Regional disparity in the changes of agricultura land use intensity in China during 1980-2002

Based on the cost-benefit data （1980-2002） of farm products and China Agriculture Yearbooks, this paper studies the regional disparity in the changes of the agricultural land use in China during the period 1980-2002 from three aspects such as the degree of intensity, the sown area and the abandoned farmland. The results show that： （1） The degree of intensity of land use in the westena region during 1980-2000 has a strong uptrend, but in the eastern and central regions the degree of intensity descends obviously and has shown a continuous downtrend since 1997. （2） The total sown area shrinks notably in the eastern region, while it enlarges constantly in the western region. （3） The sown area in the eastern, central and western regions has gone through a similar cyclic process： down （1980-1985）-up （1985-1991）-down （1991-1994）-up （1994-1999）-down （1999-2002）. However, there are obvious differences in amplitude variation and tendency among them. The sown area has shrunk in the eastern region and expanded in the central and western regions especially before 1999. （4） The most cases of abandoned farmland are reported in the central region, the second in the eastern region and the least in the western region. The abandonment phenomena chiefly occurred during 1992-1995 in the eastern region, and during 1998-2002 in the central region.     

Recultivation of abandoned agricultural lands in Ukraine: Patterns and drivers

The recent rise in agricultural commodity prices and the expectation that high price will persist have triggered a wave of farmland expansion in regions where land resources are still available. One such region is the former Soviet Union, where the collapse of socialism caused massive agricultural abandonment and where some of these lands are now being brought back into production. Yet, the extent and spatial patterns of recultivation, and what determines these patterns, remains unclear. We examined the extent of recultivation of abandoned agricultural land in Ukraine since 2007 using a new, satellite-based recultivation map and assessed the effect of biophysical and socioeconomic determinants on recultivation patterns using boosted regression trees. We found key predictors of recultivation to be related to the suitability of land for agriculture (i.e., soil quality, temperature). Accessibility to major cities was also important, with most recultivation happening closer to settlements, but this influence varied across Ukraine. Variables related to agricultural management (fertilizer input, mechanization) and demography were negligible in explaining recultivation in our analyses. These factors suggest that recultivation patterns were primarily driven by factors related to land productivity, with recultivation focusing on the most promising areas. Given the remaining large amount of unused agricultural land in Eastern Europe and the former Soviet Union, and considering that much abandonment occurred in areas only marginally suited to agriculture, our findings provide important insights into where recultivation can be expected to happen and thus for assessing the potential socioeconomic and environmental impacts of recultivation.     

Farmland Abandonment Research Progress: Influencing Factors and Simulation Model

Farmland abandonment is a global problem and considered one of the most important areas in land use change research. Farmland abandonment research currently focuses on understanding the factors that affect farmland abandonment and developing scientific models to simulate farmland abandonment. The study reviewed the natural and political factors driving farmland abandonment and summarized the main models for farmland abandonment simulation together with their advantages and disadvantages. We discuss the main ecological effects of farmland abandonment and propose farmland abandonment research directions. The study found that: (1) the influence of labor cost change and ageing labor force on farmland abandonment needs further investigation, (2) simulation models for farmland abandonment must include the decision-making mechanism of individual farmers and focus on macro large-scale abandonment prediction models, and (3) the influence of farmland abandonment on landscape culture must be investigated in detail.     

1980年以来中国农地利用变化的区域差异

依托1980~2002年的中国农产品成本收益资料与中国农业统计年鉴等基础数据,从集约度、播种面积与耕地撂荒变化三个方面,对中国1980年以来农地利用变化的区域差异进行了研究。结果表明：① 西部地区农地利用的集约度具有强劲的上升态势,而东、中部地区在1992~1993年时集约度下降显著,在1997年以后,集约度具有明显的持续下降趋势;② 东部地区农地利用的总播种面积显著下降,而西部地区却有相当稳定的扩大趋势;③ 东部、中部与西部地区三种粮食作物的播种面积变化均经历了一个“三缩二扩”的变化过程：“缩小 (1980~1985)-扩大 (1985~1991)-缩小 (1991~1994)-扩大 (1994~1999)-再缩小 (1999~ 2002)”;但在变化幅度与发展态势上,三个区域之间差异明显。东部地区的播种面积有显著的下降态势,而中部与西部地区在1999年以前,其总的态势是播种面积有所扩大,此后播种面积明显下降,但其下降幅度小于东部地区;④ 中部地区耕地撂荒案例最多,涉及地域最广,东部地区次之,西部地区相对较少;东部地区的耕地撂荒现象主要出现在1992~1995年,而中部地区高度集中在1998~2002年,西部地区耕地撂荒的时间分布较为均匀,没有高度集中出现的特点。     

