Research on crustal structure and lithosphere property in the Okinawa Trough area

A mass of geological, geophysical and geochemical data and information from the Okinawa Trough area are collected for comprehensive research in the study area from East China to Okinawa Trough and then to Ryukyu Island Are region. According to the seismic tomography result (P and S wave) and the processing result of free-air and Bouguer gravity anomaly and magnetic anomaly data in the study area, the comprehensive interpretation is carried out. The Moho depth distribution of the study area is obtained by the inversion calculation based on gravity data using the Harmonious Series method. The crust properties are analyzed. Meantime, some Cenozoic basalt data from Kuandian (NE China), Hannuoba (North China), Minxi (South China), Penghu Islands (Taiwan Strait), Okinawa Trough and Japan Island Arc regions are chosen to make the comparison research on element- isotopes. The result indicates that the lithosphere thickness in the Okinawa Trough area has obviously decreased, where a Low -velocity layer of upper-mantle has reached the Moho interface and the metasometized asthenosphere has formed. The research result on element- isotopes shows that the characteristic of the crust in the Okinawa Trough area is different from that in East China area and the Ryukyu Island Arc area. It is considered that the crust in the Okinawa Trough area belongs to the transition type, which is quite similar to the feature of the oceanic crust.

长江口水域富营养化的形成、演变与特点研究

本文以我国长江口水域富营养化为研究对象，对长江水体溶解态无机氮、磷分布特点和通量变化进行了分析，基于长江流域氮“输入-输出”关系模型探索了水体氮的来源；分析了长江口水域富营养化长期演变及特点；探索了长江口海域低氧区的发生机制。结果如下： 长江水体中NO3--N、NH4+-N、DIN和DIP浓度从上游往下游呈增加趋势，但存在季节差异。长江流域从上游往下游的DIN输送通量的变化主要受水流量的影响，但从上游往下游单位面积年产N量逐渐升高；DIP输送通量从上游往下游呈增加趋势，同时也主要受水流量控制，但从季节变化来讲，DIP的月输送通量受其浓度的控制更加明显。自20世纪60年代来，长江水体中NO3--N、NO2--N、DIN和DIP浓度都处于缓慢上升趋势，但到80年代上升速度明显加快；不同历史时期DIN和DIP的季节变化特点也不尽相同，反映出其来源的差异。同时，本研究采用长江流域氮“输入-输出”关系模型（污染负荷统计模型）对长江水体氮来源进行了分析，估算了各种氮源对水体氮的贡献率。结果表明，2006年向长江流域输入氮的总量为17.6 Tg，其中20%的输入氮转移到了水体（3.5 Tg）。本年度长江大通水文站实测氮输送通量为1.8 Tg，表明约50%的氮在水体输送过程中发生了生物、化学、物理损耗。对于长江水体氮的来源来讲，饲养牲畜粪便氮流失和大气干/湿沉降氮的贡献率较大，分别为26%和25%；农业氮肥流失和城市生活污水排放的贡献率相同，都为17%；农村人口粪便氮流失和工业废水排放的贡献率分别为6%和9%。 自20世纪60年代以来，长江口口门内和外海（盐度>30psu）水体中营养盐浓度增加显著。在表层水体盐度大于22psu海域DIN: PO43--P值表现出了明显升高的历史变化趋势。SiO3: PO43--P值从1959年到1985-86年显著下降，然后到2003-06年有所上升。根据SiO3: PO43--P值和DIN: PO43--P值的长期变化趋势，可以推出，SiO3: DIN值从20世纪50-60年代以后呈现下降趋势。在长江口海域，随着营养盐浓度的增加，浮游生物量的大幅度升高在本研究中得到证实。同时，长江口水域浮游植物种群结构对营养盐结构的长期变化产生响应，研究结果表明，硅藻种类比重从1985-86年84.6% 下降到2004-05年69.8%；年均硅藻丰度占浮游植物总丰度比重在1985-86年达到99.5%，但到2004-05年降低为75.5%，而甲藻丰度比重则由0.7%增大到25.4%。 底层水体DO浓度与Delta S（底层水体与表层水体的盐度之差）和Delta T（表层水体与底层水体的温度之差）成显著负相关，这表明了水体层化或者垂直水体交换是控制长江口水域底层水体溶解氧变化的主要因素，但水体温度层化要比盐度层化在控制低氧区形成上起到更大的作用。上升流在该海域低氧的形成和分布上起到很重要的作用，显著影响低氧水团的垂直分布，也显著影响到溶解氧的水平分布。现场生产的浮游植物可能是低氧区的形成的生物基础，日益增加的叶绿素a浓度和大规模的有害藻华可能是长江口低氧区逐渐增大的原因。本研究认为，此海域低氧区的形成主要受长江冲淡水、台湾暖流的入侵、地形、尤其是温跃层的形成和现场生产的有机物质控制。

