Monitoring atmospheric nitrogen pollution in Guiyang (SW China) by contrasting use of Cinnamomum Camphora leaves, branch bark and bark as biomonitors

Tree barks for retrospective measurement and source appointment of airborne perfluoroalkyl and polyfluoroalkyl substances

Tree bark is a useful bioindicator of atmospheric pollution. It is specially suitable for airborne perfluoroalkyl and polyfluoroalkyl substances (PFASs) investigation due to persistence of ionic PFASs. The present work firstly systematically studied tree barks as a bioindicator of airborne PFASs. Comparison with the regular active and passive samplers found barks could produce long-term measurement of airborne PFASs, and could record the historical emission of PFASs with retrospective time frame as long as decades. Factors, e.g. tree type, trunk diameter, and sampling depth, can affect PFAS accumulation in barks, and these factors should be kept consistent during sampling. In a study area spatial distribution of airborne PFASs can be obtained by interpolation of bark results, and the concerned region can be located. Properties of the emission sources can be characterized, and the potential sources can be tracked based on the bark results. Their contributions can be further estimated by the source appointment strategies. In the economically and industrially developed study area of the present study, eight cities of southern Jiangsu Province of China, total ionic PFAS concentration of camphor bark samples collected in 34 sites was 0.44-359 ng/g dw (dry weight), dominated by perfluoroalkyl carboxylic acids (PFCAs). Two types of possible sources were characterized as with long-chained PFCAs and PFOA (perfluorooctanoic acid) as the main components respectively. The sources were appointed as fluoropolymer manufacturing and textile industries, the important PFAS application fields, and their relative contribution was estimated as 32.5% and 67.5% respectively. The present study can provide useful advice to the method framework of using barks for long-term occurrence investigation, concerned region location, and emission source appointment of airborne PFASs in a study area. Based on the bark results, effective strategies can be further made for PFAS pollution elimination and risk control.

Monitoring trace element concentrations with environmentally friendly biomonitors in Artvin, Turkey

Air pollution is the change in air composition that disrupts human health and environmental balance. Although natural and anthropogenic processes include crustal movements, photosynthesis, and plant and animal emissions, other sources of contamination also include industrial operations, transportation activities, household resources, and the chemical and metal industries. Thus, biomonitoring can be employed as a quick, affordable, and efficient method for estimating air pollution. In this study, some inorganic pollutants were detected using olive trees (Olea europaea L.) at eleven different points, depending on the traffic density in Artvin, Turkey. Trace element concentrations (Cr, Ti, Fe, Ni, Co, Cu, Zn, Pb, Al, and Mn) were measured in soil once a year and seasonally in plant samples with ICP-OES. Furthermore, basic component analyses total carbon (TC), total nitrogen (TN), total hydrogen (TH), and total sulfur (TS) were done with an elemental analyzer, total chlorophyll contents with a portable chlorophyll meter, and morphological and particle-based plant analyses with SEM-EDS. The pollution levels of these metals were calculated using the enrichment factor (EF) and geoaccumulation index (Igeo) parameters. Furthermore, the accuracy and validity tests of the analyses for trace metals were tested by applying certified reference materials (CRM) (ERM-CD281) for the plant samples and CRM (LGC-6187) for soil samples. Results indicated that soil trace element pollution distributions were ranked according to the following descending order: Fe (37,873.33 mg/kg) > Al (13,300 mg/kg) > Mn (1101.33 mg/kg) > Ti (353.5 mg/kg) > Zn (252.86 mg/kg) > Cu (87.77 mg/kg) > Cr (30.52 mg/kg) > Pb (19.65 mg/kg) > Ni (17.07 mg/kg) > Co (7.65 mg/kg). Moreover, air pollution from anthropogenic sources substantially increased average trace metal concentrations and sulfur emissions in autumn and winter. The average highest values of Fe (321.08 mg/kg) > Al (304.05 mg/kg) > Mn (32.75 mg/kg) > Zn (31.01 mg/kg) > Cu (17.92 mg/kg) > Ti (11.07 mg/kg) Cr (2.57 mg/kg) > Ni (17.07 mg/kg) were found in leaf samples taken from the roadside in autumn and winter. According to the EF and Igeo values, the main polluting trace elements in the soil were Zn, Cu, and Pb, while in the plant, these were detected as Fe, Al, Ti, Cr, Ni, and Cu. Kruskal-Wallis and correlation analysis statistically supported this relationship among metals. Results show that olive leaves are an effective bioindicator for detecting urban air pollution.