水下井口回接工艺在边际油田开发中的应用及改进

水下井口回接是海洋石油钻井工程中的一项特殊工艺。为降低开发成本,提高边际油田的开发效益,利用临时弃井的井进行水下井口的回接,并在此基础上建造小型生产平台是开发边际油田一项不错的选择。于1988年钻探的BZ34-3-2D井,试油显示较好,采用了保留水下井口的临时弃井。介绍了井口回接工艺以及该工艺在BZ34-3油田的应用中遇到的困难,对常规井口回接工艺进行了改进与创新,利用水下摄像技术观察水下井口情况,最终回接成功,对今后水下井口回接作业有一定的指导作用。     

Late Glacial fluvial response of the Niers‐Rhine (western Germany) to climate and vegetation change

The Niers valley was part of the Rhine system that came into existence during the maximum Saalian glaciation and was abandoned at the end of the Weichselian. The aim of the study was to explain the Late Pleniglacial and Late Glacial fluvial dynamics and to explore the external forcing factors: climate change, tectonics and sea level. The sedimentary units have been investigated by large‐scale coring transects and detailed cross‐sections over abandoned channels. The temporal fluvial development has been reconstructed by means of geomorphological relationships, pollen analysis and ¹⁴C dating. The Niers‐Rhine experienced a channel pattern change from braided, via a transformational phase, to meandering in the early Late Glacial. This change in fluvial style is explained by climate amelioration at the Late Pleniglacial to Late Glacial transition (at ca. 12.5 k ¹⁴C yr BP) and climate‐related hydrological, lithological and vegetation changes. A delayed fluvial response of ca. 400 ¹⁴C yr (transitional phase) was established. The channel transformations are not related to tectonic effects and sea‐level changes. Successive river systems have similar gradients of ca. 35–40 cm km^?1. A meandering river system dominated the Allerød and Younger Dryas periods. The threshold towards braiding was not crossed during the Younger Dryas, but increased aeolian activity has been observed on the Younger Dryas point bars. The final abandonment of the Niers‐Rhine was dated shortly after the Younger Dryas to Holocene transition. Traces of Laacher See pumice have been found in the Niers valley, indicating that the Niers‐Rhine was still in use during the Younger Dryas. Copyright © 2005 John Wiley & Sons, Ltd.     

塔里木盆地南缘策勒绿洲近4000年来的环境变化

根据位于塔里木盆地南缘的策勒绿洲两个剖面的孢粉和化学元素的古气候意义的研究,恢复了近4.0 ka B.P.以来此地区环境变化的历史,揭示出了4个相对湿润期,分别发生于约4.0～2.0 ka B.P.、约2.0～1.0 ka B.P.、550～300 a B.P.、100 a B.P.前后.研究还揭示了1 500 a B.P.、1 000 aB.P.和200 a B.P.前后可能是此地区环境变化的重要时间界线.塔里木盆地古城废弃事件与环境变化记录之间的耦合表明,环境变化对此地区人地关系的内容及其演化具有重要的内在影响.     

