Metagenomic analysis of the microbial communities and associated network of nitrogen metabolism genes in the Ryukyu limestone aquifer.

While microbial biogeochemical activities such as those involving denitrification and sulfate reduction have been considered to play important roles in material cycling in various aquatic ecosystems, our current understanding of the microbial community in groundwater ecosystems is remarkably insufficient. To assess the groundwater in the Ryukyu limestone aquifer of Okinawa Island, which is located in the southernmost region of Japan, we performed metagenomic analysis on the microbial communities at the three sites and screened for functional genes associated with nitrogen metabolism. 16S rRNA amplicon analysis showed that bacteria accounted for 94-98% of the microbial communities, which included archaea at all three sites. The bacterial communities associated with nitrogen metabolism shifted by month at each site, indicating that this metabolism was accomplished by the bacterial community as a whole. Interestingly, site 3 contained much higher levels of the denitrification genes such as narG and napA than the other two sites. This site was thought to have undergone denitrification that was driven by high quantities of dissolved organic carbon (DOC). In contrast, site 2 was characterized by a high nitrate-nitrogen (NO3-N) content and a low amount of DOC, and this site yielded a moderate amount of denitrification genes. Site 1 showed markedly low amounts of all nitrogen metabolism genes. Overall, nitrogen metabolism in the Ryukyu limestone aquifer was found to change based on environmental factors.

Mechanism of denitrification in subsurface-dammed Ryukyu limestone aquifer, southern Okinawa Island, Japan.

Denitrification crucially regulates the attenuation of groundwater nitrate and is unlikely to occur in a fast-flowing aquifer such as the Ryukyu limestone aquifer in southern Okinawa Island, Japan. However, evidences of denitrification have been observed in several wells within this region. This study analyzed environmental isotopes (δ15NNO3 and ẟ18ONO3) to derive the rationale for denitrification at this site. Additionally, the presence of two subsurface dams in the study area may influence the processes involved in nitrate attenuation. Herein, we analyzed 150 groundwater samples collected spatially and seasonally to characterize the variations in the groundwater chemistry and stable isotopes during denitrification. The values of δ15NNO3 and δ18ONO3 displayed a progressive trend up to +59.7 ‰ and + 21 ‰, respectively, whereas the concentrations of NO3--N decreased to 0.1 mg L-1. In several wells, the enrichment factors of δ15NNO3 ranged from -6.6 to -2.1, indicating rapid denitrification, and the δ15NNO3 to δ18ONO3 ratios varied from 1.3:1 to 2:1, confirming the occurrence of denitrification. Denitrification intensively proceeds under conditions of depleted dissolved oxygen concentrations (<2 mg L-1), sluggish groundwater flow with longer residence times, high concentrations of dissolved organic carbon (>1.2 mg L-1), and low groundwater levels during the dry season with precipitation rates of <100 mm per month (Jun-Sep). SF6 analysis indicated the exclusive occurrence of denitrification in specific wells with groundwater residence times exceeding 30 years. These wells are located in close proximity to the major NE-SW fault system in the Komesu area, where the hydraulic gradient was below 0.005. Detailed geological and lithological investigations based on borehole data revealed that subsurface dams did not cause denitrification while the major NE-SW fault system uplifted the impermeable basement rock of the Shimajiri Group, creating a lithological gap at an equivalent depth that ultimately formed a sluggish groundwater area, promoting denitrification.

Self-organizing map improves understanding on the hydrochemical processes in aquifer systems.