Impacts of atmospheric copper and cadmium deposition on the metal accumulation of camphor leaves and rings around a large smelter

The atmospheric deposition of copper (Cu) and cadmium (Cd) was monitored in eight sites around a Cu smelter with similar distance to verify whether tree leaf and ring can be used as bio-indicators to track spatial pollution record. Results showed that total atmospheric deposition of Cu (103-1215 mg/m²/year) and Cd (3.57-11.2 mg/m²/year) were 4.73-66.6 and 3.15-12.2 times higher than those in background site (164 mg/m²/year and 0.93 mg/m²/year). The frequencies of wind directions significantly influenced the atmospheric deposition of Cu and Cd, and the highest atmospheric deposition of Cu and Cd were at the prevalent northeastern wind (JN), and low frequency south (WJ) and north (SW) winds for the lowest deposition fluxes. Since the bioavailability of Cd was higher than that of Cu, the atmospheric deposition of Cd was more easily adsorbed by tree leaf and ring, resulting in only significant relation between atmospheric Cd deposition and Cinnamomum camphora leaves and tree ring Cd. Although tree rings cannot correctly record the atmospheric Cu and Cd deposition, higher concentrations in the indigenous tree rings than the transplanted tree rings suggested that tree rings can reflect to some extent the variations of atmospheric deposition. Generally, spatial pollution of atmospheric deposition of heavy metals cannot reflect the distribution of soil total and available metals around the smelter, and only camphor leaf and tree ring can bio-indicate Cd deposition. A major implication of these findings is that leaf and tree ring can serve for biomonitoring purposes to assess the spatial distribution of atmospheric deposition metal with high bioavailability around a pollution source with similar distance.

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.

The multi-isotope biogeochemistry (S, C, N and Pb) of Hypogymnia physodes lichens: air quality approach in the Świętokrzyski National Park, Poland

The isotope biogeochemistry of bioindicators has widely demonstrated its added value in environmental issues by allowing to precisely identify sources of contamination. Most of the studies are based on studying one or two isotope systematics. Here, we are presenting an innovative multi-proxy approach that combines chemistry with both stable (C, S, N) and radiogenic (Pb) isotope systematics. Using Hypogymnia physodes bioindicators, we evaluated air quality in the complex environment of the Świętokrzyski National Park (ŚNP, Poland) with the ultimate objective of isotopically identifying the sources responsible for the observed contamination. Combining the isotope systematics showed that home heating is a major source of contamination in winter, whereas the contribution of road traffic increases during the summer. Pb isotope ratios identified industrial activities as the major source of this metal in the atmosphere.

Selecting Biomonitors of Atmospheric Nitrogen Deposition: Guidelines for Practitioners and Decision Makers

Environmental pollution is a major threat to public health and is the cause of important economic losses worldwide. Atmospheric nitrogen deposition is one of the most significant components of environmental pollution, which, in addition to being a health risk, is one of the leading drivers of global biodiversity loss. However, monitoring pollution is not possible in many regions of the world because the instrumentation, deployment, operation, and maintenance of automated systems is onerous. An affordable alternative is the use of biomonitors, naturally occurring or transplanted organisms that respond to environmental pollution with a consistent and measurable ecophysiological response. This policy brief advocates for the use of biomonitors of atmospheric nitrogen deposition. Descriptions of the biological and monitoring particularities of commonly utilized biomonitor lichens, bryophytes, vascular epiphytes, herbs, and woody plants, are followed by a discussion of the principal ecophysiological parameters that have been shown to respond to the different nitrogen emissions and their rate of deposition.

A preliminary study into the use of tree-ring and foliar geochemistry as bio-indicators for vehicular NOx pollution in Malta

Emissions from traffic over the past few decades have become a significant source of air pollution. Among the pollutants emitted are nitrogen oxides (NO_x), exposure to which can be detrimental to public health. Recent studies have shown that nitrogen (N) stable isotope ratios in tree-rings and foliage express a fingerprint of their major N source, making them appropriate for bio-monitoring purposes. In this study, we have applied this proxy to Aleppo pines (Pinus halepensis) at three distances from one of the busiest roads in Malta, a country known to suffer from intense traffic pollution. Our results showed that N and organic carbon (C) stable isotope ratios in tree-rings do not vary over the period 1980-2018 at any of the investigated sites; however, statistically significant spatial trends were apparent in both tree-rings and foliage. The roadside and transitional sites exhibited more positive δ¹⁵N and more negative δ¹³C values compared to those at a rural control site. This is likely due to the incorporation of ¹⁵N-enriched NO_x and ¹³C-depleted CO₂ from traffic pollution. Sampled top-soil also exhibited the δ¹⁵N trend. Our results constitute the first known application of dendrogeochemistry to atmospheric pollution monitoring in Malta.

