沉水植物黑藻对上覆水中各形态磷浓度的影响

室内模拟研究了沉水植物黑藻对上覆水中不同形态磷浓度的影响及其季节性变化,并从沉水植物生长、间隙水和碱性磷酸酶活性(APA)三方面进行了讨论,进一步揭示磷在浅水湖泊水-沉积物界面的交换机理。结果表明,在本研究条件下,上覆水中各形态磷以溶解性总磷(DTP)为主,其他形态磷浓度变异较大,黑藻降低了上覆水中总磷(TP)、溶解性活性磷(SRP)和DTP浓度,也降低了DTP和SRP占总磷的比例,从而使颗粒态总磷(PP)和溶解性有机磷(DOP)占总磷比例升高。黑藻主要通过吸收上覆水中的磷和抑止沉积物、上覆水中APA使上覆水中各形态磷浓度保持较低水平,其中对SRP和DTP浓度的影响更明显。上覆水中各形态磷浓度呈现明显的季节性变化。在7～8月,TP、SRP和DTP浓度呈下降趋势,并在8月达到最低值;9～10月间有所升高,但仍然维持在较低水平,不同采样时间存在波动。     

中国太阳能热发电站选址模型研究

太阳能热发电技术在我国新世纪能源战略中具有重要地位,太阳能热发电电站位置的合理选择对发电成本有直接影响,涉及到太阳能热发电技术本身、高时空分辨率的太阳能法直辐射分布、土地利用分布、水资源分布、社会经济分布,以及政策税收等众多因素。本文提出了一个太阳能热发电站选址的决策支持系统框架,就其中的太阳能直法辐射调查进行了初步试验。本文依据供需时空平衡原则进一步讨论了多种绿色能源互补的大能源系统运筹问题。     

Effects of Enclosure on Plant and Soil Nutrients in Different Types of Alpine Grassland

Enclosure is one of the most widely used management tools for degraded alpine grassland on the northern Tibetan Plateau, but the responses of different types of grassland to enclosure may vary, and research on these responses can provide a scientific basis for improving ecological conservation. This study took one site for each of three grassland types (alpine meadow, alpine steppe and alpine desert) on the northern Tibetan Plateau as examples, and explored the effects of enclosure on plant and soil nutrients by comparing differences in plant community biomass, leaf-soil nutrient content and their stoichiometry between samples from inside and outside the fence. The results showed that enclosure can significantly increase all aboveground biomass in these three grassland types, but it only increased the 10-20 cm underground biomass in the alpine desert. Enclosure also significantly increased the leaf nutrient content of the dominant plants and contents of total nitrogen (N), total potassium (K), and organic carbon (C) in 10-20 cm soil in alpine desert, thus changing the stoichiometry between C, N and P (phosphorus). However, enclosure significantly increased only the N content of dominant plant leaves in alpine steppe, while other nutrients and stoichiometries of both plant leaves and soil did not show significant differences in alpine meadow and alpine steppe. These results suggested that enclosure has differential effects on these three types of alpine grasslands on the northern Tibetan Plateau, and the alpine desert showed the most active ecological conservation in the responses of its soil and plant nutrients.     

天山南麓山前平原土壤盐分空间异质性对植物群落组成及结构的影响

将轮台天山南麓山前平原中下部自北至南分为4个地貌带:洪水剥蚀带、溢出带、三角洲带及两河交汇区带。并以土壤电导作为积盐程度的指标,分析了天山南麓山前平原4个地貌带土壤盐的分布特征:溢出带和三角洲带土壤盐分含量高,两端洪水剥蚀带和两河交汇区带盐分含量低。物种多样性及物种组成分析结果表明,自北至南物种多样性及物种数量都在下降,洪水剥蚀带主要为柽柳群落、琵琶柴群落,溢出带主要为柽柳群落、盐节木群落、盐角草群落,三角洲带及两河交汇区均为柽柳群落。通过相关性分析,土壤盐分与群落物种多样性相关性不显著。但是,土壤盐渍化的变化明显影响到植物群落物种组成的变化、群落类型的空间分布和演替。     

