Prediction of saturated hydraulic conductivity of compacted soils using empirical scaling factors

A new empirical-based scaling method is introduced to predict saturated hydraulic conductivity (K _s ) of compacted soils. This method is an improvement of the former non-similar media concept (NSMC) model that is generalized for tilled and untilled conditions. In this method, geometric mean particle size diameter (d_g ), geometric standard deviation (σ _g ) and saturated soil water content (total porosity) are successfully incorporated in the empirical-based scaling factor of K _s . Results showed that the scaled model overestimated K _s by ～18%, whereas the NSMC model underestimated K _s by ～21%. However, the scaled model based on the similar media concept (SMC) failed to predict K _s . Because of the complexity and high uncertainty in determining the shape factor parameter in the NSMC model, it is suggested that the new scaled model might be used reliably in practical cases to predict K _s in the various layers of compacted soils irrespective of the tillage condition. Further assessment of the new scaling model in other areas, in which new collected data are available, is recommended.     

产业政策调整下我国乳业的新发展——基于产业链视角

本文以2008年三聚氰胺事件后我国乳业产业政策调整为轴,从产业链的视角下分析了政策调整下我国乳业的新发展。产业政策调整前,奶牛的家庭式散养模式占据绝对主导,原奶质量难有保障;规模小、卫生条件差、经营不规范的私营奶站广泛存在;乳品市场中下集中寡占型的市场结构,以及不合理的利益分配机制等因素使得乳品质量安全事件频发。当前,在市场机制和产业政策的共同作用下,我国乳业产业链正由分散松散向集约紧凑型过渡。奶牛养殖的规模化、标准化和现代化水平不断提高,家庭散养逐步被区域集中养殖的奶牛养殖小区所取代。奶站数量大幅减少,标准化和现代化程度在不断提高,乳品加工企业市场结构也正逐步由中(下)集中寡占型向更为集约、紧凑型转变。     

压缩机组停机保压控制逻辑优化

结合中亚天然气管道WKC1首站2台SOLAR TITAN 130/C453型燃气轮机/离心式压缩机组的轴封形式、停机保压控制策略及存在风险,对停机保压程序、密封气供应程序和联动设备进行讨论、提出停机保压程序优化和改进策略,在未增加任何额外投资的情况下,有效解决了首站备用SOLAR机组保压时间短、启动速度慢、附属设备磨损快及天然气放空能耗大等问题.优化改进后的系统有效缩短了备用机组的启机时间,保障了压缩机组的正常运行,降低了对上游土库曼斯坦气源方的负面影响,以及停机状态下的放空损失及生产能耗.(表1,图5,参4)     

风险、信贷约束与农户新技术选择——基于湖南衡东县的实证研究

在农业科技支撑作用日益凸显,农业新技术前期投入大、风险高,农户受信贷和风险的双重约束,而农业科技转化率较低的背景下,通过对湖南衡东县水稻种植户的问卷调查,采用最优尺度回归方法,分析农户新技术选择的影响因素。研究结果显示,教育程度、耕种面积、家庭年收入、技术信息来源、有无正规风险应对机制和信贷的可得性对农户新技术选择具有显著影响;提出我国需要从提高农户素质入手、拓展信息渠道、建立有效的保险和信贷机制等方面提高农户农业新技术的应用。     

影响新疆牧民生产行为目标偏好因素的实证分析——以新疆阿勒泰地区富蕴县为例

[目的]确定影响新疆牧民生产行为目标偏好的主要因素,为进一步从微观层面探讨经济主体行为对经济发展的影响奠定基础.[方法]以阿勒泰地区牧民总体目标偏好为参照,通过比较富蕴县牧民样本目标偏好的差异,采用最优尺度回归模型来确定对牧民生产行为目标偏好影响显著的因素.[结果]牧民教育文化水平和劳均牲畜饲养规模对牧民生产行为目标偏好是负影响;劳均赡养系数、牧户生产生活方式和牧户人均收入对牧民生产行为目标偏好有显著的正影响.[结论]牧民传统上对草地财富的观念、草地畜牧业存在的风险、牧民规避风险的意识以及牧区社会保障水平等因素,决定了现有的目标偏好等级.因此,以人为本、转变牧区经济增长方式、改善牧民生活则变得非常迫切.     

镜泊湖枯水期和丰水期浮游植物群落结构

于2006年的枯水期(4月)和丰水期(7月)对牡丹江镜泊湖浮游植物进行调查,共采集到浮游植物8门77种,其中,绿藻26种,蓝藻18种,硅藻22种,其它11种;枯水期与丰水期浮游植物种数分别为64种和69种;运用多元统计多维尺度(MDS)分析方法对其浮游植物组成、分布、群落进行了分析。结果表明,枯水期、丰水期镜泊湖浮游植物均可划分为4个群落:上游(1#)、中上游(2#,3#,4#)、中下游(5#,6#,7#)、下游群落(8#),枯水期中下游浮游植物相似性较高,丰水期中上游浮游植物相似性较高。     

Succession of mosses,liverworts and ferns on coarse woody debris,in relation to forest age and log decay in Tasmanian wet eucalypt forest

