Temporal variation of heavy metal pollution in urban stormwater runoff

Stormwater runoff from three types of urban surfaces, a parking lot, a street, and a building roof, was monitored during four rainfall events that occurred in the one-year period from June 2009 to June 2010. The event mean concentrations （EMC） of dissolved copper （Cu）, lead （Pb）, zinc （Zn）, manganese （Mn）, and iron （Fe） exceeded China＇s National Water Quality Standards for Surface Water. The degree of heavy metal contamination was related to the type of underlying surfaces. Additionally, the concentration of dissolved heavy metals peaked shortly after the runoff began and then declined sharply as a result of adequate flushing. First flush effects of varying degrees were also observed during all of the monitored rainfall events based on the first flush ratio （FF25）. Redundancy analysis revealed that four environmental variables （rain- fall depth, intensity, antecedent dry weather period and type of underlying surface） had significant effects on the strengths of the first flush effects, accounting for 72.9% of the variation in the FF25. Dissolved metals presented varying first flush effects on different underlying surfaces that occurred in the following relative order： parking lot 〉 roof〉 road for low intensity and high runoff volume rainfall events; parking lot 〉 road 〉 roof for high intensity and low runoff volume events. The relative strength of the first flush for dissolved heavy metals was Fe, Mn 〉 Cu, Zn 〉 Pb.

Is urban development an urban river killer? A case study of Yongding Diversion Channel in Beijing, China

The high population and concrete environment alter urban areas by changing temperature, rainfall runoff, and water resource utilization activities. This study was conducted to investigate the water quality features of the Yongding Diversion Channel in Beijing, China, and its relationship with rainfall and urban development. Monthly water quality data were obtained from April to October of 2004 at monitoring sites of Sanjiadian, Gaojing, Luodaozhuang, and Yuyuangtan. The monthly water quality grades from 2007 to 2011 were also investigated and compared with those of other rivers. Dissolved oxygen and pH showed greater decreases after one or two moderate rainfall events than several light rainfall events. The potassium permanganate index （CODMn）, ammonia nitrogen （NH3-N） and total phosphorus （TP） increased more after several light rainfall events than after one or two moderate or heavy rainfall events. Pollutant concentrations （CODMn, NH3-N, TP） in downstream regions showed greater changes than those in upstream areas after heavy rainfall events. Intense human activities around the channel greatly influenced the water quality of the channel in rainy season because of runoff pollution; however, heavy rainfall had a strong dilution effect on the pollutant concentrations in rivers. Overall, urban development has obviously deteriorated the water quality of the Yongding Diversion Channel as indicated by an increase in the water quality index from 3.22 in 2008 to 4.55 in 2010. The Pearson correlation between monthly rainfall and water quality indices from 2007 to 2011 ranged from 0.1286 to 0.6968, generally becoming weaker as rainfall and rainfall runoff became more random and extreme.

A comparison of single- and multi-site calibration and validation： a case study of SWAT in the Miyun Reservoir watershed, China

An essential task in evaluating global water resource and pollution problems is to obtain the optimum set of parameters in hydrological models through calibra- tion and validation. For a large-scale watershed, single-site calibration and validation may ignore spatial heterogeneity and may not meet the needs of the entire watershed. The goal of this study is to apply a multi-site calibration and validation of the Soil and Water Assessment Tool （SWAT）, using the observed flow data at three monitoring sites within the Baihe watershed of the Miyun Reservoir watershed, China. Our results indicate that the multi-site calibration parameter values are more reasonable than those obtained from single-site calibrations. These results are mainly due to significant differences in the topographic factors over the large-scale area, human activities and climate variability. The multi-site method involves the division of the large watershed into smaller watersheds, and applying the calibrated parameters of the multi-site calibration to the entire watershed. It was anticipated that this case study could provide experience of multi-site calibration in a large-scale basin, and provide a good foundation for the simulation of other pollutants in follow- up work in the Miyun Reservoir watershed and other similar large areas.

Parameter transferability across spatial resolutions in urban hydrological modelling:a case study in Beijing,China

This study examined the influence of spatial resolution on model parameterization,output,and the parameter transferability between different resolutions using the Storm Water Management Model.High-resolution models,in which most subcatchrnents were homogeneous,and high-resolution-based low-resolution models (in 3 scenarios)were constructed for a highly urbanized catchment in Beijing.The results indicated that the parameterization and simulation results were affected by both spatial resolution and rainfall characteristics.The simulated peak inflow and total runoff volume were sensitive to the spatial resolution,but did not show a consistent tendency.High-resolution models performed very well for both calibration and validation events in terms of three indexes:1)the Nash-Sutcliffe efficiency, 2)the peak flow error,and 3)the volume error;indication of the advantage of using these models.The parameters obtained from high-resolution models could be directly used in the low-resolution models and performed well in the simulation of heavy rain and torrential rain and in the study area where sub-area routing is insignificant.Alternatively,sub-area routing should be considered and estimated approximately.The successful scale conversion from high spatial resolution to low spatial resolution is of great significance for the hydrological simulation of ungauged large areas.

