林业生产性服务能促进农户林地规模经营吗?--基于林地流入视角的实证分析

厘清林业生产性服务对农户林地规模经营的影响,可为盘活集体林区林地资源、促进家庭林业发展提供决策参考。为考察林业生产性服务对林地规模经营的影响,首先构建了考虑林业生产性服务及林地规模的农户生产模型,通过理论分析后提出假设:林业生产性服务投入增加,将促进农户增加林地要素投入,即林业生产性服务对农户林地规模经营有正向影响。其次,基于福建500份经营商品林农户调查数据,利用Double-Hurdle模型及工具变量处理选择性偏差、遗漏变量及联立因果等引起的内生性问题,实证分析林业生产性服务对农户林地规模经营的影响。结果发现:不同类型的林业生产性服务对农户林地规模经营影响存在差异。其中,林业信贷服务对农户林地规模经营有正向影响,正规信贷与非正规信贷分别使农户林地流入概率提升19.6%、15.9%,使农户林地流入规模分别扩大66.8%、38.5%。林业物资与技术服务仅在是否流入林地阶段对农户林地规模经营有正向影响,使农户林地流入概率提升8.9%。林业劳动力服务仅在林地流入规模阶段对农户林地规模经营有正向影响,使得农户林地流入规模扩大66.9%。林业销售服务由于买方垄断特征对农户林地规模经营有负向影响,使农户林地流入概率降低12.3%,使农户林地流入规模缩减73.2%。因而,政府应有针对地激励和规范各类林业生产性服务发展,以更好地服务于集体林区家庭林业发展。     

Fate and transport of pathogens in lakes and reservoirs

Outbreaks of water-borne disease via public water supplies continue to be reported in developed countries even though there is increased awareness of, and treatment for, pathogen contamination. Pathogen episodes in lakes and reservoirs are often associated with rain events, and the riverine inflow is considered to be major source of pathogens. Consequently, the behaviour of these inflows is of particular importance in determining pathogen transport and distribution. Inflows are controlled by their density relative to that of the lake, such that warm inflows will flow over the surface of the lake as a buoyant surface flow and cold, dense inflows will sink beneath the lake water where they will flow along the bathymetry towards the deepest point. The fate of pathogens is determined by loss processes including settling and inactivation by temperature, UV and grazing. The general trend is for the insertion timescale to be shortest, followed by sedimentation losses and temperature inactivity. The fate of Cryptosporidium due to UV light inactivation can occur at opposite ends of the scale, depending on the location of the oocysts in the water column and the extinction coefficient for UV light. For this reason, the extinction coefficient for UV light appears to be a vitally important parameter for determining the risk of Cryptosporidium contamination. For risk assessment of pathogens in supply reservoirs, it is important to understand the role of hydrodynamics in determining the timescale of transport to the off-take relative to the timescale of inactivation. The characteristics of the riverine intrusion must also be considered when designing a sampling program for pathogens. A risk management framework is presented that accounts for pathogen fate and transport for reservoirs.     

基于HHT的三峡水库蓄水后坝下游水情多尺度时频特征

利用基于噪声辅助经验模态分解（EEMD）的改进型希尔伯特-黄变换（HHT）,对三峡蓄水后8 a的三峡日入库、出库流量和坝下各水文站日水情信号进行多尺度时频分析,并与连续小波和离散小波变换进行异同性比较。结果表明,三峡蓄水后2004～2011年三峡日入库、出库流量和宜昌、大通站日径流量均具显著的1 a尺度主周期振荡规律,三峡季节性调蓄对坝下流量1 a尺度的主周期振荡规律无显著影响。三峡蓄水后河口北支江水位的半月主周期振荡特征始终占主导地位,表明三峡调蓄影响下上游来水量变化对河口北支水位波动的影响权重小于河口自身海潮波动的影响权重。与离散小波变换固定频带下的信号分解比较,基于HHT的水文信号多尺度分解有更好的自适应性;与连续小波变换比较,HHT方法在水文信号高频部分周期振荡特征的揭示和频域混叠现象的避免方面更具优势     

基于流动人口特征的环洞庭湖区县域城镇化的水平和性质分析

改革开放以来,中国的人口迁流带有明显异地城镇化的性质,这种跨大区域的异地城镇化对人口流入区和人口流出区的影响是不同的。以环洞庭湖区为例,在第六次人口普查县域资料的基础上,利用SPSS170软件定量分析了湖区县域人口净流出率与城镇化率之间的关系,得出人口净流出区县域城镇化水平与县域人口净流出率呈高度负相关的结论;进而,按县域城乡人口内外流比(城镇人口净流入与农村人口净流出之间的比例),将本区城镇化划分为主动型城镇化、内流为主的被动型城镇化、外流为主的被动型城镇化和衰退型城镇等类型,并探讨了各类城镇化的人口流动的特征、动力机制和综合效益;在此基础上,提出了环洞庭湖区合理推进城镇化的对策     

