Effects of elevated atmospheric CO2 concentration and temperature on the soil profile methane distribution and diffusion in rice–wheat rotation system

The aim of this experiment was to determine the impacts of climate change on soil profile concentrations and diffusion effluxes of methane in a rice–wheat annual rotation ecosystem in Southeastern China. We initiated a field experiment with four treatments: ambient conditions (CKs), CO₂ concentration elevated to ~ 500 μmol/mol (FACE), temperature elevated by ca. 2°C (T) and combined elevation of CO₂ concentration and temperature (FACE + T). A multilevel sampling probe was designed to collect the soil gas at four different depths, namely, 7 cm, 15 cm, 30 cm and 50 cm. Methane concentrations were higher during the rice season and decreased with depth, while lower during the wheat season and increased with depth. Compared to CK, mean methane concentration was increased by 42%, 57% and 71% under the FACE, FACE + T and T treatments, respectively, at the 7 cm depth during the rice season (p < 0.05). Mean methane diffusion effluxes to the 7 cm depth were positive in the rice season and negative in the wheat season, resulting in the paddy field being a source and weak sink, respectively. Moreover, mean methane diffusion effluxes in the rice season were 0.94, 1.19 and 1.42 mg C/(m²·hr) in the FACE, FACE + T and T treatments, respectively, being clearly higher than that in the CK. The results indicated that elevated atmospheric CO₂ concentration and temperature could significantly increase soil profile methane concentrations and their effluxes from a rice–wheat field annual rotation ecosystem (p < 0.05).     

污灌区稻田汞污染特征及健康风险评价

选择天津北排污河灌区作为研究区域,调查了土壤和水稻总汞和甲基汞的含量及分布特征,评估污灌区稻米食用汞暴露风险,并对污灌区土壤-稻米甲基汞的影响因素进行了初步分析.结果表明,1.调查的29个污灌区稻田,土壤总汞含量为(367.04 ± 129.36) μg/kg,显著高于区域土壤Hg背景值73 μg/kg,甲基汞含量为(0.87 ± 0.77) μg/kg;水稻各部位总汞含量依次为稻叶 > 稻根 > 稻茎 > 稻米,稻米总汞含量为(12.80 ± 5.14) μg/kg,甲基汞含量依次为稻米 > 稻根 > 稻茎 > 稻叶,稻米对甲基汞具有很强的富集能力,甲基汞含量为(2.09 ± 1.20) μg/kg,甲基化率均值超过10%.污灌区稻米总汞每周摄入量为0.068~1.25μg/(kg·bw),甲基汞每周摄入量为0.0095~0.49μg/(kg·bw),污灌区稻米总汞及甲基汞暴露对居民健康风险总体仍在安全阈值内,但个别汞污染较严重地块甲基汞暴露风险值得高度关注.土壤甲基汞含量仅与土壤总汞含量及黏粒含量的相关性达到显著性水平,稻米甲基汞含量与土壤总汞含量、土壤甲基汞含量、稻米总汞含量及黏粒含量的相关性达到显著性水平.     

Nitrogen fertilizer reduction in rice production for two consecutive years in the Taihu Lake area

Agricultural activities are the main source of non-point pollution in the Taihu Lake region, and therefore reduction of nitrogen (N) fertilizer is imperative in this area. A two-year experiment was carried out in a paddy field of summer rice-winter wheat rotation in the Taihu Lake area, and the rice growing seasons were mainly concerned in this research. Grain yield, N accumulation at rice crucial stages, N use efficiency, as well as N losses via run off during rice growing season were determined under different N application rates. No significant differences were observed in grain yield under N fertilizer application rates of 135-270 kg N ha⁻¹ (50-100% of the conventional N application rate). Nitrogen accumulation before the heading stage (Pre-NA) accounted for 61-95% of total nitrogen absorption in mature rice, and was positively correlated with straw dry matter at harvest. Positive correlations were found between Pre-NA and straw (0.53, p < 0.05), and between grain yield and N accumulation after the heading stage (Post-NA) (0.58, p < 0.05), suggesting that increasing nitrogen accumulation after the heading stage is crucial for grain yield improvement. Poor agronomic efficiency of applied N (AE_N), partial factor productivity of applied N (PFP_N) and internal utilization efficiency of applied N (IE_N) were observed for the higher soil fertility and a higher N fertilizer input; a simple N fertilizer reduction could significantly increase the nitrogen use efficiency in this region. Nitrogen loss via runoff was positively linearly related to N application rates and severely affected by rainfall events. The highest-yielding N rates were around 232-257 kg N ha⁻¹, accounting for 86-95% of the conventional N application rates for the rice season. To reduce N losses and enhance N use efficiency, the recommendable N fertilization rate should be lower than that of the highest yield rate for rice season. Our findings indicated that nitrogen fertilizer reduction in the Taihu Lake area is feasible and necessary for maintaining grain yield, enhancing nitrogen use efficiency, and reducing environmental impact. However, the longer-term yield sustainability for the proper N application rate needs to be further investigated.     

