Factors affecting N2O fluxes from heavy metal-contaminated mangrove soils in a subtropical estuary.

A 1-year field monitoring program was carried out to observe seasonal variation in N2O fluxes at two typical mangrove wetlands in a subtropical estuary. The soils in the island-type mangrove wetland had a higher level of heavy metal(loid) contamination and a lower level of salinity compared to the small bay-type mangrove wetland. While there was a high level of similarity in the seasonal variation pattern of N2O fluxes between the two investigated sites with both being significantly higher in summer than in other seasons, the average of N2O fluxes in the island-type mangrove wetland was 7.19 µg·m-2·h-1， which tended to be lower compared to the small bay-type mangrove wetland (15.63 µg·m-2·h-1). Overall, N2O flux was closely related to soil-borne heavy metal(loid)s, showing a trend to decrease with increasing concentration of these heavy metal(loid)s. The N2O fluxes increased with decreasing abundance of either denitrifiers or nitrifiers. But the opposite was observed for the anammox bacteria present in the soils. The anammox bacteria were more sensitive to heavy metal(loid) stress but more tolerated high salinity encountered in the investigated soils compared to the denitrifiers or nitrifiers. It appears that anammox reactions mediated by anammox bacteria played a key role in affecting the spatial variation in N2O fluxes from the mangrove soils in the study area. And an increased level of ammonium in soils tended to promote the activity of anammox bacteria and consequently enhanced N2O emission from the mangrove soils.

Exploration of the Interrelationship within Biomass Pyrolysis Liquid Composition Based on Multivariate Analysis.

The diverse utilization of pyrolysis liquid is closely related to its chemical compositions. Several factors affect PA compositions during the preparation. In this study, multivariate statistical analysis was conducted to assess PA compositions data obtained from published paper and experimental data. Results showed the chemical constituents were not significantly different in different feedstock materials. Acids and phenolics contents were 31.96% (CI: 25.30−38.62) and 26.50% (CI: 21.43−31.57), respectively, accounting for 58.46% (CI: 46.72−70.19) of the total relative contents. When pyrolysis temperatures range increased to above 350 °C, acids and ketones contents decreased by more than 5.2-fold and 1.53-fold, respectively, whereas phenolics content increased by more than 2.1-fold, and acetic acid content was the highest, reaching 34.16% (CI: 25.55−42.78). Correlation analysis demonstrated a significantly negative correlation between acids and phenolics (r2 = −0.43, p < 0.001) and significantly positive correlation between ketones and alcohols (r2 = 0.26, p < 0.05). The pyrolysis temperatures had a negative linear relationship with acids (slope = −0.07, r2 = 0.16, p < 0.001) and aldehydes (slope = −0.02, r2 = 0.09, p < 0.05) and positive linear relationship with phenolics (slope = 0.04, r2 = 0.07, p < 0.05). This study provides a theoretical reference of PA application.

Seasonal and vegetational variations of culturable bacteria concentrations in air from urban forest parks: a case study in Hunan, China.

It is important to investigate the airborne bacterial air quality in urban forest parks as tree bacteriostasis practices are being increasingly advocated as measures to improve the air quality and public health in urban green spaces around the world. The aim of the study was to quantitatively investigate airborne culturable bacteria (ACB) concentration levels based on field measurements in every season in five selected forest communities and the uncovered space in an urban forest park, as well as the effects of several factors on the culturability of airborne bacteria. Results suggested that the airborne bacterial levels of all the forest communities reached the clean air quality standard with regard to the airborne bacteria content, with the highest concentration of ACB showing in the uncovered space (1658 ± 1298 CFU/m3) and the lowest showing in the mixed community (907 ± 567 CFU/m3). The temporal distribution analysis showed that the airborne bacteria were mostly concentrated in summer, as well as in the morning and afternoon. The bacteriostatic rates of the mixed community were significantly different with seasonal variation (p < 0.05). Spearman's correlations revealed that the concentration of ACB was significantly positively correlated with the season, wind speed (WS), temperature (T), ultraviolet light (UV), negative air ion (NAI), and total suspended particles (TSP) (p<0.05) but significantly negatively correlated with the forest community type (p < 0.05). Overall, the selection of tree species plays a key role in shaping the forest structure and improving air quality, and the urban forest highlights key priorities for future efforts toward a cleaner, healthier, and more diverse regional forest environment.

