Shaohua Wu

Polycyclic aromatic hydrocarbons in soils from urban to rural areas in Nanjing: Concentration, source, spatial distribution, and potential human health risk

Polycyclic aromatic hydrocarbons (PAHs) have become a major type of pollutant in urban areas and their degree of pollution and characteristics of spatial distribution differ between various regions. We conducted a comprehensive study about the concentration, source, spatial distribution, and health risk of 16 PAHs from urban to rural soils in Nanjing. The mean total concentrations of 16 PAHs (∑16PAHs) were 3330 ng g(-1) for urban soils, 1680 ng g(-1) for suburban soils, and 1060 ng g(-1) for rural soils. Five sources in urban, suburban, and rural areas of Nanjing were identified by positive matrix factorization. Their relative contributions of sources to the total soil PAH burden in descending order was coal combustion, vehicle emissions, biomass burning, coke tar, and oil in urban areas; in suburban areas the main sources of soil PAHs were gasoline engine and diesel engine, whereas in rural areas the main sources were creosote and biomass burning. The spatial distribution of soil PAH concentrations shows that old urban districts and commercial centers were the most contaminated of all areas in Nanjing. The distribution pattern of heavier PAHs was in accordance with ∑16PAHs, whereas lighter PAHs show some special characteristics. Health risk assessment based on toxic equivalency factors of benzo[a]pyrene indicated a low concentration of PAHs in most areas in Nanjing, but some sensitive sites should draw considerable attention. We conclude that urbanization has accelerated the accumulation of soil PAHs and increased the environmental risk for urban residents.

Determining the contributions of urbanisation and climate change to NPP variations over the last decade in the Yangtze River Delta, China.

Terrestrial net primary production (NPP) is an important measure of global change, and identifying the relative contributions of urbanisation and climate change to NPP is important for understanding the impact of human and natural influences on terrestrial systems and the carbon cycle. The objective of this study was to reveal how urbanisation and climate drive changes in NPP. Satellite-based estimates of NPP collected over a 12-year period (1999-2010) were analysed to identify NPP variations in the Yangtze River Delta. Temporal and spatial analysis methods were used to identify the relationships among NPP, nighttime light urbanisation index values, and climatic factors from pixel to regional scales. The NPP of the entire Yangtze River Delta decreased slightly at a rate of -0.5 g C m(-2)a(-1) from 1999 to 2010, but this change was not significant. However, in the urban region, NPP decreased significantly (p<0.05) at a rate of -4.7 g C m(-2)a(-1) due to urbanisation processes. A spatially explicit method was proposed to partition the relative contributions of urbanisation and climate change to NPP variation. The results revealed that the urbanisation factor is the main driving force for NPP change in high-speed urbanisation areas, and the factor accounted for 47% of the variations. However, in the forest and farm regions, the NPP variation was mainly controlled by climate change and residual factors.

Heavy metals in food crops, soil, and water in the Lihe River Watershed of the Taihu Region and their potential health risks when ingested

Environmental pollution by heavy metals resulting from rapid economic development is a major concern. Soil, water, wheat, and rice samples were collected from the Lihe River Watershed in the Taihu Region (east China). In this study area, many types of industrial plants, including ceramics factories, plants working with refractory materials, and chemical plants are densely distributed and cause serious heavy metal pollution. In addition, well-developed transportation and agricultural activities are also important sources of heavy metals. Thus, the concentrations of selected heavy metals including cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in the samples were analyzed to evaluate their potential integral risk (IR) to the health of the local population. Accordingly, the spatial distribution pattern of the IR values was determined in the study. The soil in the study area showed heavy Cd pollution, whereas the pollution by other elements was relatively slight. When the proportions of grain samples in which the concentrations exceeded the tolerance limits were examined, the grains were primarily contaminated with Pb, Ni, Cd, and Zn; and less contaminated with Cu and Cr. The drinking water of the local inhabitants was safe. The average IR value was 3.53 for adults and 3.91 for children, indicating that both adults and children may experience adverse health effects. The spatial distribution pattern of the IR values among the exposed populations in the study area showed high values in the eastern and middle parts, with maximum values >5, and low values in the western part, with minimum values <2. This is consistent with the distributions of the industries and the population. The study may provide a basis for comparison to other regions both in China and worldwide.

