Estimating NOx removal capacity of urban trees using stable isotope method: A case study of Beijing, China

Dry deposition effect of urban green spaces on ambient particulate matter pollution in China

Particulate matter (PM) is a major source of urban air pollution that poses a serious threat to the environment and human health. This study quantified the dry deposition effect of PM2.5 and PM10 on vegetation using a mathematical model to overcome the limitations of traditional site-scale research. Additionally, multi-source satellite remote sensing products were combined to form a raster dataset to estimate the effect of dry deposition on PM2.5 and PM10 in China's urban green spaces from 2000 to 2020. The spatial and temporal changes in the long-term series were analyzed, and the influence of environmental factors on dry deposition was analyzed in combination with wavelet changes. The experimental results showed that: 1) from 2000 to 2020, the dry deposition effect of PM2.5 and PM10 on vegetation showed an initial increasing and then decreasing trend caused by the sudden drop in atmospheric pollutant particle concentration driven by local policies; 2) broad-leaved forests provided the main dry deposition effects in urban spaces, accounting for 89.22 %, indicating a need to increase the density of these forest types in urban development planning to improve air quality; and 3) PM2.5, PM10, and environmental impact factors have time-frequency scale coherences, and the coherence between PM2.5 reduction and these factors is more complex than that of PM10, with precipitation being the best variable to explain the change in PM2.5 and PM10. These findings are important for the prevention and control of urban air pollution, regional planning of green spaces, and sustainable development of cities.

Anthropogenic land-use activities within watersheds reduce comammox activity and diversity in rivers

Nitrogen cycling plays a key role in maintaining river ecological functions which are threatened by anthropogenic activities. The newly discovered complete ammonia oxidation, comammox, provides novel insights into the ecological effects of nitrogen on that it oxidizes ammonia directly to nitrate without releasing nitrite as canonical ammonia oxidization conducted by AOA or AOB which is believed to play an important role in greenhouse gas generation. Theoretically, contribution of commamox, AOA and AOB to ammonia oxidization in rivers might be impacted by anthropogenic land-use activities through alterations in flow regime and nutrient input. While how land use pattern affects comammox and other canonical ammonia oxidizers remains elusive. In this study, we examined the ecological effects of land use practices on the activity and contribution of three distinctive groups of ammonia oxidizers (AOA, AOB, comammox) as well as the composition of comammox bacterial communities from 15 subbasins covering an area of 6166 km² in North China. The results showed that comammox dominated nitrification (55.71%-81.21%) in less disturbed basins characterized by extensive forests and grassland, while AOB became the major player (53.83%-76.43%) in highly developed basins with drastic urban and agricultural development. In addition, increasing anthropogenic land use activities within the watershed lowered the alpha diversity of comammox communities and simplified the comammox network. Additionally, the alterations of NH₄⁺-N, pH and C/N induced by land use change were found to be crucial drivers in determining the distribution and activity of AOB and comammox. Together, our findings cast a new light on aquatic-terrestrial linkages from the view of microorganism-mediated nitrogen cycling and can further be applied to target watershed land use management.

Investigating the Effects of Air Pollution on Plant Species Resistance in Urban Areas

Context: Air pollution is a serious concern for environmental and human health, especially due to increasing the risk of respiratory and cardiovascular diseases. The purpose of this study was to investigate the effects of air pollution on plant species resistance in urban areas. Evidence Acquisition: This narrative review was conducted by searching the databases of Web of Science, Science Direct, Scopus, PubMed, Google Scholar, and Springer. Sixty-five articles were screened by reading their abstracts and full texts. In the end, 12 relevant papers published from 1993 to 2021 were finally selected. Results: The literature review showed that the green spaces created by municipalities in different areas of the city included a set of trees and shrubs compatible by the climate, grass, soil, and water of the region, leading to a significant improvement in air quality. Based on the results, urban green space has the ability to reduce the amount of artificially produced pollutants, and the use of natural potential of trees can improve the quality of the environment depending on various factors such as the climatic condition of the region and the density and amount of vegetation cover. Conclusions: The most effective ways to reduce health and economic costs include reducing the emission of pollutants from cars and industries, extending urban green space, educating citizens, and organizational planning and cooperation. The findings of this study may have important implications for selecting plant species for vegetation traffic barriers.

