Huanguang Deng

Toxic heavy metal contamination and risk assessment of street dust in small towns of Shanghai suburban area, China

The aims of this paper were to quantify the heavy metal concentrations in street dust of small towns in Shanghai suburban area compared with those in urban area, and examine their seasonal and spatial variations, and to assess their risks to water environment and local populations. Street dust samples were collected from three small towns and urban area in Shanghai in different seasons. Levels of heavy metals were determined by atomic adsorption spectrophotometer analyzer. The method of potential ecological risk index and the health risk assessment model were used to evaluate the potential risks to water bodies and local residents, respectively. The mean metal concentrations in street dust of small towns were far above soil background values but still lower than those in the urban area. No significant seasonal change was observed except for Cr, Ni, and Zn concentrations. Higher metal concentrations tended to be located in central area of towns and township roads. The integrated metal contamination was high and posed a strong potential ecological risk. Children had greater health risk than adults. The carcinogenic risk probabilities were under the acceptable level. The hazard index values to children were close to the safe level. Street dust from the studied area has been contaminated by heavy metals. The contamination of these elements is related more to the pollution source than seasonal change. The combination of the six metals may threaten the water environment and has non-cancer health risk to children, but not to adults.

Nitrous oxide emissions in the Shanghai river network: implications for the effects of urban sewage and IPCC methodology

Global nitrogen (N) enrichment has resulted in increased nitrous oxide (N(2)O) emission that greatly contributes to climate change and stratospheric ozone destruction, but little is known about the N(2)O emissions from urban river networks receiving anthropogenic N inputs. We examined N(2)O saturation and emission in the Shanghai city river network, covering 6300 km(2), over 27 months. The overall mean saturation and emission from 87 locations was 770% and 1.91 mg N(2)O-N m(-2) d(-1), respectively. Nitrous oxide (N(2)O) saturation did not exhibit a clear seasonality, but the temporal pattern was co-regulated by both water temperature and N loadings. Rivers draining through urban and suburban areas receiving more sewage N inputs had higher N(2)O saturation and emission than those in rural areas. Regression analysis indicated that water ammonium (NH(4)(+)) and dissolved oxygen (DO) level had great control on N(2)O production and were better predictors of N(2)O emission in urban watershed. About 0.29 Gg N(2)O-N yr(-1) N(2)O was emitted from the Shanghai river network annually, which was about 131% of IPCCs prediction using default emission values. Given the rapid progress of global urbanization, more study efforts, particularly on nitrification and its N(2)O yielding, are needed to better quantify the role of urban rivers in global riverine N(2)O emission.

Heavy Metal Contamination and Assessment of Roadside and Foliar Dust along the Outer-Ring Highway of Shanghai, China

Foliar and roadside dust samples were collected from five sites along the outer-ring highway of Shanghai, one of the biggest metropolitan areas of China, to assess heavy/toxic metal contamination. Concentrations of Zn, Cu, Ni, As, and Hg in foliar dust were higher than in roadside dust, whereas concentrations of Pb and Cd were higher in roadside dust. In the roadside dust, average concentrations of all metals except As in foliar and roadside dust samples were significantly above the background values of soil in Shanghai: the ratios between the average of samples and background values of Shanghai were in the order: Cd (25.1) > Zn (12.2) > Cu (6.16) > Pb (5.74) > Ni (5.50) > Hg (5.18) > As (1.05). By using the geo-accumulation index, the pollution grades of seven heavy metals at five sampling sites were calculated. Roadside dust was heavily to extremely contaminated with Cd; moderately to heavily contaminated with Zn; and moderately contaminated with Cu, Hg, Pb, and Ni. Foliar dust was heavily contaminated with Cd; moderately to heavily contaminated with Zn and Cu; and moderately contaminated with Hg, Pb, and Ni. The contamination level of heavy metals in the Puxi area was greater than that in the Pudong area, which might be related to the industrial distribution and land use. Combined with correlation analysis, hierarchical cluster analysis indicated that atmospheric deposition is the main source of Cd, Hg, As, and Pb in dust and that Cu and Zn in dust are mainly from heavy traffic on the highway. A portion of Ni in dust also comes from the parent soil.

Vertical dissolved inorganic nitrogen fluxes in marsh and mudflat areas of the yangtze estuary.

Nitrogen (N) is a dominant macronutrient in many river-dominated coastal systems, and excess concentrations can drive eutrophication, the effects of which can include hypoxia and algal blooms. The Yangtze River in China transports a large amount of dissolved inorganic N. Therefore, it is important to understand the role of the marsh and mudflat areas within the estuary on processing this exogenous N load. In situ dissolved inorganic nitrogen (DIN) fluxes across the sediment-water interface were determined monthly at Chongming Island at two sites (a vegetated marsh and an unvegetated mudflat) and were compared with rates from a previously published laboratory incubation study by our research group. Results from the in situ study showed that NO flux rates comprised the major component of total DIN flux, ranging from 55 to 97%. No significant difference was observed in the N flux rates between the marsh and mudflat sites. Overall, sediment at both sites served as a sink of DIN from surface water with mean flux rates of -178 μmol m h and -165 μmol m h for the marsh and mudflat, respectively. In general, DIN flux rates were not significantly correlated with DIN concentrations and other measured parameters (temperature, dissolved oxygen, salinity, and pH) of surface water. The in situ measured fluxes of NO and NO in this study were not significantly different from those of our previous laboratory incubation ( > 0.05), whereas NH fluxes in situ were significantly lower than those from the laboratory core incubations ( < 0.05). This result suggests that caution should be used when extrapolating rates from laboratory incubation methods to the field because the rates might not be equivalent.