激光跟踪仪在核电站主管道安装中的应用

目前,核电站的主管道焊接越来越多的采用了自动焊技术,这有利于提高焊接质量效率,还可以压缩建设成本。然而,主管道自动焊对焊缝的限差较现有工艺要求更高,高精度的测量是实现主管道自动焊的必要条件之一。本文针对主管道自动焊管口组队高精度的技术要求,提出采用激光跟踪仪对主管道自动焊相关的设备进行更为精密的三维工业测量,通过理论技术评定测量精度,然后选择测量仪器和编制具体的测量方案,最终保证了主管道自动焊精确组对的实现。     

潜艇指挥台围壳对阻力和伴流场影响数值研究

采用Reynolds平均Navier-Stokes(RANS)方法计算潜艇三维粘性流场,分析潜艇指挥台围壳对潜艇水动力性能的影响.采用全附体SUBOFF模型验证了CFD方法,通过将螺旋桨盘面处的实效伴流场、艇体表面压力分布以及模型总阻力的模拟结果与Taylor船池的实验结果进行对比.比较结果显示CFD计算结果与实验数据具有很好的一致性,表明CFD方法可以用于潜艇指挥台围壳设计的水动力计算.通过数值计算研究指挥台围壳的高度和在艇上的分布位置对其后方的流场、螺旋桨盘面处的伴流场和阻力的影响.     

淹没植物对河道糙率的影响

基于河道水动力及植物柔性变形分析,建立淹没状态下的植物河道糙率计算的理论关系,同时,利用试验资料及理论分析成果,进一步获得了植物河道糙率的附加值,借此可以分析与评价河道植物对水流阻力的影响程度.     

大型沉水植物狐尾藻不同盖度的光谱特征

地物特征与其光谱特征的关系是解译遥感影像的关键。本研究利用ASD便携式地物光谱仪对上海崇明国际湿地公园人工湖中的沉水植物狐尾藻的反射光谱进行了初步研究。结果表明,随狐尾藻盖度的增加,其光谱反射率、一阶和二阶导数红边斜率的峰值也相应增加,不同盖度狐尾藻的光谱反射率的差异主要表现在500—650nm和700—900nm波段范围。分别对狐尾藻盖度与这些波段的光谱反射率及根据一阶和二阶导数获得的光谱指数进行回归分析,得到了较好的线性关系。应用回归分析得到的线性方程,可以根据测定的光谱反射率定量反演水体中的狐尾藻盖度。研究结果可为监测大型沉水植物的高光谱遥感影像解译和分类提供技术支撑,为大尺度遥感监测沉水植物的分布和动态变化提供科学依据。     

Holocone paleovegetation and paleohydrology of a prairie pothold in southern Saskatchewan, Canada

The Andrews site represents one of countless prairie potholes found in areas of hummocky moraine on the northern Great Plains. Sediments from a depth of 5.8 to 3.1 m at this 'kettle-fill' site in the Missouri Coteau upland of southern Saskatchewan, Canada, provides a record of vegetation, climate, and hydrologic changes within a small, ca 30 m diameter, closed-drainage basin from ca 10.2 to 5.8 ka. Plant macrofossil analyses of 67 samples, 6 ¹⁴C ages, and stratigraphy were used to identify 5 zones, representing the paleohydrological changes that followed deglaciation in southern Saskatchewan.Results of this study indicate that with the melting of residual stagnant ice a pond (>2 m deep) with abundant aquatic, emergent, and shoreline plants developed in the basin at ca 10.2 ka and persisted until at least ca 8.8 ka. During this time there was a shift in upland vegetation from a white spruce forest (Zone II) to a deciduous parkland at ca 10 ka (Zone III). As climate warmed, brackish and alkaline conditions developed coincident with shallowing of the pond at the end of Zone III. The perennial water phase ended at ca 8.8 ka and was followed by a low-water stand lasting ca 1100 years. Prairie fires and slopewash from unstable slopes were dominant sedimentological processes until ca 7.7 ka (Zone IV). Water levels began to rise and between ca 7.7 and 5.8 ka a semi-permanent pond was established in a grassland setting (Zone V). After ca 5.8 ka this prairie pothole wetland became ephemeral, to the point that plant macrofossils could not be preserved, a situation continuing today. Interactions between climate change, variability in local groundwater supply, and sedimentological processes likely account for the paleohydrologic events reconstructed at the Andrews site.