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The purpose of this study was to investigate the regional Cadmium (Cd) concentration levels in soils and in leaf vegetables across the Pearl River Delta (PRD) area; and reveal the transfer characteristics of Cadmium (Cd) from soils to leaf vegetable species on a regional scale. 170 paired vegetables and corresponding surface soil samples in the study area were collected for calculating the transfer factors of Cadmium (Cd) from soils to vegetables. This investigation revealed that in the study area Cd concentration in soils was lower (mean value 0.158 mg kg(-1)) compared with other countries or regions. The Cd-contaminated areas are mainly located in west areas of the Pearl River Delta. Cd concentrations in all vegetables were lower than the national standard of Safe vegetables (0.2 mg kg(-1)). 88% of vegetable samples met the standard of No-Polluted vegetables (0.05 mg kg(-1)). The Cd concentration in vegetables was mainly influenced by the interactions of total Cd concentration in soils, soil pH and vegetable species. The fit lines of soil-to-plant transfer factors and total Cd concentration in soils for various vegetable species were best described by the exponential equation (y = ax(b)), and these fit lines can be divided into two parts, including the sharply decrease part with a large error range, and the slowly decrease part with a low error range, according to the gradual increasing of total Cd concentrations in soils.

Soil erosion is one of the most serious driving forces of ecosystem degradation in the world that strongly affected by rainfall intensity and slope gradient. Therefore, a laboratory simulated rainfall study, with three slope gradients (5°, 15°, and 25°) subjected to seven rainfall intensities (30, 60, 90, 120, 180, 210, and 270 mm/h), was conducted to determine the effect of rainfall intensity and slope gradient on runoff generation, rate, sediment yielding, erosion rate, and runoff hydraulics characteristics of the red soil slope. The results indicated that runoff generation of red soil slopes was influenced by both the slope angle and rainfall intensity, runoff rate showed a steady condition after an initial trend of an unsteadily increased with increasing rainfall duration, while it did not increase with the increasing slope gradients, especially under the high rainfall intensity. Under the influence of high rainfall intensities, sediment yielding of the red soil slope was controlled by detachment limitation and then by transport limitation under low rainfall intensity. Under low and moderate rainfall intensities, erosion rate increased with slope angle due to the factors related to slope angle can enhance soil detachment or limit the protective effect of surface layer. Furthermore, runoff hydraulic characteristics of the red soil slope indicating that overland flows on all slopes were considered as laminar, tranquil, and supercritical, and the Reynolds numbers were significantly correlated with rainfall intensity. Results from this study can expand the understanding of the relationship among slope gradient, rainfall intensity, and erosion characteristics in the red soil region.

Optimisation of models applied in sheet erosion equations could facilitate effective management of sheet erosion in the field, and sustainable agricultural production. To optimise the characterisation of sheet erosion on slope farmland in South China, the present study conducted field simulation rainfall experiments with vegetated and fallow soils. According to the results, sheet erosion rate first increased with an increase in rainfall duration and then stabilised. Exclusive P. vulgaris planting and P. vulgaris in combination with earthworms could reduce sheet erosion by 10–60%, and the combined method could better control sheet erosion. There were significant differences in erosion rate between mild and steep slopes, and light and heavy rain conditions. The influence of rain intensity on sheet erosion was greater than that of slope. Soil organic matter (SOM), rain intensity, and slope can be used to optimise sheet erosion equations of exposed slopes, and SOM and hydraulic parameters can be used to optimise sheet erosion equations in vegetated slopes. The results of the present study could facilitate the reduction of the time and space variability errors in the establishment of sheet erosion models for vegetated slopes.

Accurate knowledge of the quality and environmental impact of the highway runoff in Pear River Delta, South China is required to assess this important non-point pollution source. This paper presents the quality characterization and environmental impact assessment of rainfall runoff from highways in urban and rural area of Guangzhou, the largest city of Pear River Delta over 1 year's investigation. Multiple regression and Pearson correlation analysis were used to determine influence of the rainfall characteristics on water quality and correlations among the constituents in highway runoff. The results and analysis indicates that the runoff water is nearly neutral with low biodegradability. Oil and grease (O&G), suspended solids (SS) and heavy metals are the dominant pollutants in contrast to the low level of nutrient constituents in runoff. Quality of highway runoff at rural site is better than that of at urban site for most constituents. Depth and antecedent dry period are the main rainfall factors influencing quality of highway runoff. The correlation patterns among constituents in highway runoff at urban site are consistent with their dominant phases in water. Strong correlations (r >= 0.80) are found among chemical oxygen demand (COD), total phosphorus, Cu and Zn as well as conductivity, nitrate nitrogen and total nitrogen. O&G, COD, SS and Pb in highway runoff at urban site substantially exceed their concentrations in receiving water of Pear River. The soil directly discharged by highway runoff at rural site has contaminated seriously by heavy metals in surface layer accompanying with pH conversion from original acidic to alkaline at present.