The holistic understanding of hydrochemical features is a crucial task for management and protection of water resources. However, it is challenging for a complex region, where multiple factors can cause hydrochemical changes in studied catchment. We collected 208 groundwater samples from such region in Kumamoto, southern Japan to explicitly characterize these processes by applying machine learning technique. The analyzed groundwater chemistry data like major cations and anions were fed to the self-organizing map (SOM) and the results were compared with classical classification approaches like Stiff diagram, standalone cluster analysis and score plots of principal component analysis (PCA). The SOM with integrated application of clustering divided the data into 11 clusters in this complex region. We confirmed that the results provide much greater details for the associated hydrochemical and contamination processes than the traditional approaches, which show quite good correspondence with the recent high resolution hydrological simulation model and aspects from geochemical modeling. However, the careful application of the SOM is necessary for obtaining accurate results. This study tested different normalization approaches for selecting the best SOM map and found that the topographic error (TE) was more important over the quantization error (QE). For instance, the lower QE obtained from min-max and log normalizations showed problems after clustering the SOM map, since the QE did not confirm the topological preservation. In contrast, the lowest TE obtained from Z-transformation data showed better spatial matching of the clusters with relevant hydrochemical characteristics. The results from this study clearly demonstrated that the SOM is a helpful approach for explicit understanding of the hydrochemical processes on reginal scale that may capably facilitate better groundwater resource management.

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.

Museum-archived and recent acquisition nitrates from the Atacama Desert, Chile, South America: refinement of the dual isotopic compositions (δ15N vs. δ18O).

Sodium nitrate ores from the Atacama Desert in South America were economically important as they represented huge natural resources for the fertilizer and explosives industries during the early nineteenth to early twentieth centuries. Nitrogen and oxygen isotope ratios (δ15N and δ18O) of these desert nitrates generally show unique compositions (from close to 0 and up to ca. +50 ‰, respectively). The nitrates indicate the provenance as atmospheric in origin due to the mass-independent photochemical reaction of nitric oxide (NO) with ozone (O3) in the atmosphere to produce nitrate (NO3-). This paper examines the previously existing isotope data for specimens acquired from the Atacama Desert. It then reports new data from dual isotope analysis of historic nitrate specimens archived in museums in the UK. In the stable isotope signatures for nitrates from two areas of the Atacama Desert, Tarapacá in the north and Antofagasta in the south, were examined, and this analysis enabled a more detailed definition of their isotopic compositional ranges. This improved database is useful for tracing the provenance of the historic nitrates used in gunpowder and saltpetre, and also the cause of nitrate pollution in natural environments for which routine chemistry alone cannot provide the definite evidence for the origin.

Acesulfame as a suitable sewer tracer on groundwater pollution: A case study before and after the 2016 Mw 7.0 Kumamoto earthquakes.

On April 14th and 16th, 2016, two large-scale earthquakes (Mw 6.2 and 7.0) occurred in Kumamoto, Japan. The sewer system was seriously damaged and there were concerns about groundwater pollution by sewer exfiltration. In this study, artificial sweeteners including acesulfame (ACE) in groundwater were analyzed before and after the earthquakes to evaluate sewage pollution and its temporal variation. Before the earthquakes, ACE was detected in 31 of 49 groundwater samples analyzed, indicating that wastewater may have leaked into groundwater. Groundwater was sampled from the same locations 2, 7, 12, and 30 months after the earthquakes. The detection frequency and median concentration of ACE in groundwater increased significantly 7 months after the earthquakes, from several tens to maximumly 189 times greater than the pre-earthquake concentrations. This suggests the earthquakes caused serious damage to sewer pipes and groundwater may be polluted. However, ACE concentrations drastically decreased or remained low 30 months after the earthquakes, probably due to the recovery and restoration work of sewer infrastructure. This study shows that ACE is an excellent tracer for evaluating sewer exfiltration to groundwater. In addition, it is important to obtain data on sewage tracers under normal condition as part of preparations for large-scale earthquakes.

Stable isotopes show that earthquakes enhance permeability and release water from mountains.

