Right whales and vessels in Canadian waters     

S.S. Elvin  C.T. Taggart 《Marine Policy》2008

The North Atlantic right whale (Eubalaena glacialis) is the most critically endangered large cetacean and is threatened by vessels that travel in their habitats and migration paths. A need to address the endangered population status of the right whale emerges as current management mandates have proven ineffective at preventing vessel-strikes to right whales and current rates of strike-induced mortality can slow or prevent recovery of the species. This paper identifies the need for an internationally acceptable management strategy to minimize vessel-strikes to right whales in Canadian waters.  相似文献   

A model of turbidity maximum maintenance in the Irish Sea   总被引：1，自引：0，他引：1  

K.M. Ellis  C.E. Binding  D.G. Bowers  S.E. Jones  J.H. Simpson 《Estuarine, Coastal and Shelf Science》2008,76(4):765-774

A two-dimensional model has been developed in order to improve understanding of the processes which interact to maintain the sediment concentrations at an isolated turbidity maximum in the Irish Sea throughout the year. The model comprises two interchangeable populations of particles with different diameters, one of fine cohesive material, the other made up of flocs. Both populations are slow settling, and subject to horizontal diffusion, resuspension, settling, aggregation and disaggregation.The equations used to describe the processes of aggregation and the break-up of flocs in response to sediment concentration and turbulent shear have been developed by the tuning of the model to observations. Due to high turbulent shear at the turbidity maximum, the particles are predominantly fine, while the sediment in the surrounding water is made up of larger flocs. Diffusion of small particles out of the turbidity maximum balanced by the diffusion of aggregated material towards it provides a mechanism for its maintenance. The modelled sediment concentrations at the turbidity maximum can be reproduced year-on-year, with no loss due to diffusive processes. This is achievable with a limited, exhaustible source of material which is not replenished once resuspended.Through comparison with satellite imagery the correlation of the modelled sediment concentrations with observations is investigated, both spatially and temporally. The seasonal cycle is reproduced well by the model with winter and summer concentrations matching those observed. Spatially the model also performs well in both turbid regions and those where the surface sediment load is low.  相似文献   

The missing layer: Geo-technologies, communities, and implications for marine spatial planning   总被引：6，自引：3，他引：3  

Kevin St. Martin  Madeleine Hall-Arber   《Marine Policy》2008,32(5):779

The assessment and management of marine resources is an increasingly spatial affair dependent upon emerging geo-technologies, such as geographic information systems, and the subsequent production of diverse layers of spatial information. These rapid developments are, however, focused on biophysical processes and data collection initiatives; the social landscape of the marine environment is undocumented and remains a “missing layer” in decision-making. As a result, the resource areas upon which stakeholders and communities are dependent are neither mapped nor integrated into planning processes. We report on a participatory method to map the presence of fishing communities at-sea. The lessons learned concerning the spatial representation of communities informs not only fisheries, but other sectors struggling to incorporate similarly the human dimensions of the marine environment in assessment and planning.  相似文献   

基于拉格朗日方法的洪泽湖与巢湖河流出入湖水体追踪计算     

彭兆亮  陈昌仁  万骏  吴晓兵  张怡辉  胡维平  崔健 《海洋与湖沼》2020,51(6):1275-1287

利用耦合北斗和GPS双定位系统的拉格朗日随体法水质点追踪仪，在2018年9月至2019年10月期间开展了总数为18次的洪泽湖和巢湖主要河流河水入湖后表层、中层和底层水体运移同步追踪观测，研究了两个湖泊河水入湖后的运移轨迹和速度特征。结果表明：淮河主河道河水入洪泽湖后流向南北两侧；徐洪河河口处水体表层流速在洪泽湖5条河道出入湖口处为最大；巢湖双桥河河口处水体流速受巢湖闸运行影响强烈，各层流速在7条入湖河流中最大。洪泽湖、巢湖入湖水体流速由表层至底层逐渐降低，洪泽湖各层水体流速大于巢湖。洪泽湖河口处表层水体8次测量平均流速为6.11cm/s；巢湖为5.51cm/s；二者中层流速分别为5.32和3.85cm/s；底层则分别为4.96和3.67cm/s。  相似文献   

Effects of the undecomposed layer and semi-decomposed layer of Quercus variabilis litter on the soil erosion process and the eroded sediment particle size distribution     

