大鹏澳牡蛎养殖对浮游植物种群结构的影响研究     

张玲  李政菊  陈飞羽  江涛  吕颂辉  江天久 《海洋与湖沼》2015,46(3):549-555

于2013年8、10月及2014年2、5月对大鹏澳牡蛎养殖区及其邻近海域进行了采样调查。利用设置的3个站位(牡蛎养殖区S1、养殖区外S2、靠近湾口S3)的数据研究了牡蛎养殖对海区浮游植物种群结构和丰度的影响。本次考察共鉴定出大鹏澳浮游植物58属144种,丰度为6.15×103—5.94×106cells/L。其中,硅藻36属100种,占种类总数的69.4%,丰度在4.5×103—5.93×106cells/L之间;甲藻15属34种,占总种类的23.6%,丰度范围为1.5×102—4.53×104 cells/L;蓝藻、绿藻、隐藻等共7属10种。在牡蛎养殖期(8月至2月),养殖区内养殖水层浮游植物总丰度低于非养殖区,硅藻丰度占浮游植物总丰度的90%以上,硅藻丰度与总浮游植物细胞丰度的空间分布特征一致;与硅藻空间分布特点不同,养殖区内甲藻丰度显著低于非养殖区。牡蛎收获后的5月,养殖区内的甲藻丰度高于非养殖区。牡蛎养殖区站位S1浮游植物多样性指数平均值为1.35,明显低于非养殖区S2(2.68)和S3(2.69)。与此相似,养殖区内站位S1均匀度J(0.27)明显低于非养殖区站位S2(0.49)和S3(0.51)。本研究表明,大鹏澳牡蛎养殖对浮游植物群落结构造成了一定影响,能够显著降低浮游植物丰度、种类多样性和均匀度。  相似文献   

现代服务业集聚区经济特性及其启示     

钟韵  刘微 《热带地理》2012,32(5):515-520,574

通过对文献梳理,在界定现代服务业集聚区概念的基础上,借鉴制造业集群的经济特性,结合服务业的行业特色,对现代服务业集聚区的根植性、网络性和创新性3个经济特性展开了分析,进而从培育现代服务业集聚区经济特性的角度,对中央商务区(CBD)、高新科技园、文化创意产业园三类现代服务业集聚区的培育管理机制进行了分析,研究发现,CBD应该加强区内金融服务机构与专业服务机构的网络性建设,并由此强化区内企业的根植性;高新科技集聚区应加强网络性的建设,形成由相关科技服务组成的科技综合体;文化创意产业集聚区的建设则首先应培养区内企业与机构的创新性。  相似文献   

产业有序转移与区域产业协调发展——基于广东产业有序转移的经验     

覃成林  熊雪如 《地域研究与开发》2012,31(4):1-4

阐明了产业有序转移、区域产业协调发展的内涵,构建了产业有序转移对区域产业协调发展作用机制的分析框架。根据这个分析框架,从理论和广东产业转移经验两个方面进一步揭示了产业有序转移促进区域产业协调发展的机制。结果表明,产业有序转移是在政府有效干预下所形成的有利于区域产业协调发展的一种产业转移形式。产业有序转移通过诱致或促进区域产业结构优化调整、区际产业合理分工、区际产业关联互动,以及提高区域产业发展总体效率等路径,促进区域产业协调发展。  相似文献   

Overall efficiency of a V-shaped nylon net fence in preventing sand damage to the Mogao Grottoes     

GuoShuai Li  JianJun Qu  WanFu Wang  Wei Yang 《寒旱区科学》2012,4(2):0163-0174

A V-shaped nylon net fence installed in 1990 on top of the Mogao Grottoes is shown to be effectively resisting aeolian sand damage to the grottoes. The structure guides and causes deposition of sand from westerly wind (the primary hard wind), but to some extent hinders the inverse function of easterly wind carrying sand away from the grottoes toward Mount Mingsha. The gobi side by the fence experiences higher wind speed, so that on which are easily formed undercutting pits, and the deposited sands on it generally form double-peak structures due to abundant sand sources. If the earth surface characteristics in gobi areas by both sides of the fence are quite varied, the erosion and deposition features of the accumulating sand section are similar in different seasons; however, if the earth surface characteristics are similar, the features become irregular in different seasons. Sand depositions with long slope feet are formed along the south and north sides of V-shaped nylon net fence. Disrupted by strong westerly wind and northwesterly wind, sand accumulations by north of the fence are in form of single peaks. Although the operation duration of the V-shaped nylon net fence has exceeded its design life (10 years), our observations indicate that it is still effective in reducing wind-driven sand damages to the Mogao Grottoes, so it should not be withdrawn.  相似文献   

Precise dating of the Middle Permian: Zircon U–Pb geochronology from volcanic ash beds in the basal Gufeng Formation,Yangtze region,South China     

《Gondwana Research》2013,24(4):1599-1606

Direct radiometric dating of the Lower/Middle Permian epochs has not been well accomplished. Shales and bedded cherts of the geologically well-documented Middle Permian Gufeng Formation are exposed in the Chaohu area, Anhui province, South China. Through detailed field examination and mapping of the Gufeng stratigraphic section, we found at least four volcanic ash beds within the basal shale strata. This new discovery indicates the existence of prominent volcanic activity during Gufeng sedimentation and provides the opportunity to precisely date the age of the Middle Permian. Zircon grains separated from two near-basal horizon yield LA‐ICP‐MS U–Pb ages of 272.0 ± 5.5 Ma (MSWD = 2.6) and 271.5 ± 3.3 Ma (MSWD = 1.7). As the first precise isotopic age (272 Ma) of the Middle Permian Gufeng Formation in South China, our data offer precise geochronological constraints for the division and correlation of Middle Permian not only in South China but also worldwide.  相似文献   