Density and Stability of Soil Organic Carbon beneath Impervious Surfaces in Urban Areas

Installation of impervious surfaces in urban areas has attracted increasing attention due to its potential hazard to urban ecosystems. Urban soils are suggested to have robust carbon (C) sequestration capacity; however, the C stocks and dynamics in the soils covered by impervious surfaces that dominate urban areas are still not well characterized. We compared soil organic C (SOC) densities and their stabilities under impervious surface, determined by a 28-d incubation experiment, with those in open areas in Yixing City, China. The SOC density (0–20 cm) under impervious surfaces was, on average, 68% lower than that in open areas. Furthermore, there was a significantly (P<0.05) positive correlation between the densities of SOC and total nitrogen (N) in the open soils, whereas the correlation was not apparent for the impervious-covered soils, suggesting that the artificial soil sealing in urban areas decoupled the cycle of C and N. Cumulative CO2-C evolved during the 28-d incubation was lower from the impervious-covered soils than from the open soils, and agreed well with a first-order decay model (C tu200a=u200aC 1+C 0(1-e -kt)). The model results indicated that the SOC underlying capped surfaces had weaker decomposability and lower turnover rate. Our results confirm the unique character of urban SOC, especially that beneath impervious surface, and suggest that scientific and management views on regional SOC assessment may need to consider the role of urban carbon stocks.

Installation of impervious surface in urban areas affects microbial biomass, activity (potential C mineralisation), and functional diversity of the fine earth

Artificial soil sealing in urban areas has attracted increasing attention due to its potential hazard to urban ecosystems. It has negative impacts on soil function and the urban environment, since the impervious surface can hamper the exchange of material and energy between the soil and other environmental compartments. However, information about the effects of artificial soil sealing in urban area on soil quality and properties, especially the microbiological components, is still limited. Ten plots which differed in land use were selected from Nanjing City, China, to investigate the effects of impervious surfaces on microbiological characteristics in urban soil. Plot types were paved road, residential paved square, residential paved alley, and grassed area. Soil microbial biomass carbon (Cmic) and nitrogen (Nmic), and activities were analysed, and the microbial functional diversity of fine earth (<2u2009mm material) was characterised by the Biolog EcoPlate technique. Mean concentrations of soil organic carbon (SOC), Cmic, and Nmic in fine earth from the impervious areas (0–20u2009cm) were, respectively, 6.5u2009gu2009kg–1, 55.8u2009mgu2009kg–1, and 12.2u2009mgu2009kg–1, which were significantly lower than concentrations from grass areas. Urban sealing also resulted in decreases in soil microbial activity and functional diversity, but the influences on soil microbial diversity varied among land uses, with road pavement having the most negative effect. Substrate use patterns showed that microorganisms in urban sealed soils had higher utilisation of polymers (Pu2009<u20090.05) but lower use of carbohydrates and amines/amides (Pu2009<u20090.05). These findings demonstrate that SOC in the sealed soils was more stable than in open soils, and the installation of impervious surfaces such as asphalt and concrete, which are very common in urban areas, can result in decreases in SOC content, soil microbial activity, and diversity in urban soil.

Modeling and mapping of critical loads for heavy metals in Kunshan soil

The assessment of critical loads of metals in soil can be used as an important tool for evaluation and for risk precaution of future inputs of metal in order to avoid the occurrence of heavy metal pollution and its long-term risks for people. In this study, critical loads of Cd, Cu, and Pb in farming and non-farming areas of Kunshan were calculated based on three main effects. Two of these effects, limit value of daily metals dose and different environmental water quality criteria are new ways to calculate the critical content of heavy metals. The mean value of critical loads decreased in the order Cu>Pb>Cd when calculated using mass balance effects, child health risk effects, and adult health risk effects. Critical loads were highest in the areas near construction land, areas of low critical load were scattered throughout the city. The areal proportion of critical load exceedance is greatest for Pb based on mass balance effects, followed by Cu based on water quality effects, and Cd based on mass balance effects. Exceedances only occurred in 6% and 3% of farming areas for water quality effects for Cd and Pb when compared critical load values to the input fluxes in the Yangtze River delta. However, for these metals, values were up to 83% and 100%, respectively, based on mass balance effects. Exceedances completely covered non-farming areas for each effect for Pb. Most exceedances occurred in the north and south of the city in non-farming areas. Spatially explicit critical loads of heavy metals based on the different effects can serve as a reference for controlling the emissions of heavy metals effectively and meeting the demands of different management objectives.

An approach to partition the anthropogenic and natural components of heavy metal accumulations in roadside agricultural soil

This paper describes a new approach that allows us to partition the anthropogenic and natural contributions to heavy metal accumulations in roadside agricultural soils. This approach, combining trend analysis and multivariate statistical analysis, partitions total heavy metals into three components: anthropogenic, natural, and unexplained residual. The approach was applied in a case study in Yixing City, China, to determine the spatial distributions of heavy metal accumulations. The results show that anthropogenic components of Pb, Cu, Zn, and Cd account for 52.4%, 23.04%, 5.09%, and 10.9% of total content, respectively. Spatial distributions of anthropogenic components are characterized by decreasing accumulation with increasing distance from the road. Ranges of influence of traffic for Pb, Cu, and Cd are beyond 300xa0m, whereas the range of Zn is less than 200xa0m. The spatial distributions of the four elements’ natural components show relatively similar distribution patterns. Assessments of variable partition methods show that the predicted values of Pb, Cu, Zn, and Cd are consistent with their measured values. The anthropogenic components extracted from total contents of heavy metal will be useful for modeling heavy metal accumulations produced by human activities.