Hydrogeological properties can change in response to large crustal earthquakes. In particular, permeability can increase leading to coseismic changes in groundwater level and flow. These processes, however, have not been well-characterized at regional scales because of the lack of datasets to describe water provenances before and after earthquakes. Here we use a large data set of water stable isotope ratios (n = 1150) to show that newly formed rupture systems crosscut surrounding mountain aquifers, leading to water release that causes groundwater levels to rise (~11 m) in down-gradient aquifers after the 2016 Mw 7.0 Kumamoto earthquake. Neither vertical infiltration of soil water nor the upwelling of deep fluids was the major cause of the observed water level rise. As the Kumamoto setting is representative of volcanic aquifer systems at convergent margins where seismotectonic activity is common, our observations and proposed model should apply more broadly.

Dual isotopic (δ15N-δ18O) characterization of saltpetre currently prevailing in Lao PDR and its global compilation: new insight into isotope fractionation during production processes.

Saltpetre (KNO3; potassium nitrate) is one of the major ingredients of gunpowder. Simplex saltpetre (total 126 samples) together with gunpowder (total 93 samples) commodities which are currently prevailing in local markets as used for wildlife hunting and rocket festivals (local name in Lao: Boun Ban Fai) were collected from throughout Lao PDR. Dual isotopic composition of nitrates (δ15N, δ18O) was analyzed by the microbial denitrification method. Binary plotting of the data was conducted to characterize the mode of formation. In Lao PDR, almost all the commodities were imported from neighbouring Thailand, and to a lesser extent from Israel. Binary plotting of δ15N vs. δ18O of nitrates shows their intrinsic origin manufactured by Haber-Bosch and subsequently Ostwald processes. We observed an inverse correlation (δ15Nnitrate: up to + 12 ‰; δ18Onitrate: down to + 15 ‰), deviating from the reservoir values (free air) of δ15N (dinitrogen; up to 0 ‰) and δ18O (oxygen; +23.5 ‰), interpreted this as an indication of isotope fractionation during manufacture. The most plausible interpretation for this is the fractionation associated with formation of NO following NO2 and finally NO3 products. A nearly comparable inverse relationship is also observed for nitrates in pyrotechnics manufactured in China.

Controlling factors and driving mechanisms of nitrate contamination in groundwater system of Bandung Basin, Indonesia, deduced by combined use of stable isotope ratios, CFC age dating, and socioeconomic parameters.

Number of populations, industry, and economic activities in Indonesia are growing rapidly and these impacts on natural environments raise awareness about water quality issue over the country. Bandung Basin, one of the most growing rapidity urban areas in Indonesia, was assessed for NO3- contamination in groundwater systems, and its controlling factors and driving mechanisms were investigated with the aim to demonstrate novelty on the use of combination of parameters of stable isotope ratios in nitrate (δ15N and δ18O in NO3-), groundwater age (using CFC-12 age tracer), and socioeconomic parameters (land-use, population, and economic database). Groundwater NO3- concentrations at present time did not exceed HWO limit for all the analyzed samples (3.00 mg/L in average with maximum value of 20.69 mg/L, n = 102). Dual stable isotopic analysis together with CFC-12 groundwater age determination suggest that anthropogenic activities are the major causes for increasing NO3- concentrations in groundwater. Those activities under respective land-use are industrial and domestic wastes for urban areas and chemical fertilizers for paddy and plantations areas. In general shallow unconfined aquifer is more vulnerable to NO3- contamination compared with deep confined aquifer because denitrification partly occurs in deep anoxic aquifer and this led attenuation of NO3- pollution in groundwater flowing. However, it seems likely at groundwater depression cones in urban areas that more concentrated waters are transported from shallow aquifer into deep aquifer system through downward vertical fluxes due to excessive pumping. Principal component analysis (PCA) on NO3- concentrations with socioeconomic parameters indicated that industrial and population growths are the main factors related to groundwater NO3- contamination. This result corresponds to CFC-age dating which shows younger (more recently recharged) groundwaters as being more contaminated than older ones do. Our study implies that NO3- contamination in this area may become more severe in future with a lack of necessary controls and treatment for human-induced nitrogen sources. Proposed approach is useful to understand how the NO3- contaminant behaves in large basin aquifer system under urban environments and might be applicable in other developing regions too because increasing populations may be associated with increasing nitrogen loadings.