Metal release/accumulation during the decomposition of Potamogeton crispus in a shallow macrophytic lake

Changes in metal concentrations in the litter of Potamogeton crispus were monitored during a consecutive 40-day in situ decomposition experiment using the litterbag method. The accumulation index was calculated and used to indicate the changes in the metals in litter. The results showed that the concentrations of Al, Cd, Cr, Fe, Mn, and Pb in litter increased significantly during the decomposition, while Cu and Zn concentrations decreased dramatically. Significant positive correlations were found between the concentrations of Al, Cr, Fe, and Mn and between Cu and Zn. Moreover, Cu and Zn both negatively correlated with Al and Fe. The remaining dry mass was negatively correlated with Al and Fe concentrations but positively correlated with Cu and Zn concentrations. Generally the accumulation index values of metals other than Al were less than one, indicating that the litter of P. crispus acted as a source of metals to the surrounding water body. Al was the only metal that showed continuous net accumulation in litter. The net accumulation of Fe and Mn in litter during the last 10 days of the experiment may indicate the precipitation of Fe- and Mn-oxides. It was estimated that 160 g/m(2) (dry weight) P. crispus was decomposed in 40 days. This was equivalent to releasing the following amounts of metals: 0.01 mg Cd, 0.03 mg Cr, 0.71 mg Cu, 0.55 mg Mn, 0.02 mg Pb and 13.8 mg Zn into surrounding water, and accumulating 149 mg Al and 11 mg Fe, in a 1m(2) area.

Carbon dioxide and methane dynamics in a human‐dominated lowland coastal river network (Shanghai, China)

Evasion of carbon dioxide (CO2) and methane (CH4) in streams and rivers play a critical role in global carbon (C) cycle, offsetting the C uptake by terrestrial ecosystems. However, little is known about CO2 and CH4 dynamics in lowland coastal rivers profoundly modified by anthropogenic perturbations. Here, we report results from a long-term, large-scale study of CO2 and CH4 partial pressures (pCO2 and pCH4) and evasion rates in the Shanghai river network. The spatiotemporal variability of pCO2 and pCH4 were examined along a land-use gradient and the annual CO2 and CH4 evasion were estimated to assess its role in regional C budget. During the study period (August 2009 – October 2011), the overall mean pCO2 and median pCH4 from 87 surveyed rivers were 5846±2773 μatm and 241 μatm, respectively. Internal metabolic CO2 production and DIC input via upstream runoff were the major sources sustaining the widespread CO2 supersaturation, coupling pCO2 to biogeochemical and hydrological controls, respectively. While CH4 was oversaturated throughout the river network, CH4 hotpots were concentrated in the small urban rivers and highly discharge-dependent. The Shanghai river network played a disproportionately important role in regional C budget, offsetting up to 40% of the regional terrestrial net ecosystem production (NEP) and 10% of net C uptake in the river-dominated East China Sea fueled by anthropogenic nutrient input. Given the rapid urbanization in global coastal areas, more research is needed to quantify the role of lowland coastal rivers as a major landscape C source in global C budget.

Methane and nitrous oxide dissolved concentration and emission flux of plain river network in winter

Methane (CH4) and nitrous oxide (N2O) concentration, saturation and fluxes in river network of Shanghai city (Yangtze Delta) and Tianjin city (Haihe watershed) were investigated in winter. Results showed that CH4 and N2O concentration were high in river network and supersaturated. The average of CH4 concentration was 0.86 μmol/L (saturation: 758%), and ranged from 0.043±0.001 to 25.3±9.32 μmol/L. The average of N2O concentration was 86.8 nmol/L (saturation: 488%), and ranged from 9.71±0.41 to 691±35.2 nmol/L. CH4 and N2O concentration in two sewage draining rivers of Tianjin city were clearly higher than other rivers (Average CH4 and N2O concentration were 38.4 μmol/L and 88.9 nmol/L, respectively). There is significant spatial variation of CH4 and N2O concentration and saturation, data of concentration and saturation in Shanghai river network was significant higher than in Tianjin city. Air-water interface fluxes of CH4 and N2O widely varied from -1.35±0.22 to 665±246 μmol/m2 h (Average was 24.1 μmol/m2 h), and from -0.19±0.02 to 22.6±5.05 μmol/m2 h (Average was 2.28 μmol/m2 h), respectively. CH4 concentration had significant negative correlation with dissolved oxygen (DO), but positive with ammonium (NH4+), and N2O concentration had significant positive correlation with NH4+ and nitrate and nitrite (NO3-+NO2-). Air-water interface fluxes of CH4 and N2O in urban area were evidently higher than in suburban and rural area, implicating that seriously polluted river is a potential source of atmospheric CH4 and N2O.