Biomarker records of phytoplankton productivity and community structure changes in the Japan Sea over the last 166 kyr     

Lei Xing  Rongping Zhang  Yanguang Liu  Xiaochen Zhao  Sumei Liu  Xuefa Shi  Meixun Zhao 《Quaternary Science Reviews》2011,30(19-20):2666-2675

Glacial-interglacial sea level changes have caused drastic variations in the surface hydrography, ventilation and ecosystem structure in the Japan Sea. Previous reconstructions using microfossils and geochemical proxies suggested decreased productivity and a more calcareous plankton community during glacial periods. However, the inferred community structure change is not consistent with significantly lower salinity in the Japan Sea during the glacials, which would have had a deleterious effect on calcareous plankton growth. Here, biomarker records of ODP Site 797 are generated to further evaluate phytoplankton productivity and community structure changes in the Japan Sea over the last 166 kyr. Although the contents of the phytoplankton biomarkers changed by two to three orders of magnitude, there were no clear glacial-interglacial patterns as sediment biomarker contents reflected the combined effect of production and water column degradation. The collective assessments of our biomarker records and published records support previous conclusions of decreased productivity in the Japan Sea during the glacials. However, a community structure proxy based on the alkenone/brassicasterol ratio reveals a shift from a diatom-dominated community during the glacials to a coccolithophorid-dominated community during the interglacials, mainly as a result of surface salinity variations in the Japan Sea controlled by sea-level changes. Previous community structure reconstruction using biogenic carbonate/silica ratio could have been complicated by the different environmental factors governing silica and CaCO₃ dissolution in the Japan Sea.  相似文献   

Coupled flow and salinity transport modelling in semi-arid environments: The Shashe River Valley,Botswana     

《Journal of Hydrology》2006,316(1-4):163-183

Numerical groundwater modelling is used as the base for sound aquifer system analysis and water resources assessment. In many cases, particularly in semi-arid and arid regions, groundwater flow is intricately linked to salinity transport. A case in point is the Shashe River Valley in Botswana. A freshwater aquifer located around an ephemeral stream is depleted by the combined effect of transpiration and pumping. Quantitative system analysis reveals that the amount of water taken by transpiration is far more than the quantities pumped for water supply. Furthermore, the salinity distribution in and around Shashe River Valley as well as its temporal dynamics can be satisfactorily reproduced if the transpiration is modelled as a function of groundwater salinity. The location and dynamics of the saltwater–freshwater interface are highly sensitive to the parameterization of evaporative and transpirative salt enrichment. An existing numerical code for coupled flow/transport simulations (SEAWAT) was adapted to this situation. Model results were checked against a large set of field data including water levels, water chemistry, isotope data and ground and airborne geophysical data. The resulting groundwater model was able to reproduce the long-term development of the freshwater lens located in Shashe River Valley as well as the decline in piezometric heads observed over the last decade. Furthermore, the old age of the saline water surrounding the central freshwater lens could be explained.  相似文献   

A field study on the conversion ratio of phytoplankton biomass carbon to chlorophyll-<Emphasis Type="Italic">a</Emphasis> in Jiaozhou Bay,China     

吕淑果  王旭晨  韩博平 《中国海洋湖沼学报》2009,27(4):793-805

A one-year field study was conducted to determine the conversion ratio of phytoplankton biomass carbon (Phyto-C) to chlorophyll-a (Chl-a) in Jiaozhou Bay, China. We measured suspended particulate organic carbon (POC) and phytoplankton Chl-a samples collected in surface water monthly from March 2005 to February 2006. The temporal and spatial variations of Chl-a and POC concentrations were observed in the bay. Based on the field measurements, a linear regression model II was used to generate the conversion ratio of Phyto-C to Chl-a. In most cases, a good linear correlation was found between the observed POC and Chl-a concentrations, and the calculated conversion ratios ranged from 26 to 250 with a mean value of 56 μg μg⁻¹. The conversion ratio in the fall was higher than that in the winter and spring months, and had the lowest values in the summer. The ratios also exhibited spatial variations, generally with low values in the near shore regions and relatively high values in offshore waters. Our study suggests that temperature was likely to be the main factor influencing the observed seasonal variations of conversion ratios while nutrient supply and light penetration played important roles in controlling the spatial variations.  相似文献   

软土流变特性的模型研究     

刘林超  闫启方  孙海忠 《岩土力学》2006,27(Z1):214-217

对于具有流变特性的软土来说,模型的选取将直接影响其力学行为描述的准确性,经典模型在描述软土流变特性方面存在着一定的缺陷;对经典流变模型和分数导数流变模型进行了分析,得出了分数导数流变模型在描述软土流变特性方面具有准确性和广泛的使用性的特性。  相似文献   

软土次固结特性试验研究   总被引：6，自引：2，他引：4  

周秋娟  陈晓平 《岩土力学》2006,27(3):404-408

对广州南沙原状软土进行了一系列的固结试验,探讨了应力历史、加荷比、超载预压对软土次固结的影响。试验结果表明：软土的主次固结的划分与加荷比有关,加荷比对次固结系数C?也有影响;次固结系数主要受到先期固结压力pc的影响,当ppc时,次固结系数表现出不同的变化规律;经预压处理后土样的次固结系数与压缩指数Cc之比近似为一常数：C?/Cc≈0.03,试验成果所揭示的次固结特性对先期固结压力的依赖,为降低地基工后沉降提供了明确的思路。  相似文献