Monsoon climate controls metal loading in global hotspot region of transboundary air pollution.

Eastern Asia is a major source of global air pollution. The distribution and intensity of these emissions are becoming well characterized, but their impact on the earth surface considering regional hydroclimatological settings has yet to be quantified. Here we show high-resolution spatiotemporal trace metal distributions of precipitation samples collected throughout the Japanese archipelago in 2013, when the world's coal consumption was the greatest, to depict the mass transportation and deposition of pollution. The results show that metals emitted through coal combustion transported from the continent via prevailing wind were intensively deposited along the western coast of the archipelago during winter due to heavy snowing, resulting in lead (Pb) concentration of precipitations exceed the critical level (> 10 µg l-1). About 1497 tons of Pb of continental origin loaded through wet deposition accounted for over ca. 87% of the total annual flux in 2013, which constituted ca. 18.5% of the total emissions from China in 2012. This study presents the first detailed picture of monsoon climate-controlled atmospheric metal transportation and loading in the hotspot region after the phase-out of leaded gasoline in the twentieth century. The dataset can serve as a base for evaluating the effect of countermeasures implemented recent year.

Seasonal variability of stable isotopes in precipitation and spring water around Mt Kimpo, Kumamoto, southwestern Japan.

Stable isotopes in precipitation and spring water were observed in a low mountain region, because seasonal variability in isotope altitude and amount effects based on their simultaneous observations in low latitude area have not been studied so much. Seasonal variability in spatial averages of monthly δ18O and d-excess in precipitation ranged from -11.96 to -5.16 ‰ and from 8.0 to 24.2 ‰, respectively, while those in spring water ranged from -7.64 to -7.18 ‰ and from 11.0 to 13.6 ‰. The seasonal variability in spatial average of monthly δ18O in precipitation was much wider than in spring water. Monthly isotopic composition in spring water was mostly plotted along the local meteoric water lines for precipitation in warm months, suggesting that precipitation in warm months is the main source of spring water. Annual isotope altitude effects in precipitation (-0.12 ‰/100 m) and spring water (-0.13 ‰/100 m) were almost the same, and monthly isotope amount effects for cold months (-7.9 to -0.9 ‰/100 mm) were relatively higher than those for the warm months (-12.0 to -9.6 ‰/100 mm). The isotope amount effect at each sampling sites appeared using only the data in the warm months without extreme weather.

Geographic effects on stable isotopic composition of precipitation across Thailand.

This study investigated the spatial variation of isotopes in precipitation over Thailand in relation to geographic condition. Monthly data (2013-2015) of stable isotopes (δ2H and δ18O) in precipitation within the region 5°37'-20°27'N, 98°04'-105°31'E were analysed using the least squares regression method to determine the possible effects of latitude and longitude on δ18O and d-excess in precipitation. Results showed that the spatial variability of isotopes in precipitation is affected by both continental and amount effects and that the variation is slightly greater in terms of latitude than longitude. Latitude and longitude effects both exhibited negative and positive correlations. Negative correlation, whereby isotopic values decreased with increasing latitude, was found during the June-August and September-November periods. Conversely, a positive relationship appeared in the December-February and March-May seasons. These effects had opposite correlation owing to the various moisture sources and different precipitation patterns between seasons. Furthermore, weak correlation for both latitude and longitude effects was revealed during September-November because of the intraseasonal variation of the monsoon. Consequently, the isotopic composition of precipitation in Thailand is controlled not only by geography but also by moisture source and precipitation pattern.

Spatial analysis of annual mean stable isotopes in precipitation across Japan based on an intensive observation period throughout 2013.