Seasonal Variation in Chemical Compositions of Essential Oils Extracted from Lavandin Flowers in the Yun-Gui Plateau of China.

Lavandin, as an important cash crop, is cultivated in Kunming, Yun-Gui Plateau of China. For the special growing environment, Lavandin was grown here and used to investigate the changes in the yield and chemical compositions of essential oils extracted from the flowers in different seasons. The essential oils were extracted by hydro-distillation and analysis by gas chromatography-mass spectrometry (GC-MS). Results indicated great changes in chemical composition depending on the season of harvesting. The yields of essential oils ranged from 2.0% to 3.8% among the seasons, and the highest yield was in the summer. Chemical composition data showed that the extracted oils were rich in oxygenated monoterpenes (55.4-81.4%), eucalyptol (38.7-49.8%), camphor (8.41-14.26%), α-bisabolol (6.6-25.5%), and linalool (4.6-12.5%). The contents of eucalyptol and α-bisabolol changed in a contrary trend with seasonal variations. The results provided new insight for Chinese Lavandin germplasm to be used in application and development, and reference to the researcher, the farmer, and investor for sustainable industrialization of the plant grown in the Yun-Gui Plateau of China, but also the similar plateau area of the sustainable developments.

Heavy metal pollution increases CH4 and decreases CO2 emissions due to soil microbial changes in a mangrove wetland: Microcosm experiment and field examination.

Mangrove plays an important role in modulating global warming through substantial blue carbon storage relative to their greenhouse gas emission potential. The presence of heavy metals in mangrove wetlands can influence soil microbial communities with implications for decomposition of soil organic matter and emission of greenhouse gases. In this study, field monitoring and a microcosm experiment were conducted to examine the impacts of heavy metal pollution on soil microbial communities and greenhouse gas fluxes. The results show that heavy metal pollution decreased the richness and diversity of the overall soil microbial functional groups (heterotrophs and lithotrophs); however, it did not inhibit the activities of the methanogenic communities, possibly due to their stronger tolerance to heavy metal toxicity compared to the broader soil microbial communities. Consequently, the presence of heavy metals in the mangrove soils significantly increased the emission of CH4 while the emission of CO2 as a proxy of soil microbial respiration was decreased. The soil organic carbon content could also buffer the effect of heavy metal pollution and influence CO2 emissions due to reduced toxicity to microbes. The findings have implications for understanding the complication of greenhouse gas emissions by heavy metal pollution in mangrove wetlands.

[Risk assessment and analysis of polycyclic aromatic hydrocarbons in the surface sediments of Xinglin Bay Suburb Rivers of Xiamen].

The concentrations of 16 polycyclic aromatic hydrocarbons (PAHs), declared as carcinogens by USEPA, were measured in the sediment samples (n = 19) collected along Xinglin Bay rivers/canals present in Xiamen. PAHs were extracted using accelerated solvent extraction system and analyzed using gas chromatography-mass spectrometry (GC-MS). The possible sources of PAHs and their health risk were investigated. Among selected PAHs, 13 PAHs were detected in the surface sediments. Total concentrations of PAHs in the surface sediments ranged from 413.00 to 2748.81 ng x g(-1), with a mean value of 949.56 ng x g(-1). The mean concentration of highly carcinogenic compounds such as benzo [k] fluoranthene (BkF) and benzo [g, h, i] perylene (BghiP) were 69.15 ng x g(-1) and 49.86 ng x g(-1), respectively and counted for 73.68% out of the total samples. The dominant PAH compounds were 2, 3 and 4 rings and counted for 61.03% and 23.53% , respectively; while 5-6 rings containing PAHs were accounted for 15.82%. According to the results, 68.42% of samples were moderately contaminated, while 31.58% were highly contaminated with PAHs. Based on the ratios of Ant/(Ant + Phe) and Fla/(Fla + Pyr), it cleared that PAHs in surface sediments were mainly derived from fossil fuel and combustion products. Principal component analysis results and sediment quality benchmarks (mSQG-Q) were used for risk assessment of these PAH contaminated sediments. The risk SQG-Q of 16 PAHs were less than 0.50. Comprehensive content, composition and SQG-Q showed that a certain degree of ecological risks of PAH pollution existed in the surface sediments, particularly in the sites close to Xinglin Industrial Zone (2, 3, 5 and 9) and Gangtou(13), which need further research work and proper attentions.