苏北浅滩腰沙围填海控制线研究

围填海控制线是在工程可行的前提下,不显著改变区域海洋动力格局和岸滩演变趋势的最大围填外包络线,能够最大限度地协调围填海与海洋资源环境保护之间的关系。以苏北浅滩腰沙为例,在对围填海控制性因素进行筛选、识别与分析的基础上,根据各控制性因素的控制要求,设计了围填海控制性指标。应用潮流数值模拟和泥沙回淤预测技术,采用分层次筛选和迭代逼近的方法,构建围填海控制线迭代优选模型,分析不同围填海方案对海洋动力格局演变的影响,计算得到腰沙的围填海控制线为理论基面+28 m。提出的研究方法和迭代优选模型可为沿海省市围填海控制线的制定提供参考和方法借鉴,为制定围填海规模总量控制指标提供科学依据     

汶川地震后四川省安县黄洞子沟泥石流特征

2008年5月12日汶川地震诱发了黄洞子沟流域规模巨大的大光包滑坡,部分滑体前冲堆积于沟道内,直接为后期泥石流的形成提供了丰富的松散固体物质,改变了黄洞子沟泥石流形成条件,使黄洞子沟从一条非泥石流沟演变成了一条高频泥石流沟。震后黄洞子沟几乎每年雨季都会暴发不同规模的泥石流,其中以2013年"7·09"泥石流灾害规模和危害最大。本文着重分析了黄洞子沟泥石流形成特征,并从地形、降水和地质三个方面将黄洞子沟和文家沟进行对比,得出了物源堆积体颗粒粒径与泥石流形成的关系。     

气候变化和人类活动对丹江口入库径流的影响及评估

科学估算气候变化和人类活动对河川径流的影响,可以更为合理地规划利用地球水资源。针对丹江口水库入库径流的减少问题,分别采用Mann-Kendall方法和Pettitt检验,对1960~2012年间丹江口水库入库径流的年际和年内变化趋势进行了分析,并与同时期汉江上游20个地面观测站的降水、气温的年际和年内演化趋势进行了比较,从气候变化和人类活动影响的两个方面分析了入库径流减少的原因。在此基础上,利用气候弹性模型分别估算了气候变化和人类活动对径流的影响度。结果表明:近年来丹江口入库径流的减少主要受春季和秋季径流减少的影响,在春季径流的减少总量中,气候变化的贡献度为67%,人类活动为33%;秋季径流的减少总量中,气候变化的贡献度为88%,人类活动为12%。气候变化是导致丹江口入库径流减少的主要原因。     

生态岛建设过程中环境类指标构建研究——以崇明岛为例

提出了将压力 状态 响应（PSR）模型与系统分析法理论集成起来构建生态岛建设过程中环境类指标的方法和步骤。指标构建过程分为4个步骤：（1）首先利用已有生态区域（岛）相关环境类指标确定备选指标集;（2）利用PSR模型对指标逻辑关系进行分析筛选;（3）以2010年为近期目标年,利用系统分析法确定指标核心要素,得到二次筛选指标;（4）以2030年为远期目标年,以综合性和动态性为依据确定最终指标。以上海市崇明岛为例,确定水、气、土为核心考核要素,构建了基于崇明生态岛建设过程的近期及远期目标的环境类考核指标体系。指标评价结果表明,崇明生态岛建设过程中环境类综合指数为72,其中环境压力指数、环境质量指数、环境保护指数分别为85、80和51,与崇明岛实际较为吻合。部分研究结果已在崇明岛生态建设过程中得到实际应用。     

An Analysis on the Spatial Distribution of Population Aging Pressure in China

Based on comprehensive analysis of the impact of population aging to social and economic development,a comprehensive evaluation system including 18 indexes was constructed for evaluating regional pressure of population aging on social and economic development.Using statistics data of 31 regions in China from 2004 to 2008,the pressure of population aging on social and economic development,was comprehensively evaluated by using the factor analysis method.The spatial distribution of population aging in China was also analyzed.This study is to provide scientific basis for government to make strategies of coping with population aging according to regional pressure of population aging on social and economic development in China.     

Development of a land-use forecast tool for future water resources assessment: case study for the Mekong River 3S Sub-basins

Land-use change is one of the major factors that alter local and regional hydrology. For areas experiencing fast expansion of urban and agriculture areas, land-use changes often adversely affect stream flow and water resources at the local and watershed scale. The Sekong, Sesan, and Srepok (3S) Sub-basins are a part of the Lower Mekong River Basin and include land in Cambodia, Lao People’s Democratic Republic (Laos), and Viet Nam. The region is experiencing a dynamic land-use transition because of rapid changes in its economy, society, and environment. Major land-use changes include deforestation of native rain forest, expansion of agricultural and urban areas, and expansion of commercial plantation such as rubber trees. These land-use alterations have affected local and regional hydrologic processes, resulting in stream flow shortages during the dry season and flash flooding due to deforestation. In this research, deforestation in the 3S Sub-basins over the period 1993–1997 was analyzed using multi-logistic regression. The regression analysis indicated that density of agricultural cells within a 5-km radius from each forest cell and slope strongly affected the deforestation process. A land-use forecast model to simulate deforestation and urbanization sites was developed in GIS based on local land-use change trends. The model was applied to 2003 land use to forecast 2033 land use and future water demand, which was further compared with present stream flow measurements during the dry season at various places in the region. The entire approach from the land-use forecast to its impact assessment on stream flow could help local stakeholders understand watershed-wide future water resources risks and develop future water resources plans. With the 3S Sub-basins being used as a case study area, this article presents a land-use forecast tool; simulated 2033 land-use and water demand; and the estimation of the impact of the forecasted future water demand on the local stream flow.