海水养殖业资源与环境的可持续发展     

宁修仁  刘诚刚  郝锵  乐凤凤 《海洋学研究》2007,25(3):75-83

概述了我国海水养殖业在快速发展过程中由于出现养殖产业规划滞后和养殖生态环境恶化而带来的若干问题。简要介绍"浙江省重点养殖海湾养殖生态和养殖容量研究"的立项背景和研究目的,鱼类、贝类和大型藻类的养殖容量研究方法以及相关的主要研究成果,展示了近海养殖生态和养殖容量的研究思路,为相关研究的进一步展开提供了一个范例。海水养殖的长远发展必须走可持续发展之路,良好的沿岸生态环境、资源与环境的和谐是支撑海水养殖业健康、持续发展的前提。总结了我国海水养殖业管理取得的进步并指出尚存在的问题。针对海水养殖业保持可持续发展的基本途径,提出了海水养殖业的规划管理和海水养殖技术改进等方面的科学建议。  相似文献   

Mining-induced seismicity in faulted geologic structures: An analysis of seismicity-induced slip potential     

P. L. Swanson 《Pure and Applied Geophysics》1992,139(3-4):657-676

Relationships between the locations of mining-induced seismic events, local fault structure, and mine geometry were examined in a deep hard-rock mine in northern Idaho. Stopes experiencing rock bursts and other large seismic events were found to fall into two structural regimes: the Silver Vein, and the N48°W Trend, a steeply dipping plane of seismic activity that is subparallel to major local steeply dipping faults which bound blocky structures. The N48°W Trend also intersects a shaft that was seriously damaged when fault gouge was expelled into the opening during a 3-month period of high seismic energy release. Models of stress interaction are used to support the hypothesis that mining-induced deformation was mobilized along a 1.5 km length of the N48°W Trend. Specifically, numerical models are used to simulate rupture of seismic events and estimate induced changes in the quasi-static stress field. A Coulomb failure criterion is used with these results to estimate the spatial variation in potential for slip on planes parallel to local faulting. Increases in the potential for slip on fault planes subparallel to the N48°W Trend are consistent with activation of deformation along its 1.5 km length. For events with constant seismic moment, stress drop is shown to be far more important than source dimension in elevating slip potential along the observed plane of seismic activity  相似文献   

论西安地裂缝   总被引：5，自引：0，他引：5       下载免费PDF全文

王景明 《地震地质》1989,11(3):85-93

西安地裂缝具定向延伸、多级羽列和成带、等距的分布格局,为水平左旋和南盘依次下落的同步位错。是基底断裂在统一区域应力场作用下,长期蠕动形成的隐伏微细裂缝,在地下水活动的附加作用下显现出来的一系列构造地裂缝。其发生方式为多点双向破裂,发生时间和活动高峰依次由南向北迁移。它们不均匀地蠕滑、时隐时现,有4、20、400和750年四种活动周期,可与渭河盆地的地震活动对应,是区域构造应力场加强的信息  相似文献   

The role of non‐coaxiality in the simulation of strain localization based on classical and Cosserat continua          下载免费PDF全文

J. Chang  X. Chu  Y. Xu 《国际地质力学数值与分析法杂志》2017,41(3):382-399

It is normally accepted that materials inside the shear band undergo severe rotation of the principal stress direction, which causes non‐coaxiality between the principal stress and principal plastic strain rate. However, classical plasticity flow theory implicitly assumes that the principal stress and the principal plastic strain rate are coaxial; thus, it may not correctly predict the onset of the shear band. In addition, classical continuum does not contain any internal length scales; as a result, it cannot provide a reasonable shear band thickness. In this study, the original vertex non‐coaxial plastic model based on the classical continuum is extended to the Cosserat continuum. The corresponding codes are implemented via the interface of the user defined element subroutine in ABAQUS. Through a simple shear test, the effectiveness of the user's codes is verified. Through a uniaxial compression test, the influence of non‐coaxiality on the onset, the orientation, and the thickness of the shear band is investigated. Results show that the onset of the shear localization is delayed, and the thickness of the shear band is widened when the non‐coaxial degree increases, while the orientation of the shear band is little affected by the non‐coaxial degree. In addition, it is found that the non‐coaxiality can weaken the micro‐polar effect to some extent; nonetheless, the Cosserat non‐coaxial model still has its advantage over the classical non‐coaxial model in capturing the pre‐bifurcation as well as the post‐bifurcation behaviors of strain localization. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Rainfall interception in a lower montane forest in Ecuador: effects of canopy properties     

