Occurrence, potential sources, and ecological risk assessment of microplastics in the inland river basins in Northern China.

Microplastics (MPs) are the pollutants, found widely across various environmental media. However, studies on the MP pollution in urban rivers and the necessary risk assessments remain limited. In this study, the abundance and characteristics of microplastics in a typical urban river were examined to evaluate their distribution, sources, and ecological risks. It was observed that the abundance of MPs in sediments (220-2840 items·kg-1 dry weight (DW)) was much higher than that in surface water (2.9-10.3 items·L-1), indicating that the sediment is the "sink" of river MPs. Surface water and sediment were dominated by small particle size MPs (< 0.5 mm). Fiber and debris were common shapes of MPs in rivers and sediments. The microplastics in river water and sediments were primarily white and transparent, respectively. Polypropylene (PP) and polyethylene (PE) were the major polymers found.

Microplastic pollution in typical seasonal rivers in northern China: temporal variation and risk assessment.

Rivers are important channels for the transport of microplastics (MPs) from land to sea. In this work, the temporal variation and risk assessment of MP pollution in the surface water of the Wei River, a typical seasonal river in northern China, were quantified. The number abundance of MPs in the dry season was significantly higher than that in the wet season (p < 0.05). Fiber was the most abundant type of MP in both dry and wet seasons. Infrared spectrometer and Raman spectroscopy identification showed that polypropylene (PP) and polyethylene (PE) were the major polymers found in both dry and wet seasons, and the mixture of different MP polymers was more diverse in the dry season. The risk assessment showed that the average pollution load index (PLI) and risk quotient (RQ) were 2.10 and 1.19 in the dry season, which significantly decreased to 1.25 and 0.74, respectively, in the wet season (p < 0.05). In total, the results from this study highlight the characteristics of seasonal rivers that influence the temporal distribution and risk assessment of microplastics, providing scientific reference for policymakers and river managers to effectively deal with MP pollution.

Spatiotemporal Variation Air Quality Index Characteristics in China's Major Cities During 2014-2020.

The temporal and spatial variation characteristics of air quality index (AQI) in major cities in China were explored in this paper using statistical analysis, hot spot analysis, spatial autocorrelation, mean center, and geographic detector based on the daily AQI data from 2014 to 2020. The results show that ① the annual AQI average value dropped from 94 to 67 from 2014 to 2020. The percentage of cities with daily AQI excellent rates between 0.8 and 1 is significantly increasing, reaching 77% in 2020. ② AQI is highest and lowest in winter and summer, respectively. The trend of the monthly AQI average value is roughly in a U shape. Moreover, the AQI in January and December is high, and the AQI in August and September is low. ③ The spatial distribution of the annual AQI average in China's major cities shows agglomeration effects. The hot spots are distributed in North China and Xinjiang, and the cold spots are mainly distributed in the northeast and southern regions of China. ④ The average center of the annual AQI average of major cities in China was distributed in Sanmenxia City and Luoyang City, Henan Province, from 2014 to 2020 with a relatively small mean center migration range. ⑤ Based on the geographical detector model, the impact of total precipitation, 10-m u component of wind, 10-m v component of wind, surface pressure, and 2-m temperature on AQI is analyzed, and it is concluded that 2-m temperature has the greatest impact on AQI. Meanwhile, it is explored that GDP and population density have a certain impact on air quality. Therefore, analyzing the temporal and spatial characteristics of air quality provides some scientific basis for the regional collaborative governance of air pollution and the in-depth fight against pollution in China.

A shallow constructed wetland combining porous filter material and Rotala rotundifolia for advanced treatment of municipal sewage at low HRT.