In managed forest landscapes, understanding successional processes is critical to management for sustainable biodiversity. Coarse woody debris is a key substrate for forest biodiversity, particularly because it undergoes complex succession reflecting the effects of changes in both forest structure and substrate characteristics. The present study used a chronosequence approach to investigate succession of mosses, liverworts and ferns on coarse woody debris following clearfell, burn, sow native forest silviculture in wet eucalypt forest in Tasmania, focussing on discriminating between the effects of forest age and log decay. It also compared successional processes following wildfire with those following clearfell, burn, sow silviculture. Forest regenerating after the latter form of regeneration showed clear ecological succession up to 43 years (the limit of available sites), characterised by increasing diversity and cover, and clearly delineated specialisation among species with regard to successional stage. Analyses of subsets of the full data-set indicated that the effects of forest age dominated this succession, with minimal effects of substrate change independent of forest age. Analysis of within forest microenvironments were consistent with the inference that microenvironmental changes related to forest age drive major successional changes in these forests. Comparative analysis indicated similarity between successional states in post-wildfire and post- clearfell, burn, sow regeneration after 43 years for logs of the same decay stages, and continuing succession on post-wildfire sites to at least 110 years. Overall, these data suggest that management to sustain fern and bryophyte diversity should ensure that areas of forest beyond 110 years are represented in the landscape at appropriate spatial scales.     

基于尺度推绎方法的生态脆弱区耕作适宜性研究——以山西省寿阳县为例

以山西寿阳县的玉米和小麦为研究对象,应用尺度推绎方法开展机械化与传统耕作方式下区域粮食作物耕作适宜性的对比研究。结果表明：（1）传统耕作方式下玉米与小麦适宜种植面积皆要大于机械化耕作方式下两种作物适宜种植面积,而无论是机械化种植还是传统耕作小麦适宜种植区面积皆大于玉米种植适宜区.（2）两种作物种植适宜区空间分布呈两极化特征,即高度适宜区与永久非适宜区占据研究区绝大部分区域.（3）两种粮食作物高度种植适宜区基本集中在寿阳县北部黄土高原的塬、沟地貌区及坡度较小的山区。建议在机械化种植与传统耕作方式下皆是中、高度种植适宜区域采取机械化种植方式,而在仅适宜传统耕作的种植适宜区采取传统方式耕作。     

Is fisheries production within Large Marine Ecosystems determined by bottom‐up or top‐down forcing?

Understanding the mechanisms driving fisheries production is essential if we are to accurately predict changes under climate change and exploit fish stocks in a sustainable manner. Traditionally, studies have sought to distinguish between the two most prominent drivers, ‘bottom‐up’ (resource driven) and ‘top‐down’ (consumer driven); however, this dichotomy is increasingly proving to be artificial as the relative importance of each mechanism has been shown to vary through space and time. Nevertheless, the reason why one predominates over another within a region remains largely unknown. To address this gap in understanding, we identified the dominant driver of commercial landings within 47 ecosystems, encompassing a wide range of biogeochemical conditions and fishing practices to elucidate general patterns. We show that bottom‐up and top‐down effects vary consistently with past fishing pressure and oceanographic conditions; bottom‐up control predominates within productive, overfished regions and top‐down in relatively unproductive and under‐exploited areas. We attribute these findings to differences in the species composition and oceanographic properties of regions, together with variation in fishing practices and (indicative) management effectiveness. Collectively, our analyses suggest that despite the complexity of ecological systems, it is possible to elucidate a number of generalities. Such knowledge could be used to increase the parsimony of ecosystem models and to move a step forward in predicting how the global ocean, particularly fisheries productivity, will respond to climate change.     

3种棒果芥属植物生物量分配及异速生长分析

类短命植物是准噶尔荒漠早春草本植物类群的重要而独特的组成部分,研究其生物量分配和异速生长关系,有助于深入了解类短命植物的生存策略与生态功能。以棒果芥（ Sterigmostemum tomentosum ）、福海棒果芥（ S ． fuhaiense ）和黄花棒果芥（ S ． sulfureum ）为研究对象,采用挖掘法获取野外成株全株生物量,对三者的器官生物量、分配比例及异速生长关系进行了对比分析。结果表明,3种植物器官生物量及其分配比例均差异明显。福海棒果芥生物量最大,但根冠比（R／S）和叶冠比（L／S）最小;棒果芥生物量最小,但L／S最大;黄花棒果芥则具有最大的R／S。棒果芥和黄花棒果芥的根冠比（R／S）均随个体的增大而显著下降,表明二者地上（AGB）与地下生物量（BGB）分配受到个体大小的强烈影响。福海棒果芥AGB－BGB间为等速生长关系（幂指数α＝1）,而另外2种均为异速生长关系;棒果芥、福海棒果芥的叶生物量（LB）与AGB间为等速生长关系,而黄花棒果芥符合异速生长关系（α＜1）;3个物种的LB－BGB间具有共同的异速生长指数（0．816）,表现出强烈的功能趋同性。总之,3个物种间的生物量分配及异速生长关系没有一致规律,但体现了类短命植物生物量分配的特点。