Katrin Fleischbein  Wolfgang Wilcke  Rainer Goller  Jens Boy  Carlos Valarezo  Wolfgang Zech  Klaus Knoblich 《水文研究》2005,19(7):1355-1371

Rainfall interception in forests is influenced by properties of the canopy that tend to vary over small distances. Our objectives were: (i) to determine the variables needed to model the interception loss of the canopy of a lower montane forest in south Ecuador, i.e. the storage capacity of the leaves S and of the trunks and branches S_t, and the fractions of direct throughfall p and stemflow p_t; (ii) to assess the influence of canopy density and epiphyte coverage of trees on the interception of rainfall and subsequent evaporation losses. The study site was located on the eastern slope of the eastern cordillera in the south Ecuadorian Andes at 1900–2000 m above sea level. We monitored incident rainfall, throughfall, and stemflow between April 1998 and April 2001. In 2001, the leaf area index (LAI), inferred from light transmission, and epiphyte coverage was determined. The mean annual incident rainfall at three gauging stations ranged between 2319 and 2561 mm. The mean annual interception loss at five study transects in the forest varied between 591 and 1321 mm, i.e. between 25 and 52% of the incident rainfall. Mean S was estimated at 1·91 mm for relatively dry weeks with a regression model and at 2·46 mm for all weeks with the analytical Gash model; the respective estimates of mean S_t were 0·04 mm and 0·09 mm, of mean p were 0·42 and 0·63, and of mean p_t were 0·003 and 0·012. The LAI ranged from 5·19 to 9·32. Epiphytes, mostly bryophytes, covered up to 80% of the trunk and branch surfaces. The fraction of direct throughfall p and the LAI correlated significantly with interception loss (Pearson's correlation coefficient r = −0·77 and 0·35 respectively, n = 40). Bryophyte and lichen coverage tended to decrease S_t and vascular epiphytes tended to increase it, although there was no significant correlation between epiphyte coverage and interception loss. Our results demonstrate that canopy density influences interception loss but only explains part of the total variation in interception loss. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Evaluating the effectiveness of road‐crossing drainage culverts in ephemeral streams     

C. Conesa‐García  R. García‐Lorenzo 《水文研究》2013,27(12):1781-1796

The present study proposes a method for evaluating the effectiveness of road‐crossing drainage culverts in ephemeral streams. This approach is focused on estimating the culvert capacity in road–stream crossings and the probable runoff generated on the road from hydrological thresholds associated with hydromorphological criteria. In particular, discharges at bankfull and flood‐prone stages have been used in combination with 2.5 and 100‐year peak discharges. Different hydraulic variables have been considered for calculating the discharge through culverts under these conditions (e.g. tailwater and headwater depth, inlet control, pipe roughness, pipe cross‐area and slope, pipe outlet velocity, critical water depth, and flow rate over the road). Geomorphological factors such as bed stability, bed load transport, and channel roughness have also been considered because of their potential for obstructing the drains in this type of channel. In addition, a potential obstruction index (PI_OBSTR) has been calculated, as a dependent parameter of the obstacle index (I_OBST) and the potential build‐up of coarse sediments (PB_CS). The study has been carried out on the Mediterranean coast in the region of Murcia (Spain), where there are numerous examples of road–stream crossings equipped with culverts in ephemeral channels that could cause highly dangerous situations for road traffic. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Bearing capacity of two interfering strip footings from lower bound finite elements limit analysis     

Jyant Kumar  Paramita Bhattacharya 《国际地质力学数值与分析法杂志》2013,37(5):441-452

A rigorous lower bound solution, with the usage of the finite elements limit analysis, has been obtained for finding the ultimate bearing capacity of two interfering strip footings placed on a sandy medium. Smooth as well as rough footing–soil interfaces are considered in the analysis. The failure load for an interfering footing becomes always greater than that for a single isolated footing. The effect of the interference on the failure load (i) for rough footings becomes greater than that for smooth footings, (ii) increases with an increase in ?, and (iii) becomes almost negligible beyond S/B > 3. Compared with various theoretical and experimental results reported in literature, the present analysis generally provides the lowest magnitude of the collapse load. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Ultimate bearing capacity of equally spaced multiple strip footings on cohesionless soils without surcharge     