Spatial distribution of annual mean stable isotopes in precipitation (δ(18)O, δ(2)H) was observed at 56 sites across Japan throughout 2013. Annual mean δ(18)O values showed a strong latitude effect, from -12.4 ‰ in the north to -5.1 ‰ in the south. Annual mean d-excess values ranged from 8 to 21 ‰, and values on the Sea of Japan side in Northern and Eastern Japan were relatively higher than those on the Pacific Ocean side. The local meteoric water line (LMWL) and isotope effects were based on the annual mean values from all sites across Japan as divided into distinct regions: the Sea of Japan side to the Pacific Ocean side and Northeastern to Southwestern Japan. Slopes and intercepts of LMWL ranged from 7.4 to 7.8 and 9.8 to 13.0, respectively. Slopes for latitude, altitude, and temperature effects ranged from -0.27 to -0.48 ‰/°N, -0.0034 to -0.0053 ‰/m, and 0.36 to 0.46 ‰/°C, respectively, with statistically significance at the 99 % level. However, there was no precipitation amount effect. From the result of a multiple regression analysis, the empirical formula of annual mean δ(18)O in precipitation from latitude and altitude for all sites across Japan was determined to be δ(18) O = -0.348 (LAT) - 0.00307 (ALT) + 4.29 (R(2) = 0.59). Slopes for latitude and altitude ranged from - 0.28 to - 0.51, and - 0.0019 to - 0.0045, respectively. Even though site distribution was uneven, these equations are the first trial estimation for annual mean stable isotopes in precipitation across Japan. Further research performed on the monthly basis is required to elucidate factors controlling the spatiotemporal variability of stable isotopes in precipitation across Japan.

Verification of the isotopic composition of precipitation simulated by a regional isotope circulation model over Japan.

The isotopic composition (δ(18)O and δ(2)H) of precipitation simulated by a regional isotope circulation model with a horizontal resolution of 10, 30 and 50 km was compared with observations at 56 sites over Japan in 2013. All simulations produced reasonable spatio-temporal variations in δ(18)O in precipitation over Japan, except in January. In January, simulated δ(18)O values in precipitation were higher than observed values on the Pacific side of Japan, especially during an explosively developing extratropical cyclone event. This caused a parameterisation of precipitation formulation about the large fraction of precipitated water to liquid detrained water in the lower troposphere. As a result, most water vapour that transported from the Sea of Japan precipitated on the Sea of Japan side. The isotopic composition of precipitation was a useful verification tool for the parameterisation of precipitation formulation as well as large-scale moisture transport processes in the regional isotope circulation model.

Application of continuous 222 Rn monitor with dual loop system in a small lake.

To estimate the spatial distribution of groundwater discharge from the bottom of a small lake of Kumamoto in Japan, we applied continuous radon measurements with a dual loop system and verified the results obtained using the radon method by visual diving surveys. Time-shifting correction in the dual-loop system is reasonable to obtain the true radon activity in water. Distributions of radon activity and water temperature in the study area reveal the effects on groundwater discharge and mixing situation of lake water. The estimated discharge zone ascertained using the radon method agrees with the groundwater discharge distribution observed through diving surveys. Although the data resolution of the radon method is much greater than the width of observed discharge zones, the general distribution of groundwater discharge is recognizable. The dual loop system of radon measurement is useful for smaller areas.

Evaluation of groundwater quality and its suitability for drinking, domestic, and agricultural uses in the Banana Plain (Mbanga, Njombe, Penja) of the Cameroon Volcanic Line.

Groundwater quality of the Banana Plain (Mbanga, Njombe, Penja-Cameroon) was assessed for its suitability for drinking, domestic, and agricultural uses. A total of 67 groundwater samples were collected from open wells, springs, and boreholes. Samples were analyzed for physicochemical properties, major ions, and dissolved silica. In 95% of groundwater samples, calcium is the dominant cation, while sodium dominates in 5% of the samples. Eighty percent of the samples have HCO(3) as major anion, and in 20%, NO(3) is the major anion. Main water types in the study area are CaHCO(3), CaMgHCO(3), CaNaHCO(3), and CaNaNO(3)ClHCO(3). CO(2)-driven weathering of silicate minerals followed by cation exchange seemingly controls largely the concentrations of major ions in the groundwaters of this area. Nitrate, sulfate, and chloride concentrations strongly express the impact of anthropogenic activities (agriculture and domestic activities) on groundwater quality. Sixty-four percent of the waters have nitrate concentrations higher than the drinking water limit. Also limiting groundwater use for potable and domestic purposes are contents of Ca(2+), Mg(2+) and HCO(3) (-) and total hardness (TH) that exceed World Health Organization (WHO) standards. Irrigational suitability of groundwaters in the study area was also evaluated, and results show that all the samples are fit for irrigation. Groundwater quality in the Banana Plain is impeded by natural geology and anthropogenic activities, and proper groundwater management strategies are necessary to protect sustainably this valuable resource.