Water scarcity is a worldwide problem. Recycled municipal wastewater is considered a useful alternative to the conventional types of water resources. In this study, a shallow constructed wetland (SCW) with porous filter material and Rotala rotundifolia was used for advanced municipal sewage treatment. The wetland without plant was set as the control (SCW-C). The pollutant removal performance of the system at different hydraulic retention times (HRTs) was investigated. The diversity of the microbial community was analyzed, and the fate of nutrients, mainly N and P, in the system was discussed. Results showed that SCW was efficient in pollutant removal. Effluent concentrations of chemical oxygen demand (COD), total phosphorus (TP), and ammonium nitrogen (NH4+-N) were 15.0-23.6, 0.19-0.28, and 0.83-1.16 mg/L, separately, with average removal efficiencies of 61.2%, 46.3%, and 88.1% at HRT 18 h, which met the requirements of type [Formula: see text] water set by the environmental quality standards for surface water in China. The richness and evenness of the bacterial community were significantly higher in the plant-rooted SCW. They increased along with the system. The dominant genera in the system were phosphate-solubilizing bacteria, nitrifying bacteria, and denitrifying bacteria. The P in the influent mainly flowed to the substrate and plant. At the same time, most N was removed by nitrification and denitrification. These findings suggested that the SCW could remove pollutants from the municipal sewage effluent and meet the standard requirement at low HRT.

Effects of vegetation patterns on soil nitrogen and phosphorus losses on the slope-gully system of the Loess Plateau.

The slope-gully system, the erosion unit on the Loess Plateau, suffers from severe soil erosion and loss of soil nutrients. Restoring vegetation can effectively reduce soil erosion, thereby reducing the loss of nitrogen and phosphorus. In the Loess Plateau, owing to the shortage of water resources and the adverse effects of over-revegetation, the restoration of vegetation in large areas is limited. To efficiently prevent the loss of soil nutrients and reduce non-point source pollution, vegetation patterns need to be reasonably restored. However, it is currently not clear as to how this can be achieved. Different slope-gully systems were established in this study, including pattern A (no vegetation), pattern B (up-slope vegetation), pattern C (middle-slope vegetation), and pattern D (down-slope vegetation). Then, the effects of vegetation patterns on soil total nitrogen (TN) and soil total phosphorus (TP) losses associated with runoff and sediment processes was quantitatively evaluated through the simulated rainfall. The results showed that (1) vegetation pattern markedly affected the yields of runoff, sediment, soil nitrogen, and soil phosphorus, resulting in the following order: pattern A > pattern B > pattern C > pattern D. (2) The correlation between TN and runoff was higher than that between TN and sediment; conversely, TP was more strongly correlated with sediment than with runoff. (3) Nitrogen loss with runoff was the main source of TN (58.76-90.74%), while phosphorus loss with sediment was the main source of TP (48.51-89.30%). Compared with other vegetation patterns, the down-slope can more effectively reduce the yields of runoff and sediment, thereby reducing the loss of TN and TP. Therefore, it was suggested that the lower part of the slope should be considered when revegetating.

An Eco-tank system containing microbes and different aquatic plant species for the bioremediation of N,N-dimethylformamide polluted river waters.

An Eco-tank system of 10m was designed to simulate the natural river. It consisted of five tanks sequentially connected containing microbes, biofilm carriers and four species of floating aquatic plants. The purification performance of the system for N,N-dimethylformamide (DMF) polluted river water was evaluated by operating in continuous mode. DMF was completely removed in Tanks 1 and 2 at influent DMF concentrations between 75.42 and 161.05mg L-1. The NH4+-N concentration increased in Tank 1, followed by a gradual decrease in Tanks 2-5. Removal of NH4+-N was enhanced by aeration. The average effluent NH4+-N concentration of Tank 5 decreased to a minimum of 0.89mg L-1, corresponding to a decrease of 84.8% when compared with that before aeration. TN concentration did not decrease significantly as expected after inoculation with denitrifying bacteria. The average effluent TN concentration of the system was determined to be 4.58mg L-1, still unable to satisfy the Class V standard for surface water environmental quality. The results of this study demonstrated that the Eco-tank system is an efficient process in removing DMF, TOC, and NH4+-N from DMF polluted river water. However, if possible, alternative technologies should be adopted for controlling the effluent TN concentration.