Sequence of the main geochemical controls on the Cu and Zn fractions in the Yangtze River estuarine sediments

Metal speciation can provide sufficient infor- mation for environmental and geochemical researches. In this study, based on the speciation determination of Cu and Zn in the Yangtze Estuary sediments, roles of eight geochemical controls （i.e., total organic carbon （TOC）, clay, Fe/Mn in five chemical fractions and salinity） are fully investigated and sequenced with correlation analysis （CA） and principal components analysis （PCA）. Results show that TOC, clay and Fe/Mn oxides are key geochemical factors affecting the chemical speciation distributions of Cu and Zn in sediments, while the role of salinity appears to be more indirect effect. The influencing sequence generally follows the order： TOC 〉 clay 〉 Mn oxides 〉 Fe oxides 〉 salinity. Among the different fractions of Fe/Mn oxides, residual and total Fe content, and exchangeable and carbonate Mn exert the greatest influences, while exchangeable Fe and residual Mn show the poorest influences.

Multiphase redistribution differences of polycyclic aromatic hydrocarbons （PAHs） between two successive sediment suspensions

Successive sediment suspensions often happen in estuary, yet little research has probed into the difference in the release behaviors of organic compounds among different suspensions. This study took polycyclic aromatic hydrocarbons （PAHs） as typical organic contaminants and investigated the release behaviors between two successive suspensions with a particle entrainment simulator （PES）. Results showed that successive sediment suspensions lowered the concentration of dissolved PAHs in the overlying water via facilitating the re-adsorption of dissolved PAHs onto the suspended particles. Fast-release and slow-release periods of PAHs were successively observed in the both suspensions. The concentration changes of dissolved PAHs in the second suspension were generally similar with but hysteretic to those in the first suspension. More vigorous desorption and re-absorp- tion of PAHs were induced in the second suspension. Successive sediment suspensions obviously decreased the concentrations of mineral composition and organic matters in the overlying water, which significantly affects multi- phase distribution of PAHs.

Temporal-spatial variation and the influence factors of precipitation in Sichuan Province,China

Precipitation is a key factor in the water cycle.At the same time,precipitation is the focus of study in meteorology and climatology,ecological environmental assessment,non-point source pollution and so on.Understanding the temporal-spatial variation and the corresponding factors of precipitation has become the object of hydrology and environmentology.Based on the annual precipitation data,we analyzed the spatial distribution of precipitation in Sichuan Province in China as well as the temporal-spatial variation and the corresponding influence factors involved.The results show that the amount of precipitation was abundant,but the spatial distribution was not consistent with it and the amount of precipitation gradually declined from the south-east to the north-west in Sichuan Province,China.Moreover,the spatial distribution was different throughout the years.The result of correlation analysis indicated that elevation,temperature and air pressure were three key factors affecting the amount and distribution of precipitation,and the correlation coefficients were 20.56,0.38 and 0.45 respectively.Notably,the relationship between the slope of topography and precipitation were significantly negative and the average correlation coefficient was 20.28.

Temporal dimension and water quality control in an emission trading scheme based on water environmental functional zone

Emission trading is one of the most effectivealternatives to controlling water pollution.Water environmentalfunctional zone(WEFZ)is used to determine thewater quality standard and identify the zone boundary foreach river or reach.In this study,a new emission tradingscheme was addressed based on WEFZ,accounting forboth the temporal dimension and water quality control.Atemporal factor of emission trading was proposed based onvariations in the environmental capacity within a year bydividing the year into three periods,including high,normal,and low periods of environmental capacity.Duringeach period,emission trading was implemented exclusively.A water quality-control scheme was suggestedbased on the water quality requirement in the waterfunctional zone,in which the water quality at thedownstream boundary of the zone was required to meetthe water standard following auto-purification in thestream.Two methods of calculating water quality controlare addressed for point-source pollution and non-pointsourcepollution.The calculated temporal dimension andwater quality control were located in Dongxi River of theDaning Watershed in the Three Gorges Watershed.Thehigh period was during June,July,and August,the normalperiod was during April,May,September,and October,and the low period was during January,February,March,November,and December.The results from the waterquality calculation demonstrated that the discharge ofpoint-source and non-point-source pollutions led to anexcess of common contaminants at the downstreamboundary of WEFZ.The temporal and spatial factorsabove should be incorporated into the emission tradingscheme based on WEFZ.