The tenth dragon: controlled seasonal flooding in long-term policy plans for the Vietnamese Mekong delta

Recently the Vietnamese government has endorsed a long-term policy plan in which it is proposed to restore controlled seasonal flooding in the upper regions of the Vietnamese part of the Mekong delta. Restoring controlled flooding would contrast a period of several decades characterized by a dominant flood prevention approach to enable intensive rice production in the delta. This article investigates a series of long-term policy plans, which have been developed for the Mekong delta since the 1960s, on their take on flood control sensu flood prevention, or the opposite, controlled seasonal flooding. By doing so it is demonstrated how perspectives on flood management have gradually evolved and, in the specific case of suggesting controlled flooding, have been framed in various ways by various actors. Contemporary proposals for controlled seasonal flooding are supported by actors ranging from governmental institutes to environmental NGOs, and connect to on-going debates about environmental challenges and sustainable development of the Mekong delta. We adopt a systems approach to analyze social, environmental and technological dynamics in the Mekong delta, and discuss whether the different interpretations of controlled flooding may contribute to the long-term sustainability of the delta.     

辽河三角洲湿地景观空间格局变化分析

以1988年和2001年2个时相的Landsat-TM/ETM影像为信息源,选取斑块数量、斑块平均面积、边界密度、斑块密度、形态指数和斑块分维数等6个代表性格局指数,对辽河三角洲湿地景观格局变化进行了定量分析。结果表明,1988~2001年,水田、内陆水体和养殖用地呈现明显的增加趋势,苇田、光滩、河口潮间带水域和碱蓬面积呈减少趋势。受人类的区域综合开发活动的影响,研究区斑块数量和边界密度分别增加了32.76%和21.4%,而斑块平均面积减小了30.2%,平均斑块密度由17.43个/km2增加至24.21个/km2,斑块形态指数由84.03增至103.20,斑块分维数由1.057增至1.059。     

大气中多环芳烃(PAHs)在松针和SPMD上的分布

通过松针监测与半渗透膜被动式采样技术 (SPMD ) ,分析了我国珠江三角洲地区大气中多环芳烃的含量特征、来源及其分布 ,同时对这两种被动式采样技术进行了比较 松针及SPMD主要富集气态多环芳烃 (2— 4环 ) ,气态多环芳烃在松针和SPMD样品中的总含量分别为 313 9— 30 4 3 5ng·g-1和 14 5—116 9ng·SPMD-1·d-1 大气中多环芳烃含量的区域差异明显 ,珠江三角洲中部地区 (广州、佛山和东莞 )大气中多环芳烃的含量高 ,沿海地区的珠海、香港偏低 ,分子标志物指数表明 ,珠江三角洲大气中的多环芳烃主要是热成因 (燃烧 )来源 松针和SPMD对气态多环芳烃的监测具有很好的一致性 ,是进行区域大气污染评价的良好生物指示物     

基于数学模型的海平面上升对咸潮上溯的影响

气候变化导致的海平面上升对沿海地区构成极大的威胁,海平面上升已经成为全球重要的环境问题,受到社会各界的高度重视。研究建立了一维动态潮流-含氯度数学模型,计算了海平面上升对咸潮上溯的影响,结果显示:250 mg/L的咸度线随着上游来水频率的增大,咸潮上溯距离明显增大;一定上游来水条件下,随着海平面的上升,咸潮上溯界线向上游方向移动显著。并详细计算了代表口门在海平面上升10 cm、30 cm和60 cm的情况下,咸潮界线的具体上移距离,以期给三角洲地区城市供水、农业灌溉引水等提供理论指导,减轻海平面上升危害,以确保21世纪中国沿海地区资源、环境、经济和社会的可持续发展。     

Willingness to pay for agricultural flood insurance in the Mekong River Delta

Increasing urbanization and industrial development upstream of the Mekong River Delta of Vietnam (MRD) including the construction of a series of dams for hydroelectricity generation is changing the downstream risk of flooding. Concerns about the likely influence of global climate change and rising sea levels add further uncertainty to this risk that threatens the livelihood of farmers. With this in mind and in view of the under-developed state of the market for crop insurance in the MRD, we survey rice growers to explore their willingness-to-pay (WTP) for crop insurance by using a choice experiment. The experimental design comprised five attributes, including the type of peril covered – riverine flooding (flooding); flooding triggered by tidal regimes (inundation); or flooding, inundation and wind damage – type of provider; extent of cover and deductible and premium. Two hundred and twenty-six rice-growing farmers were surveyed with each farmer responding to six different choices. Our study shows that WTPs for an insurance plan covering a loss up to 2 million VND/1000m²/farming season and having a deductible of 25% of the potential (profit) crop value varied between 200,000 and 500,000?VND/1000m² (1USD?=?22,550 Vietnamese Dong – VND) for each rice growing season, implying a potential market for crop insurance.     

