Response of alluvial fan systems to the late Pleistocene to Holocene climatic transition: contrasts between the margins of pluvial Lakes Lahontan and Mojave, Nevada and California, USA

Dated shorelines of late Pleistocene pluvial Lakes Lahontan (Great Basin Desert, northwest Nevada) and Mojave (Mojave Desert, eastern California) provide timelines for the assessment of alluvial fan sedimentation at the lake margins during the late Pleistocene to early Holocene. Two sets of alluvial fan systems have been mapped: the Stillwater fans, feeding Lake Lahontan; and the Zzyzx fans, feeding Lake Mojave. Their contrasting morphologies suggest different responses of the two fan systems to late Pleistocene to early Holocene climatic change. At the time the Stillwater fan systems underwent minimal sedimentation, with the catchment hillslopes apparently stable. The Zzyzx fans experienced major changes in water and sediment supply from the catchment hillslopes. There was a major phase of hillslope debris-flow activity, followed by fanhead trenching and distal fan progradation. Both areas were wetter and colder in the late Pleistocene than they are today, but during the transition to the Holocene the Zzyzx area was more likely to experience intense rains associated with the monsoonal penetration of warm moist tropical air into the Southwest. Vegetation reconstructions for the late Pleistocene to the early Holocene suggest that catchment hillslopes in the Mojave supported a desert shrub vegetation, but those in the Stillwaters supported juniper woodland and grasses at low elevations and pine at higher elevations. Contrasts in hillslope vegetation cover together with storm activity may account for the different responses of the alluvial fans to climatic change during the Pleistocene to Holocene climatic transition. After the falls in lake levels of Lakes Lahontan and Mojave in the early Holocene, both areas underwent aridification, resulting in reductions in hillslope vegetation cover. Increased storm runoff led to fanhead trenching and distal progradation of the alluvial fans. Variations in fan style at that time may relate primarily to base-level conditions resulting from different gradients on the exposed lake shores.     

Historical Trace Metal Accumulation in the Sediments of an Urbanized Region of the Lake Champlain Watershed, Burlington, Vermont

This study documents the history ofpollution inputs in the Burlington region of LakeChamplain, Vermont using measurements of anthropogenicmetals (Cu, Zn, Cr, Pb, Cd, and Ag) in four age-datedsediment cores. Sediments record a history ofcontamination in a region and can be used to assessthe changing threat to biota over time and to evaluatethe effectiveness of discharge regulations onanthropogenic inputs.Grain size, magnetic susceptibility, radiometricdating and pollen stratigraphy were combined withtrace metal data to provide an assessment of thehistory of contamination over the last 350 yr inthe Burlington region of Lake Champlain. Magneticsusceptibility was initially used to identify land-usehistory for each site because it is a proxy indicatorof soil erosion. Historical trends in metal inputs inthe Burlington region from the seventeenth through thetwentieth centuries are reflected in downcorevariations in metal concentrations and accumulationrates. Metal concentrations increase above backgroundvalues in the early to mid nineteenth century. Themetal input rate to the sediments increases around1920 and maximum concentrations and accumulation ratesare observed in the late 1960s. Decreases inconcentration and accumulation rate between 1970 andthe present are observed for most metals. Theobserved trends are primarily a function of variationsin anthropogenic inputs and not variations in sedimentgrain size. Grain size data were used to removetexture variations from the metal profiles and resultsshow trends in the anthropogenic metal signals remain. Radiometric dating and pollen stratigraphy providewell-constrained dates for the sediments therebyallowing the metal profiles to be interpreted in termsof land-use history.     