Earthquake-induced structural deformations enhance long-term solute fluxes from active volcanic systems.

Evidence for relationships between seismotectonic activity and dissolved weathering fluxes remains limited. Motivated by the occurrence of new springs emerging after the 2016 Kumamoto earthquake and supported by historical groundwater data, this study focuses on the long-term effect of near-surface structural deformation on the contribution of deep, highly saline fluids to the solute fluxes from the Aso caldera, Kyushu, Japan. Available hydrologic and structural data suggest that concentrated, over-pressured groundwaters migrate to the surface when new hydraulic pathways open during seismic deformation. These new springs have a hydrochemical fingerprint (including δDH2O, δ18OH2O, δ7Li, δ11B, δ18OSO4, and δ34SSO4) indistinguishable from long-established confined groundwater that likely reflects a mixture of infiltrated meteoric water with high-sulfate hydrothermal fluids. A comparison of historical hydrochemistry data and patterns of past seismicity suggests that discharge of deep fluids is associated with similar deformation structures to those observed during the Kumamoto earthquake, and that seismic activity plays an important role over historic timescales in delivering the majority of the solutes to the caldera outlet, sustaining fluxes that are amongst the world's highest. This upwelling mechanism might be relevant for other systems too, and could contribute to the over-proportional share of active volcanic areas in global weathering fluxes.

Dual (oxygen and nitrogen) isotopic characterization of the museum archived nitrates from the United States of America, South Africa and Australia.

Dual (oxygen and nitrogen) isotopic composition of the museum archived nitrates from the United States of America, South Africa and Australia was studied. The analyzed specimens were collected in middle 19th to early 20th centuries, and represent world-wide acquisition of the Smithsonian Institution Natural Museum of Natural History (Washington, D. C., USA) and the Natural History Museum (London, UK). The samples consist of transparent to semi-transparent aggregates of minute nitrate, euhedral crystallites which imply precipitation from percolating fluids under ample space and dry regimes. The major nitrate chemistry is saltpetre (KNO3) with minor nitratine (NaNO3). A binary plot of δ15N vs. δ18O of almost all nitrates indicates a trend, reflecting microbial origin through nitrification of ammonium. The diagram excludes the contribution of meteoric origin formed by mass-independent, photochemical reaction of NO with ozone in stratosphere. Calculated paleo-ambient fluid compositions responsible for microbial nitrification imply extreme evaporative concentration of relevant fluids under dry climatic regimes in the Northern Cape Province (South Africa) and in the Northern Territory (central Australia), and even throughout the United States of America. The dual isotopic characterization provides direct evidence to the origin of the museum archived nitrates.

Lead isotope ratios in six lake sediment cores from Japan Archipelago: Historical record of trans-boundary pollution sources.

Sediment cores from six lakes situated from north to south on the Japanese Archipelago were collected during 2009-2010 to investigate the hypothesis that deposition of lead (Pb) was coming from East Asia (including China, South Korea and eastern part of Russia). Accumulation rates and ages of the lake sediment were estimated by the (210)Pb constant rate of supply model and (137)Cs inputs to reconstruct the historical trends of Pb accumulation. Cores from four lakes located in the north and central Japan, showed clear evidence of Pb pollution with a change in the (206)Pb/(207)Pb and (208)Pb/(207)Pb ratios in the recent sediment as compared to the deeper sediment. Among the six studied lakes, significant inputs of anthropogenic lead emissions were observed at Lake Mikazuki (north Hokkaido in north Japan), Lake Chokai (north of Honshu), and Lake Mikuriga (central part of Honshu). Pb isotopic comparison of collected core sediment and previously reported data for wet precipitation and aerosols from different Asian regions indicate that, before 1900, Pb accumulated in these three lakes was not affected by trans-boundary sources. Lake Mikazuki started to receive Pb emissions from Russia in early 1900s, and during the last two decades, this lake has been affected by trans-boundary Pb pollution from northern China. Lake Chokai has received Pb pollutant from northern China since early 1900s until 2009, whereas for the Lake Mikuriga the major Pb contaminant was transported from southern China during the past 100years. The results of our study demonstrate that Japan Archipelago has received trans-boundary Pb emissions from different parts of East Asian region depending on location, and the major source region has changed historically.

