An urban ecological zone (UEZ) is an important part of a city, focusing on environmental conservation and ecological economic development simultaneously. During the past decade, the urban scale of Xi’an city in China has been expanding, and the population has been increasing rapidly. This dramatic change is a huge challenge to urban sustainability. It puts forward higher requirements for the construction of an UEZ. Under different spatial resolution scales, this study adopted Landsat8-OLI and gaofen-2 (GF-2) satellite high-resolution remote sensing data to interpret the land use/cover change (LUCC) of the Weihe River UEZ. The ecosystem service value (ESV) was assessed, and the ecological effect was analyzed based on LUCC. The results showed that the spatial distribution of land types in the Weihe River UEZ changed significantly from 2014 to 2020. The construction land gathered to the southeast. Especially, the vegetative land (i.e., forestland, grassland and other green land) and water body showed a slightly increasing trend since the official establishment of the UEZ in 2018. The cultivated land area gradually reduced, and the vegetative land area tended to be concentrated as well as expanded. Through the interpretation of GF-2 remote sensing data, the ESV at the Weihe River UEZ showed a downward trend in general. The high-value areas were mainly distributed in the Weihe River and its surrounding beach areas, which were greatly affected by river water scope. Construction land normally had low ESV, and it was affected by human activities obviously. Therefore, the development of urban construction had significant impacts on the Weihe River UEZ.

The growth status, root exudates, radial oxygen loss, and sewage purification effect of plants acclimated with sewage and cultured with a nutrient solution were studied by selecting Acorus gramineus Aiton, Pistia stratiotes L., and Eichhornia crassipes (Mart.) Solms with the same individual size. The results showed that the root oxygen secretion rate of the Acorus gramineus Aiton was higher in light and dark conditions. For a single plant species, the oxygen secretion rate under light conditions was much higher than that under dark conditions. The root oxygen secretion rate of Acorus gramineus Aiton was the highest (2.03 µmol O₂/h/plant), followed by Pistia stratiotes L. (1.68 µmol O₂/h/plant), and the root oxygen secretion rate of Eichhornia crassipes (Mart.) Solms was the lowest (1.15 µmol O₂/h/plant). After a period of adaptation, plants showed strong removal effects on COD, NH₃-N, TN, and TP. The removal intensity was in the order of Acorus gramineus Aiton > Pistia stratiotes L. > Eichhornia crassipes (Mart.) Solms; the higher the temperature, the bigger the removal rate. These results were consistent with Acorus gramineus Aiton‘s organic matter secretion and radial oxygen loss, which were better than those of Pistia stratiotes L. and Eichhornia crassipes (Mart.) Solms. Three kinds of plants had better COD removal effects in an acidic environment and better TP removal effects in an alkaline environment. The results show that using the Acorus gramineus Aiton can achieve better remediation of polluted water bodies.

Large-scale fumaric acid chemical brownfield sites have posed a significant obstacle to environmental safety, public safety, and the redevelopment of brownfield sites. A comprehensive study was conducted to determine the main pollution indicators, soil pollution characteristics, and the multiple potential risks to the environment and the ecosystem of a fumaric acid brownfield site in northwestern China. The results showed that 1,2,3-trichloropropane(1,2,3-TCP) was the primary pollutant at the fumaric acid brownfield site. The atmospheric volatile organic compounds (VOCs) in this brownfield site did not exceed the Chinese standard limits. The soil contamination was more severe within the site, with a total of about 30 VOCs detected, including the uncommon brominated pollutants. The level of longitudinal soil contamination decreased with increasing soil depth. The distillation area was more contaminated with a maximum exceedance multiple of 11,291.8. The longitudinal contamination depths in the distillation and reactor zones were 10.0 m and 4.0 m, respectively. Soil texture and production processes are considered to be one of the influencing factors for the depth of vertical soil contamination. Our findings heighten the awareness of brownfield site soil contamination and provide a reference for contamination controls and the comprehensive management of fumaric acid brownfield sites.

In this study, a modified horizontal settling tank with rotating biological discs was developed to treat slightly polluted surface water, and its performance on the simultaneous removal of turbidity, organics, and ${\mathrm{NH}}_4^{\mathrm{+}}$-N was investigated on a lab scale. Results show that the effluent quality of the modified settling tank is stable in more than two months of continuous operation. At a hydraulic retention time (HRT) of 2.0 h, 73.65 ± 5.15% turbidity, 53.98 ± 5.17% TOC, and 77.01 ± 10.02%, ${\mathrm{NH}}_4^{\mathrm{+}}$-N could be removed by the modified settling tank with an average of 1.96 NTU turbidity, 1.98 mg/L TOC, and 0.46 mg/L ${\mathrm{NH}}_4^{\mathrm{+}}$-N residue in the effluent. Due to the improvement in DO supply, higher removal efficiencies of both organics and ${\mathrm{NH}}_4^{\mathrm{+}}$-N were achieved with increased disc rotating speed (r < 4 r/min). Further study showed that the genus Hyphomicrobium dominant on the posterior discs and the genus Nitrospira dominant on the anterior discs mainly contributed to the enhanced bio-oxidation of organics and ${\mathrm{NH}}_4^{\mathrm{+}}$-N, respectively.

In recent years, the relocation sites of heavy industrial enterprises have caused great harm to human health, environmental and ecological safety, society and economy. Taking a relocation site of the chemical plant as research object, 18 soil samples of 0~20 cm were collected, and the contents of seven heavy metal elements, including Ni, Cu, Cd, Pb, Hg, As and Zn, were tested. The quality ratio statistical analysis, pollution characteristics analysis and potential ecological risk were used to determine the heavy metal pollution. Results show that mean concentration of Ni, Cu, Cd, Pb, Hg, As and Zn were 30.16 mg/kg, 35.10 mg/kg, 0.28 mg/kg, 31.74 mg/kg, 0.92 mg/kg, 18.99 mg/kg and 72.63 mg/kg, respectively. Compared with the background value of Guanzhong area, Shaanxi, China, the heavy metal exceeding rate of sample points was 83.3%. Hg and As were the main pollution source, and they had exceeded the risk screening values in (Soil environmental quality Risk control standard for soil contamination of development land) (GB36600-2018). Geo-accumulation index and potential ecological risks showed that the mercury of Hg was polluted heavily. All these showed that the potential ecological risk in the chemical plant was extremely strong which was mainly determined by industrial production and human activity at the same time.

Urban soil is one of the main components of urban ecosystem. Taking organic pollution in a chemical plant after relocation as the research object, which is left behind by a chemical plant after relocation, 13 deep soil samples were collected. According to the requirements of “Soil environmental quality Risk control standard for soil contamination of development land” (GB36600-2018), 43 organic contents were tested and analyzed. Mass ratio statistical analysis, single pollution index method and Nemerow synthetic evaluation index were used to analyze the organic pollution in the site. Results show that chloroform, benzene, trichloroethylene (TCE), 1,2-dichloropropane and 1,2,3-trichloropropane were significantly enriched in the reactor and the sewage pool, and the pollution depth was up to 10m. This shows that the chemical plant has a great impact on the site, and there may be leakage or stolen discharge, which is also an important source of soil organic pollution in this area, so detailed monitoring and remediation work should be carried out in the later stage.