Human health risks of polycyclic aromatic hydrocarbons in the urban soils of Nanjing, China

Polycyclic aromatic hydrocarbons (PAHs) are a major group of toxic pollutants in urban areas. We calculated the critical concentrations of PAHs in the urban soils of Nanjing, China based on a human health risk assessment. In the study area, the risk was divided into four levels and toxic equivalent values of benzo[a]pyrene (BaPeq) corresponded to <70ngg-1, 70-700ngg-1, 700-7000ngg-1, and >7000ngg-1. By this standard, most urban areas in Nanjing fall under level II (potentially low risk), while older urban districts, commercial centers, and transportation centers exceed the critical concentration (level III) at present. Additionally, the correlations between PAH concentrations, factors associated with urbanization, and soil properties were analyzed. Population density and black carbon content were determined to be the key factors involved. Multiple linear regression models and the scenario simulation method were used to predict PAH levels in urban soils through 2030. The results indicated that the future distribution characteristics of soil BaPeq under various scenarios were different than at present, but PAH concentrations remained stable only under the low‑carbon scenario. Therefore, the consumption of traditional fossil fuels should be controlled and replaced with alternative energy sources. In addition, the growth of traffic land use should be controlled in the southern and southwestern parts of the urban area.

Land-use regionalization based on landscape pattern indices using rough set theory and catastrophe progression method

This study presents the rough set theory and catastrophe progression method to regionalize the land-use change and to analyze the land ecological process. It uses the land-use database of Yixing City of Jiangsu Province, an urbanized and industrialized city in Yangtze River Delta of China, as an exemplification. The study area is divided into six kinds of land-use types according to the national standard of land-use classification. It includes arable land, garden, woodland, urban–rural construction land, water, and unused land. The six kinds of land-use types are formed into their corresponding landscape types in the scale of 1:10,000 by the aid of ArcGIS9.3 software of ESRI. In ArcGIS9.3, the landscape pattern indices are calculated by using Fragstats (raster version 3.3) software. Based on these landscape pattern indices, an integrated indicator system of landscape regionalization of land use in Yixing was established, and land-use regionalization models are set up using the catastrophe theory. Rough set theory is introduced to avoid the subjectivity in the indicator’s importance in catastrophe models. The hidden rule among the raw data is acquired by knowledge reduction of the data mining in the rough set theory. In the process, indicators needed to be arranged according to the computed importance of an attribute without considering the determination of weight function. This greatly avoids the subjectivity in the process of weight factor determination. The zoning of land use based on landscape indices finally is made by the multi-indicator integrated catastrophe progression method. According to these indices, Yixing is divided into four grading land-use zones when the rough set and catastrophe progression methods are combined. The zones include high-, medium-, low-, and weak-intensity zones, indicating that land use primarily varies the landscape pattern. With the increase of water and forest area proportion, the human disturbance to land system wanes; patch fragmentation reduces; patch shape complexity enhances; and landscape diversity decreases. Moreover, it can mostly avoid the subjective evaluation in artificially determining factor weights by using rough set theory. It makes the zoning results more objective and exact.

Spectral response of different eroded soils in subtropical china: A case study in Changting County, China

Hyper-spectral data is widely used to determine soil properties. However, few studies have explored the soil spectral characteristics as response to soil erosion. This study analysed the spectral response of different eroded soils in subtropical China, and then identify the spectral characteristics and soil properties that better discriminate soils with different erosion degrees. Two methods were compared: direct identification by inherent spectral characteristics and indirect identification by predictions of critical soil properties. Results showed that the spectral curves for different degrees of erosion were similar in morphology, while overall reflectance and characteristics of specific absorption peaks were different. When the first method is applied, some differences among different eroded groups were found by integration of associated indicators. However, the index of such indicators showed apparent mixing and crossover among different groups, which reduced the accuracy of identification. For the second method, the correlation between critical soil properties, such as soil organic matter (SOM), iron and aluminium oxides and reflectance spectra, was analysed. The correlation coefficients for the moderate eroded group were primarily between −0.3 to −0.5, which were worse than the other two groups. However, the maximum value of R2 was obtained as 0.86 and 0.94 for the non-apparent eroded and the severe group. Furthermore, these two groups also showed some differences in the spectral response of iron complex state (Fep), Aluminium amorphous state (Alo) and the modelling results for soil organic matter (SOM). The study proved that it is feasible to identify different degrees of soil erosion by hyper-spectral data, and that indirect identification by modelling critical soil properties and reflectance spectra is much better than direct identification. These results indicate that hyper-spectral data may represent a promising tool in monitoring and modelling soil erosion.