大辽河口营养物基准推导方法     

王蕾  单阳阳  边均翠  李正炎 《海洋科学》2020,44(12):1-13

河口富营养化与流域氮、磷营养物的输入直接相关，制定河口营养物基准，可用于控制河口及其近岸海域富营养化，为环境管理的科学决策提供依据。大辽河是渤海最大的入海河流之一，河口污染较为严重；本文采用频数分布法、非参数分析法和实验室模拟压力响应关系法探讨大辽河口及近岸海域营养物基准的推导，最终得到大辽河口总氮（TN）、总磷（TP）及叶绿素a（Chl-a）推荐基准值分别为1.008 mg/L，0.067 mg/L和1.175 mg/m³，以期为大辽河口及其近岸海域富营养化评估和营养物标准制定提供科学依据。  相似文献   

Throughfall enrichment and stream nutrient chemistry in small headwater catchments with different land cover in southern Chile          下载免费PDF全文

Pedro Hervé‐Fernandez  Carlos E. Oyarzún  Stefan Woelfl 《水文研究》2016,30(26):4944-4955

Land cover changes have a great impact on nitrogen (N) and phosphorous (P) fluxes catchments. In this study, we wanted to compare different land covers: deciduous (D), evergreen (E) (both native forests), and exotic Eucalyptus globulus plantation (EP), affected precipitation, and stream discharge on N and P species concentrations and fluxes, under a low deposition climate in south‐central Chile. For this, we collected bulk precipitation, throughfall, and stream water samples after 41 rainfall events in E and EP, during the period June 2009–March 2011, and 31 rainfall events in D, during the period October 2009–March 2011. The highest canopy enrichment of N and P species for throughfall was observed in deciduous forest, while E. globulus showed the minimum enrichment. Total nitrogen (total‐N) discharge in EP was about 8.6 times higher than that of E and D catchments. Total‐N annual retention was positive only in E and D catchments. However, EP catchment showed a net loss (?4.79 kg N ha/year). The biggest difference was observed in nitrate stream concentrations, which showed low values for E (3.4 ± 1.3 μg/L), while EP and D showed higher nitrate concentrations (84.9 ± 16.7 and 134.7 ± 36.7 μg/L, for EP and D, respectively). Total phosphorous (total‐P) discharge flux was low in EP (0.4 kg P ha/year), and negligible in E and D forests (<0.1 kg P ha/year). Total‐P annual retention was near to 1.0 kg N ha/year (on E and D), while a net loss (?1.5 kg N ha/year) was observed for EP. We attribute the observed differences in nutrient throughfall enrichment due to high multi‐stratified canopies in the native forests. Both deciduous and evergreen native forest‐covered catchments showed the highest retention of total‐N and total‐P, in contrast to Eucalyptus‐covered plantation.  相似文献   

胶州湾的生态环境演变与营养盐变化的关系   总被引：1，自引：0，他引：1  

宋金明  袁华茂  李学刚  段丽琴 《海洋科学》2020,44(8):106-117

作为我国人为影响海洋研究与海洋学基础研究的典型海域，胶州湾历经90年的科学调查和研究，获得了系统的对胶州湾海洋学的认识。本文总结归纳了近年来胶州湾的生态环境变化状况、营养物质输入以及百年来生态环境演变的主要结果和结论。近年来，胶州湾海水呈现“高氮-低磷-低硅富营养化”状况较明显，浮游生物生物量有增加的趋势，输入到胶州湾营养物质的量巨大，总溶解态氮的年输入通量为6 945.4 t/a，其中无机氮、有机氮分别为4 453.1 t/a，2 492.3 t/a。点源和河流是总溶解态氮的主要输入方式，分别占无机氮输入通量的39%和20%，有机氮输入通量的31%和41%。总溶解态磷的年输入通量为160.6 t/a，其中无机磷的输入略高于有机磷，二者分别为88.0 t/a，72.6 t/a。河流和点源是无机磷的主要输入方式，分别占无机磷输入通量的40%和30%，而对于有机磷而言，河流是其主要的输入方式，可占其输入通量的51%，而地下水和点源也分别占输入通量的24%和15%，这些大量输入的营养物质对胶州湾生态环境变化起了关键作用。胶州湾百年来经历了三个阶段的演变，20世纪70年代以前，胶州湾受人为影响很小，其化学要素水平基本呈现“背景值”且比较稳定，从20世纪80年代起，胶州湾明显受到人为活动的影响，其沉积物中的化学组分持续增加，直到20世纪90年代中到2000年达到高峰，2000年后，由于环保治理措施的加强，沉积物中的化学组分呈明显降低趋势，基本稳定在较低的水平。  相似文献   