Soil aggregates exert a significant influence on the retention and availability of heavy metal(loid)s in soil. In this study, the concentration distribution and chemical forms of heavy metals (Cu, Zn, Cd, Pb, and Hg) and a metalloid (As) in different aggregate-sized fractions (2–0.25, 0.25–0.05, 0.05–0.002, and < 0.002 mm) along the profile (0–1, 1–5, 5–15, and 15–25 cm) of a contaminated paddy field were investigated. The results showed that the values of pH, free Fe oxides (Fe d ), bulk density, and catalase activity gradually increased, whereas the soil organic matter (SOM), cation exchange capacity (CEC), electrical conductivity (EC), microbial biomass carbon (MBC), and urease activity decreased with depth. Long-term heavy metal pollution might impact the catalase activity but showed no obvious influence on the urease activity. Additionally, there was a notable difference in physicochemical properties among the soil aggregates of various particle sizes. The 2–0.25-mm fraction aggregates contained more organic matter, whereas the highest values of CEC and Fe d were observed in the < 0.002-mm fraction. The concentrations of all six heavy metals/metalloid decreased with depth. In different layers, Cu and Cd showed the highest concentrations in the 2–0.25 mm-fraction, followed by the < 0.002-mm fraction, whereas the highest concentrations of Zn, Pb, and As appeared in the < 0.002-mm fraction. No obvious distribution regularity was observed for Hg among the aggregates. All of the metal(loid)s had lower activity in the deeper soil layers, except for Hg. Furthermore, Cu and Cd displayed more stable forms in the < 0.002-mm fraction aggregates.

Biochar is widely used for immobilizing heavy metals in soil as a kind of high-effective passivator. This research conducted incubation and simulated rainfall experiments to study the effects of biochar application on the loss characteristics of runoff and sediment, as well as the transportation of the Cd during the water erosion process. Two rainfall intensities (60 and 120 mm h −1 ) and five biochar application rates (0%, 1%, 3%, 5%, and 7%) were considered in the experiment. The result showed that slaking had a greater effect than mechanical stirring in aggregate breakdown of the soil, and the addition of biochar generally increased the sensitivity of the soil to wet stirring, while had no obvious influence on the resistance to slaking. The H 2 O and CaCl 2 extractable Cd in soil significantly decreased with the increase of biochar application rate. The runoff yields decreased with the increase of biochar application rate at both the two rainfall intensities, while the eroded sediment generally decreased at the 120 mm h −1 rainfall intensity. The addition of biochar tended to increase the loss of the middle-sized (1–0.05 mm) aggregates at the 60 mm h −1 rainfall intensity, whereas reduced their loss at the 120 mm h −1 rainfall intensity. Biochar application could significantly reduce the concentration of Cd in the runoff and decreased the total loss amount of Cd (sediment+runoff) in most of the cases. Excessively high level (7%) of biochar application may aggravate soil erosion and result in more Cd loss.

Soil and water loss is a severe environmental problem in tropical and subtropical Asia (TSA). This review systematically summarizes the techniques that have been widely applied in the TSA region and compares the conservation efficiency of these techniques based on the runoff and sediment reduction ratios (ηr and ηs). The results show that the current techniques can be divided into biological, engineering and agricultural practice measures, and in most cases, their efficiencies in reducing sediment loss (ηs = 14.0–99.5%, 61.3–100.0% and 0.6–95.4%, respectively) were higher than in reducing runoff loss (ηr = 2.8–9.38%, 0.28–83.3% and 1.62–70.2%, respectively). Monocultures of single tree species (e.g., Pinus massoniana) sometimes showed very limited conservation effects. Vetiver and alfalfa were more effective at reducing soil loss than other hedgerow species. Contour tillage, ridge farming, and reduced tillage generally showed high efficiencies in reducing soil loss compared with other agricultural practice measures. The combination of engineering and biological techniques could more effectively reduce soil and water loss compared with the application of these techniques along. Future works should be conducted to build unified technical standards and reasonable comprehensive evaluation systems, to combine these techniques with environmental engineering technologies, and to develop new amendment materials.