Recovery and fate of three species of marine dinoflagellates after yellow clay flocculation

The recovery and fate of three species of dinoflagellates, Alexandrium tamarense, Cochlodinium polykrikoides and Scrippsiella trochoidea, after having been sedimented by yellow clay, were investigated in the laboratory. The effect of burying period in yellow clay pellet and mixing on the recovery of settled algal cells were studied. The morphological changes of algal cells in yellow clay pellet were also tracked. Results showed that there was almost no recovery for A. tamarense and C. polykrikoides, and the cells decomposed after 2-3 days after visible changes in morphology and chloroplasts. There was some recovery for S. trochoidea. Moreover, S. trochoidea cysts were formed in clay pellet during the period of about 14 days, with the highest abundance of 87 000 cysts g(-1) clay and the incidence of cyst formation of 6.5%, which was considered as a potential threat for the further occurrence of algal blooms. S. trochoidea cysts were isolated from yellow clay and incubated to test their viability, and a germination ratio of more than 30% was obtained after incubation for 1 month. These results showed the species specificity of the mitigation effect of yellow clay. It is suggested that cautions be taken for some harmful species and thorough risk assessments be conducted before using this mitigation strategy in the field.

Screening of surfactants for harmful algal blooms mitigation

Screening experiments were conducted in order to find promising synthetic surfactants for harmful algal blooms (HABs) mitigation. The chemically synthesized surfactant cocamidopropyl betaine (CAPB) showed characteristics of relatively high inhibition efficiency, high biodegradability and low cost. The motility inhibition ratios of 10 mg/L CAPB on Cochlodinium polykrikoides and Alexandrium tamarense were about 60% after 5 min. The biodegradation test indicated that the half-life of CAPB in seawater was shorter than one day and 90% was biodegraded after five days under the initial concentration of 100 mg/L at 25degreesC. Further cell lysis experiments revealed the selective lysis effect of CAPB on different HAB organisms. More than 90% of C. polykrikoides lysed at the concentration of 10 mg/L CAPB after 24 h and at 15 mg/L CAPB after 4 h, whereas the lysis effect of CAPB on A. tamarense was slight, no more than 10% after 2 h interaction with 50 mg/L CAPB. This research provided preliminary data for CAPB as a candidate in harmful algal blooms mitigation and pointed out unresolved problems for its practical application in the meantime. (C) 2003 Elsevier Ltd. All rights reserved.

Synergistic effect of sophorolipid and loess combination in harmful algal blooms mitigation

The inhibition effect of sophorolipid and removal efficiency of loess on Cochlodinium polykrikoides and Alexandrium tamarense was investigated separately in the laboratory. Based on this, the combination of sophorolipid and loess for harmful algal bloom mitigation was proposed. Algal sedimentation tests in the laboratory and in the field revealed that the combination of sophorolipid and loess showed synergistic effects both on the removal efficiencies and on the mitigation cost. The concentration of 1 g/l loess and 5 mg/l sophorolipid was determined as the optimum ratio for C polykrikoides mitigation. In the field test, the effective concentration of loess and sophorolipid in the combination group was reduced to 10% and 25%, respectively, compared to the non-combination group, and the cost decreased more than 60%. The combination of loess and sophorolipid was considered as a promising novel method in harmful algal bloom mitigation. (C) 2003 Elsevier Ltd. All rights reserved.