鄱阳湖生态经济区土地生态安全研究

土地生态安全评价是生态安全评价的的重要组成部分,也是当前土地可持续利用研究的前沿课题,对其进行研究有着极其重要的意义。利用2001-2007年的相关数据,借助于物元模型对鄱阳湖生态经济区的土地生态安全进行研究。结果表明:（1）鄱阳湖生态经济区土地生态安全状况,由2001年较安全状态下降到2005不安全状态。（2）2005-2007年土地生态安全由不安全状态到临界安全状态,状态有所好转。研究也证明了利用物元模型进行区域土地生态安全评价是可行的,这种方法可作为土地生态安全评价研究的新方法。     

厄尔尼诺和大气环流异常与1998年洞庭湖区洪涝的关系

分析了厄尔尼诺与湖南洞庭硝区洪涝的统计相关和西太平洋副热带高压（简称副高）与１９９８年洞庭湖区洪涝的关系。结果表明,在厄尔尼诺次年洞庭湖区域出现洪涝的频率较大,副高 形成１９９８年洞庭湖区洪涝的重要原因。     

江西98特大洪涝卫星遥感监测及鄱阳湖水体淹没模型的研究

通过洪涝发生前后卫星遥感资料和有关气象,水等资料进行综合分析,研究江西省尤其鄱 阳湖区１９９８年６月、７月特大洪涝灾害的发生特点和危害程度。根据近年来卫星遥感监测实况资料鄱阳湖主体及其附近区域水体淹没模型。     

鄱阳湖自然保护区湿地生态旅游资源的保护与利用

论述了鄱阳湖自然保护区生态旅游资源的特色，对其发展前景进行了评价与分析。提出了生态旅游资源保护与开发利用的地位及对策。     

基于改进萤火虫算法的投影寻踪太湖水质综合评价

针对水质评价中指标的多样性及不相容性,提出了基于改进的萤火虫算法的投影寻踪水质评价方法。该方法根据水质标准等级样本集所划分的标准,构建投影指标函数,并用改进的萤火虫算法进行优化,使搜索步长逐步减小,寻优后期也可具有良好的局部搜索能力,得到最佳投影方向,使综合评价结果能够客观准确地反映出水质状况。运用该方法对太湖的水质数据进行综合评价,并与传统方法综合评分法(F值法)得到的结果进行对比,评价结果更符合当地水质状况实际情况,且对水质等级划分更为清晰。     

宝鸡金渭湖湿地小气候效应初探

以宝鸡市金渭湖湿地为研究对象,在金渭湖拦河闸桥附近进行气象及大气颗粒物观测,将拦河闸桥看作湿区,公路旁看作干区,对比分析湿地小气候特征的结果表明:宝鸡市金渭湖湿地具有明显的降温增湿作用,距离湿区越远,温度越高,相对湿度越低;冬季的相对湿度大于夏季,冬夏季的湿区温度始终低于干区,干湿两区的温度和相对湿度的日变化规律基本一致;湿区的PM2.5质量浓度小于干区,最多可小47%,表明金渭湖湿地对局地大气环境中的细颗粒物质量浓度具有显著削减作用。     

2007-2017年洞庭湖平原耕地生态安全评价及障碍因子诊断

[目的]研究洞庭湖平原耕地生态安全状况,并诊断其障碍因子,为区域耕地合理利用和耕地污染治理提供参考依据.[方法]基于DPSIR模型构建洞庭湖平原耕地生态安全评价指标体系,从县域尺度,采用基于熵权的改进TOPSIS模型测度洞庭湖平原2007-2017年耕地生态安全指数,并采用障碍度模型诊断耕地生态安全状态的主要障碍因子....     

岱海表层沉积物中影响氨氮释放的模拟研究

以北方半干旱地区典型内陆封闭湖泊岱海为研究对象,采用室内模拟实验方法,开展了温度、pH、溶解氧及水生植物对湖泊沉积物中NH+4-N释放的影响研究.结果表明,温度升高,中性条件,厌氧条件均有利于NH+4-N的释放.狐尾藻对上覆水NH+4-N含量的有效控制作用是其抑制底泥释放、同化吸收作用和增强上覆水氧化条件等综合作用的结果,植物修复是控制湖泊富营养化水平的有效措施.