Application of T-bar in numerical simulations of a monopile subjected to lateral cyclic load     

Jian Yu  Chun Fai Leung  Ser Chai Jeremy Goh 《Marine Georesources & Geotechnology》2018,36(6):643-651

A series of centrifuge tests were performed to investigate the response of a free-head monopile due to cyclic lateral loading in normally consolidated clay. By linking the maximum reaction-force point of the final cycles in all tests with various amplitudes, a postcyclic reaction-force curve is obtained, which can be used to assess the postcyclic remolded lateral stiffness. To numerically analyze the tests, a strength degradation model of the clay is calibrated by the T-bar cyclic test. However, this model is T-bar-dependent, which is unable to capture the degrading behavior of the monopile stiffness. Thus, a modification approach is proposed based on the upper bound theory, and the modified model is further combined with finite element analysis to simulate the cyclic behavior of the model pile. The simulation results show similar degrading trend and consistent postcyclic remolded lateral stiffness with the model tests. This further demonstrates that the remolded lateral stiffness mainly depends on the soil remolded strength, which is one of the parameters calibrated by the T-bar tests. Based on this finding, a simplified numerical analysis is proposed, which can predict the postcyclic reaction-force curve by performing one monotonic loading instead of modeling the whole process of cyclic loading.  相似文献   

Experimental studies on sand plug formation in suction caisson during extraction     

Yukun Zhang  Fuquan Chen 《Marine Georesources & Geotechnology》2018,36(7):795-804

A series of model tests were conducted on Perspex-made suction caissons in saturated dense marine sand to study the sand plug formation during extraction. Suction caissons were extracted by pullout loading or by pumping air into the suction caisson. Effects of the pullout rates, aspect ratios and loading ways (monotonic or sustained) on the pullout capacity, and plug formation were investigated. It was found that the ultimate pullout capacity of the suction caisson increases with increasing the pullout rate. The sand plug formation under the pullout loading is significantly influenced by the pullout rate and the loading way. When the suction caisson is extracted at a relatively slow rate, the general sand boiling through the sand plug along the inner caisson wall occurs. On the contrary, the local sand boiling will occur at the bottom of the suction caisson subjected to a rapid monotonic loading or a sustained loading. Test results of the suction caisson extracted by pumping air into the caisson show that the pressure in the suction caisson almost follows a linear relationship with the upward displacement. The maximum pressures for suction caissons with aspect ratios of 1.0 and 2.0 during extraction by pumping air into the caisson are 1.70 and 2.27 times the maximum suction required to penetrate the suction caisson into sand. It was found that the sand plug moves downward during extraction by pumping air into the caisson and the variation in the sand plug height is mainly caused by the outflow of the sand particles from the inside of the suction caisson to the outside. When the suction caisson model is extracted under the pullout rate of 2?mm/s (0.28?mm/s for the prototype), the hydraulic gradient along the suction caisson wall increases to the maximum value with increasing the penetration depth and then reduces to zero. On the contrary, when extracted under the pullout rate of 10?mm/s (1.4?mm/s for the prototype), the hydraulic gradient along the suction caisson wall increases with increasing the pullout displacement. When extracted by pumping air into the caisson, the hydraulic gradient reaches the critical value, and at the same time, the seepage failure occurs around the suction caisson tip.  相似文献   

Anthropogenic influence on the degradation of an urban lake - The Pampulha reservoir in Belo Horizonte, Minas Gerais, Brazil     

Kurt Friese  Gerald Schmidt  Jorge Carvalho de Lena  Dieter W. Zachmann 《Limnologica》2010,40(2):114-125

