Impact of a scallop drag on the sediment chemistry, microbiota, and faunal assemblages of a shallow subtidal marine benthic community

Scallops are usually obtained by means of a heavy metal dredge that is pulled over the sea bottom. Most studies of the impact of this gear type have shown that larger invertebrates, in particular, are severely disturbed. These studies, however, have been conducted on coarse sediments, ranging from sands to cobble, and have dealt only with faunal changes. In this paper the impact of a New England type scallop dredge on the fauna and sedimentary nutritional characteristics of a silty sand community is detailed. The site, in the Damariscotta River, Maine, USA, was sampled during the fall and winter prior to, then again immediately following, the dragging event, and twice more over the ensuing six months. Loss of surficial sediment, lowered food quality of the sediment (as measured by microbial populations, enzyme hydrolysable amino acids, and chlorophyll a), and changes in the faunal composition of the dragged site were observed. While some taxa returned to the drag track relatively quickly, others such as the cumaceans, phoxocephalid and photid amphipods, and nephtyid polychaetes, were not seen in abundances comparable to those of the adjacent undragged site until the food quality also recovered.     

A re-configuring sliding-mode controller with adjustable robustness

In this paper, a controller design method for underwater vehicles is presented, which is based on re-configuration of a sliding-mode controller in case of disturbances caused by shallow water conditions. The disturbance distribution information can be obtained and used to update the corrective gain vector of the sliding-mode controller. This increases the robustness of the controller and, hence, keeps the system performance within acceptable limits. Proposed method is validated with simulations on a submarine model.     

怒江流域云南段生物多样性保护地人为干扰分析

基于乡镇单元选取具有代表性的人为干扰社会经济指标,计算怒江流域云南段2005、2010、2015年各乡镇人为干扰指数（HDI-Human Disturbance Index）,分析了怒江流域云南段乡镇单元、已建自然保护区和相关保护优先区的人为干扰强度变化。结果表明：2005年以来,研究区乡镇HDI整体呈增长趋势,低和较低HDI乡镇数量减少但整体HDI增长,中度和较高HDI乡镇数量和整体HDI都增加,高HDI乡镇数量增加不大但整体HDI增幅最大;各级自然保护区人为干扰强度都呈增加趋势,国家自然保护区增幅最大达到较低人为干扰强度,省级自然保护区一直为较低人为干扰强度,县级自然保护区处于中度人为干扰强度,需加强永德大雪山、龙陵小黑山、临沧澜沧江、南捧河4个自然保护区所涉中度及以上HDI乡镇的人为干扰管理,避免人为干扰压力的大幅增加;研究区分布的3类保护优先区人为干扰强度缓慢增长,至2015年基本为低或较低人为干扰状态,有优化的空间和潜力;建议在怒江流域云南段上游增设碧罗雪山自然保护区,在下游考虑已建自然保护区外部空间扩展和自然保护区斑块间的生态廊道构建,在其他中度或较高HDI乡镇可根据保护需求开展迁地保护或自然保护小区建设。     

The influence of plant removal on succession in Wyoming big sagebrush

Restoration treatments are based on the largely untested notion that desired recovery of plant communities following disturbance wouldn’t occur in the absence of active intervention. We identified rate of short-term (10 year) floristic changes following removal of plant functional groups in Wyoming big sagebrush plant communities in 1999-2005 and 2008. Treatments imposed on 6 × 6 m plots were: 1) removal of all plant functional groups, 2) perennial grass removal, 3) shrub removal and 4) control. Our data suggest recovery of the shrub component on shrub removal plots could take decades. Similarly, perennial grass cover and density on perennial grass removal plots was less than half that of unaltered plots 10 years after treatment. When all functional groups were removed, cover of annual forbs, annual grasses, and shrubs returned to unaltered levels within ten years or less. Perennial forbs were unaffected (p > 0.05) by treatment. The fact that natural recovery of some components occurred within a relatively short post-disturbance time interval (i.e. <10 years) suggests that intervention may not be necessary for some functional groups. Restoring shrubs in areas dominated by perennial grasses may require targeted reductions of competing perennial grasses. Conversely, shrub dominance may limit perennial grass re-establishment.     

