Behavior of a Small Pulsed River Plume in a Strong Tidal Cross-Flow in the Akashi Strait

We carried out a field study of a small river plume emptying into Osaka Bay near the Akashi Strait in western Japan, to understand the fate of its urban-runoff-laden waters. As the river is weak compared to tidal currents, we find that the behavior of the plume is strongly influenced by phasing between tidal stage and currents (a westward-traveling progressive tidal wave). When the tidal stage rises, sea water floods up the river, and concentrated river effluent cannot be seen in Osaka Bay. During most of the river’s ebb, a topographic eddy transports river effluent towards the energetic Akashi Strait, while strong vertical shear in the tidal flow mixes the effluent with seawater. However, there is a short interval of time during which the direction of tidal flow in the Strait changes direction and the magnitude of the current is weak. At this time, shear is weak enough to allow a stratified plume of concentrated river water to form, and this plume is driven offshore, and into Osaka Bay, by baroclinic circulation. A sewage outfall, which is located very close to the river mouth, is subjected to these same conditions and therefore exhibits similar behavior. Understanding the relation between tidal phase and plume behavior will be useful to Kobe City, as well as other cities in a similar environment, for minimizing the environmental effects of their wastewater and non-point-source runoff.     

水库热分层期藻类水华与温跃层厌氧成因分析

以西安市李家河水库为研究对象,通过对水体理化因子和浮游植物的连续监测,对热分层期藻类垂向分布与温跃层厌氧成因进行了初步分析.结果表明:①6～9月,李家河水库水体稳定指数为2～10 m~(-1),处于稳定热分层状态,水体溶解氧呈明显的垂向以及季节差异,p H、电导率均与溶解氧呈现相同的分层结构;②李家河水体的富营养状态诱导夏季藻类水华暴发;藻细胞密度垂向差异大,集中悬停于水深0～5 m区域内,最高为2. 95×10~8cells·L~(-1),叶绿素a含量最大为46. 42mg·m~(-3);高密度藻类在温跃层内堆积分解,水深5～24 m内出现较大面积的厌氧区,pH下降、电导率和高锰酸盐指数升高;③高密度藻类分解耗氧是夏季分层期温跃层厌氧形成的主要原因.     

A Modelling Study of Transient,Buoyancy-Driven Exchange Flow over a Descending Barrier

Results are presented from a series of model studies of the transient exchange flow resulting from the steady descent of an impermeable barrier separating initially-quiescent fresh and saline water bodies having density ₀ and ₀+()₀, respectively. A set of parametric laboratory experiments has been carried out (i) to determine the characteristic features of the time-dependent exchange flow over the barrier crest and (ii) to quantify the temporal increase in the thickness and spatial extent of the brackish water reservoir formed behind the barrier by the outflowing, partly-mixed saline water. The results of the laboratory experiments have been compared with the predictions of a theoretical model adapted from the steady, so-called maximal exchange flow case and good qualitative agreement between theory and experiment has been demonstrated. The comparisons indicate that head losses of between 7% and 3% are applicable to the flow over the ridge crest in the early and late stages, respectively, of the barrier descent phase, with these losses being attributed to mixing processes associated with the counterflowing layers of fresh and saline water in the vicinity of the ridge crest. The experimental data show (and the theoretical model predictions confirm) that (i) the dimensionless time of detection t _det(g/H _b)^1/2 of the brackish water pool fed by the dense outflow increases (at a given distance from the barrier) with increasing values of the descent rate parameter g'H _b/(dh _b/dt)² and (ii) the normalised thickness (x,t)/H _b of the pool at a given reference station increases monotonically with increasing values of the modified time (t–t _det)/(H _b/g)^1/2, with the rate of thickening decreasing with increasing values of the descent rate parameter g'H _b(dh _b/dt)². Here, g=(g/₀)()₀ is the modified gravitational acceleration, H _b is the mean depth of the water and dh _b/dt denotes the rate of descent of the barrier height h _b with elapsed time t after the two water bodies are first brought into contact.     

