely used on the bedrock samples and the detrital synorogenic sediments in basins to constrain the surface uplift time of the orogenic belt. Hence, in the first parts of the paper we summarize and sort out the research results of basin-mountain coupling process in the Jianghan-Dongting Basin, evaluate the research results, identify the existing problems, and propose new research directions. After that, we introduce the applications of low-temperature thermochronology on the bedrock within the orogenic belt, basin and river sediments, combined with the actual situation of Jianghan-Dongting Basin, and put forward a new research breakthrough point. It is found that the Jianghan-Dongting Basin is very suitable for the study of low-temperature thermalchronology on detrital minerals. However, it should combine the low-temperature thermochronology results of both orogenic belt and river sediments with the provenance analysis on the same target minerals, building the connection between the exhumation and provenance information on the orogenic belt, thus providing the detailed evolution of mountain-basin coupling process.     

The paleoenvironmental significance of spatial distributions of grain size in groundwater‐recharged lakes: A case study in the hinterland of the Badain Jaran Desert,northwest China

For lakes in desert hinterlands that are not recharged by river runoff, sediment input solely comes from wind transport. While the processes of sediment transport and deposition in these lakes differ significantly from those with river discharge, the spatial distribution of sediment grain size in these groundwater‐recharged lakes remains largely unknown. Moreover, whether the grain size distribution in these lake sediments can be used as a proxy in the study of past climatic change and environmental evolution studies is unclear. In this study, five lakes with a range of surface areas that had no runoff recharge were selected from the hinterland of the Badain Jaran Desert of north‐western China, and a total of 108 samples of lake surface sediments were collected to examine the spatial distribution of grain size. Moreover, an end‐member‐modeling algorithm was used to calculate end members from all grain size measurements. Our results showed that both the median and mean grain sizes in the lake sediments decreased from the nearshore to the offshore, deep‐water zone. However, the lowest median and mean grain sizes were not found in the center of the lakes, in contrast to lakes recharged by surface runoff. The median grain size of sediment in the lake center was negatively correlated with lake level, and thus could help reveal lake evolution at low resolutions. Moreover, EM1 and EM2 were interpreted as wind transported sediment, and sediment perturbed by lake waves after wind transport, respectively. The modal grain size of EM1 varied slightly between lakes, while changes in the modal grain size of EM2 were related to lake area. Given the positive relationship found between EM2 content and lake level, changes in the EM2 content (%) can serve as a rough indicator of lake level fluctuations at low temporal resolutions. Copyright © 2017 John Wiley & Sons, Ltd.     

近200 a来云南阳宗海摇蚊群落多样性及稳定性变化

云南省拥有丰富的生物多样性,其生态系统稳定性对于发挥生态系统服务功能十分重要,但近几十年以来的人类活动以及气候变化带来的干扰削弱了该区域的生态系统功能.本文以阳宗海为研究对象,探讨了1820s—2006年间人类活动背景下摇蚊群落多样性和稳定性的变化过程,并进一步探讨阳宗海摇蚊群落多样性与稳定性之间的关系.利用沉积物中的营养指标(总有机碳(TOC)含量、总氮(TN)含量和TOC/TN摩尔比)及摇蚊分别重建了湖泊营养变化及摇蚊群落物种丰富度、均匀度、相似度和稳定性(ar1),利用PCA第1轴代表摇蚊群落以检测突变点.研究发现摇蚊群落组成与湖泊营养变化有较好的一致性,二者在1990年左右发生突变,物种丰富度、均匀度和相似度指数分别在1950s、1990s初以及1970s初升高,说明摇蚊群落组成逐渐多样化,种属分布更加均匀.通过检测发现摇蚊群落稳定性在1960s初开始降低,比湖泊系统突变提前30 a左右.摇蚊群落的物种丰富度、均匀度以及稳定性指标伴随着湖泊外源营养物质输入比例增加而升高,群落多样性与稳定性之间的相关性分析表明群落稳定性随物种丰富度的升高而降低.     

新疆艾比湖主要入湖河流同位素及水化学特征的季节变化

通过野外调查取样和室内测试分析,利用水文化学以及氢氧稳定同位素技术,分析艾比湖主要入湖河流氢氧同位素及水化学的组成特征,并探讨其季节性变化.结果表明：地表水水质指标高值多出现于博乐市、温泉市和精河县及艾比湖湿地附近,主要污染为水体富营养化、工矿业污染以及有机质污染,其污染程度夏、秋季高于春、冬季.河水的δ¹⁸O与δ²H存在明显的线性关系,其相关指数为夏季（R²=0.99） > 春季（R²=0.98） > 秋季（R²=0.96） > 冬季（R²=0.90）,均沿当地大气降水线分布,受西北干旱区强烈的蒸发作用影响,各季节河流斜率均小于8,氘过量参数值多为正值.博尔塔拉河与精河地表水体δ¹⁸O值整体上表现为沿流程逐渐偏正的趋势,博尔塔拉河水体氢氧同位素与高程相关指数表现为春季（R²=0.70） > 冬季（R²=0.57） > 夏季（R²=0.45） > 秋季（R²=0.30）,精河因其海拔差异不大,流程简短,与高程相关性低.博尔塔拉河和精河氢氧同位素与氯化物、硫酸盐、五日生物需氧量等指标间存在相关性,且在夏、秋季最大,相关系数R>0.75,与总磷、Cu²⁺、色度、浊度等指标基本都不显著相关,相关系数R<0.25.     

富营养化浅水湖泊藻源性湖泛的短期数值预报方法——以太湖为例

本文建立了一种富营养化浅水湖泊藻源性湖泛的短期数值预报方法.选取表征藻源性湖泛的代表性指标叶绿素a和溶解氧浓度作为预测变量,以天气预报中的风场为驱动力,求解浅水湖泊三维水动力水质耦合数值模型,计算未来3 d浅水湖泊叶绿素a和溶解氧浓度的时空分布,然后结合未来3 d的气象因子信息建立经验公式,计算湖泛易发水域发生湖泛的概率,并进一步确定湖泛发生位置和面积.以太湖为例,采用构建的方法于2013 2014年夏、秋季对太湖7段湖泛易发水域的湖泛发生概率及发生面积进行未来3 d的预测预报,预报正确率在80%以上.