长江口斜压诊断模式三维流场数值模拟

建立了σ坐标系下长江口斜压诊断模式三维流场数学模型,采用k-kl二方程紊流闭合模型求解垂向涡粘系数,计算域内恒定、非均匀盐度场反映了计算域密度斜压效应。验证结果表明,斜压诊断模式的模拟成果较切合实际。模型成功复演了长江口水域由往复流向旋转流过渡的流场特性;潮波从四条汊道传入后在分汊口附近相遇形成多个会潮点,其位置随着径流的大小、潮汐的强弱、汊道的形态等因素而变化。     

珠江河口夏季缺氧现象的模拟

夏季底层水体缺氧现象是珠江河口存在的环境问题之一。使用三维水动力-生态耦合模型来分析珠江口缺氧现象的分布状况和产生原因。模拟结果表明:模型能很好的再现珠江口的缺氧敏感性区域和强度。珠江口存在的底层水体缺氧现象是水体强烈层化和生化耗氧过程共同作用的结果。缺氧现象的发展与减退受潮汐涨落的影响。珠江口盐度-潮汐混合锋面和层化作用控制低氧水团的范围和强度。     

Multi-resolution clustering analysis and 3-D visualization of multitudinous synthetic earthquakes

We use modern and novel techniques to study the problems associated with detection and analysis of multitudinous seismic events, which form the background for isolated great earthquakes. This new approach involves multivariate analysis of low and large magnitude events recorded in space over a couple of centuries in time. We propose here the deployment of the clustering scheme both for extracting small local structures and large-scale trends in synthetic data obtained from four numerically simulated models with: uniform properties (U), a Parkfield-type asperity (A), fractal brittle properties (F), and multi-size-heterogeneity fault zone (M). The mutual nearest neighbor (mnn) clustering scheme allows for extraction of multi-resolutional seismic anomalies in both the spatio-temporal and multi-dimensional feature space. We demonstrate that the large earthquakes are correlated with a certain pathway of smaller events. Visualization of the anomalies by using a recently introduced visualization package Amira reveals clearly the spatio-temporal relationships between clusters of small, medium and large earthquakes, indicating significant stress relaxation across the entire fault region. We demonstrate that this mnn scheme can extract distinct clusters of the smallest events, which precede and follow a singularly large magnitude earthquake. These clusters form larger spatio-temporal structures comprising a series of large earthquakes. The link between the large and medium magnitude events is not so clearly understood. Short-ranged correlations are dominated by strong spatio-temporal anomalies, thus reflecting the global seismic properties of the entire fault zone.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.     

珠江口咸潮入侵分析与经验模型——以磨刀门水道为例

收集了2004-2006年珠江口磨刀门水道咸潮发生时测站(1~7)逐日定时观测的的含氯度、水位与流量数据,分析了各监测站含氯度与水位的日变化与年变化,导出了咸潮演变各过程中,含氯度与径流、潮流、河口地形等的关系式,建立了珠江口地区磨刀门水道咸潮入侵的经验模型。据此,模拟了2006年1月12日的磨刀门地区的咸潮入侵态势,经过和沿途各观测点验证发现与实测数据非常吻合。以含氯度等于250mg/L(饮用水的含氯度最大值)的点作为咸潮入侵的最远点,用简化修改后的盐度模拟模型计算了磨刀门咸潮入侵最大距离,并根据2006年1月12~20日的河口含氯度与最近的上游天河站的径流量实测数据计算出相应的咸潮入侵最大距离。研究表明,在河流枯水期(珠江河口通常是12月至翌年3月),只要获得当天河口的含氯度和上游测站的径流量数据,就能利用此经验模型估算出河流各点的含氯度,作出盐度模拟图,并估算出相应的咸潮入侵最大距离。     

Heavy metal distribution in sediment profiles of the Pearl River estuary,South China

The Pearl River estuary is created by the inflow of freshwater from the largest river system that drains into the South China Sea. In recent years, massive economic growth and development in the region has led to excessive release of waste into the environment. The accumulation of contaminants in sediments is likely to pose serious environmental problems in surrounding areas. The study of sediment profiles can provide much information on the metal contamination history and long term potential environmental impacts. In this project, 21 core samples (up to 3.65 m deep) were collected in the Pearl River estuary. About 15 subsamples from each core were analysed for moisture content, total organic matter (L.O.I.), particle size and heavy metal and major element concentrations. The results show that Pb and Zn contents are elevated in the sediments at most of the sampling sites. Compared with historical monitoring results, the sediment metal contents have increased over the last 20 a, particularly for Pb. The west side of the Pearl River estuary tends to be more contaminated than the east side due to the contaminants inputs from the major tributaries and different sedimentation conditions. There are close associations between Fe, Co, Ni and Cu concentrations in the sediments. Zinc and Pb contents in the sediment profiles reflect a combination of the natural geochemical background, anthropogenic influences and the mixing effects within the estuary. The distribution of Pb in the sediments shows strong influences of atmospheric inputs, probably from the coal burning activities in the region.     