暴雨径流对分层水库水质的影响

为探明西安金盆水库热分层演变特征和降雨径流对水库水质的影响,对水库垂向不同点位的水温、溶解氧、浊度、pH、总磷、总氮、氨氮、总有机碳等水质指标进行了持续监测和分析,结果表明：RWCS/H指数能有效判断热分层稳定水平,稳定分层期RWCS/H指数在1.56~6.99 m-1之间;RWCS/H指数与TP、厌氧层厚度显著相关,温跃层的变化特征对厌氧层变化起支配作用,分层期水库底部厌氧条件致使沉积物中营养盐大量释放,其中滞水层TP最高达0.062 mg·L-1;汛期暴雨径流一方面破坏水体热分层稳定性,另一方面携带大量颗粒态污染物以间层流的形式潜入水库中下层水体,使污染负荷提高,TP、TN、NH4+-N、TOC浓度分别达到0.052、1.589、0.42和3.784 mg·L-1;随暴雨径流潜入带来的大量颗粒态污染物和下层水温、pH上升导致沉积物厌氧释放加剧,雨后下层水体TP、TN、NH4+-N、TOC浓度分别达0.022、1.474、0.595和4.559 mg·L-1,显著高于上层水体。分层期内源释放是加快金盆水库富营养化过程的关键因素,汛期暴雨径流引发的水库水环境系统改变使得水质突发性污染风险加大。     

三峡库区支流回水区水体分层与藻类生长

三峡水库自2003年蓄水以来,库区支流形成了长短不一的回水河段,缓慢的水流和蓄积的营养盐导致回水河段由库区蓄水之初在短时间内出现水华,逐步发展到一年内水华可维持数月。为了研究回水区水环境与水华发生的关系,从2013年4月—12月,对库区北岸最大支流澎溪河的长年回水区——高阳平湖进行了定点监测。监测结果显示,季节性变化及三峡库区特殊的调度方式,导致高阳平湖水体在春、夏和秋季有明显分层。春季水华期间藻类群落结构单一,只出现4门9属,以蓝藻门的微囊藻(Microcystis)、绿藻门的实球藻(Pandorina)和空球藻(Eudorina)为主,秋季藻类结构组成增至7门52属,优势属逐渐被硅藻门的小环藻(Cyclotella)和针杆藻(Synedra)取代,水体各层藻类细胞密度差异消失。研究结果说明高阳平湖水体分层状况影响藻类生长和分布。     

Optimal pollution permit endowments in markets with endogenous emissions

In a permit market with endogenous emissions, both firms and citizens purchase permits. Presented here are static and dynamic models of pollution permit markets with endogenous emissions. The optimal permit endowments are characterized when the regulator faces uncertainty about damages and uncertainty about the severity of the citizens’ collective action problem. Due to the possibility of learning over time, the regulator issues a larger number of permits in the first period of the dynamic model than in the static model.     

银川市冬季两次典型持续大气污染过程对比分析

为了探究边界层气象要素时空分布及其变化对银川市冬季持续污染天气过程污染物质量浓度变化的影响机制,利用2016年12月1日-2017年1月31日逐时空气质量以及地面和逐日定时探空气象观测数据,根据大气污染级别和过程持续时间,选取2016年12月9-21日（简称"1211过程"）和2016年12月29日-2017年1月9日（简称"1231过程"）为研究对象,采用统计和天气诊断相结合的方法,在分析比较银川市冬季两次典型持续污染过程演变特征及其与地面气象要素关系的基础上,探讨了大气环流、边界层要素变化对银川市冬季典型污染过程的可能影响机制.结果表明:①银川市冬季两次大气污染过程持续阶段,地面均以偏东或偏南风为主,风速较小,相对湿度较大,能见度较低;在污染清除阶段,地面风向转为西北或偏北风,风速较大,相对湿度较小,能见度较高.②当冬季欧亚大陆中纬度区域500 hPa高空盛行纬向气流,850 hPa高度上银川市受反气旋环流和暖温度脊控制,并且有弱暖平流从西南部向北输送时,银川市易出现静稳型持续污染天气.③冬季银川市持续大气污染过程中,ρ（PM_2.5）与风速呈负相关（R平均值为-0.326）,与相对湿度呈正相关（R平均值为0.688）,与能见度呈显著负相关（R平均值为-0.905）,与边界层高度呈较显著负相关（R平均值为-0.575）.④银川市冬季静稳型持续污染天气主要分为弱西北和平直西风气流型两种,弱西北气流型具有近地面层逆温弱,污染物积累慢,清除快的特征;平直西风气流型具有近地面层逆温强,污染物积累快,清除慢的特征.研究显示,冬季银川市上空500 hPa高度盛行纬向气流,地面主导风向为偏东或偏南风时,随着地面相对湿度增大、近地层风速减小、大气垂直上升运动减弱、边界层高度降低,大气中ρ（PM_2.5）将迅速升高,银川市易出现以PM_2.5为首要污染物的静稳型持续污染天气.      