Decontamination of anaerobically digested slurry in a paddy field ecosystem in Jiaxing region of China

Anaerobic digestion has become increasing popular for managing biowastes in rural China as it has the advantage of generating biogas, a renewable energy. A new challenge, however, is minimizing the environmental pollution resulting from the anaerobically digested slurry (ADS). The aim of this study was to assess the feasibility of using a paddy field to remediate ADS while simultaneously cultivating rice. A field experiment was trialed using six treatments based on varying nitrogen loadings over the period of a rice-growing season. These treatments were adjusted to the content of the N within the ADS and had loadings of 270, 405, 540 and 1080 kg N ha⁻¹. These treatments were compared to a negative control (no fertilizer) and a positive control (chemical fertilizer) that consisted of urea applied at 270 kg N ha⁻¹. The effects of these N sources and slurry remediation were monitored using standard methods to measure water quality, soil properties and changes in rice production. Rice grain yields were generally higher for all ADS treatments than for the urea N treatment. Standing water quality in the field could reach national discharge standards for all treatments within 7-8 days after each ADS irrigation. Groundwater quality and heavy metal concentrations in both soil and the rice grain were not affected by the ADS treatments. We suggest that the quantities of ADS irrigated in 867-1734 m³ ha⁻¹ was not only safe for food quality (rice grain) and the receiving environment (water and soil), but also beneficial to soil fertility and rice grain yield.     

Deficit irrigation: An option to mitigate arsenic load of rice grain in West Bengal, India

Farmers in arsenic (As) contaminated areas of West Bengal, India grow rice during dry months (January to April) and use underground water for irrigation with As concentration above WHO defined critical (0.01 mg l⁻¹) limit. In each season they add 50-150 mg As per m² soil area. Thus growing rice under deficit irrigation in these areas will reduce As load in soil-root-shoot-leaf-grain continuum of rice ecosystem. Suitable deficit irrigation system has to be screened so that As load will decrease with insignificant reduction in grain yield. With this objective, rice grown under four irrigation regimes (i) continuous ponding (CP), (ii) intermittent ponding (IP), (iii) saturation (SAT) and (iv) aerobic (AER) was tested to assess the arsenic load in soil and various parts of rice on 45 and 80 days after transplanting (DAT). Conditions described in treatments ii, iii and iv were imposed during 15-45 DAT. Highest value (18.18 and 18.74 mg kg⁻¹) of soil arsenic was attained under CP followed by IP, SAT and AER. Root arsenic content under AER at 45 and 80 DAT was at the lowest level (6.14 and 20.54 mg kg⁻¹) and this was 31 and 7.0% lower as compared to CP. As content in leaf and grain attained the lowest values under IP. Grain yield insignificantly differed under IP (4.33 Mg ha⁻¹) over CP (4.69 Mg ha⁻¹). Compared to soil As, As added through irrigation showed stronger relationship with As status of various plant parts. Imposition of IP only during vegetative stage was found to be optimum in terms of reduction of As content in straw and grain respectively by 23 and 33% over farmers irrigation practice with insignificant decrease in grain yield.     