Response of underwater light transmittance in the Rhode River estuary to changes in water-quality parameters

A year-long study of incident and underwater light transmittance (400–800 nm) in the Rhode River, Maryland, a tidal tributary to Chesapeake Bay, indicated that light transmittance responded in both intensity and spectral quality to changes in the amount and type of dissolved and suspended materials in the water. At times of relatively clear water, transmittance was similar to that previously reported in the literature for coastal waters. With high concentrations of suspended and dissolved materials in the water, attenuation of irradiance was high in the upper part of the water column and different for the various wave bands, depending on the type of material present. At such times, attenuation was higher in the upper part of the water column under sunny, clear skies than on cloudy days. We believe this to be due to higher concentrations of pigments and suspended particles in the water on sunny days, increasing the scattering and adsorption. A second factor was a lower average cosine on cloudy days, decreasing the effect of scattering on the average path length per meter of depth. High attenuation coefficients in the middle of the spectrum are attributed to accessory pigments. Regression of the diffuse attenuation coefficient on eight water-quality parameters explained up to 93% of the variance in the attenuation coefficient. Chlorophylls a and c and mineral suspensates were the three most important variables for data taken under clear skies. In contrast, under cloudy skies, the three most important variables were different for different wavelengths. Models of irradiance attenuation in turbid estuarine waters require the use of more variables than models for open ocean waters.     

An institutional analysis of the evolution of inland waterway transport and inland ports on the Pearl River

Inland waterway transport (IWT) is the most appropriate means of transportation in the pursuit of a sustainable development strategy. The development of IWT varies per region. Public entities and institutions play an important role in the development of IWT. This paper analyses the development of IWT on the Pearl River from an institutional perspective. Chinese national fiscal reforms, land use reforms and the transfer of power from the central government to local governments impact the governance of IWT. The paper demonstrates that the privatization of inland ports was triggered by the mismatch between the objectives of IWT operators and either public objectives or market demand. This process unfolded while top-level governors did not aim for privatization. The paper shows how formal institutional changes of IWT on the Pearl River are both the result of deliberate design and a path creation in the transformation from the Chinese planned economy to the Chinese market economy. It also shows how institutional changes resulted in a dual development path (i.e. a rapid development of inland terminals but underdevelopment of inland waterways) of IWT in the Pearl River. Policy recommendations are provided based on the research findings with specific attention to the factors hindering IWT development on the Pearl River at the level of the waterway infrastructure and inland ports.     

Sedimentary record of black carbon in the Pearl River estuary and adjacent northern South China Sea

The concentrations of black carbon (BC) and δ¹³C_BC were determined in sediments of three dated cores from the Pearl River estuary (core PR-3) and adjacent northern South China Sea (cores SS-30, E2). For comparison, the total organic C (TOC) contents and δ¹³C_TOC in the sediments were also measured. Relatively higher concentrations and fluxes of BC were found in sedimentary core PR-3, taken in the Pearl River estuary. The BC concentration profiles or fluxes correlated well with fossil-fuel usage in the Pearl River Delta. Maximum BC fluxes occurred in the late 1970s to early 1980s as recorded in core PR-3, and in the 1950s (core SS-30), reflecting the maximum BC emission in the Pearl River Delta and Hong Kong region, respectively. After the 1980s, a rapid decrease of BC fluxes and a light δ¹³C_BC excursion were presumably due to improvements in combustion and pollution-control technologies and a shift of energy structure from biomass and coal to a mixture of coal, gas, oil and biomass. The fossil BC that contributed to total BC in core PR-3 increased from 20–30% to 70–80% during the last five decades. The study also shows that BC correlates well with terrestrial organic matter and that the ratio of BC to TOC is a good pollution indicator in relation to anthropogenic activities.     

基于反射光谱的珠江口咸潮遥感方法

为监测珠江口河网区水体的盐度变化,基于同步测量的水体黄色物质、盐度和水体表面光谱数据,利用MATLAB分析了水体光谱反射率和黄色物质浓度之间的关系。结果表明:在磨刀门水道,反射率与黄色物质在400nm处的吸收系数g₄₀₀有较好关系,在R₇₀₄/R₅₁₃处,R²=0.70;在虎门水道,g₄₀₀与反射率比值R₇₀₃/R₄₈₈之间也有较强的负相关,R²=0.58。同样,又分析了磨刀门和虎门水道黄色物质吸收系数与表面盐度的关系,都发现了较好的相关性,R²>0.67。根据以上分析,得到了一种珠江口河网区水体表面盐度监测的新方法,并采用中等分辨率成像光谱仪(MERIS)的模拟数据来进行模型验证,结果表明利用MERIS数据对珠江口河网区咸潮进行监测是可行的(均方根误差小于0.308%)。