Large‐scale connectivity of fluvio‐deltaic stratigraphy: Inferences from simulated accommodation‐to‐supply cycles and automated extraction of chronosomes

Multiscale simulation of fluvio‐deltaic stratigraphy was used to quantify the elements of the geometry and architectural arrangement of sub‐seismic‐scale fluvial‐to‐shelf sedimentary segments. We conducted numerical experiments of fluvio‐deltaic system evolution by simulating the accommodation‐to‐sediment‐supply (A/S) cycles of varying wavelength and amplitude with the objective to produce synthetic 3‐D stratigraphic records. Post‐processing routines were developed in order to investigate delta lobe architecture in relation to channel‐network evolution throughout A/S cycles, estimate net sediment accumulation rates in 3‐D space, and extract chronostratigraphically constrained lithosomes (or chronosomes) to quantify large‐scale connectivity, that is, the spatial distribution of high net‐to‐gross lithologies. Chronosomes formed under the conditions of channel‐belt aggradation are separated by laterally continuous abandonment surfaces associated with major avulsions and delta‐lobe switches. Chronosomes corresponding to periods in which sea level drops below the inherited shelf break, that is, the youngest portions of the late falling stage systems tract (FSST), form in the virtual absence of major avulsions, owing to the incision in their upstream parts, and thus display purely degradational architecture. Detailed investigation of chronosomes within the late FSST showed that their spatial continuity may be disrupted by higher‐frequency A/S cycles to produce “stranded” sand‐rich bodies encased in shales. Chronosomes formed during early and late falling stage (FSST) demonstrate the highest large‐scale connectivity in their proximal and distal areas, respectively. Lower‐amplitude base level changes, representative of greenhouse periods during which the shelf break is not exposed, increase the magnitude of delta‐lobe switching and favour the development of system‐wide abandonment surfaces, whose expression in real‐world stratigraphy is likely to reflect the intertwined effects of high‐frequency allogenic forcing and differential subsidence.     

河流阶地演化与走滑断裂滑动速率

断裂滑动速率是活动构造定量研究的最重要参数之一,不仅可以直接应用于活动构造的地震危险性预测和工程场地的地震安全性评价,还为地球动力学研究提供不可缺少的重要信息。原理上,断裂滑动速率可以用总位移量除以其累积时间而获得,但准确地确定断裂滑动速率并不是一件容易的事情,不同方法和研究者测定的同一条断裂的滑动速率可以相差3倍。文中通过对河流基座阶地演化及其对走滑断裂错动响应过程的分析发现,当一条山前河流切入河漫滩使其废弃形成阶地后,断裂的走滑位移使得河流两侧的阶地陡坎都遭到错动,其中一侧的下游阶地陡坎被错入河道而遭到河流的侵蚀,另一侧的下游阶地陡坎被错离河道,受到河流上游右侧地貌的保护而免遭侵蚀。因此,被错离河道一侧的阶地陡坎的位移在上阶地形成时就开始积累,阶地面的暴露年龄相当于位移累积的起始年代。另外,被错离河道一侧的阶地陡坎在下阶地停止侧蚀(可能同时开始接受沉积)时就开始累积位移,下阶地的初始沉积年代也代表阶地陡坎位移开始累积的时间。当然,如果能够获得被位移阶地陡坎的上下阶地年龄,就更能够把滑动速率限定在可靠的范围之内。在上述分析的基础上,提出3种利用河流阶地确定走滑断裂滑动速率的方法:第一是利用上下阶地年龄限定     

Regional disparity in the changes of agricultural land use intensity in China during 1980–2002

Based on the cost-benefit data (1980–2002) of farm products and China Agriculture Yearbooks, this paper studies the regional disparity in the changes of the agricultural land use in China during the period 1980–2002 from three aspects such as the degree of intensity, the sown area and the abandoned farmland. The results show that: (1) The degree of intensity of land use in the western region during 1980–2000 has a strong uptrend, but in the eastern and central regions the degree of intensity descends obviously and has shown a continuous downtrend since 1997. (2) The total sown area shrinks notably in the eastern region, while it enlarges constantly in the western region. (3) The sown area in the eastern, central and western regions has gone through a similar cyclic process: down (1980–1985)–up (1985–1991)–down (1991–1994)–up (1994–1999)–down (1999–2002). However, there are obvious differences in amplitude variation and tendency among them. The sown area has shrunk in the eastern region and expanded in the central and western regions especially before 1999. (4) The most cases of abandoned farmland are reported in the central region, the second in the eastern region and the least in the western region. The abandonment phenomena chiefly occurred during 1992–1995 in the eastern region, and during 1998–2002 in the central region.