Urban Atmospheric Environment Quality Assessment by Naturally Growing Bryophytes in Central China

Bryophytes are popular biomonitoring plants for atmospheric environments. The objectives of this study were to examine the characteristics of bryophyte communities, determine a suitable monitor species, and assess urban atmospheric environment quality by the joint use of bryophyte features and chemical properties in a large city in China. A pleurocarpous feather moss Haplocladium angustifolium was recognized as a good biomonitor of atmospheric deposition in central China by investigating bryophyte communities and habitat environment in various ecological function regions of the urban areas in Wuhan. The concentrations of trace elements, including As, Cd, Co, Cr, Cu, Mn, Ni, V, Pb, and Zn, in moss and soil samples from 25 sampling sites were analyzed by inductively coupled plasma mass spectrometry. The concentrations of Cd and Zn in Haplocladium angustifolium collected from the entire study area were much higher than those in substrate soil. Cd was at the highest ecological risk level among the 10 elements, which contributed 34.5% to the potential ecological risk index (RI). An RI value of 392.8 indicated that urban atmospheric quality in Wuhan was in a considerable potential ecological risk. The index of atmospheric purity, regarding species richness, cover, and frequency of bryophytes, was spatially and negatively correlated with RI, also demonstrated the atmospheric quality. Effective measures should be considered to alleviate certain airborne trace element contamination and protect the environment and human health in this metropolis.

Abiotic and Biological Degradation of Atmospheric Proteinaceous Matter Can Contribute Significantly to Dissolved Amino Acids in Wet Deposition

Atmospheric proteinaceous matter is characterized by ubiquity and potential bioavailability. However, little is known about the origins, secondary production processes, and biogeochemical role of proteinaceous matter in wet deposition. Precipitation samples were collected in suburban Guiyang (southwestern China) over a 1 year period to investigate their chemical components, mainly including dissolved combined amino acids (DCAAs), dissolved free AAs (DFAAs), and nonleachable particulate AAs (PAAs). Glycine was most abundant in the DFAAs, while the dominant species in DCAAs and PAAs was glutamic acid (including deaminated glutamine). The total DCAA, DFAA, and PAA concentrations peaked on average in spring (min. in summer). On average, the contribution of DCAA-nitrogen (median of 3.44%) to dissolved organic nitrogen was 5-fold higher than that of DFAA-nitrogen (median of 0.60%). Correlation analyses of AAs with ozone, nitrogen dioxide, and the quantitative degradation index suggest that DC(/F)AAs are linked with both abiotic and biological degradation of proteinaceous matter. Moreover, the high FAA scavenging ratios indicate the presence of postdepositional degradation of atmospheric proteinaceous matter. Further, the positive matrix factorization results suggest that the degradation of atmospheric proteinaceous matter markedly contributes to DCAAs and DFAAs in precipitation. Overall, the results suggest that the secondary processes involved in the degradation of atmospheric proteinaceous matter significantly promote direct bioavailability of AA-nitrogen.

Vehicle emissions and fertilizer impact the leaf chemistry of urban trees in Salt Lake Valley, UT

