Application of an ecosystem model for the environmental assessment of the reclamation and mitigation plans for seagrass beds in Atsumi Bay   总被引：1，自引：0，他引：1  

Akio Sohma  Yasuyuki Sekiguchi  Kisaburo Nakata 《Estuarine, Coastal and Shelf Science》2009

An ecosystem model was used to evaluate the effects of reclaiming seagrass beds and creating artificial shallows with seagrass beds to mitigate the effects of the reclamation. The applied model can simulate the pelagic and benthic ecosystems including seagrass beds and tidal flats. The objectives of this study were (a) to investigate the likelihood of cultivating and maintaining seagrass beds in artificial shallows (Part 1), and (b) to understand the effects of the reclamation of seagrass beds and the creation of artificial shallows on the water quality in the estuary (Part 2). In Part 1, first, the nutrient turnover rates due to both biochemical and physical processes in the natural seagrass beds where reclamation is proposed were analyzed. Biological processes rather than physical processes were the most significant driving forces of nutrient cycles in seagrass beds. Second, the effects of filter feeding benthic fauna (suspension feeders) in the seagrass beds were analyzed. The scenario with suspension feeders resulted in higher transparency of the water column (8.7% decrease in the light attenuation coefficient) and an increase in nutrient supply (24.9% increase in NH₄-N in the water column) contributing to the high specific growth rate of seagrass. Third, the specific growth rate of seagrass on the proposed artificial shallows was measured. The value on the artificial shallows set at a depth of datum line minus 0.8 m (D.L. − 0.8 m) was approximately the same as that of the natural seagrass beds. In Part 2, first, water quality in the estuary was compared among the scenarios with/without natural seagrass beds and artificial shallows. Then, the defined values of the water purification capability of (a) artificial shallows with/without seagrass beds, and (b) natural seagrass beds per unit area were evaluated. The reclamation of the natural seagrass beds resulted in a decrease of the removal of phytoplankton and detritus from the pelagic system (i.e. resulted in a loss in the purification rate). In contrast, the creation of artificial shallows resulted in an increase of the removal of phytoplankton and detritus from the pelagic system (i.e. resulted in a gain in the purification rate). Based on an annual average, approximately twice as much phytoplankton was removed from the artificial shallows at the depth D.L. − 0.8 m, than at the depth, D.L. − 1.5 m, and the artificial shallows with seagrass beds removed pelagic DIN and DIP at a rate 120% higher than that without seagrass beds.  相似文献   

多模式控制在关联系统中的应用研究     

陈昌忠  谭飞  王帮容 《成都信息工程学院学报》2009,24(5):466-469

根据多模式控制器的设计理论,以偏差分段为基础,将控制过程分为几个阶段,用不同的模式加以控制,用加速储能控制来解决响应快速性的要求;用快速放能控制来解决响应平稳性要求;用稳态能量控制来解决系统的准确性要求。把控制模式用于双输入双输出关联系统的解耦系统中进行了仿真研究,与常规控制方法做了比较,多模式控制在关联系统中具有良好的动态响应性能。  相似文献   

人地系统耦合下生态系统服务与人类福祉关系研究进展与展望   总被引：3，自引：1，他引：2  

邱坚坚  刘毅华  袁利  陈澄静  黄清瑶 《地理科学进展》2021,40(6):1060-1072

21世纪以来生态系统服务退化与人类需求提升间的矛盾愈发激烈,如何有效推进生态系统服务与人类福祉的协调平衡成为当前可持续发展的核心主题.论文通过梳理生态系统服务与人类福祉关系研究的阶段演进发现,现有研究主要从服务对福祉的影响与福祉对服务的反馈切人,逐步聚焦到供需关系与空间流动、权衡/协同的利益博弈、文化服务的价值化、生态...  相似文献   