井下地电阻率观测中地表电流干扰影响计算

本文把地电阻率台站地下介质简化为水平三层均匀介质模型,以点电流模拟地表干扰电流,针对对称四极观测装置,计算了在不同电性结构中的不同深度观测时,地表电流干扰源对对称四极装置地电阻率观测的影响,计算得到:地表干扰源对电阻率观测的影响取决于电性结构的类型和层参数、供电电极和测量电极的埋深以及避开干扰源的距离.本文研究结果对实施井下电阻率观测中台址电性结构的选择、电极埋深、干扰源避让距离等有参考意义.     

对流强度对雷暴云微物理发展和电荷结构影响的数值模拟

为了探讨对流强度大小对雷暴云内微物理发展和起电过程的影响,基于已有的二维积云起、放电模式,改变其扰动温度进行敏感性试验。试验结果表明:对流强度对雷暴云内微物理过程、起电率及后续电荷结构的产生均有一定程度的影响:1）对流强度较小时,冰晶粒子极大值在高温区（高于-13.8℃）出现,对流强度较大时,上升风明显增强,将更多的水汽带入高空,气溶胶活化过程明显增强,使得云滴粒子明显增多,冰晶粒子较早产生,冰晶粒子极大值在低温区（低于-13.8℃）出现,发展过程更为剧烈;同时,较高的对流强度也使得降雨量增多,霰粒子数目也在对流发展旺盛时期显著增多。2）非感应起电率主要和冰晶-霰的碰并分离过程有关,对流强度较大时,非感应起电率较大,电荷结构持续时间较长,过程明显,感应起电率也较强。3）对流强度较大时,电荷结构更为复杂,雷暴云发展初期基本呈现为三极性,发展旺盛时期底部正电荷区域嵌入一个较小的负电荷区,呈现四极性电荷结构,雷暴云发展末期基本呈现偶极性电荷结构;对流强度较小时,发展初期、旺盛时期均呈现三极性电荷结构,发展末期呈现偶极性电荷结构。     

First observations in a high rocky-shore community after the Erika oil spill (December 1999, Brittany,France)

The high mediolittoral rocky-shore community on the island of Groix (Brittany, France), was studied for the year immediately following the Erika oil spill (12/12/1999). The macrofaunal assemblages of three habitats (exposed bedrock, crevices, boulders) under three situations (non-impacted, impacted and not washed, impacted and washed) were monitored monthly. The assemblage of each habitat showed specific responses to the impacts and initiated various patterns of succession: the bed rock assemblage changed in terms of abundance but no species-richness variations occurred; in the crevices richness variations occurred both in the disappearance of some species and the immigration of opportunistic ones; the boulder assemblage lost many species and remained unstructured one year after the oil spill. These first results of this most recent oil spill in Europe, raised the question of the relative importance of habitat-species and species interactions on the community structure.     

南极中山站地磁台的建设与观测研究

南极中山站于1991年3月建立临时地磁台，1992年2月建立正式地磁台，台上建有地磁观测室、记录室和各种探头室．它们均采用高架结构和用无磁性材料建成；能保温、防潮、防积雪和抗强风．1991～1993年分别安装有数字化地磁仪，地磁脉动仪，哨声与VLF仪和地震仪，并不断获得极区地磁与高空物理资料．1991年与1992年中山站地磁观测报告（第一卷与第二卷）已整理成册，资料分析表明，极区地磁扰动与中低纬区地磁扰动特征有很大差异，这些差异主要是由极区各种电流体系所造成．     

耀斑-激波的南-北非对称性传播

本文根据宇宙线Forbush下降幅度随源耀斑纬度分布的新近结果,采用无量纲化的MHD平面斜激波跃变条件,推算得到子午面内一种可能的耀斑-激波模型。发现耀斑-激波在太阳子午面内的传播相对耀斑法线方向是非对称的,激波面后的动力学参数与磁场具有截然相反的非对称性分布;激波传播的最快方向倾向日球电流片方向。该模型可以解释太阳耀斑-地磁、宇宙线效应中的南-北非对称性现象,有助于了解高速等离子体和非均匀背景场之间的相互作用过程。     

二维波状地形上的流场

在一个简化的二层模式中，求解大气波动方程，得到了二维波状起伏地形上扰动流线的分析解。研究了在上、下两层大气中，不同的温度廓线和风速廓线情况下，地形引起扰动的流场形式，同时讨论了支配扰动振幅的大气因子和地形特征。分析解的结果表明:若大气低层为深厚的不稳定层，地形引起的波动很微弱;如低层大气强稳定，上层大气弱稳定，则可能产生较强的波动;而当上层稳定度增加时，可产生非陷波，有利于高层动量下传，造成较大的地面风速。