Bio-climatic imprints on a Holocene loess palaeosol from China

Micromorphology, heavy minerals, pollen and soil properties were examined in a typical Holocene loess profile in the north of the Loess Plateau, consisting of a palaeosol (locally known as the Ansai palaeosol) underlain by the Malan loess and overlain by modern loess. The palaeosol consists of an upper humus-rich (AB) horizon over a clay-rich (Bt) horizon. The humus-rich horizon is intensely weathered, contains precipitated calcitic material derived from the overlying modern loess, and has both high pollen content and diversity. Clay coatings in the clay-rich horizon indicate formation by eluviation–illuviation of clay. Pedogenetic characteristics and pollen analysis imply that the vegetation during the time of most intensive soil development is likely to have been a warm-temperate forest. A complex interpretation of the loess–palaeosol sequence recognizes several development stages. The phase of soil development, maximum and minimum limiting ages for which are ca. 8800 and 4400 ¹⁴C years BP, involved continuing but reduced loess deposition, and successive Holocene bio-climatic environment overprinted new features on the palaeosol.     

基于不同退耕模式的黄土丘陵区生态环境建设地域分异特征

退耕是目前国家关于黄土丘陵区生态环境建设的主体措施。在总结"赈济退耕25"、"赈济退耕15"和"梯田退耕"各模式基本特点的基础上,根据土地利用、耕地坡度分级数据、农业人口数据和不同模式生态环境建设标准,分别计算了黄土丘陵区各县(市、区)退耕25°和15°以上坡耕地、新建园地、新修梯田、林草植被恢复的面积以及相应的投资需求额度。在构建并采用生态环境建设指数、政策性补贴资金密度指数和投资需求密度指数等指标,对55个县(市、区)进行类型划分的基础上,分析了黄土丘陵区不同退耕模式下的生态环境建设规模及投资需求地域分异特征。     

攀西生物资源综合开发的项目设计与时序

从攀西生物资源综合开发的指导思想、设计思路和总体目标出发,对生物资源综合开发的项目和实施时序进行系统的设计。对项目实施的时间序列按照三个阶段进行划分:一是生物资源开发的起步阶段(2003-2008); 二是生物资源开发的发展阶段(2009-2015);三是生物资源开发的提高阶段(2016-2020)。生物资源综合开发项目设计按项目层次分:24个国家级项目,39个地方级项目;按资源开发类型分:木本果品类9项,纤维及造纸类3 项,木本油脂类2项,中药材开发与生物制药类8项,生活保健类10项,淀粉类1项,观赏植物及花卉产业开发类5 项,香精香料类2项,特色农业类3项,经济作物类3项,饲料类1项,真菌类3项,生物农药类2项,动物类2项,生态功能类5项,生态旅游类4项;按自然地域分:攀枝花自然地域28项,西昌-德昌自然地域35项,会理-会东自然地域7项;按项目类型分:科技攻关项目20项,科技示范与技术推广项目14项,产业化项目36项。     

攀西地区特色生物资源综合开发与示范意义

在首次对特色生物资源的内涵科学界定的基础上,探讨了特色生物资源开发的理论基础及战略意义,重点介绍了国家“十五”重大科技攻关项目——“攀西地区特色生物资源综合开发与示范”项目的设计思路、研究内容及实施路线,对项目实施的社会、生态与经济效益进行分析,认为该项目为我国特色生物资源开发提供了一些可借鉴的经验。     

攀西地区特色水果的市场定位

攀西地区具有发展各类果树得天独厚的自然资源优势。根据攀西特色水果的特点和产业发展的条件,在大区域背景下,分析了攀西地区特色水果在国内市场的竞争优势,明确了攀西地区特色水果的市场定位:大力发展早熟枇杷、石榴和晚熟芒果及深加工,以品质的优良、上市时间的优势占领高端市场,把资源优势转化为产品优势和经济优势。在此基础上,提出了攀西地区特色水果发展中需要重视的问题。     

灌溉后的黄土剪切特征变化

在中国甘肃省的黑方台阶地上从上世纪60年代开始出现人类定居和开垦活动,并自1968年发展为灌溉农业。随着灌溉的进行地面已出现沉陷和滑坡。地表沉陷是由灌溉水的充填引起黄土结构崩塌造成的。然而崩塌和湿润化对剪切特征的影响目前还不清楚。为了研究湿化后的黄土剪切特征的变化,进行了对马兰黄土未经扰动和重塑土样的直接剪切盒测试。结果显示未扰动土样的粘合力和内摩擦角在湿润化后都下降了,而所观察到的重塑土的弹度参数只有少许变化。未扰动土的不饱合粘合力,据认为其受胶结物质的影响,在饱合后消失了。经灌溉的土的不饱合强度参数与未灌溉土相比表现出差异,它们可能受土壤水分的强烈影响。     

Leaf area index retrieval based on canopy reflectance and vegetation index in eastern China

The aim of this paper is to investigate the feasibility of using Landsat TM data to retrieve leaf area index (LAI). To get a LAI retrieval model based ground reflectance and vegetation index, detailed field data were collected in the study area of eastern China, dominated by bamboo, tea plant and greengage. Plant canopy reflectance of Landsat TM wavelength bands has been inversed using software of 6S. LAI is an important ecological parameter. In this paper, atmospheric corrected Landsat TM imagery was utilized to calculate different vegetation indices (VI), such as simple ratio vegetation index (SR), shortwave infrared modified simple ratio (MSR), and normalized difference vegetation index (NDVI). Data of 53 samples of LAI were measured by LAI-2000 (LI-COR) in the study area. LAI was modeled based on different reflectances of bands and different vegetation indices from Landsat TM and LAI samples data. There are certainly correlations between LAI and the reflectance of Tm3, TM4, TM5 and TM7. The best model through analyzing the results is LAI = 1.2097*MSR + 0.4741 using the method of regression analysis. The result shows that the correlation coefficient R2 is 0.5157, and average accuracy is 85.75%. However, whether the model of this paper is suitable for application in subtropics needs to be verified in the future.     

