Abstract. The stable isotopic compositions of nitrate in precipitation (wet deposition) and groundwater (spring, lake, and stream water) were determined for the island of Rishiri, Japan, so as to use the 17 O anomalies ( 17 O) to trace the fate of atmospheric nitrate that had deposited onto the island ecosystem, which is a representative background forest ecosystem for eastern Asia. The deposited nitrate had large 17 O anomalies with 17 O values ranging from +20.8‰ to +34.5‰ (n = 32) with +26.2‰ being the annual average. The maximum 17 O value of +34.5‰, obtained for precipitation on the 23rd to 24th of February 2007, was an extraordinarily large value among values for all samples of precipitation in Rishiri. Most nitrate in the sample might have been produced via NO 3 radical in a highly polluted air mass that had been supplied from megacities on the eastern coast of the Asian continent. On the other hand, nitrate in groundwater had small 17 O values ranging from +0.9‰ to 3.2‰ (n = 19), which corresponds to an mixing ratio of atmospheric nitrate to total nitrate of (7.4±2.6)%. Comparing the inflow and outflow of atmospheric nitrate in groundwater within the island, we estimated that the direct drainage accounts for (8.8±4.6)% of atmospheric nitrate that has deposited on the island and that the residual portion has undergone biological processing before being exported from the forest ecosystem.
The past decade marked record high air pollution episodes in Indonesia. In this study, we specifically focus on vegetation fires in Palangkaraya located near a Mega Rice Project area in Indonesia. We analyzed various gaseous air pollution data such as particulate matter (PM10), SO2, CO, O3, and NO2 study region. We also conducted elemental analysis at two different sites. Results from 2001 to 2010 suggested the longest hazardous air pollution episode during 2002 lasting about 80 days from mid-August to late-October. Maximum peak concentrations of PM10, SO2, CO, and O3 were also observed during 2002 and their values reached 1905, 85.8, 38.3, and 1003×10(-6) gm(-3) respectively. Elemental analysis showed significant increase in concentrations during 2011 and 2010. Satellite retrieved fires and weather data could explain most of the temporal variations. Our results highlight peat fires as a major contributor of photochemical smog and air pollution in the region.
Abstract. Temporal variations in the stable isotopic compositions of nitrate dissolved in stream water eluted from a cool-temperate forested watershed (8 ha) were measured to quantify the biogeochemical effects of clear-cutting of trees and subsequent strip-cutting of the understory vegetation, dwarf bamboo (Sasa senanensis), with special emphasis on changes in the fate of atmospheric nitrate that had been deposited onto the watershed based on 17 O values of nitrate. A significant increase in stream nitrate concentration to 15 µmol L −1 in spring of 2004 was correlated with a significant increase in the 17 O values of nitrate. Additionally, the high 17 O values of +14.3 ‰ suggest that the direct drainage of atmospheric nitrate accounted for more than 50 % of total nitrate exported from the forested watershed peaking in spring. Similar increases in both concentrations and 17 O values were also found in spring of 2005. Conversely, low 17 O values less than +1.5 ‰ were observed in other seasons, regardless of increases in stream nitrate concentration, indicating that the majority of nitrate exported from the forested watershed during seasons other than spring was remineralized nitrate: those retained in the forested ecosystem as either organic N or ammonium and then been converted to nitrate via microbial nitrification.When compared with the values prior to strip-cutting, the annual export of atmospheric nitrate and remineralized nitrate increased more than 16-fold and fourfold, respectively, in 2004, and more than 13-fold and fivefold, respectively, in 2005. The understory vegetation (Sasa) was particularly important to enhancing biological consumption of atmospheric nitrate.
Abstract. Atmospheric nitrate deposition resulting from anthropogenic activities negatively affects human and environmental health. Identifying deposited nitrate that is produced locally vs. that originating from long-distance transport would help inform efforts to mitigate such impacts. However, distinguishing the relative transport distances of atmospheric nitrate in urban areas remains a major challenge since it may be produced locally and/or be transported from upwind regions. To address this uncertainty we assessed spatiotemporal variation in monthly weighted-average 17 O and δ 15 N values of wet and dry nitrate deposition during one year at urban and rural sites along the western coast of the northern Japanese island of Hokkaido, downwind of the East Asian continent. 17 O values of nitrate in wet deposition at the urban site mirrored those of wet and dry deposition at the rural site, ranging between ∼ +23 and +31 ‰ with higher values during winter and lower values in summer, which suggests the greater relative importance of oxidation of NO 2 by O 3 during winter and OH during summer. In contrast, 17 O values of nitrate in dry deposition at the urban site were lower (+19 -+25 ‰) and displayed less distinct seasonal variation. Furthermore, the difference between δ 15 N values of nitrate in wet and dry nitrate deposition was, on average, 3 ‰ greater at the urban than rural site, and 17 O and δ 15 N values were correlated for both forms of deposition at both sites with the exception of dry deposition at the urban site. These results suggest that, relative to nitrate in wet and dry deposition in rural environments and wet deposition in urban environments, nitrate in dry deposition in urban environments forms from relatively greater oxidation of NO by peroxy radicals and/or oxidation of NO 2 by OH. Given greater concentrations of peroxy radicals and OH in cities, these results imply that dry nitrate deposition results from local NO x emissions more so than wet deposition, which is transported longer distances. These results illustrate the value of stable isotope data for distinguishing the transport distances and reaction pathways of atmospheric nitrate pollution.
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