Nitrogen, carbon, and sulfur isotopic change during heterotrophic (Pseudomonas aureofaciens) and autotrophic (Thiobacillus denitrificans) denitrification reactions.

In batch culture experiments, we examined the isotopic change of nitrogen in nitrate (δ(15)NNO3), carbon in dissolved inorganic carbon (δ(13)CDIC), and sulfur in sulfate (δ(34)SSO4) during heterotrophic and autotrophic denitrification of two bacterial strains (Pseudomonas aureofaciens and Thiobacillus denitrificans). Heterotrophic denitrification (HD) experiments were conducted with trisodium citrate as electron donor, and autotrophic denitrification (AD) experiments were carried out with iron disulfide (FeS2) as electron donor. For heterotrophic denitrification experiments, a complete nitrate reduction was accomplished, however bacterial denitrification with T. denitrificans is a slow process in which, after seventy days nitrate was reduced to 40% of the initial concentration by denitrification. In the HD experiment, systematic change of δ(13)CDIC (from -7.7‰ to -12.2‰) with increase of DIC was observed during denitrification (enrichment factor εN was -4.7‰), suggesting the contribution of C of trisodium citrate (δ(13)C=-12.4‰). No SO4(2-) and δ(34)SSO4 changes were observed. In the AD experiment, clear fractionation of δ(13)CDIC during DIC consumption (εC=-7.8‰) and δ(34)SSO4 during sulfur use of FeS2-S (around 2‰), were confirmed through denitrification (εN=-12.5‰). Different pattern in isotopic change between HD and AD obtained on laboratory-scale are useful to recognize the type of denitrification occurring in the field.

Combined use of δ(13)C, δ(15)N, and δ(34)S tracers to study anaerobic bacterial processes in groundwater flow systems.

We present an approach for determining the major anaerobic bacterial processes in aquifers, using the combined stable isotope ratios of major elements (C, N, and S) as net recorders of the biogeochemical reactions. The Kumamoto groundwater is constituted of two major flow systems, A-A' and B-B', within 10(3) km-scale area. Previous study [Hosono, T., Tokunaga, T., Kagabu, M., Nakata, H., Orishikida, T., Lin, I-T., Shimada, J., 2013. The use of δ(15)N and δ(18)O tracers with an understanding of groundwater flow dynamics for evaluating the origins and attenuation mechanisms of nitrate pollution. Water Res. 47, 2661-2675.] investigated the nitrate sources and extent of denitrification using [Formula: see text] and [Formula: see text] tracers. In the present study, we studied a type of denitrification (heterogenic vs. autotrophic) and occurrence of sequential anaerobic processes along the flow systems with newly measured δ(13)CDIC and [Formula: see text] . In A-A' flow system, C, N, and S isotopic compositions did not change along the flow direction. However, in B-B' flow system significant sulfate reduction (with a maximum [Formula: see text] enrichment of +55‰) occurred along with denitrification (with a maximum [Formula: see text] enrichment of +38‰) as the groundwater flowed down-gradient. Depletions in [Formula: see text] (-8‰ maximum) were found only sporadically. These observations imply that autotrophic denitrification could occur in very limited parts of the study area. Moreover, the occurrence of methanogenic reactions was suggested by the enriched δ(13)CDIC signature (+8‰ maximum) at a denitrification hotspot. By characterizing C, N, and S isotope compositional changes in wide redox range (from aerobic oxidation of organic carbon, through denitrification, to sulfate reduction, until methanogenesis), we could develop the model of C, N, and S isotopic evolutional patterns under different redox scenarios. Proposed model is useful in obtaining a comprehensive understanding of the major anaerobic bacterial processes in aquifer systems, including distinguishing between heterotrophic and autotrophic denitrification.