若尔盖与西秦岭地震反射岩石圈结构和盆山耦合   总被引：10，自引：0，他引：10       下载免费PDF全文

王海燕  高锐  马永生  朱铉  李秋生  匡朝阳  李朋武  卢占武 《地球物理学报》2007,50(2):472-481

松潘地块北缘的若尔盖盆地与西秦岭造山带相接触,构成青藏高原东北缘典型的新生代盆山构造.其岩石圈结构与深部构造关系,记录了青藏高原东北缘板块碰撞的深部过程,同时又关联着若尔盖盆地油气远景的评价.2004年秋冬季,我们完成了第一条跨越若尔盖盆地和西秦岭造山带的深地震反射剖面.整个剖面全长254 km,分5段完成,其中第2段剖面（简称SP04_2）横过盆山结合部位.SP04_2剖面首次揭示若尔盖盆地－西秦岭造山带盆山结合部位的岩石圈结构,发现了若尔盖盆地和西秦岭造山带下地壳均以北倾为主的强反射特征,提供出若尔盖盆地下地壳整体向西秦岭造山带俯冲的地震学证据,揭示了若尔盖盆地和西秦岭造山带在挤压构造体系下形成的深部构造关系.而近于平的Moho反射特征又反映出两者在造山后期经历了强烈的伸展作用.  相似文献   

沟谷型沙漠泥流堆积体起动过程中的孔压变化特性     

王之君  何瑶龄  周兆书 《中国沙漠》2022,42(5):212-220

以黄河上游宁蒙段典型风水复合侵蚀流域为研究区域,重点针对堆积体堵塞沟道极端条件下的沟谷型沙漠泥流,从堆积体起动成灾的环节入手,开展直槽概化模型试验,并采用基于有效应力原理的流固耦合模型,概化模拟上游暴雨洪水入渗条件下堆积体内孔隙水压力变化特性及其起动过程,从微观角度揭示其成灾机理。结果表明：堆积体起动过程中孔隙水压力与时间呈指数为0.5的幂函数关系;流固耦合作用下堆积体内经历了应力场→体积应变→孔隙率→孔隙水压力→渗流场→塑性应变→屈服破坏的复杂非线性变化过程。  相似文献   

Consolidation in spatially random unsaturated soils based on coupled flow‐deformation simulation          下载免费PDF全文

Y. Cheng  L.L. Zhang  J.H. Li  L.M. Zhang  J.H. Wang  D.Y. Wang 《国际地质力学数值与分析法杂志》2017,41(5):682-706

This paper integrates random field simulation of soil spatial variability with numerical modeling of coupled flow and deformation to investigate consolidation in spatially random unsaturated soil. The spatial variability of soil properties is simulated using the covariance matrix decomposition method. The random soil properties are imported into an interactive multiphysics software COMSOL to solve the governing partial differential equations. The effects of the spatial variability of Young's modulus and saturated permeability together with unsaturated hydraulic parameters on the dissipation of excess pore water pressure and settlement are investigated using an example of consolidation in a saturated‐unsaturated soil column because of loading. It is found that the surface settlement and the pore water pressure profile during the process of consolidation are significantly affected by the spatially varying Young's modulus. The mean value of the settlement of the spatially random soil is more than 100% greater than that of the deterministic case, and the surface settlement is subject to large uncertainty, which implies that consolidation settlement is difficult to predict accurately based on the conventional deterministic approach. The uncertainty of the settlement increases with the scale of fluctuation because of the averaging effect of spatial variability. The effects of spatial variability of saturated permeability k_sat and air entry parameters are much less significant than that of elastic modulus. The spatial variability of air entry value parameters affects the uncertainties of settlement and excess pore pressure mostly in the unsaturated zone. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Polar regionSq     

Wen-Yao Xu 《Pure and Applied Geophysics》1989,131(3):371-393

Geomagnetically quiet day variations in the polar region are reviewed with respect to geomagnetic field variation, ionospheric plasma convection, electric field and current. Persistently existing field-aligned currents are the main source of the polar regionSq. Consequently, the morphology and variability of the polar regionSq largely depend upon both field-aligned currents and ionospheric conductivity. Since field-aligned currents are the major linkage between the ionosphere and the magnetosphere, the latter is controlled by solar wind state, in particular, the interplanetary magnetic field, the polar regionSq exhibits remarkable IMF dependence.  相似文献   

An unusual zone of seismic coupling in the Bonin arc: The 1972 Hachijo-Oki earthquakes and related seismicity     

Tetsuji Moriyama  Fumiko Tajima  Tetsuzo Seno 《Pure and Applied Geophysics》1989,129(1-2):233-261