The urban nitrogen (N) and carbon (C) cycles are substantially influenced by human activity. Alterations to these cycles include increased inputs from fossil fuel combustion and fertilizer use. The leaf chemistry of urban trees can be used to distinguish between these different N and C sources. Here, we evaluated relationships between urban vegetation and different N and C sources in street and residential trees in the Salt Lake Valley, Utah. We tested three hypotheses: 1) unfertilized street trees on high traffic density roads will have higher leaf %N, more enriched δ¹⁵N and more depleted δ¹³C than unfertilized street trees on low traffic density roads; 2) trees in high income residential neighborhoods will have higher leaf %N, more depleted δ¹⁵N and more enriched δ¹³C than trees in lower income neighborhoods; and 3) unfertilized street trees will have lower leaf %N, more enriched δ¹⁵N and more depleted δ¹³C than fertilized residential trees. Leaf δ¹⁵N was more enriched near high traffic density roads for one study species. However, street tree δ¹⁵N and δ¹³C were largely influenced by vehicle emissions from primary and secondary roads within 1000 m radius rather than the immediately adjacent road. Leaf δ¹³C was correlated with neighborhood income, although this relationship may be the result of variations in irrigation practices rather than variations in C sources. Finally, unfertilized trees in downtown Salt Lake had lower leaf %N, more enriched δ¹⁵N and more depleted δ¹³C than fertilized trees. These results highlight that urban trees can serve as biomonitors of the environment. Moreover, they emphasize that roads can have large spatial footprints and that the leaf chemistry of urban vegetation may be influenced by the spatial patterns in roads and road densities at the landscape scale.

Traffic-related dustfall and NOx, but not NH3, seriously affect nitrogen isotopic compositions in soil and plant tissues near the roadside

Ammonia (NH₃) emissions from traffic have received particular attention in recent years because of their important contributions to the growth of secondary aerosols and the negative effects on urban air quality. However, few studies have been performed on the impacts of traffic NH₃ emissions on adjacent soil and plants. Moreover, doubt remains over whether dry nitrogen (N) deposition still contributes a minor proportion of plant N nutrition compared with wet N deposition in urban road environments. This study investigated the δ¹⁵N values of road dustfall, soil, moss, camphor leaf and camphor bark samples collected along a distance gradient from the road, suggesting that samples collected near the road have significantly more positive δ¹⁵N values than those of remote sites. According to the SIAR model (Stable Isotope Analysis in R) applied to dustfall and moss samples from the roadside, it was found that NH₃ from traffic exhaust (8.8 ± 7.1%) contributed much less than traffic-derived NO₂ (52.2 ± 10.0%) and soil N (39.0 ± 13.8%) to dustfall bulk N; additionally, 68.6% and 31.4% of N in mosses near the roadside could be explained by dry N deposition (only 20.4 ± 12.5% for traffic-derived NH₃) and wet N deposition, respectively. A two-member mixing model was used to analyse the δ¹⁵N in continuously collected mature camphor leaf and camphor bark samples, which revealed a similarity of the δ¹⁵N values of plant-available deposited N to ¹⁵N-enriched traffic-derived NO_x-N. We concluded that a relatively high proportion of N inputs in urban road environments was contributed by traffic-related dustfall and NO_x rather than NH₃. These information provide useful insights into reducing the impacts of traffic exhaust on adjacent ecosystems and can assist policy makers in determining the reconstruction of a monitoring network for N deposition that reaches the road level.

Differential patterns of nitrogen and δ15N in soil and foliar along two urbanized rivers in a subtropical coastal city of southern China

Urbanization usually pollutes the environment leading to alterations in key biogeochemical cycles. Therefore, understanding its effects on forest nitrogen (N) saturation is becoming increasingly important for addressing N pollution challenges in urban ecosystems. In this study, we compared soil (N availability, net N mineralization, net nitrification, and δ¹⁵N) and foliar (N concentrations and δ¹⁵N) variables in upstream, midstream and downstream forest stands of Bailongjiang River (BJR; more urbanized) and Wulongjiang River (WJR; less urbanized), the two branches of the Minjiang River Estuary. Total soil N, ammonium, nitrate, net N mineralization and nitrification rates, as well as soil δ¹⁵N were significantly higher in BJR compared with WJR forest stands. While no substantial difference in foliar N concentrations was noted between rivers, foliar δ¹⁵N was on average more than 2.5 times higher in BJR than WJR forest stands. Across the study area, foliar δ¹⁵N was positively related to soil δ¹⁵N, which also had positive linear relationships with soil nitrate concentrations, net N mineralization and net nitrification rates. Moreover, all variables except foliar δ¹⁵N and ammonium concentrations showed decreasing patterns in the order: upstream > midstream > downstream along the BJR forest stands. Soil ammonium and foliar values (N concentrations and δ¹⁵N) revealed clear patterns along the WJR, with the former increasing and the latter decreasing from the upstream to downstream forest stands. Our findings indicate an increase in urbanization-induced N inputs from the WJR to BJR and that forest stands along the BJR especially at the upstream have higher N availability and are shifting rapidly towards N saturation state. These results emphasize the need for effective N pollution control in urban environments through sustainable urban planning.