A method for evaluating the longitudinal functional connectivity of a river–lake–marsh system and its application in China

The longitudinal functional connectivity of a river–lake–marsh system (RLMS) refers to the actual water-mediated transport of material from upstream to downstream areas along a spatial gradient and is fundamental to understand hydrological and biogeochemical cycles. However, due to a lack of consensus on appropriate data and methods, the quantification of connectivity is still a challenge, especially at the catchment scale. We developed a new method to evaluate longitudinal functional connectivity based on fluxes of materials (water, sediment, and chemicals) along a RLMS. The calculation of fluxes is based on the longitudinal pattern of terrain gradient, which influences transport efficiency, and on contributions from hillslopes, which set the initial spatial template of material loading to the RLMS. We evaluate the contributions from hillslopes to RLMS based on a new modified version of the index of sediment connectivity (IC) proposed by Borselli et al. (2008) and revised by Chartin et al. (2017).We applied this method to the Baiyangdian Basin covering an area of 3.4 × 10⁴ km² in China and quantified longitudinal functional connectivity during normal, wet, and dry periods(April, July and December) in year 2016. We found that areas with good structural connectivity exhibited poor functional connectivity during the normal and dry periods. Modelling testing with discharge data from hydrological stations and measured chemicals from Baiyangdian Lake was satisfactory in test periods. We conclude that public data and Digital Elevation Model-derived information can be used to reliably map the longitudinal functional connectivity of RLMSs. The proposed method provides a useful tool for monitoring and restoring the longitudinal functional connectivity of RLMSs and our results indicate that efforts aimed at restoring functional connectivity in RLMSs should take into account landscape patterns that can greatly influence fluxes in the watershed.     

Ensemble modelling of ice cover for a reservoir affected by pumped‐storage operation and climate change

Ensemble modelling was used to assess the robustness of projected impacts of pumped‐storage (PS) operation and climate change on reservoir ice cover. To this end, three one‐dimensional and a two‐dimensional laterally averaged hydrodynamic model were set up. For the latter, the strength of the impacts with increasing distance from the dam was also investigated. Climate change effects were simulated by forcing the models with 150 years of synthetic meteorological time series created with a weather generator based on available air temperature scenarios for Switzerland. Future climate by the end of the 21^st century was projected to shorten the ice‐covered period by ~2 months and decrease ice thicknesses by ~13 cm. Under current climate conditions, the ice cover would already be affected by extended PS operation. For example, the average probability of ice coverage on a specific day was projected to decrease by ~13% for current climate and could further be reduced from ~45% to ~10% for future climate. Overall, the results of all models were consistent. Although the number of winters without ice cover was projected to increase for all one‐dimensional models, studying individual segments of the two‐dimensional model showed that the impact was pronounced for segments close to the PS intake/outlet. In summary, the reservoir's ice cover is expected to partially vanish with higher probability of open water conditions closer to the PS intake/outlet.     

欧亚大陆中北部末次盛冰期以来的湖泊水位变化及其古气候指示意义

湖泊水位高低通常能有效地指示湖盆内湿润条件的变化,进而反映区域有效降水（降水—蒸发）变化,成为重建第四纪古气候演变的重要指标之一。通过对苏联和蒙古国古湖泊数据库以及中国晚第四纪古湖泊数据库中149个湖泊水位变化资料的梳理总结,探讨了末次盛冰期（18 cal. ka BP）以来该地区干湿变化规律及区域分异。根据研究区气候特征、地理位置及已有研究成果将其分为东欧湖泊区、中东亚干旱区和中国北方季风区三大湖区。根据不同水位记录在整个湖泊历史中出现的频率,采用3级重新分类区分出高、中、低3级水量,并把每个湖泊数字化的3级古水量表示成与现代的差值,得到每个湖泊样点每千年时间间隔内相对现代的5级水量变化（很湿润、湿润、无变化、干旱和很干旱）。结果表明,三大湖区末次盛冰期以来可能经历了不同的干湿变化过程：东欧地区湖泊水量记录在晚冰期之前较少,至全新世逐渐增多,且基本表现为早全新世干旱、中晚全新世相对湿润的状况。中东亚干旱区整体呈现出末次盛冰期至中全新世均较湿润而晚全新世干旱的气候状况,但区域内部不同湖泊在起讫时间和强度上存在显著差异。中国北方季风区的湿润期主要发生在早中全新世,但是不同湖泊有所不同。对比分析显示,早全新世时东欧地区东部气候随着斯堪的那维亚冰流的逐渐消退而逐渐变湿润,中全新世由于夏季北欧反气旋东翼的气旋气流增强而达到最湿润状态,西部地区早全新世由于强劲的西伯利亚热高压存在而整体偏干旱,中全新世由于夏季亚洲季风的渗透而转为湿润。中东亚干旱区冰期内的湿润条件可能主要与西风带降水及低温低蒸发有关,而全新世则可能主要与夏季风深入内陆导致降水增加有关。中国北方季风区全新世湿度变化可能主要受东亚季风控制。     

DEM在湖泊水文变化研究中的应用进展

在全球变化背景下,湖泊水文的动态变化不仅是评估和预测气候与环境变化的重要指示剂,同时对社会可持续发展、水资源的开发与利用、生态文明建设等产生重要影响。湖泊水文的动态变化受到湖滨及湖底地形的控制,数字高程模型（DEM）成为湖泊水文研究的重要数据源。随着遥测技术的发展,高分辨率、区域/全球大尺度DEM数据的获取手段快速发展、数据源不断丰富,DEM对推动湖泊水文动态研究进展起到了关键作用。本文首先基于Web of Science平台对DEM在湖泊水文动态研究中的相关文献进行了分析,阐述了该主题现有研究在发文时间、发文数量增减态势、研究区域与热点地区、文献所涉及的DEM数据等方面的特点。接着,围绕着DEM在湖泊水文动态的研究中4个主要方向：湖泊水域变化、湖泊水位变化、湖泊水量变化、湖泊水文灾害情势,重点总结：DEM与其他遥感观测平台、实地观测及模型模拟等多源数据的融合策略,数字地形分析与水文学分析、遥感影像分析等方法的集成策略,以及DEM数据不确定性等对湖泊水文变化研究的影响。最后,本文论述了目前DEM在湖泊水文研究中存在的关键问题,并结合技术发展趋势和研究热点问题,提出了可能的解决路径和未来的研究前景。     