The 1972 February and December Hachijo-Oki earthquakes (M _s=7.3 and 7.4), in the northernmost part of the Izu-Bonin subduction zone, are the only major events (M _s>7.0) in the Bonin arc for the past 80 years. Relocation of the hypocenters, using one smaller event having a wellconstrained focal depth as a master event, shows that the depth of the February event is 10 km shallower than that of the December event. We have determined the rupture process for both events by minimizing the error in waveform between observed and synthetic seismograms. Although the number of available stations are limited, the depth range of the major energy release for the December event extends deeper than for the February one. The rupture propagated up-dip for both events. It is likely that the rupture zone of the two events overlapped, and that the December event ruptured the deeper part. This suggestion is consistent with the observation that the aftershock zones of both events overlap with that of the December event shifted landward. The waveforms of the December event have a smaller high frequency component than those of the February event, suggesting that the stress at the thrust zone became more uniform or reduced after the February event.No thrust type smaller event occurred near the rupture zone. Instead, theP-axes of smaller events are parallel to the dip of the slab and theirT-axes dip to the southwest. Focal depths of these events estimated byP-wave forward modeling are generally between 40–50 km and located beneath the thrust zone. We thus interpret them as the events within the Pacific slab near the zone ruptured by the two major events. The stress concentration around the rupture zone of the major events is suggested to have triggered these slab events. After the occurrence of the large events, the slab events are concentrated near the deeper portion of the rupture zone. These events may have been caused by the loading of the down-dip compressional stress near the down-dip end of the rupture zone due to the rupture. The occurrence of the doublet of large earthquakes and a number of down-dip compressional events beneath their rupture zones in a shallow portion of the subducting slab indicates an unusual zone of seismic coupling in the Bonin arc, most of which is seismically quiescent.  相似文献   

Subduction and back-arc activity at the Hikurangi convergent Margin,New Zealand     

Euan G. C. Smith  Tim Stern  Martin Reyners 《Pure and Applied Geophysics》1989,129(1-2):203-231

The Hikurangi Margin is a region of oblique subduction with northwest-dipping intermediate depth seismicity extending southwest from the Kermadec system to about 42°S. The current episode of subduction is at least 16–20 Ma old. The plate convergence rate varies along the margin from about 60 mm/a at the south end of the Kermadec Trench to about 45 mm/a at 42°S. The age of the Pacific lithosphere adjacent to the Hikurangi Trench is not known.The margin divides at about latitude 39°S into two quite dissimilar parts. The northern part has experienced andesitic volcanism for about 18 Ma, and back-arc extension in the last 4 Ma that has produced a back-arc basin onshore with high heaflow, thin crust and low upper-mantle seismic velocities. The extension appears to have arisen from a seawards migration of the Hikurangi Trench north of 39°S. Here the plate interface is thought to be currently uncoupled, as geodetic data indicate extension of the fore-arc basin, and historic earthquakes have not exceededM _s=7.South of 39°S there is no volcanism and a back-arc basin has been produced by downward flexure of the lithosphere due to strong coupling with the subducting plate. Heatflow in the basin is normal. Evidence for strong coupling comes from historic earthquakes of up to aboutM _s=8 and high rates of uplift on the southeast coast of the North Island.The reason for this division of the margin is not known but may be related to an inferred increase, from northeast to southwest, in the buoyancy of the Pacific lithosphere.  相似文献   

Development of the ultrasonic measurement technique and its application in the observation of rock mass stability     

Yonglian Sun  Shiliang Lu  Chuliang Zhou 《Geotechnical and Geological Engineering》1993,11(4):273-284

Summary A method of measuring ultrasonic wave properties in rocks during the complete stress-strain process is described. The relevant experimental laboratory study, to reveal the change of the amplitude spectrum parameters with strain (or stress) has been carried out. A preliminary study was conducted on the application of the ultrasonic measurement technique at a belt conveyor roadway of the north wing in Baodian coal mine, Shandong province. A borehole ultrasonic device with dry coupling was developed to provide better coupling and more accurate measurement data in comparison with those of a water coupled situation. Based on the interrelations between the complete stress-strain properties of specimens and their wave properties, the structural properties of surrounding rocks, the range of yield zones, and the change of stresses within the rocks surrounding a roadway which was subjected to mining influence of upper longwall face were analysed. Amplitude spectrum parameters were used to give a better prediction of the physico-mechanical state of the surrounding rocks.  相似文献