Vertical variations and transport mechanism of soil moisture in response to vegetation restoration on the Loess Plateau of China

Soil moisture is essential for vegetation restoration in arid and semi-arid regions. Ascertaining the vertical distribution and transportation of soil moisture under different vegetation types has a profound effect on the ecological construction. In this study, the soil moisture at a depth of 500 cm for four typical vegetation types, including Robinia pseudoacacia, Caragana korshinskii, Stipa bungeana, and corn, were investigated and compared in the Zhifanggou watershed of the Loess plateau. Additionally, hydrogen and oxygen stable isotopes were detected to identify the transport mechanism of soil moisture. The results showed vertical distribution and transportation of soil moisture were different under different vegetation types. Depth-averaged soil moisture under S. bungeana and corn generally increased along the profile, while C. korshinskii and R. pseudoacacia showed weakly increasing and relatively stable after an obvious decreasing trend (0–40 cm). The soil moisture under R. pseudoacacia was lower than that under other vegetation types, especially in deep layer. However, the effect of R. pseudoacacia on soil moisture in the topsoil (< 30 cm) could be positive. For R. pseudoacacia (160–500 cm), C. korshinskii (0–500 cm), and S. bungeana (0–100 cm), the soil moisture declined with increased in vegetation age. Planting arbor species such as R. pseudoacacia intensified the decline of soil moisture on the Loess Plateau. The capacity of evaporation fractionation of soil moisture followed the sequence: corn > S. bungeana > R. pseudoacacia > C. korshinskii. The δ¹⁸O values in soil water fluctuated across the profile. The δ¹⁸O values changed sharply in upper layer and generally remained stable in deep layer. However, in middle layer, the vertical distribution characteristics of the δ¹⁸O values were different under different vegetation types. We estimated that piston flow was the main mode of precipitation infiltration, and the occurrence of preferential flow was related to vegetation types. These results were helpful to improve the understanding of the response of deep soil moisture to vegetation restoration and inform practices for sustainable water management.     

Multi‐temporal scale changes of streamflow and sediment load in a loess hilly watershed of China

Global climate change and diverse human activities have resulted in distinct temporal–spatial variability of watershed hydrological regimes, especially in water‐limited areas. This study presented a comprehensive investigation of streamflow and sediment load changes on multi‐temporal scales (annual, flood season, monthly and daily scales) during 1952–2011 in the Yanhe watershed, Loess Plateau. The results indicated that the decreasing trend of precipitation and increasing trend of potential evapotranspiration and aridity index were not significant. Significant decreasing trends (p < 0.01) were detected for both the annual and flood season streamflow, sediment load, sediment concentration and sediment coefficient. The runoff coefficient exhibited a significantly negative trend (p < 0.01) on the flood season scale, whereas the decreasing trend on the annual scale was not significant. The streamflow and sediment load during July–August contributed 46.7% and 86.2% to the annual total, respectively. The maximum daily streamflow and sediment load had the median occurrence date of July 31, and they accounted for 9.7% and 29.2% of the annual total, respectively. All of these monthly and daily hydrological characteristics exhibited remarkable decreasing trends (p < 0.01). However, the contribution of the maximum daily streamflow to the annual total progressively decreased (?0.07% year^?1), while that of maximum daily sediment load increased over the last 60 years (0.08% year^?1). The transfer of sloping cropland for afforestation and construction of check‐dams represented the dominant causes of streamflow and sediment load reductions, which also made the sediment grain finer. Copyright © 2015 John Wiley & Sons, Ltd.     

南京周家山下蜀黄土石英颗粒特征及其物源意义

下蜀黄土的成因和物源一直是学术界研究的热点。对南京周家山下蜀黄土的石英粒度和石英表面微结构进行分析,结果显示:粉砂粒级石英颗粒（5~50 μm）占绝对优势;<20 μm组分平均含量为42.76%,<30 μm组分平均含量为62.98%;粒度分布曲线和累积曲线总体具有颗粒偏细,呈正偏态,分选较差,峰形尖锐,双峰曲线不对称的特征;粒级-标准偏差曲线呈“双峰”分布,两个明显的标准偏差峰值分别出现在7.962 1 μm和39.905 2 μm。石英颗粒表面形态主要以次棱角状为主;表面机械结构具有丰富的蝶形坑、曲脊、贝壳状断口,部分表面出现平行节理面、V形坑;不同粒级组分表面形态和机械结构特征存在差异。分析表明,南京周家山下蜀黄土属典型风成成因堆积物,是多源区物质高度混合搬运堆积的结果。