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31.
From pollen percentage to vegetation cover: evaluation of the Landscape Reconstruction Algorithm in western Norway 总被引:1,自引:0,他引:1 下载免费PDF全文
KARI LOE HJELLE INGVILD KRISTINE MEHL SHINYA SUGITA GIDSKE LEKNÆS ANDERSEN 《第四纪科学杂志》2015,30(4):312-324
The Landscape Reconstruction Algorithm (LRA) with the two models REVEALS and LOVE is developed to transform pollen percentage data to vegetation cover. This paper presents the first study to evaluate LRA in a region with large topographic variations within a short distances. The REVEALS model estimates regional vegetation abundance based on pollen assemblages from large lakes (100–500 ha). Pollen surface samples from one large and 28 small lakes are used together with a combination of regionally derived pollen productivity estimates and available estimates from other regions of Europe. The results show a good relationship between REVEALS‐estimated forest cover and vegetation abundance based on the CORINE land‐cover data. The REVEALS results using various sets of pollen assemblages from small lakes were comparable to those using one large lake. Local vegetation abundance using the LOVE model was estimated around 26 lakes. For common taxa, such as Pinus and Poaceae, the LOVE‐based estimates of plant abundance match well with the distance‐weighted plant abundances based on vegetation maps. Our results indicate that the LRA approach is effective for reconstruction of long‐term vegetation changes in western Norway and other regions with high topographic relief when no major gradients exist in the pollen data. 相似文献
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Lan Chen Chen Jing an Zeng Yan Guo Jianyang Zhang Runyu Wang Jingfu Yang Haiquan Ji Yongxue 《地球科学进展》2015,30(10):1172-1181
Deep lakes always maintain vertical thermal stratification due to their physical structure. The thermocline prevents the transfer of oxygen from epilimnion to hypolimnion, leading to the formation of anoxic conditions in deeper water, the enhanced release of endogenous pollutants and the deterioration of water quality. Oxygenation is an effective measure to improve the water quality of deep lakes and mitigate the release of endogenous pollutants via the increase of the oxygen level in water. This paper provided an overview of the method and theory of oxygenation in deep lakes. Advantages and limitations of different methods of oxygenation, including artificial destratification, airlift aerators, Speece cone and bubble plume diffusers, were discussed. In addition, challenges and prospects of oxygenation were assessed based on the analyzing of typical examples of oxygenation in deep lakes and the difference in oxygenation system used in deep lakes and shallow lakes. 相似文献
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运用时间序列的沉积物捕获器对海岸与陆架海域沉降颗粒物进行采集,估算沉降通量,并运用多学科综合研究手段分析沉降颗粒物的来源、组成、时空变化及控制因素,可以为海岸与陆架沉积动力过程的研究提供新的研究手段。福建罗源湾的实验表明,夏季罗源湾潮下带小潮至中潮期间的沉降通量为133.20~256.18g/(m2·t);由中潮向大潮变化期间单个潮周期的沉降通量明显增大,台风过后的大潮期间的沉降通量为373.99~590.51g/(m2·t);台风显著影响期间的沉降通量为746.34g/(m2·t);粒度分析及水动力观测结果显示,观测期间罗源湾潮下带沉降颗粒物主要来源于海底沉积物的再悬浮。台湾海峡西北部内陆架海域的实验研究表明,该海域近底部悬浮颗粒物沉降通量最大值为13.34g/(m2·d),由小潮向中潮沉降通量逐渐增大,这主要是由于近底部温盐跃层层位上移,近底部垂向混合作用增强,致使底部再悬浮沉积物向上扩散,并最终被沉积物捕获器捕获。沉积物捕获器可以接收到再悬浮沉积物,结合底部边界层过程的观测研究,可以深入认识海底沉积物的侵蚀、沉降及埋藏过程,在研究海岸与陆架区沉积动力学、泥质区沉积记录的形成过程与保存潜力中扮演着十分重要的角色。 相似文献
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手持GPS定位精度与误差的研究 总被引:2,自引:0,他引:2
分别探讨在绝对定位和相对定位两种模式下手持式GPS定位的稳定性,得出合理的观测时间长。通过不同时长的观测数据的对比分析给出:实时定位与长时间定位观测值之差在1m之内。手持GPS绝对定位的准确度即测量的结果与其真实位置符合程度非常高,能够控制在亚米级的范围之内。在卫星个数较多的情况下,实时定位的精度也能控制在亚米级的范围之内。利用单点定位系统误差改正模型,消除或减弱某些误差后能得到更高的精度,使得单点定位精度达到半米之内甚至更高。 相似文献
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The relative abundance of the different picoplankton components (eukaryotic picophytoplankton (Peuk), picocyanobacteria (Pcy) and bacterioplankton), and their relationships with the lake conditions were studied in three types of shallow lakes from the Pampa Plain (Argentina) that differ in their optical properties: clear-vegetated, phytoplankton-turbid and inorganic-turbid. All the selected lakes, but one, are characterized by their different alternative steady state (clear-vegetated and phytoplankton-turbid water phases) following the model proposed by Scheffer et al. (1993).Autotrophic and heterotrophic picoplankton abundances were analyzed seasonally in relation to environmental variables. All the lakes presented high concentrations of total nitrogen (TN) (>229 μg L−1), total phosphorus (TP) (>46 μg L−1) and dissolved organic carbon (DOC) (>13.7 mg L−1). Clear-vegetated lakes were characterized by vertical diffuse PAR (photosynthetic active radiation) attenuation coefficient (kdPAR) lower than 11 m−1, whereas inorganic-turbid lake always showed values higher than 21.1 m−1. The euphotic zone depth (Z1%) was wider in clear-vegetated lakes (40–140 cm) and thinner in the inorganic-turbid (10–20 cm). The phytoplankton-turbid lakes presented a wide range in the values of these variables (kdPAR: 5.2–35.8 m−1; Z1%: 10–90 cm). Phytoplankton chlorophyll-a (Chl-a) strongly differed, ranging from 1.6 to 334.6 μg L−1. Picophytoplankton was mainly represented by phycocianine-rich (PC-rich) Pcy in all cases, dominating over Peuk algae. The total and relative abundances of eukaryotic picophytoplankton, Pcy and bacterioplankton, as well as the size structure of the phytoplankton community differed among the water bodies. In general, clear-vegetated water bodies exhibited similar abiotic characteristics, picophytoplankton/bacterioplankton ratios, and phytoplankton size structure. Contrarily, no clear trend was identified for the group of turbid lakes. The contrasting results obtained for the importance of the picoplankton components in phytoplankton-turbid shallow lakes evidence that the availability of the energetical and nutrient resources cannot be solely considered to predict their relative importance in this type of shallow lake. 相似文献
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