基于FAI-L方法的巢湖水域藻华提取方法研究

近年来随着人类的活动日益加剧,水体富营养化问题已经严重威胁到湖泊生态安全。为了快速并准确地获取藻华爆发的范围,本文提出浮游藻类指数线性拟合模型（FAI linear fitting model, FAI-L）。在以往的研究中,NDVI(normalized difference vegetation index)已经广泛应用于藻华的识别中,且采用坡度计算获取NDVI阈值的方法也得到验证,相对于NDVI,FAI对环境条件的改变敏感度较低,且由于FAI增加了短红外波段,能够有效地降低部分大气和薄云的影响,对藻华的识别有较高的精度,但是FAI识别藻华的阈值如何确定的问题没有有效的解决办法。本文通过建立NDVI与FAI的线性拟合方程,利用NDVI阈值确定FAI阈值,能够有效地解决FAI阈值确定问题。通过Landsat8和Sentinel-2的提取结果显示：（1）FAI-L相对于NDVI提取结果在精度上有较大提升。采用该方法对于Landsat8影像的藻华提取精度为97.16%,相对于NDVI的提取精度（91.72%）提高了5.44%。（2）以Sentinel-2数据为基础探究FAI-L的适用性情...     

青藏高原水体碳源汇过程的重新认知与挑战

陆地-大气和陆地-水体的碳输送与碳交换共同决定了陆地生态系统的碳平衡,但长期以来青藏高原水体由于缺乏有效的观测数据,导致青藏高原水体一直是全球碳循环研究中被忽视的碳汇功能区。本研究聚焦青藏高原水体,重新认知水体碳侵蚀与碳沉积对青藏高原固碳的重要作用,系统分析河湖库-大气间的碳运移与交换时空格局与驱动机制。通过归纳总结发现:(1)青藏高原河流岩石风化速率以及CO₂消耗速率较高,强烈的侵蚀作用对地球系统吸收和平衡CO₂浓度起着重要的调控作用;(2)青藏高原湖泊是内陆生态系统的重要碳库,12 ka以来湖泊沉积物碳储量约为73 kg C/m²;(3)青藏高原湖泊浮游植物和水生植物影响内陆水体C沉积,年均初级生产力达(553±36) mg C/(m²·d)。(4)青藏高原湖泊目前为“碳源”,碳排放量约为2.27 Tg C/a。此外,本文还阐明青藏高原水体碳源汇过程评估的不确定性,以及从方法学角度分析如何加强其水体的碳循环研究,厘清全球变化下青藏高原水体的碳源汇机制,并展望了青藏高原水体碳源汇功能未来研究所面临...     

波场模拟有限差分参数优化选取

有限差分方法(Finite-difference Method, FD)广泛用于地震波场数值模拟, 但其存在固有的数值频散问题, 影响模拟的计算效率和数值精度.本文主要研究了有限差分方法的空间数值频散误差和网格划分精度以及差分算子的关系, 基于计算量最小准则, 提出了最优化有限差分参数选取流程, 为有限差分数值模拟参数选取提供理论指导.本文主要工作包括: (1) 提出了空间数值频散正变换过程(Forward Space Dispersion Transform, FSDT)方法, 该方法可以高效模拟出不同网格划分精度(波长采样点数)的带有空间数值频散的波场; (2) 提出了波场空间数值频散误差衡量准则, 可以定量地判断出数值模拟导致的波形频散程度, 选取合适的频散误差阈值; (3) 研究了给定空间数值频散误差阈值下, 差分算子系数、差分算子阶数、网格划分精度与计算量之间的关系.文中基于雷米兹交换方法(Remez Exchange Method, RE)和泰勒级数展开方法(Taylor-series Expansion Method, TE)的差分系数, 在空间数值频散误差阈值0.01时, 数值模拟了不同差分算子阶数、网格划分精度与计算量的关系, 并给出了有限差分参数选取的参考值.

     

随机方法模拟地震动的应用研究

对随机方法模拟地震动的实际应用进行了研究。通过实际模拟验证,此方法简单有效,可为结构抗震设计提供验算依据,同时为设计反应谱的拟合提供参照数据,有一定的实用性,但仍存在一定的不足。     

常熟地震台形变与流体数字观测资料报表打印软件

概述了常熟地震台形变与流体数字观测资料报表打印软件设计思路、使用功能及使用效果。     

Major-ion bulk deposition around an active volcano (Mt. Etna, Italy)

Bulk atmospheric deposition of major cations (Na, K, Ca, Mg) and anions (Cl, F, SO₄) were measured at 15 sites around an active volcano, Mount Etna, from 2001 to 2003. Their composition indicates several natural sources, among which deposition of plume-derived volcanogenic gas compounds is prevalent for F, Cl and S. Plume-derived acidic compounds are also responsible for the prevailing acidic composition of the samples collected on the summit of the volcano (pH in the 2.45–5.57 range). Cation species have complex origin, including deposition of plume volcanogenic ash and aerosols and soil-dust wind re-suspension of either volcanic or carbonate sedimentary rocks. Variation of the deposition rates during the March 2001–March 2003 period, coupled with previous measurements from 1997 to 2000 (Appl Geochem 16:985–1000, 2001), were compared with the variation of SO₂ flux, volcanic activity and rainfall. The deposition rate was mainly controlled by rainfall. Commonly, about 0.1–0.9% of HF, HCl and SO₂ emitted by the summit crater's plume were deposited around the volcano. We estimate that ∼2 Gg of volcanogenic sulphur were deposited over the Etnean area during the 2002–2003 flank eruption, at an average rate of ∼24 Mg day⁻¹ which is two orders of magnitude higher than that typical of quiescent degassing phases.     