Effects of water regime, crop residues, and application rates on control of Fusarium oxysporum f. sp. cubense

Biological soil disinfestation is an effective method to control soil-borne disease by flooding and incorporating with organic amendments, but field conditions and resources sometimes limited its practical application. A laboratory experiment was conducted to develop practice guidelines on controlling Fusarium wilt, a widespread banana disease caused by Fusarium oxysporum f. sp. cubense(FOC). FOC infested soil incorporated with rice or maize straw at rates of 1.5 tons/ha and 3.0 tons/ha was incubated under flooded or water-saturated(100% water holding capacity) conditions at 30℃ for 30 days. Results showed that FOC populations in the soils incorporated with either rice or maize straw rapidly reduced more than 90% in the first 15 days and then fluctuated till the end of incubation, while flooding alone without organic amendment reduced FOC populations slightly. The rapid and dramatic decrease of redox potential(down to- 350 m V) in straw-amended treatments implied that both anaerobic condition and strongly reductive soil condition would contribute to pathogen inactivation. Water-saturation combined with straw amendments had the comparable effects on reduction of FOC, indicating that flooding was not indispensable for inactivating FOC. There was no significant difference in the reduction of FOC observed in the straw amendments at between 1.5 and 3 tons/ha. Therefore,incorporating soil with straw(rice or maize straw) at a rate of 3.0 tons/ha under 100%water holding capacity or 1.5 tons/ha under flooding, would effectively alleviate banana Fusarium wilt caused by FOC after 15-day treating under 30℃.     

Effects of water regime,crop residues,and application rates on control of Fusarium oxysporum f. sp. cubense

Biological soil disinfestation is an effective method to control soil-borne disease by flooding and incorporating with organic amendments, but field conditions and resources sometimes limited its practical application. A laboratory experiment was conducted to develop practice guidelines on controlling Fusarium wilt, a widespread banana disease caused by Fusarium oxysporum f. sp. cubense (FOC). FOC infested soil incorporated with rice or maize straw at rates of 1.5 tons/ha and 3.0 tons/ha was incubated under flooded or water-saturated (100% water holding capacity) conditions at 30°C for 30 days. Results showed that FOC populations in the soils incorporated with either rice or maize straw rapidly reduced more than 90% in the first 15 days and then fluctuated till the end of incubation, while flooding alone without organic amendment reduced FOC populations slightly. The rapid and dramatic decrease of redox potential (down to − 350 mV) in straw-amended treatments implied that both anaerobic condition and strongly reductive soil condition would contribute to pathogen inactivation. Water-saturation combined with straw amendments had the comparable effects on reduction of FOC, indicating that flooding was not indispensable for inactivating FOC. There was no significant difference in the reduction of FOC observed in the straw amendments at between 1.5 and 3 tons/ha. Therefore, incorporating soil with straw (rice or maize straw) at a rate of 3.0 tons/ha under 100% water holding capacity or 1.5 tons/ha under flooding, would effectively alleviate banana Fusarium wilt caused by FOC after 15-day treating under 30°C.     

Unraveling the size distributions of surface properties for purple soil and yellow soil

Soils contain diverse colloidal particles whose properties are pertinent to ecological and human health, whereas few investigations systematically analyze the surface properties of these particles. The objective of this study was to elucidate the surface properties of particles within targeted size ranges (i.e. > 10, 1–10, 0.5–1, 0.2–0.5 and < 0.2 μm) for a purple soil (Entisol) and a yellow soil (Ultisol) using the combined determination method. The mineralogy of corresponding particle-size fractions was determined by X-ray diffraction. We found that up to 80% of the specific surface area and 85% of the surface charge of the entire soil came from colloidal-sized particles (< 1 μm), and almost half of the specific surface area and surface charge came from the smallest particles (< 0.2 μm). Vermiculite, illite, montmorillonite and mica dominated in the colloidal-sized particles, of which the smallest particles had the highest proportion of vermiculite and montmorillonite. For a given size fraction, the purple soil had a larger specific surface area, stronger electrostatic field, and higher surface charge than the yellow soil due to differences in mineralogy. Likewise, the differences in surface properties among the various particle-size fractions can also be ascribed to mineralogy. Our results indicated that soil surface properties were essentially determined by the colloidal-sized particles, and the < 0.2 μm nanoparticles made the largest contribution to soil properties. The composition of clay minerals within the diverse particle-size fractions could fully explain the size distributions of surface properties.     