Isotopic composition (δ13C and δ15N) in the soil-plant system of subtropical urban forests

This study brings information on the dynamics of C and N in urban forests in a subtropical region. We tested the hypothesis that C and N isotopic sign of leaves and soil and physiological traits of trees would vary from center to periphery in a megacity, considering land uses, intensity of automotive fleet and microclimatic conditions. 800 trees from four fragments were randomly chosen. Soil samples were collected at every 10 cm in trenches up to 1 m depth to analyze C and N contents. Both, plants and soil were assessed for δ¹³C, δ¹⁵N, %C and %N. Physiological traits [carbon assimilation (A)], CO₂ internal and external pressure ratio (Pi/Pa) and intrinsic water use efficiency iWUE were estimated from δ¹³C and Δ δ¹³C in leaves and soil ranged from -27.42 ‰ to -35.39 ‰ and from -21.22 ‰ to -28.18 ‰, respectively, and did not vary along the areas. Center-periphery gradient was not evidenced by C. Emissions derived from fossil fuel and distinct land uses interfered at different levels in δ¹³C signature. δ¹⁵N in the canopy and soil varied clearly among urban forests, following center-periphery gradient. Leaf δ¹⁵N decreased from the nearest forest to the city center to the farthest, ranging from <3 ‰ to <-3 ‰. δ¹⁵N was a good indicator of atmospheric contamination by NO_x emitted by vehicular fleet and a reliable predictor of land use change. %N followed the same trend of δ¹⁵N either for soils or leaves. Forest fragments located at the edges of the center-periphery gradient presented significantly lower A and Pi/Pa ratio and higher iWUE. These distinct physiological traits were attributed to successional stage and microclimatic conditions. Results suggest that ecosystem processes related to C and N and ecophysiological responses of urban forests vary according to land use and vehicular fleet.

Supply-Demand Evaluation of Green Stormwater Infrastructure (GSI) Based on the Model of Coupling Coordination

The rational spatial allocation of Green Stormwater Infrastructure (GSI), which is an alternative land development approach for managing stormwater close to the source, exerts a crucial effect on coordinating urban development and hydrological sustainability. The balance between the supply and demand of urban facilities has been an influential standard for determining the rationality of this allocation. However, at this stage, research on evaluating planning from the perspective of supply-demand in GSI is still limited. This study proposed an evaluation method for assessing supply-demand levels in GSIs in Guangzhou, China, using the coupling coordination model consisting of Coupling Degree (CD) and Coupling Coordination Degree (CCD). Furthermore, the spatial distributions of supply-demand balance and resource mismatch were identified. The results indicated that the supply and demand levels of GSI exhibited significant spatial differences in distribution, with most streets being in short supply. The GSI exhibited a high CD value of 0.575 and a poor CCD value of 0.328, implying a significant imbalance in facility allocation. A lot of newly planned facilities failed to effectively cover the streets in need of improvement, so it became essential to adjust the planning scheme. The findings of this study can facilitate the decision-makers in assessing the supply-demand levels in GSI and provide a reference of facility allocation for the sustainable construction of Sponge City.

Assessment of NO2 Purification by Urban Forests Based on the i-Tree Eco Model: Case Study in Beijing, China

Air quality issues caused by nitrogen dioxide (NO2) have become increasingly serious in Chinese cities in recent years. As important urban green infrastructure, urban forests can mitigate gaseous nitrogen pollution by absorbing NO2 through leaf gas exchange. This study investigated spatiotemporal variations in the NO2 removal capacity of urban forests in Beijing city from 2014–2019, based on the i-Tree Eco deposition model. The results show that the annual removal capacity of administrative districts within Beijing city ranged from 14,910 to 17,747 tons, and the largest capacity (2684 tons) was found in the Fangshan district. The annual removal rate of NO2 by urban forests in administrative districts within Beijing was estimated at between 0.50–1.60 g/m2, reaching the highest (1.47 g/m2) in the Mengtougou district. The annual average absorption of NO2 by urban forests can account for 0.14–2.60% of annual total atmospheric NO2 and potentially reduce the NO2 concentration by 0.10–0.34 µg/m3 on average. The results of a principal component analysis suggest that the distribution of urban forests in Beijing is not optimized to maximize their NO2 removal capacity, being higher in suburban areas and lower in urban areas. This study provides insights into botanical NO2 removal capacity in Beijing city to mitigate atmospheric N pollution, addressing the key role of urban forests in improving human wellbeing.