Using Rock‐Eval 6 pyrolysis for tracking fossil organic carbon in modern environments: implications for the roles of erosion and weathering

This work relates to the debate on the fossil organic carbon (FOC) input in modern environments and its possible implication for the carbon cycle, and suggests the use of Rock‐Eval 6 pyrolysis as a relevant tool for tracking FOC in such environments. Considering that such a delivery is mainly due to supergene processes affecting the continental surface, we studied organic matter in different reservoirs such as bedrocks, alterites, soils and rivers in two experimental catchments at Draix (Alpes de Haute Provence, France). Samples were subjected to geochemical (Rock‐Eval 6 pyrolysis) investigations and artificial bacterial degradations. After comparing the geochemical fingerprint of samples, geochemical markers of FOC were defined and tracked in the different reservoirs. Our results confirm the contribution of FOC in modern soils and rivers and display the various influences of weathering and erosional processes on the fate of FOC during its exchange between these pools. In addition, the contrasting behaviour of these markers upon the supergene processes has also highlighted the refractory or labile characters of the fossil organic matter (FOM). Bedrock to river fluxes, controlled by gully erosion, are characterized by a qualitative and quantitative preservation of FOM. Bedrock to alterite fluxes, governed by chemical weathering, are characterized by FOC mineralization without qualitative changes in deeper alterites. Alterite to soils fluxes, controlled by (bio)chemical weathering, are characterized by strong FOC mineralization and qualitative changes of FOM. Thus weathering and erosional processes induce different FOM evolution and affect the fate of FOC towards the global carbon cycle. In this study, gully erosion would involve maintenance of an ancient sink for the global carbon cycle, while (bio)chemical processes provide a source of CO₂. Finally, this study suggests that Rock‐Eval 6 pyrolysis can be considered as a relevant tool for tracking FOC in modern environments. Copyright © 2006 John Wiley & Sons, Ltd.     

Sustainable Yield of a Hydrothermal Area: From Theoretical Concepts to the Practical Approach

Sustainable use of groundwater in the hydrothermal area of Viterbo (Central Italy) was analyzed. In this area, multipurposes utilization of groundwater coexists: several thermal springs and wells supply spas and public pools, cold and fresh water is used for irrigation and drinking-water. Starting from theoretical concepts, a management plan has been developed to ensure groundwater sustainability in response to the increased demand of withdrawal from thermal wells, by integrating previous hydrogeological studies, new investigations and a new finite-difference model. The most stringent constraints considered are: to maintain the quality of thermal and fresh waters, to limit the effects on the hydraulic equilibrium existing between overlapping aquifers, to ensure a significant flow to the natural thermal springs and the quality and flow rate of the spring used for drinking purposes. The practical approach included identification of the maximum pumping rate from the wells of the spas, analysis of the response time of the system under development and drafting of a safeguard and monitoring plan. The case examined takes into account the complexity of the task in defining practical measures for groundwater management on the basis of theoretical concepts of its sustainable use. A participative approach among the different water decision-makers and adaptive management in the use of groundwater resources with different quality represent the key points to overcome conflicts between different users, with the awareness of the ineludible uncertainties of the hydrogeological model.     

Physicochemical characterization of the microhabitat of the epibionts associated with Alvinella pompejana, a hydrothermal vent annelid

Alvinella pompejana is a polychaetous annelid that inhabits narrow tubes along the walls of high-temperature hydrothermal vent chimneys. The worm hosts a rich community of epibiotic bacteria that coats its dorsal surface. Although the worm tube microhabitat is a challenging environment to sample, characterizing the thermal and geochemical regime is important for understanding the ecology of the worm and its bacteria, as the worm spends most of its time inside the tube. We characterized the physicochemical conditions of diffuse hydrothermal flow inside inhabited worm tubes using in situ analysis and wet chemical analysis of discrete water samples. Thermistor probes deployed inside worm tubes measured temperatures ranging from 28.6°C to 84.0°C, while temperatures at tube orifices ranged from 7.5°C to 40.0°C. In situ electrochemical analysis of tube fluids revealed undetectable oxygen (<5 μM) and surprisingly low levels of free H₂S (<0.2 μM), with most of the sulfide existing as aqueous FeS molecular clusters. Acid-volatile sulfide measured on discrete samples of tube fluids ranged from 62.9 to 359.3 μM, while free sulfide (H₂S) ranged from undetectable (<0.2 μM) to 46.5 μM. The pH ranged from 5.33 to 6.40, and sulfate ranged from 22.5 mM to 27.5 mM. Nitrate ranged from 13.9 to 20.0 μM, whereas ammonium ranged from 2.5 to 9.7 μM. Total Fe ranged from 72.1 to 730.2 μM. Mn, Zn, Ni, V, P, and Cu were present in micromolar amounts; Pb, Cd, Co, and Ag were present in nanomolar levels. The worm tube fluids contained between 72% to 91% of Mg concentrations typically found in deep seawater. Plots of Mg concentrations vs. other fluid components showed that the tube fluid is geochemically altered from theoretical mixing values. Values of SO₄²⁻ were enriched inside the worm tube fluids, whereas NO₃⁻, Sr, Mn, Fe, Zn, and acid-volatile sulfide were depleted. The geochemistry of the tube microhabitat likely influences the structure of resident microbial communities.