Understanding landscape connectivity and population genetic parameters is imperative for threatened species management. However, such information is lacking for the snow leopard (Panthera uncia). This study sought to explore hierarchical snow leopard gene flow patterns and drivers of genetic structure in Mongolia and China. A total of 97 individuals from across Mongolia and from the north-eastern edge of the Qinghai-Tibetan Plateau in Gansu Province to the middle of Qinghai Province in China were genotyped across 24 microsatellite loci. Distance-based frameworks were used to determine a landscape scenario best explaining observed genetic structure. Spatial and non-spatial methods were used to investigate fine-scale autocorrelation and similarity patterns as well as genetic structure and admixture. A genetic macro-division between populations in China and Mongolia was observed, suggesting that the Gobi Desert is a substantial barrier to gene flow. However, admixture and support for a resistance-based mode of isolation suggests connective routes that could facilitate movement. Populations in Mongolia had greater connectivity, indicative of more continuous habitat. Drivers of genetic structure in China were difficult to discern, and fine-scale sampling is needed. This study elucidates snow leopard landscape connectivity and helps to prioritize conservation areas. Although contact zones may have existed and occasional crossings can occur, establishing corridors to connect these areas should not be a priority. Focus should be placed on maintaining the relatively high connectivity for snow leopard populations within Mongolia and increasing research efforts in China.

PurposeHow the stability of soil organic carbon (SOC) is affected by soil erosion is still not clear. The main purpose of this study was to characterize how SOC stability is affected by erosion and assess the effects of different soil properties on SOC stability.Materials and methodsSoils from eroding and depositional sites in a typical small watershed in subtropical China were collected, and soil samples from four different depths (0–5, 5–10, 20–30, and 120–150 cm) were selected to represent the profile. Soil physicochemical properties as well as soil organic matter (SOM) chemical structure were measured. Thermal analysis and mineralization incubation experiments were performed to study the SOM stability. The effects of the soil properties on the SOM stability were evaluated via redundancy analysis.Results and discussionThe results showed that the eroding and depositional sites had different SOC contents but had similar organic functional groups. Furthermore, the OC in the eroded soils was more stable than that in the deposited soils, but this difference was only observed in the surface layers (0–5 and 5–10 cm). The selected variables (including soil texture, bulk density, pH, SOC, dissolved organic carbon (DOC), iron, soil aggregates, depth, erosion, and deposition) significantly explained the variations in SOC stability. A total of 91.4% of the variation in the thermogravimetry (TG)-T50 (the temperature resulting in 50% of SOM loss) and 98.9% of the variation in the CO2 emissions were explained by these variables. SOC alone contributed to 68% of the variation in the TG-T50, whereas DOC individually contributed 93.9% of the variation in the CO2 emissions.ConclusionsSOC and DOC contents are the most important soil properties influencing SOC stability, and SOC stability affected by soil erosion is mainly by displacing SOM.

PurposeParticle size poses important influence on the adsorption and enrichment of heavy metals in soil aggregates. In this study, we conducted adsorption experiments to compare the effect of particle size on the adsorption behavior of cadmium (Cd) in aggregates of soils with different properties.Materials and methodsEight types of acid red soils sampled from South China were partitioned into aggregates of different particle sizes (2–0.25, 0.25–0.05, and < 0.05 mm). The adsorption and desorption characteristics of Cd onto the aggregates were examined through batch experiments. The influence of organic matter and free Fe/Al oxides were also examined by selectively removing the corresponding component.ResultsBoth the Langmuir and Freundlich models are suitable for describing the isothermal adsorption characteristics of Cd in these soil particles. The maximum adsorption capacity (qm) of the < 0.05 mm fraction aggregates of most of the soils was the highest (1823.38–5365.75 mg/kg), while the desorption rate (Dr) was the lowest (15.37–37.91%) in this fraction. Organic matter content and pH were more important factors influencing the adsorption and desorption of Cd. The adsorption amount of all the soil particles decreased after organic matter was removed, while after the removal free Fe/Al oxides, obvious increase in adsorption amount was only observed in four types of the soils.ConclusionsCadmium tended to enrich in the fine-sized soil aggregates as a whole. The adsorption/desorption behavior of Cd in aggregates not only depend on the content of the soil components but also on their properties and combination condition with each other.