K. M. Kouzer  Jyant Kumar 《国际地质力学数值与分析法杂志》2008,32(11):1417-1426

The ultimate bearing capacity of a group of equally spaced multiple rough strip footings was determined due to the contribution of soil unit weight. The analysis was performed by using an upper bound theorem of limit analysis in combination with finite elements and linear programming. Along the interfaces of all the triangular elements, velocity discontinuities were considered. The value of ξ_γ was found to increase continuously with a decrease in S/B, where (i) ξ_γ is the ratio of the failure load of an interfering strip footing of a given width (B) to that of a single isolated strip footing having the same width and (ii) S is the clear spacing between any two adjacent footings. The effect of the variation of spacing on ξ_γ was found to be very extensive for small values of S/B; ξ_γ approaches infinity at S/B=0. In all the cases, the velocity discontinuities were found to exist generally in a zone only around the footing edge. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Harnessing scientific and local knowledge to face climate change in small-scale fisheries     

《Global Environmental Change》2021

Small-scale fisheries in developing regions are particularly vulnerable to climate change, but the assessment of climate-induced changes and impacts are often hampered by the data poor-situation of these social-ecological systems. Based on 40 years of scientific and local ecological knowledge, we provide a coherent narrative about the effects of a marine hotspot of climate change on a small-scale fishery across different geographical and temporal scales. We applied a mixed-methods approach to assess biophysical changes, social-ecological impacts, and the incremental spectrum of actions implemented at multiple levels to increase the adaptive capacity of a small-scale clam fishery. The warming hotspot here analyzed was the fastest-warming region in the South Atlantic Ocean. Long-term changes in wind intensity and direction were also noticeable at a regional scale. Both sea surface temperature and winds showed a clear shifting pattern in the late 1990 s. These climate-related stressors determined ecosystem and targeted population changes (e.g. clam mass mortalities, slow stock recovery rates after ecological shocks, habitat narrowing), and favored harmful algal bloom-forming organisms. Climate-induced drivers also affected the human component of the social-ecological system, preventing fishers from securing a fulltime livelihood and limiting the fishery economic potential. Adaptive responses at multiple levels provided some capacity to address climate change effects, and transformative pathways are being taken to adapt to climate-induced changes over the long-term. Transformative changes were fostered by the local perception of environmental change, shared narratives, sustained scientific monitoring programs, and the interaction between knowledge systems, facilitated by a bridging organization within a broader process of governance transformation. The combination of autonomous adaptations (based on linking social capital and fishery leaders agency) and government-led adaptations were essential to face the challenges imposed by climate change. Our results serve as a learning platform to anticipate threats and envision solutions to a wide range of small-scale fisheries in fast-warming regions worldwide.  相似文献   

Rainfall partitioning and its effects on regional water balances: Evidence from the conversion of traditional cropland to apple orchards in a semi-humid region     

Di Wang  Li Wang 《水文研究》2020,34(24):4628-4639

Rainfall partitioning by vegetation cover plays an important role in local and regional water balances. Large areas of traditional cropland have been converted to apple orchards on the Loess Plateau, China, so the effect of the conversion of traditional cropland to these orchards on rainfall partitioning cannot be ignored. In this study, we measured precipitation, throughfall (TF), and stemflow (SF) and calculated canopy interception (I) and canopy storage capacity (S) in two neighbouring apple orchards (8 and 18 years old in 2013) on the plateau during the four growing seasons of 2013, 2014, 2015, and 2016. Besides, we also summarized the percentage of rainfall partitioning of various crops and tree species and assessed the effect of land use change on regional water balances. The results showed that the percentage of rainfall partitioning and S differed between the two orchards. Mean annual I, TF, and SF for the young and mature orchards during the 4 years accounted for 7.9, 89.8, and 2.6% and for 10.3, 87.5, and 2.3%, respectively, of the rainfall partitioning. The percentage accounted for by mean annual I and TF differed significantly between the two orchards, but the percentage of mean annual SF did not differ significantly between the two orchards. Mean annual S for 2013–2016 was significantly higher for the mature than the young orchard. Although the conversion of traditional cropland to apple orchards led to a more serious soil desiccation in this region, the I loss percentage was higher in maize (12.5%) than the apple orchards. Therefore, we inferred that the effect of the conversion of traditional cropland to apple orchards on regional water balances was likely not caused by differences in rainfall partitioning. Differences in tree morphology due to tree age accounted for the differences in rainfall partitioning and S between the two orchards. Thus, tree age should be taken into account when assessing the effect of apple orchards on rainfall partitioning in this or similar regions.  相似文献