Xiaona Liu  Guodong Jia  Xinxiao Yu 《水文研究》2021,35(5):e14195

Simulated rainfall experiments were performed on bare, undecomposed litter layer and semi-decomposed litter layer slopes with litter biomasses of 0, 50, 100 and 150 g m⁻², respectively, to evaluate the effect of the undecomposed layer and semi-decomposed layer of Quercus variabilis litter on the soil erosion process and the particle size distribution of eroded sediment. The undecomposed layer and semi-decomposed layer of litter reduced the runoff rate by 10.91–27.04% and 12.91–36.05%, respectively, and the erosion rate by 13.35–40.98% and 17.16–59.46%, respectively. The percentage of smaller particles (clay and fine silt particles) decreased and the percentage of larger particles (coarse silt and sand particles) increased with an increased rainfall duration on all treated slopes, while the extent of the eroded sediment particle content varied among the treated slopes with the rainfall duration, with bare slopes exhibiting the largest variability, followed by undecomposed litter layer slopes and finally semi-decomposed litter layer slopes. The clay and sand particles were transported as aggregates, and fine silt and coarse silt particles were transported as primary particles. Compared with the original soil, sediment eroded from all treated slopes was mainly enriched in smaller particles. Furthermore, the loss of the smaller particles from the undecomposed litter layer slopes was lower than that from the semi-decomposed litter layer slopes, indicating that the undecomposed litter layer alleviated soil coarsening to some extent. The findings from this study improve our understanding of how litter regulates slope erosion and provide a reference for effectively controlling soil erosion.  相似文献   

Numerical simulation of particle plugging in hydraulic fracture by element partition method     

Yujie Wang  Xinyong Li  Bing Zhao  Zhennan Zhang 《国际地质力学数值与分析法杂志》2020,44(14):1857-1879

Hydraulic fracturing (HF) treatment often involves particle migration and is applied for propping or plugging fractures. Particle migration behaviors, e.g., bridging, packing, and plugging, significantly affect the HF process. Hence, it is crucial to effectively simulate particle migration. In this study, a new numerical approach is developed based on a coupled element partition method (EPM). The EPM is used to model natural and hydraulic fractures, in which a fracture is allowed to propagate across an element, thereby avoiding remeshing in fracture simulations. To characterize the water flow process in a fracture, a fully hydromechanical coupled equation is adopted in the EPM. To model particle transportation in fractures with water flow, each particle is treated as a discrete element. The particles move in the fracture as a result of being dragged by fluid. Their movement, contact, and packing behaviors are simulated using the discrete element method. To reflect the plugging effect, an equivalent aperture approach is proposed. Using this method, the particle migration and its effect on water flow are well simulated. The simulation results show that this method can effectively reproduce particle bridging, plugging, and unblocking in a hydraulic fracture. Furthermore, it is demonstrated that particle plugging significantly affects water flow in a fracture and hence the propagation of hydraulic fracture. This method provides a simple and feasible approach for the simulation of particle migration in a hydraulic fracture.  相似文献   

Evaluation of high-flow rate continuous-flow centrifugation and filtration devices for sampling and concentrating fine-grained suspended sediment     

Masoud Goharrokhi  David A. Lobb  Philip N. Owens 《水文研究》2020,34(19):3882-3893

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中国和葡萄牙海洋科技合作实践          下载免费PDF全文

洪丽莎  毛洋洋  曾江宁 《海洋开发与管理》2020,37(5):10-13

中葡海洋合作是构建人类命运共同体和海洋共同体的重要实践。为了更好地推动中葡两国的合作，文章以中葡双方海洋科技合作为视角，分析了两国间开展合作的优势及合作现状，并提出了建立中葡海洋科技交流机制性平台、推动建立中葡联合海洋研究中心、积极推进中葡海洋科技项目务实合作等建议，期望对今后中葡海洋领域深入合作提供参考。  相似文献   

基于粒子群算法优化的BP神经网络在海水水质评价中的应用     

李海涛  王博睿 《海洋科学》2020,44(6):31-36

针对目前存在的海水水质受多因素影响、评价难的现状，提出了一种基于粒子群算法（PSO）优化误差反向传播（BP）神经网络的海水水质评价模型。该模型通过PSO得到BP神经网络最优的权值和阈值，结合青岛东部海域10个监测站点的数据得到水质评价结果。实验证明，该模型和单因子评价、传统的BP神经网络评价相比较，具有训练时间短、预测精度高的特点，在海水水质评价中具有良好的应用价值。  相似文献   

戈壁沙砾质地表沉积物全粒径分布模式及其对分选作用的指示意义     

熊鑫  王海兵  肖建华  左合君 《中国沙漠》2019,39(2):202-208

戈壁地表沉积物组分呈多峰态分布的特征，研究其全粒径分布模式是认识戈壁成因及形成过程的基础。目前粒度分布模式（对数正态分布、Weibull分布等）难以正确表达呈多峰态的沉积物粒度分布特征，本文利用单调递减函数P（d_i）=Cd_i^-μexp（-d_i/Dc），对戈壁地表沉积物粒度的全粒径分布模式进行解析。结果表明：（1）该函数能够反映出戈壁地表沉积物组分的全粒径分布特征，拟合优度R²>0.99，参数C值范围为52.64~166.75，μ为-0.083~0.108，Dc为0.103~2.336；（2）在分选作用下，以富沙组分为主的戈壁地表，跃移组分含量高，μ值、Dc值偏小，以富砾组分为主的戈壁地表，蠕移及风蚀残余组分含量高，μ值、Dc值偏大；（3）全粒径分布模式参数值可以揭示洪积扇戈壁的分选沉积特征，为解析戈壁地表的成因以及风蚀风积作用提供新的指标参数。  相似文献