Comparison of two methods for detection of fecal indicator bacteria used in water quality monitoring of the Three Gorges Reservoir

Scientifically sound methods to rapidly measure fecal indicator bacteria are important to ensure safe water for drinking and recreational purposes.A total of 200 water samples obtained from the Three Gorges Reservoir during three successive one-year study periods(October 2009 to September 2012) were analyzed using multiple-tube fermentation(MTF)and most probable numbers combined with polymerase chain reaction(MPN–PCR).The MPN–PCR method was found to be significantly more sensitive than the MTF method for detecting Escherichia coli and Enterococcus spp.,and of equal sensitivity for detecting total coliforms when all surface water samples were grouped together.The two analytical methods had a strong,significant relationship,but MPN–PCR took only 12–18 hr,compared with the 3–8 days needed using the MTF method.Bacterial concentrations varied per sampling site but were significantly lower in the mainstream of the Yangtze River than those in the backwater areas of tributaries.The water quality of 85.8% of water samples from the mainstream was suitable for use as a centralized potable water source,while the water quality of 52.5% of water samples from the backwater areas was unsuitable for recreational activities.Relationships between fecal indicator bacteria showed significant correlation(r = 0.636–0.909,p 0.01,n = 200),while a weak but significant correlation was found between fecal indicators and water turbidity,water temperature,daily inflow,and total dissolved solids(r = 0.237–0.532,p 0.05,n = 200).The study indicated that MPN–PCR is a rapid and easily performed deoxyribonucleic acid(DNA)-based method for quantitative detection of viable total coliforms,E.coli,and Enterococcus spp.in surface water.     

Effects of aging process on adsorption–desorption and bioavailability of fomesafen in an agricultural soil amended with rice hull biochar

Biochar has been introduced as an acceptable soil amendment due to its environmental benefits such as sequestering soil contaminants. However, the aging process in biochar amended soil probably decreases the adsorption capacity of biochar through changing its physico-chemical properties. Adsorption, leaching and bioavailability of fomesafen to corn in a Chinese soil amended by rice hull biochar after 0, 30, 90 and 180 days were investigated.Results showed that the addition of 0.5%–2% fresh biochar significantly increases the adsorption of fomesafen 4–26 times compare to unamended soil due to higher SSA of biochar. Biochar amendment also decreases fomesafen concentration in soil pore water by5%–23% resulting lower risk of the herbicide for cultivated plants. However, the aging process decreased the adsorption capacity of biochar since the adsorption coefficient values which was 1.9–12.4 in 0.5%–2% fresh biochar amended soil, declined to 1.36–4.16, 1.13–2.78 and 0.95–2.31 in 1, 3 and 6-month aged treatments, respectively. Consequently, higher desorption, leaching and bioavailable fraction of fomesafen belonged to 6-month aged treatment. Nevertheless, rice hull biochar was effective for sequestering fomesafen as the adsorption capacity of biochar amended soil after 6 months of aging was still 2.5–5 times higher compared to that of unamended soil.     

Importance of storage time in mesophilic anaerobic digestion of food waste

Storage was used as a pretreatment to enhance the methanization performance of mesophilic anaerobic digestion of food waste. Food wastes were separately stored for 0, 1,2, 3, 4, 5, 7, and 12 days, and then fed into a methanogenic reactor for a biochemical methane potential(BMP) test lasting up to 60 days. Relative to the methane production of food waste stored for 0–1 day(285–308 m L/g-added volatile solids(VSadded)), that after2–4 days and after 5–12 days of storage increased to 418–530 and 618–696 m L/g-VSadded,respectively. The efficiency of hydrolysis and acidification of pre-stored food waste in the methanization reactors increased with storage time. The characteristics of stored waste suggest that methane production was not correlated with the total hydrolysis efficiency of organics in pre-stored food waste but was positively correlated with the storage time and acidification level of the waste. From the results, we recommend 5–7 days of storage of food waste in anaerobic digestion treatment plants.     