亚热带深水水库——龙滩水库季节性分层与富营养化特征分析

为揭示亚热带大型深水水库——龙滩水库水体季节性分层和富营养化特征,于2012年11月(枯水期),2013年4月(平水期)和7月(丰水期)对其环境因子及富营养化指标进行研究.结果表明:1龙滩水库分层结构呈不完全混合型湖泊特征,枯水期为单温跃层结构,表层至60 m为混合层,60~80 m为温跃层,80 m以后为永滞层.平水期和丰水期为双温跃层结构,表层到10 m为混合层,10~20 m为温跃层,20~40 m为混合层,40~60 m为次温跃层,60 m以后为混合层.2水温分层主导其它环境因子的分层结构,分层结构限制了水体上下对流,尤其永滞层的存在减少了内源污染的危害.3水库枯水期综合营养指数(TLI)在23.4~32.8之间,平水期在27.1~38.6之间,丰水期在26.0~45.1之间,均呈贫营养到中营养状态,其中总氮营养状态指数TSIc(TN)在60.3~72.5之间,呈富营养到重度富营养状态,氮磷比为107∶1,呈磷限制型.     

活性污泥胞外聚合物(EPS)的分层组分及其理化性质的变化特征研究

针对活性污泥的胞外聚合物(EPS),采用阳离子交换树脂(CER)法和离心/超声波法对总EPS和分层EPS(由外至内依次为slime,LB-EPS,TB-EPS)分别进行提取,测定EPS中多糖(PS)、蛋白质(PN)和DNA的含量,并对各EPS溶液的理化特性随溶液条件的变化特征进行了探讨.结果表明,EPS的化学组分(PS、PN和DNA)在TB-EPS层中含量最高,其亲水性组分的含量高于疏水性组分,但PN的疏水比高于PS.各层EPS中PS/PN的值对其Zeta电位和等电点有重要的影响.其中,PS/PN越高,各层EPS的Zeta电位越小,分层EPS的等电点越高.各种EPS溶液pH的增加导致其Zeta电位基本呈下降趋势,对应的等电点分别为pH总EPS=2.9、pHslime=2.2、pHLB-EPS=2.3、pHTB-EPS=1.3.离子强度的增加可以导致EPS溶液的电导率呈直线上升,对应的Zeta电位却迅速增加然后趋于稳定,但并未出现电位逆转现象.此外,升高温度(<40℃)可以降低各种EPS溶液的表观黏度,并在40～60℃之间时逐渐趋于稳定.     

太湖水温分层现象的监测与分析

水温是湖泊环境研究中的重要物理参数之一。湖泊中水温的状况及其分层现象将直接或间接的影响到湖库水环境中的各种物理、化学和生物过程。深水型湖泊的温度成层现象为众多学者所公认,也是研究热点之一,而浅水型湖泊的温度成层温差小、持续时间短,因此鲜有此方面的研究。本文以典型浅水湖泊－－太湖为研究对象,根据现场近3个月的监测资料,分析了太湖的水温结构,证明了太湖水温日成层现象的存在,并对太湖日成层现象发生规律及其影响因素做了初步的探讨。