Macrozoobenthic community structure in a large shallow lake: Disentangling the effect of eutrophication and wind-wave disturbance

Biological communities in shallow lakes are often subject to the combined effects of eutrophication and wind-wave disturbance. However, their relative importance in regulating macrozoobenthic community assembly has not been well addressed. In the present study, a monthly sampling of macrozoobenthos and environmental parameters was conducted at ten sites from December 2012 to November 2013 in Lake Hongze, the fourth largest freshwater lake in China, which has undergone serious water quality deterioration over the past few decades. A total of 30 taxa were recorded during the 12 sampling occasions, including 6 chironomids, 6 bivalves, 4 gastropods, 4 oligochaetes, 4 polychaetes, 4 crustaceans and 2 other aquatic insects. The mean abundance and biomass of total macrozoobenthos varied greatly among the ten sites and presented distinctive taxonomic composition between the protected bays and the offshore zone. Three eutrophication parameters (including permanganate index (COD_Mn), chlorophyll a, and total phosphorus in surficial sediments) and three wind-wave variables (including Secchi depth, turbidity, and mean effective fetch) were highly related to spatial variation of macrozoobenthic assemblages. When eutrophication variables were controlled, there was a significant correlation between community similarity and wind-wave disturbance condition, and vice versa. Variation partitioning showed that wind wave disturbance explained 15.9% of the variation in benthic community composition, slightly lower than that explained by eutrophication (17.9%). These results indicate that wind-wave disturbance is as important as eutrophication in regulating benthic community structure in this large shallow lake. Wind-wave disturbance imposed opposite effects on benthic community relative to eutrophication, and were more prominent in the offshore zone weakening the role of eutrophication.     

Schmidt‐hammer exposure‐age dating (SHD) of snow‐avalanche impact ramparts in southern Norway: approaches,results and implications for landform age,dynamics and development

Schmidt‐hammer exposure‐age dating (SHD) was applied to the problem of dating the diachronous surfaces of five distal river‐bank boulder ramparts deposited by snow avalanches plunging into the Jostedøla and Sprongdøla rivers in the Jostedalsbreen region of southern Norway. Approaches to local high‐precision linear age calibration, which controlled in different ways for boulder roundness, were developed. The mean age (SHD_mean) and the maximum age (SHD_max) of surface boulders were estimated for whole ramparts, crests and distal fringes. Interpretation was further assisted by reference to R‐value distributions. SHD_mean ages (with 95% confidence intervals) ranged from 520 ± 270 years to 5375 ± 965 years, whereas SHD_max ages (expected to be exceeded by <5% of surface boulders) ranged from 675 to 9065 years. SHD ages from the Jostedøla ramparts tended to be older than those associated with the Sprongdøla, rampart crests were younger than the respective distal fringes, and use of relatively rounded boulders yielded more consistent SHD ages than angular boulders. The SHD_mean ages indicate differences in recent levels of snow‐avalanche activity between ramparts and provide insights into rampart dynamics as boulders are deposited on rampart crests and, in smaller numbers, on the distal fringes. SHD_max ages provide minimum age estimates of rampart age (i.e. the time elapsed since the ramparts began to form) and suggest that at least some of the ramparts have been developing since the early Holocene. Copyright © 2015 John Wiley & Sons, Ltd.     

地表岩石侵蚀速率对宇生核素暴露测年影响的研究

利用原地生宇生核素测定暴露年代时,通常会假设地貌体侵蚀速率为0。研究表明,该假设会低估地貌体的真实暴露年代。搜集2009~2012年全球不同区域56个岩石样品的宇生核素¹⁰Be测年数据,探讨侵蚀速率为0对于侵蚀速率为0.5、1以及2 mm/ka的样品,在不同暴露尺度上对暴露年代计算的影响幅度。结果表明,对于1×10⁴a尺度的样品暴露年代可能低估约0.5%,1%,2%;对于10×10⁴a尺度的样品可能低估约5%,7%,20%;对于50×10⁴a尺度的样品可能低估约40%,70%甚至100%以上。     

Effects of soil compaction,rain exposure and their interaction on soil carbon dioxide emission

Soils release more carbon, primarily as carbon dioxide (CO₂), per annum than current global anthropogenic emissions. Soils emit CO₂ through mineralization and decomposition of organic matter and respiration of roots and soil organisms. Given this, the evaluation of the effects of abiotic factors on microbial activity is of major importance when considering the mitigation of greenhouse gases emissions. Previous studies demonstrate that soil CO₂ emission is significantly affected by temperature and soil water content. A limited number of studies have illustrated the importance of bulk density and soil surface characteristics as a result of exposure to rain on CO₂ emission, however, none examine their relative importance. Therefore, this study investigated the effects of soil compaction and exposure of the soil surface to rainfall and their interaction on CO₂ release. We conducted a factorial laboratory experiment with three soil types after sieving (clay, silt and sand soil), three different bulk densities (1·1 g cm^–3, 1·3 g cm^–3, 1·5 g cm^–3) and three different exposures to rainfall (no rain, 30 minutes and 90 minutes of rainfall). The results demonstrated CO₂ release varied significantly with bulk density, exposure to rain and time. The relationship between rain exposure and CO₂ is positive: CO₂ emission was 53% and 42% greater for the 90 minutes and 30 minutes rainfall exposure, respectively, compared to those not exposed to rain. Bulk density exhibited a negative relationship with CO₂ emission: soil compacted to a bulk density of 1·1 g cm^–3 emitted 32% more CO₂ than soil compacted to 1·5 g cm^–3. Furthermore we found that the magnitude of CO₂ effluxes depended on the interaction of these two abiotic factors. Given these results, understanding the influence of soil compaction and raindrop impact on CO₂ emission could lead to modified soil management practices which promote carbon sequestration. Copyright © 2012 John Wiley & Sons, Ltd.     