Environmental behaviors of phoxim with two formulations in bamboo forest under soil surface mulching

Phoxim (emulsifiable concentrate (EC) and granules (G)) has been widely used in bamboo forests. The persistence and magnitude of phoxim residues in the crop and soil must be investigated to ensure human and environmental safety. The environmental behaviors of the two formulations were investigated in a bamboo forest under soil surface mulching conditions (CP) and non-covered cultivation conditions (NCP). The half-lives of phoxim in soil under the two conditions in soil were 4.1–6.2 days (EC) and 31.5–49.5 days (G), respectively. Phoxim in EC could be leached from the topsoil into the subsoil. A minimized leaching effect was observed for G under NCP. Inversely, an enhanced leaching effect was observed for G under CP. The G formulation resulted in more parent compound (in bamboo shoots) and metabolite (in soil) residues of phoxim than in the case of EC, especially under CP conditions. In addition, the intensity and duration of the formulation effect on soil pH adjustment from G were more obvious than that from EC. Results showed that the environmental behaviors (distribution, degradation, residue) of phoxim in the bamboo forest were significantly influenced by the type of formulation. The prolongation effect from phoxim G might cause persistence and long-term environmental risk. However, bamboo shoot consumption could be considered relatively safe after applying the recommended dose of the two phoxim formulations.     

Elevated CO2 facilitates C and N accumulation in a rice paddy ecosystem

Elevated CO₂ can stimulate wetland carbon (C) and nitrogen (N) exports through gaseous and dissolved pathways, however, the consequent influences on the C and N pools are still not fully known. Therefore, we set up a free-air CO₂ enrichment experiment in a paddy field in Eastern China. After five year fumigation, we studied C and N in the plant–water–soil system. The results showed: (1) elevated CO₂ stimulated rice aboveground biomass and N accumulations by 19.1% and 12.5%, respectively. (2) Elevated CO₂ significantly increased paddy soil TOC and TN contents by 12.5% and 15.5%, respectively in the 0–15 cm layer, and 22.7% and 26.0% in the 15–30 cm soil layer. (3) Averaged across the rice growing period, elevated CO₂ greatly increased TOC and TN contents in the surface water by 7.6% and 11.4%, respectively. (4) The TOC/TN ratio and natural δ¹⁵N value in the surface soil showed a decreasing trend under elevated CO₂. The above results indicate that elevated CO₂ can benefit C and N accumulation in paddy fields. Given the similarity between the paddies and natural wetlands, our results also suggest a great potential for long-term C and N accumulation in natural wetlands under future climate patterns.     

Effects of ZnO nanoparticles on perfluorooctane sulfonate induced thyroid-disrupting on zebrafish larvae

Perfluorooctane sulfonate(PFOS) and ZnO nanoparticles(nano-ZnO) are widely distributed in the environment.However,the potential toxicity of co-exposure to PFOS and nano-ZnO remains to be fully elucidated.The test investigated the effects of co-exposure to PFOS and nano-ZnO on the hypothalamic–pituitary–thyroid(HPT) axis in zebrafish.Zebrafish embryos were exposed to a combination of PFOS(0.2,0.4,0.8 mg/L) and nano-ZnO(50 mg/L)from their early stages of life(0–14 days).The whole-body content of TH and the expression of genes and proteins related to the HPT axis were analyzed.The co-exposure decreased the body length and increased the malformation rates compared with exposure to PFOS alone.Co-exposure also increased the triiodothyronine(T3) levels,whereas the thyroxine(T4)content remained unchanged.Compared with the exposure to PFOS alone,exposure to both PFOS(0.8 mg/L) and nano-ZnO(50 mg/L) significantly up-regulated the expression of corticotropin-releasing factor,sodium/iodidesymporter,iodothyronine deiodinases and thyroid receptors and significantly down-regulated the expression of thyroid-stimulating hormone,thyroglobulin(TG),transthyretin(TTR) and thyroid receptors.The protein expression levels of TG and TTR were also significantly down-regulated in the co-exposure groups.In addition,the expression of the thyroid peroxidase gene was unchanged in all groups.The results demonstrated that PFOS and nano-ZnO co-exposure could cause more serious thyroid-disrupting effects in zebrafish than exposure to PFOS alone.Our results also provide insight into the mechanism of disruption of the thyroid status by PFOS and nano-ZnO.     

