生态退耕政策实施前后甘肃正宁县土地利用生态风险时空变化分析

本文选取甘肃省正宁县1995,2000和2010年土地利用数据和相关耕地统计数据为分析依据,以ENVI,ArcGIS和Fragstats主要工作平台,对研究区的土地利用生态风险时空变化进行了分析。为了避免了评价指标选取的主观性,在景观水平上针对土地利用斑块数量、形状和蔓延度等特点选取了相应的景观指数,结合生态系统服务价值,构建了区域土地利用的生态风险评价指数。为了研究生态风险的空间变化和验证生态退耕政策实施的效果,本文引入了生态风险质心迁移模型和土地利用的空间分布模型,定量描述了甘肃正宁县实施生态退耕工程前后生态风险的相对大小和时空变化规律。结果表明：（1）生态退耕工程的实施使得正宁县东、中、西部的生态风险均减小,减小幅度在空间分布上表现为：东部〉西部〉中部。东部为生态风险防范管理的最重要地区;（2）正宁县生态退耕前后生态风险质心向西南方向迁移了4288m,东部和西部景观破碎度的大幅度变化对县域生态风险质心的迁移起到了主要的作用。研究结果提示：为了进一步加强正宁县生态安全管理,东部地区应以林地和草地生态保护为主,中部地区应保证耕地的质量并强化对新增建设用地的规划和控制,而西部地区则需构建水土保持型农业生态系统。     

The evolution of the transboundary Evros river delta (Northeast Aegean Sea) under human intervention: a seven-decade analysis

ABSTRACT

The Evros deltaic plain (North Aegean Sea, Greece) covers an area of 188 km² and is shared by Greece and Turkey by its current main channel. This paper investigates deltaic plain evolution during the last seven decades (1945–2017), taking into consideration human interventions and their impacts on deltaic processes. Outcomes indicate that the construction of more than 25 major dams in the Evros River catchment resulted in >80% reduction in fluvial suspended load. Moreover, the alignment and relocation of the main distributary channel to the southeast was accompanied by the transformation of >40% of the deltaic plain to agricultural land. The combination of human interventions supports the coastline advance of the active main mouth (current rate of 3.9 *10^?3 km²/yr), retreat of the old (abandoned) Evros mouth (current rate 7.7 *10^?3 km²/yr), and signs of remarkable vulnerability in the middle mouth area.     

Holocene variability in climate and oceanic conditions in the winter rainfall zone of South Africa—inferred from a high resolution diatom record from Verlorenvlei

We present a diatom record from a well-dated 15.25 m composite sedimentary core from Verlorenvlei, a shallow coastal lake on the west coast of South Africa. We show that fluctuations in the diatom record occur in response to changes in sea level, ocean–atmosphere interactions and latitudinal shifts in the wind belts. During the early to mid-Holocene, the system primarily responds to sea level changes. A marine community that favours high nutrients is evident, particularly during 9200–8000, 7420–7000 and 6200–5600 cal a bp , corroborating periods of Benguela upwelling linked to fluctuations in the southeast trade winds. Increases in bioproductivity (%TOC, C/N) and fresher-water diatoms are associated with wetter conditions over the region and the northward migration of the southern westerly wind belt, most notably between 8000 and 7500 cal a bp and over the last 700 years. The latter trends are concomitant with changes in the extent of Antarctic sea ice and availability of moisture in southern South America. During the late Holocene, as sea levels stabilised to modern levels, climate variability is more strongly evident. The body of evidence further reveals the sensitivity of the region to high-latitude atmospheric mechanisms, but also showcases the significance of the southeast trade winds.     

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吹填土自重沉淤阶段孔隙水压力消散的试验研究

利用真空预压法处理吹填土时,细颗粒常堵塞排水管,导致土体排水不畅。为提高吹填土固结效率,采用自重沉淤排水与加负压排水固结相结合的方式在室内进行吹填土固结试验。试验第一阶段用排水管作为吹填土自重沉淤的竖向排水通道;第二阶段以装入中粗砂的排水管作吹填土排水通道,同时也是压力传递通道。试验监测到吹填土固结过程中不同位置孔隙水压力的变化,通过监测数据着重研究自重沉淤排水阶段吹填土的固结规律。借助渗流平衡方程确定吹填土在自重沉淤阶段孔隙水压力变化主要由排水管中水位、单位土面积控制,解释自重沉淤阶段孔隙水压力变化机理。同时,为了减小由于排水距离远近造成的固结不均,利用自重沉淤与加压固结结合的方法使吹填土达到较为理想的固结效果,将砂井设计理论与孔隙水压力变化曲线相结合确定排水管有效排水范围等效直径,为实际工程提供排水管间距的设计参数。     

云南省工业试点县耕地数量变化特征及其驱动力分析——以兰坪县为例

根据兰坪县2001～2008年的统计资料,对兰坪县耕地数量变化的影响因素进行了研究。应用灰色关联分析的方法,定量地诊断出各影响因素与耕地数量变化的关联度,然后依据关联度的大小,从诸因素中找出主要影响因素以及次要影响因素,并在此基础上提出建议,以促进耕地资源的可持续利用。研究表明：总人口的增加,农业科技的应用和农业经济结构的调整以及经济的发展是近8年来兰坪县耕地面积变化的主要影响因素。     

Assessing changes in extreme sea levels: Application to the English Channel, 1900–2006

A recently extended and spatially rich English Channel sea level dataset has been used to evaluate changes in extreme still water levels throughout the 20th century. Sea level records from 18 tide gauges have been rigorously checked for errors and split into mean sea level, tidal and non-tidal components. These components and the interaction between surge and tide have been analysed separately for significant trends before determining changes in extreme sea level. Mean sea level is rising at 0.8–2.3 mm/year, depending on location. There is a small increase (0.1–0.3 mm/year) in the annual mean high water of astronomical tidal origin, relative to mean sea level, and an increase (0.2–0.6 mm/year) in annual mean tidal range. There is considerable intra- and inter-decadal variability in surge intensity with the strongest intensity in the late 1950s. Storm surges show a statistically significant weak negative correlation to the winter North Atlantic Oscillation index throughout the Channel and a stronger significant positive correlation at the boundary with the southern North Sea. Tide–surge interactions increase eastward along the English Channel, but no significant long-term changes in the distribution of tide–surge interaction are evident. In conclusion, extreme sea levels increased at all of the 18 sites, but at rates not statistically different from that observed in mean sea level.     

长春地区中更新世晚期古环境重建的沉积地球化学与孢粉学证据

通过对长春地区HDBZK-1孔沉积序列的热释光测年和沉积物粒度分析,选取对气候变化较为敏感的K₂O、Na₂O、MgO、CaO、Al₂O₃等氧化物及K₂O/ Na₂O、Al₂O₃/(Al₂O₃+CaO+Na₂O)作为环境代用指标,并与孢粉分析资料相结合,分析了长春地区中更新世晚期（约280～120 kaB.P.）的气候环境变化。结果表明：该区中更新世晚期总体经历了4次明显的冷干-暖湿气候变化,即寒冷干旱（281.6～244.0 kaB.P.）-温凉稍湿（244.0～215.0 kaB.P.）-寒冷干旱（215.0～ 131.8 kaB.P.）-以淡水藻类花粉突然增多为明显标志的暖湿（131.8～126.4 kaB.P.）;这与深海氧同位素曲线所反映的气候变化旋回有较好的对应关系。