The artificial reservoir Lagoa da Pampulha in central Brazil has been increasingly affected by sediment deposition and pollution from urban and industrial sources. This study investigates water chemistry and heavy metal concentrations and their fractionation in the lake sediment using ICP-OES, ICP-MS, and XRD analyses. Fractionation analysis was done by sequential extraction under inert gas as well as after oxidation. The lake exhibits a permanent stratification with an oxygen-free hypolimnion below 2 m depth. Nutrient concentrations are enriched for phosphorous components (SRP, PO₄). In the sediment it was not possible to detect oxygen. Carbon, sulfur, and most of the analyzed heavy metals are enriched in the top sediment layer with a pronounced downward decrease, indicating the presence of an anthropogenic influence. Statistical analysis, including correlations and a Principal Component Analysis (PCA) of depth-related total concentration data, helps to distinguish presumably anthropogenic heavy metals from geogenic components. Some samples with high element concentrations in the sediment also show elevated concentrations in their pore water. Analyses of element distribution between sediment and pore water suggest a strong bonding of heavy metals to the anoxic sediment. The trend towards elevated solubility in the pore water of oxidized samples is clear for most of the analyzed elements. Fractionation analysis reveals characteristic associations of selected elements to specific mineral bonding forms. In addition, it indicates that the behavior of heavy metals in the sediment is strongly influenced by organic substances. These substances provide buffering against oxidation, acidification, and metal release. The high nutrient loading causes reducing conditions in the lake sediment. These conditions trigger the accumulation of sediments rich in S²⁻, which stabilizes the fixation of heavy elements. In the future, care must be taken to reduce the supply of contaminants and to prevent the release of heavy metals from sediments dredged for remediation purposes.  相似文献   

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田云锋 《大地测量与地球动力学》2010,30(5):64-67

??????????????????й??????????????GPS?????????,?????????????????????·?????????????????????????????ATML??????????????3????а?????????????????С????????????????????????????ATML????????????????????????????????????????ATML??????????????????????:?????????????????????????????С???????????????????????????????????????????С??  相似文献   

Chronology and nutrients change in recent sediment of Taihu Lake,lower Changjiang River Basin,east China   总被引：1，自引：0，他引：1  

Shuchun Yao  Bin Xue  Deyang Kong 《中国地理科学(英文版)》2010,20(3):202-208

Two short sediment cores named ZS and THS dated by the 210Pb or 137Cs method were collected from the northwest and southwest of Taihu Lake respectivly,and total organic carbon(TOC) and nutrients including total nitrogen(TN) and total phosphorus(TP) were determined to analyze the chronology and nutrients change in recent sediment.The results show that 137Cs activities are low(less than 15 Bq/kg) in the two cores,attributed to the 137Cs migration.Based on 210Pb constant rate of supply(CRS) model,the sedimentation accumulation rates range from 0.13 g/(cm2·yr) to 0.76 g/(cm2·yr) in the ZS core,and from 0.10 g/(cm2·yr) to 0.56 g/(cm2·yr) in the THS core.A remarkable increase in organic matter and nutrients has occurred in the two dated cores since the mid-1980s.The historical changes of organic matter and nutrients in the two cores are consisitent with the monitoring data for surface sediment after the 1960s.The TP accumulation rates after the early 1980s are 0.97 and 0.92 times higher than those from the 1950s to the 1980s in ZS and THS cores,respectively.Higher TP concentrations in the past two-decade deposits of Taihu Lake are due to both diagenetic factors and human activities.  相似文献   

黄土高原沟壑区原状土壤氮素迁移     

杨毓峰  李世清 《广东海洋大学学报》2010,30(6)

以中国生态系统研究网络CERN长武王东沟实验站的坡耕地和塬耕地为供试土壤,研究了黄土高原沟壑塬区旱耕地原状土壤氮素迁移和时空变异。结果表明:耕作土壤NO3--N为23.1~33.8 mg/kg,NH4+-N为0.23~0.50mg/kg,DOC为9.17~13.38 mg/kg,P为0.18~0.23 mg/kg;坡耕地和塬耕地的NO3--N和NH4+-N主要集中在0~20 cm的上层土壤,中下层土壤NO3--N和NH4+-N起源于上层淋溶迁移和累积;高含量时养分淋溶溶出呈指数衰减型;NO3--N、NH4+-N、DOC向下层的迁移塬耕地慢于坡耕地。  相似文献   

动荷载作用下结构性软土微结构变化的分形研究   总被引：1，自引：0，他引：1  

姜岩  雷华阳  郑刚  杨雄建 《岩土力学》2010,31(10):3075-3080

为探讨天津滨海新区典型结构性软土的动力特性,采用动三轴试验和压汞试验,对交通荷载作用下结构性软土微观结构变化进行了研究。取原状土和动荷载作用后的土样进行压汞测试,用分形理论对压汞测试数据进行分析,探讨孔隙分布特征,提出孔径划分的方法,给出了卓越频率与土体孔隙变化的规律。研究结果表明：在动荷载作用后,天津滨海新区典型软土的孔隙分布发生改变,可分为3种类型;利用Menger海绵模型研究交通荷载作用下结构性软土的孔隙分布特性是可行的;用孔隙分维数可实现对卓越频率的预测以及路基土体变形行为的机制分析。  相似文献