A high resolution proxy-climate record from an arctic lake with annually-laminated sediments on Devon Island, Nunavut, Canada

Sediments from a 3 ha lake (75 °34.34N, 89 °18.55W) from the coastal region of northern Devon Island, Nunavut, Canada, contain discrete laminations in the deepest part of the basin. The laminations are varves as indicated by the correspondence between counts and thickness measurements of the couplets and ²¹⁰Pb dating. A 14 cm core representing 150 years of sedimentation contained laminated couplets consisting of a lighter inorganic layer with a higher percentage of calcium and magnesium, alternating with fine darker bands, typically more cohesive, and comprising higher proportions of silica and carbon. A reddish oxidation zone with higher iron and aluminum frequently separates the laminations. The dark layer represents a biogenic component deposited in summer and is made cohesive by bacterial filaments among the other particles. The light inorganic layer represents clastic deposition from allochthonous sources. Deposition rates were relatively consistent through the core with an increase in varve thickness in the 1950s. Diatom concentrations in the sediments increased by two orders of magnitude in this century, with major increases in the 1920s and 1950s. The increase in varve thickness and diatom abundance coincides with an increase in summer melt percentage in an ice core from the Devon Island Ice Cap (Koerner, 1977). The relatively high sedimentation rate (0.15 cm yr^-1) coupled with the consistency of deposition makes this lake a significant indicator for recent climate changes of the Canadian Arctic Archipelago.     

云南属都湖近百年环境演变的湖泊沉积记录与器测资料对比研究

通过对属都湖湖心钻取的短岩芯Esdr1进行放射性核素137Cs和常规的元素分析,利用137Cs建立精确的年代标尺,开展地球化学记录环境演变与器测资料的对比研究。器测资料表明,近50年来,该地区主要的气候变化特征:1958～1983年,气候偏冷湿;1983～2002年,气候逐渐暖干化,这些气候波动特征被沉积岩芯忠实记录。研究表明属都湖沉积物地球化学代用指标指示的气候演化特征与器测资料可很好的对比印证,属都湖沉积岩芯完整的记录了区域气候变化的信息     

科尔沁沙地风沙与湖泊景观演变及影响因素分析

以科尔沁沙地为研究区,基于1975~2015年中等分辨率卫星影像,采用景观格局指数计算及数理统计分析方法,研究该区近40 a来沙地与湖泊景观格局的变化过程,并对其影响因素进行分析。结果表明,近40 a科尔沁沙地风沙地貌覆盖面积呈减少趋势,年均变化率-0.31%,而灌草丛沙丘地、抛物线形沙丘等固定半固定型沙丘面积增加,沙地逆转化趋势明显。沙地景观蔓延度整体下降了2.13,优势度增加了16.55,说明科尔沁沙地斑块连通性与多样性降低。湖泊群面积净减61.24 km²,斑块数减少了66个,湖泊群质心朝ESE方向迁移了35.76 km,湖泊景观分离度呈下降趋势,而集群性有所增加、景观演变趋于稳定。气候因素和人类活动因素是科尔沁沙地演化的驱动因素,尤其社会经济和政策因素可短时间内促进沙地景观的演变过程。     

沉积物记录的亚高山湖泊环境变化——以鄂东南云中湖为例

根据云中湖27 cm长沉积岩芯进行元素、粒度和硅藻多指标分析以及²¹⁰Pb测年,结合流域气候和人类活动等历史资料,反演1958年以来云中湖在气候变化和人类活动影响下的环境变化。冗余分析结果显示云中湖沉积硅藻组合变化与Al、Fe、Pb和温度四个变量显著相关。硅藻属种聚类分析的结果表明云中湖环境变化经历了两个阶段：1958-1993年间喜碱性水体的Achnanthes minutissima和Fragilaria nanana属种大量出现与较高CIA指数响应于气候调控下的流域侵蚀过程;1993年以来气候变暖与旅游发展引起入湖营养盐增加是Cyclotella pseudostelligera和Aulacoseira alpigena等中—富营养硅藻种增殖的主要诱因。重建亚高山湖泊在气候变化以及人类活动影响下湖泊生态系统的演化,为保护亚高山湖泊生态环境和改善流域水质提供参考。     

氯化物型和硫酸盐型卤水物性参数变化规律研究

在野外自然条件下光照和温度对盐湖卤水的物性参数有很大影响,在实验室条件下模拟一里坪盐湖卤水和黑北凹地卤水,研究了温度对氯化物型和硫酸盐型卤水多元体系的pH、黏度和密度的影响规律。结果表明,一里坪硫酸盐型和黑北凹地氯化物型卤水的pH和黏度随着温度升高而减小,密度随着温度升高而增大。     

岩土勘察与盐湖卤水矿产开发

通过对盐湖地区岩土类型复杂性及特性的叙述,分析了盐湖矿产开发中不良地质现象产生的原因和岩土条件对开发规模、工程布局、工程安全、经济效益等方面产生的影响。论述岩土工程勘察在盐湖矿产开发中的特殊地位和重要价值,总结出岩土勘察与盐湖卤水矿产开发的关系,提出盐湖岩土勘察方案的相关建议。