The adsorption of PCBs to Yangtse River sediment

The adsorption of six PCB congeners to natural sediments from the Yangtse River was investigated. Experiments were conducted at different PCB concentrations to get the adsorption isotherm for each compound. Analytical determinations were carried out using gas chromato‐graphy with ECD detector. Results showed that the adsorption mechanism of PCBs on Yangtse River sediment fitted the best to the Langmuir adsorption model. It was also found that the adsorption rate decreased as the solubility increased or the octanol‐water partition coefficient decreased for each compound.     

Organochlorine pesticides and PCBs in sediments from the Yangtse River,China

Organochlorine Pesticides and PCBs pollution levels were determined in sediment samples taken from three sites along the Yangtse River (Nanjing part). The concentrations of various pesticides were in the range of 1.42–8.06 ng/g (t‐HCH), and <0.01–4.12ng/g (t‐DDT), while the concentrations of PCBs were below detection limit at all three sites. The contamination by Organochlorine Pesticides and PCBs in sediments from the Yangtse River was not significant when compared with that reported in the literature from some other countries’ rivers, which may be due to the high flow velocity and water amount of the Yangtse River.     

长江三角洲平原南部上新世以来古环境演变及多重地层划分

对长江三角洲平原BZK01钻孔进行沉积物¹⁴C测年、粒度、磁学、孢粉和微体古生物分析,结合伽玛测井、岩性地层讨论了上新世以来钻孔揭示的孢粉组合、沉积环境演化、沉积相和古气候特征,建立了钻孔的第四纪多重地层划分对比框架。结果表明,受原始地形地貌、海平面变化、海陆变迁、古气候冷暖更替及新构造运动的影响,研究区上新世以来经历了多次环境变化。钻孔自下而上揭示岩性地层依次为基岩长河组、新近纪-第四纪沉积的嘉兴组、前港组、东浦组、宁波组、镇海组,孢粉组合可划分出16个孢粉带,按暖期温暖潮湿-冷期寒冷干燥古气候旋回变化的周期律,BZK01钻孔反映该区域共存在7个古气候旋回。建立的钻孔多重地层划分对比揭示151.9～278.0 m为河流相和河湖相交替沉积的上新世-早更新世时期,存在两个气候旋回过程;83.5～151.9 m为河流相-河湖相-浅湖相沉积环境的中更新世,包含两个气候旋回过程;15.4～83.5 m为晚更新世,沉积环境自下而上为河口相-河湖相-潮坪相-滨海相-河湖相,与王店海侵-杭州海侵时期对应,包括两个气候旋回;0～15.4 m为河口相-河湖相-泻湖相沉积环境的全新世,对应富阳海侵,包括一个气候旋回。     

Persistent organic pollutants associated to water fluxes and sedimentary processes in the Colorado River delta, Baja California, México

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) were studied in sediment cores from two distinctive modern channels of the Colorado River (CR) delta. Their abundance and temporal changes are associated with flood-flows from the CR across the USA-Mexico border. The CR channel is directly exposed to river flood-flows while the Hardy River (HR) is a local channel derived mainly from agricultural runoff, geothermal effluents, and treated urban wastewater. Different headwater compositions and degrees of exposure to flood-flows appear to be the factors controlling the composition of persistent organic pollutants (POPs). Enrichment of OCPs (46 ng g⁻¹ dwt in HR and 4.37 ng g⁻¹ dwt in CR) occurred during or a few years after flooding. PCB-138 (4.2 ng g⁻¹ dwt) is enriched in HR suggesting its origin in dielectric oils from the geothermal power plant. PCB-28 (2.1 ng g⁻¹ dwt) in CR may be related with atmospheric input and/or re-deposition of upstream sediments. In surficial sediments (0-3 cm), only HR exceeds international sediment quality guidelines (4,4′-DDE = 8.16 ng g⁻¹ dwt and ΣDDT = 8.34 ng g⁻¹ dwt).     

长江三角洲城市群城乡统筹发展的空间差别化研究

以长江三角洲地区为研究对象,根据城乡统筹的内涵及特点,构建了城乡统筹发展水平的综合评价指标体系。采用全局主成分分析方法,对2000、2008年两个年份的城乡统筹水平进行了定量评估,并分析了影响长三角地区城乡统筹发展水平的影响因素。研究结果表明:①各城市城乡统筹水平差异显著,2000～2008年相对差距有微弱扩大的趋势,局部发生变动;②各城市城乡统筹水平由城市群外围向中心逐渐递增;③影响长三角城市群各城市城乡统筹发展水平的四大因子是城镇化因子、外向型经济因子、城乡收入水平及城乡交流因子。最后对长江三角洲城市群城乡统筹发展提出了有关的对策建议。