Accumulation of polybrominated diphenyl ethers in breast milk of women from an e-waste recycling center in China

Polybrominated diphenyl ethers(PBDEs) can be transferred to infants through the ingestion of breast milk, resulting in potential health risk. In this study, PBDEs, hydroxylated polybrominated diphenyl ethers(OH-PBDEs) and 2,2′,4,4′,5,6′-hexachlorobiphenyl(CB-153)in human milk from women living adjacent to e-waste recycling sites of Wenling,China, were investigated. The median level of PBDEs in samples from residents living in the e-waste recycling environment 20 years(R_20group, 19.5 ng/g lipid weight(lw))was significantly higher than that for residents living in Wenling 3 years(R_3group,3.88 ng/g lw)(p 0.05), likely ascribable to specific exposure to PBDEs from e-waste recycling activities. In the R_20 group, most congeners(except for BDE-209) were correlated with each other(p 0.05). Moreover, CB-153 showed significant association with most PBDE congeners, rather than BDE-209. The relationship indicated that most BDE congeners other than BDE-209 shared common sources and/or pathways with CB-153, e.g., dietary ingestion. The correlations between BDE-209 and other congeners were different in the two groups, likely suggesting their different exposure sources and/or pathways for PBDEs.Although estimated dietary intake of PBDEs for infants via breast milk was lower than the minimum value affecting human health, the PBDE exposure of infants should be of great concern because of their potential effect on the development of neonates over long-term exposure. OH-PBDEs were not detected in the collected samples, which is in accordance with reports in published literature, likely indicating that they were not apt to be accumulated in human milk.     

Removal of heavy metals and arsenic from a co-contaminated soil by sieving combined with washing process

Batch experiments were conducted with a heavy metals and arsenic co-contaminated soil from an abandoned mine to evaluate the feasibility of a remediation technology that combines sieving with soil washing.Leaching of the arsenic and heavy metals from the different particle size fractions was found to decrease in the order: 0.1,2–0.1,and 2 mm.With increased contact time,the concentration of heavy metals in the leachate was significantly decreased for small particles,probably because of adsorption by the clay soil component.For the different particle sizes,the removal efficiencies for Pb and Cd were75%–87%,and 61%–77% for Zn and Cu,although the extent of removal was decreased for As and Cr at 45%.The highest efficiency by washing for Pb,Cd,Zn,and As was from the soil particles 2 mm,although good metal removal efficiencies were also achieved in the small particle size fractions.Through SEM-EDS observations and correlation analysis,the leaching regularity of the heavy metals and arsenic was found to be closely related to Fe,Mn,and Ca contents of the soil fractions.The remediation of heavy metal-contaminated soil by sieving combined with soil washing was proven to be efficient,and practical remediation parameters were also recommended.     

Optimization of the T3-induced Xenopus metamorphosis assay for detecting thyroid hormone signaling disruption of chemicals

T3-induced Xenopus metamorphosis is an ideal model for detecting thyroid hormone(TH)signaling disruption of chemicals. To optimize the T3-induced Xenopus assay and improve its sensitivity and reproducibility, we intend to develop quantitatively morphological endpoints and choose appropriate concentrations and exposure durations for T3 induction.Xenopus laevis at stage 52 were exposed to series of concentrations of T3(0.31–2.5 nmol/L)for 6 days. By comparing morphological changes induced by T3, we propose head area,mouth width, unilateral brain width/brain length, and hindlimb length/snout-vent length as quantitative parameters for characterizing T3-induced morphological changes, with body weight as a parameter for indicating integrated changes. By analyzing time-response curves, we found that following 4-day exposure, T3-induced grossly morphological changes displayed linear concentration–response curves, with moderate morphological changes resulting from 1.25 nmol/L T3 exposure. When using grossly morphological endpoints to detect TH signaling disruption, we propose 4 days as exposure duration of T3, with concentrations close to 1.25 nmol/L as induction concentrations. However, it is appropriate to examine morphological and molecular changes of the intestine on day 2 due to their early response to T3. The quantitative endpoints and T3 induction concentrations and durations we determined would improve the sensitivity and the reproducibility of the T3-induced Xenopus metamorphosis assay.     

