Showing papers by "Rong Xiao published in 2013"

Distribution and pollution, toxicity and risk assessment of heavy metals in sediments from urban and rural rivers of the Pearl River delta in southern China

Abstract: Sediments were collected from the upper, middle and lower reaches of both urban and rural rivers in a typical urbanization zone of the Pearl River delta. Six heavy metals (Cd, Cr, Cu, Ni, Pb and Zn) were analyzed in all sediment samples, and their spatial distribution, pollution levels, toxicity and ecological risk levels were evaluated to compare the characteristics of heavy metal pollution between the two rivers. Our results indicated that the total contents of the six metals in all samples exceeded the soil background value in Guangdong province. Based on the soil quality thresholds of the China SEPA, Cd levels at all sites exceeded class III criteria, and other metals exhibited pollution levels exceeding class II or III criteria at both river sites. According to the sediment quality guidelines of the US EPA, all samples were moderately to heavily polluted by Cr, Cu, Ni, Pb and Zn. Compared to rural river sites, urban river sites exhibited heavier pollution. Almost all sediment samples from both rivers exhibited moderate to serious toxicity to the environment, with higher contributions from Cr and Ni. A "hot area" of heavy metal pollution being observed in the upper and middle reaches of the urban river area, whereas a "hot spot" was identified at a specific site in the middle reach of the rural river. Contrary metal distribution patterns were also observed along typical sediment profiles from urban and rural rivers. However, the potential ecological risk indices of rural river sediments in this study were equal to those of urban river sediments, implying that the ecological health issues of the rivers in the undeveloped rural area should also be addressed. Sediment organic matter and grain size might be important factors influencing the distribution profiles of these heavy metals.

Levels, sources and risk assessment of trace elements in wetland soils of a typical shallow freshwater lake, China

Abstract: The deteriorating environmental conditions of Baiyangdian Lake have caused a wide public concern. Surface soils (0–20 cm) were collected at 10 sites of reed wetlands in raised fields of the Baiyangdian Lake. They were analyzed for total contents of trace elements to investigate their distribution and pollution levels in wetland soils of this region. Results showed that the mean contents of As, Cd, Cr, Cu, Ni, Pb and Zn all exceeded their environmental background values of Hebei Province and had various degree of spatial variations. As, Cr and Ni contents exceeded considerably the probable effect levels. Multivariate analysis indicated that Cr, Cd, Ni, Cu, Pb and Zn had common sources and As had different sources for these trace elements. The average toxic units (TU) of trace elements in the Baiyangdian Lake followed the order As > Ni > Cr > Zn > Pb > Cu > Cd. As, Ni and Cr made the higher contributions to ΣTUs (i.e., 41.3 ± 7.2, 21.8 ± 4.1 and 16.2 ± 2.8 %, respectively). The potential ecological risk index of Cd $$ \left( {E_{r}^{i} } \right) $$ was 213.44, which was the highest value in the Baiyangdian Lake. The other trace elements had lower potential ecological risk indices ( As > Cu > Pb = Ni > Cr > Zn. Potential toxicity response indices (RI) of trace elements for the whole lake region was 269.81, with a moderate potential toxicity response.

Soil organic carbon as affected by land use in young and old reclaimed regions of a coastal estuary wetland, China

Abstract: Soil organic carbon (SOC) and selected soil properties were measured in fringe and ditch marshes and cropland of old and young reclaimed areas in a subtropical estuary in China in order to investigate the effects of land use and reclamation history on SOC. The results show that after the conversion of wetlands to cropland, a longer reclamation history (>20 yr) resulted in greater soil bulk density, salinity, clay and silt, and lower soil moisture, SOC and sand content, whereas a shorter reclamation history (<20 yr) induced smaller values for soil pH, moisture and sand. Ditch marshes had greater average SOC in the top 50 cm than fringe marshes and cropland. SOC decreased generally down soil profiles from 0 to 50 cm in depth, except for the obvious accumulation of SOC in deeper soils from old fringe and young ditch marshes. Ditch marshes had the greatest SOC densities in the top 50 cm in both regions compared to the other land uses. SOC densities in the top 50 cm were less in croplands than in fringe marshes in the young region, while there were no significant differences between them in the older one. Except for cropland, SOC densities in the top 50 cm of the fringe or ditch marshes in the old region were not significantly different from those in the young region. SOC in both regions was reduced by 13.53 9 10 4 t (12.98%) in the top 50 cm of the marshes after conversion to cropland, whereas the regional SOC storage increased by 29.25 t when ditch marshes were included. The results from regression analysis show that bulk density and soil moisture significantly influenced SOC. The total SOC stored in both ditch marshes and croplands was higher compared to fringe marshes. The regional SOC storage in the top 50 cm was not reduced after reclamation due to C accumulation in the ditch marshes. The regional effects of cultural practices should be taken into account in devising strategies for managing soils in coastal wetlands, particularly in the developing world.

Ammonium Transport Simulation in Horizontal Soil Columns from a Natural Inland Alkaline Wetland

Abstract: Ammonium transport was simulated in horizontal soil columns from an inland alkaline wetland (Fulaowenpao wetland) of Northeast China The primary objectives of this work are to investigate the changes in ammonium transport rate with increasing distances along horizontal soil column and to determine the effects of water diffusion rate and volumetric water content on ammonium transport rate Our results showed that water diffusion coefficient was the lowest at the soil layer of 10–20 cm, followed by the 0–10 cm soil layer, and the highest value occured at the soil layer of 20–60 cm The highest ammonium transport rate also appeared at the soil layer of 20–60 cm, while the lowest value was observed at the soil layer of 10–20 cm Ammonium transport rates decreased with increasing distances along horizontal soil columns The ammonium transport rates showed higher values at the distance from 0 to 6 cm and then decreased rapidly from 6 to 18 cm However, they nearly kept constant and approached to zero after exceeding the distance of 18 cm Ammonium transport rates increased exponentially with increasing volumetric water contents and water diffusion rates The alkaline wetland soils prevented ammonium from horizontal diffusion at all soil layers under drying conditions