����RFID������POS�������ڶ����ƶ���Ӱ���������о�

?о???????????????????????RFID????POS??????????????????????????????RFID?????????????????????????д洢??Ψ???????е??????????????????????????λ????????????????????????????????????????????,?????????????????????????Щ??????????????????????????????????????????????     

�˼������ڵ�Ӱ������ǷDZ���������������㷨�о�

??????????????????????????????????????????????????????????????????????????????????????С????????????????????????????????????????????????????????????????,??????????????????????????????????????????????壬??????????????????????????????????Ч???б???????ж?????????????????????????????????????δ?????????????????ó??????????????????????GRACE?????????????????????????????????????Ч??????????????????     

ENDOLITHIC LICHENS,RAPID BIOLOGICAL WEATHERING AND SCHMIDT HAMMER R‐VALUES ON RECENTLY EXPOSED ROCK SURFACES: STORBREEN GLACIER FORELAND,JOTUNHEIMEN, NORWAY

The endolithic lichen Lecidea auriculata is known to enhance rock surface weathering on the Little Ice Age moraines of the glacier Storbreen in Jotunheimen, central southern Norway. This study demonstrates the reduction in Schmidt hammer Rvalues that followed the rapid colonization by this lichen of pyroxene‐granulite boulders on terrain deglaciated over the last 88 years. In the absence of this lichen, the characteristic mean R‐value of boulder surfaces is 61.0 ± 0.3; where this lichen is present, R‐values are lower by at least 20 units on surfaces exposed for 30–40 years. A similar reduction in rock hardness on rock surfaces without a lichen cover requires about 10 ka. The rapid initial weakening of the rock surfaces is indicative of rates of biological weathering by endolithic lichens that may be two orders of magnitude (200–300 times) faster than rates of physico‐chemical weathering alone. If not avoided, the effects of this type of lichen are likely to negate the effectiveness of the Schmidt hammer and other methods for exposure‐age dating, including cosmogenic‐nuclide dating, in severe alpine and polar periglacial environments. The results also suggest a new method for dating rock surfaces exposed for <50 years.     

空基下视时序影像瞬时成像模型研究

物方空间的物体随着时间的推移进行着绝对运动,运动导致了相对位置的变化,时间序列影像记录了物方三维空间的动态变化。本文基于下视时间序列影像的动态特性,在共线方程中引入时间元素,提出了空基下视时间序列影像瞬时成像模型,描述了动态“物像”间的瞬时投影关系;针对地表不同类型动态物体,构建了“由像到物”的应用模型,实现了从像方动态特征计算地表物体特征的目的。通过仿真和真实航空下视序列影像的试验与分析,验证了序列影像瞬时成像模型能够定量计算像地动态特征。     

横断山区垂直带谱的分布模式与坡向效应

根据收集到的横断山区山地垂直带谱数据,对山地垂直带的坡向效应和空间分布规律进行了分析和研究.结果表明:1)主要的垂直带和垂直带界线如林线、暗针叶林带、雪线等的纬度和经度地带性分布规律明显并且分布模式都相似,纬向上呈开口向下的二次曲线分布模式,经向上呈开口向上的二次曲线分布模式,两者共同形成"双曲抛物面"分布模式,充分反映了横断山区的环境与生态的复杂性和独特性,也进一步丰富和发展了山地垂直带谱的二次曲线假说; 2)横断山区山地垂直带谱表现出明显的基于水分驱动的坡向效应,主要表现为同一山体的东、西坡往往具有不同的基带和带谱结构,相同类型的带谱出现的海拔和分布范围不同,迎风坡表现出较为湿润的类型和带谱结构,而背风坡则表现出更为干旱的类型和组成结构;横断山区的坡向效应主要是由于山体对当地盛行季风的影响,造成迎风坡和背风坡水热条件相差很大,从而发育不同的山地垂直带谱类型.从横断山区山地垂直带谱的空间分布规律来看, 28°～29°N、98°～101°E范围内,即大致在澜沧江以东-雅砻江以西,山地垂直带谱普遍表现出干热的特点,为横断山区干热气候的核心地带.但如何定量分析山地的坡向效应尚有待于进一步的研究和讨论.此外、数据质量和数据误差也对分析的结果,尤其是空间分布模式的数学模拟结果产生一定的影响,在以后的研究中尚需进一步完善.     

单层带支撑异形柱框架的高温性能研究

针对单层异形柱框架,通过高温数值分析,考察了支撑设置和受火位置对结构高温变形及内力的影响。研究结果表明：对于单层多跨异形柱框架,当只有一端有支撑跨时,会在一定程度上增大另一端的边节点水平位移和边柱侧向变形,对结构整体抗火不利;当左、右两端均有支撑跨时,非支撑跨在火灾作用下的梁轴力比很大,升温后期可能因梁跨中竖向位移急剧增大而发生破坏。基于上述研究结果,给出了4类单层带支撑异形柱框架火灾行为的初步判定方法。