Can arbuscular mycorrhiza and fertilizer management reduce phosphorus runoff from paddy fields?

Our study sought to assess how much phosphorus (P) runoff from paddy fields could be cut down by fertilizer management and inoculation with arbuscular mycorrhizal fungi. A field experiment was conducted in Lalin River basin, in the northeast China: six nitrogen–phosphorus–potassium fertilizer levels were provided (0, 20%, 40%, 60%, 80%, and 100% of the recommended fertilizer supply), with or without inoculation with Glomus mosseae. The volume and concentrations of particle P (PP) and dissolved P (DP) were measured for each runoff during the rice growing season. It was found that the seasonal P runoff, including DP and PP, under the local fertilization was 3.7 kg/ha, with PP, rather than DP, being the main form of P in runoff water. Additionally, the seasonal P runoff dropped only by 8.9% when fertilization decreased by 20%; rice yields decreased with declining fertilization. We also found that inoculation increased rice yields and decreased P runoff at each fertilizer level and these effects were lower under higher fertilization. Conclusively, while rice yields were guaranteed arbuscular mycorrhizal inoculation and fertilizer management would play a key role in reducing P runoff from paddy fields.     

Gaseous emissions from compressed natural gas buses in urban road and highway tests in China

The natural gas vehicle market is rapidly developing throughout the world, and the majority of such vehicles operate on compressed natural gas(CNG). However, most studies on the emission characteristics of CNG vehicles rely on laboratory chassis dynamometer measurements, which do not accurately represent actual road driving conditions. To further investigate the emission characteristics of CNG vehicles, two CNG city buses and two CNG coaches were tested on public urban roads and highway sections. Our results show that when speeds of 0–10 km/hr were increased to 10–20 km/hr, the CO_2, CO, nitrogen oxide(NO_x), and total hydrocarbon(THC) emission factors decreased by(71.6 ± 4.3)%,(65.6 ± 9.5)%,(64.9 ± 9.2)% and(67.8 ± 0.3)%, respectively. In this study, The Beijing city buses with stricter emission standards(Euro Ⅳ) did not have lower emission factors than the Chongqing coaches with Euro Ⅱ emission standards. Both the higher emission factors at 0–10 km/hr speeds and the higher percentage of driving in the low-speed regime during the entire road cycle may have contributed to the higher CO_2 and CO emission factors of these city buses. Additionally, compared with the emission factors produced in the urban road tests, the CO emission factors of the CNG buses in highway tests decreased the most(by 83.2%), followed by the THC emission factors, which decreased by 67.1%.     

Particle size distribution and characteristics of heavy metals in road-deposited sediments from Beijing Olympic Park

Due to rapid urbanization and industrialization, heavy metals in road-deposited sediments (RDSs) of parks are emitted into the terrestrial, atmospheric, and water environment, and have a severe impact on residents' and tourists' health. To identify the distribution and characteristic of heavy metals in RDS and to assess the road environmental quality in Chinese parks, samples were collected from Beijing Olympic Park in the present study. The results indicated that particles with small grain size (< 150 μm) were the dominant fraction. The length of dry period was one of the main factors affecting the particle size distribution, as indicated by the variation of size fraction with the increase of dry days. The amount of heavy metal (i.e., Cu, Zn, Pb and Cd) content was the largest in particles with small size (< 150 μm) among all samples. Specifically, the percentage of Cu, Zn, Pb and Cd in these particles was 74.7%, 55.5%, 56.6% and 71.3%, respectively. Heavy metals adsorbed in sediments may mainly be contributed by road traffic emissions. The contamination levels of Pb and Cd were higher than Cu and Zn on the basis of the mean heavy metal contents. Specifically, the geoaccumulation index (I_geo) decreased in the order: Cd > Pb > Cu > Zn. This study analyzed the mobility of heavy metals in sediments using partial sequential extraction with the Tessier procedure. The results revealed that the apparent mobility and potential metal bioavailability of heavy metals in the sediments, based on the exchangeable and carbonate fractions, decreased in the order: Cd > Zn ≈ Pb > Cu.