The use of δ15N and δ18O tracers with an understanding of groundwater flow dynamics for evaluating the origins and attenuation mechanisms of nitrate pollution.

During early 2000, a new analytical procedure for nitrate isotopic measurement, termed the "denitrifier method", was established. With the development of the nitrate isotope tracer method, much research has been reported detailing sources of groundwater nitrate and denitrification mechanisms. However, a shortcoming of these tracer studies has been indicated owing to some overlapping of isotope compositions among different source materials and denitrification trends. In order to reduce these uncertainties, we examined nitrate isotope ratios within a frame of "regional groundwater flow dynamics" to eliminate unnecessary uncertainties in elucidating nitrate sources and behaviors. A total of 361 samples were collected from the Kumamoto area: the circulated groundwater system with a scale of 10(3) km(2) in southern Japan. Subsequently, the nitrate pollution was examined within the above-mentioned framework. As a result, a reasonable identification of the sources and attenuation behaviors (both denitrification and dilution) of groundwater nitrate pollution was obtained over the study area. This study demonstrates that the use of nitrate isotope tracers efficiently improves with a comprehensive understanding of groundwater flow dynamics. The approach emphasized in this study is important and should be applicable in other areas.

Spatial distribution of submarine groundwater discharge and associated nutrients within a local coastal area.

To understand the local-scale distribution of submarine groundwater discharge (SGD) and dissolved nutrients, a multiple-detector (222)Rn monitoring survey was undertaken along the Mt. Chokai volcanic coast in northern Japan. The surveys revealed that the highest SGD (calculated to be 6.2 × 10(4) m(3) d(-1), within an area of 2 × 10(4) m(2)) with the greatest nutrient fluxes (sum of NO(3)(-), NO(2)(-), and NH(4)(+) (DIN): 9.2 × 10(2) mol d(-1); PO(4)(3-) (DIP): 56 mol d(-1)) is present at the edge of the youngest volcanic lava flow in the area. Recharged groundwater transports nutrients through porous volcanic flows and discharges as SGD near shore. Our results demonstrate that the spatial distribution of SGD in the study area is closely regulated by the local geology and topography. Furthermore, we show that continuous (222)Rn monitoring with a multidetector system at boat speeds of 1-2 knots provides details at a scale one order of magnitude greater than has been reported previously. In addition, the results of our study suggest that SGD-borne DIP may play an important role in the important local oyster production.

Spring water quality and usability in the Mount Cameroon area revealed by hydrogeochemistry.

Groundwater is the only reliable water resource for drinking, domestic, and agricultural purposes for the people living in the Mount Cameroon area. Hydrogeochemical and R-mode factor analysis were used to identify hydrogeochemical processes controlling spring water quality and assess its usability for the above uses. Main water types in the study area are Ca-Mg-HCO(3) and Na-HCO(3). This study reveals that three processes are controlling the spring water quality. CO(2)-driven silicate weathering and reverse cation exchange are the most important processes affecting the hydrochemistry of the spring waters. While tropical oceanic monsoon chloride-rich/sulfate-rich rainwater seems to affect spring water chemistry at low-altitude areas, strong correlations exist between major ions, dissolved silica and the altitude of springs. In general, the spring waters are suitable for drinking and domestic uses. Total hardness (TH) values indicate a general softness of the waters, which is linked to the development of cardiovascular diseases. Based on Na %, residual sodium carbonate, sodium adsorption ratio, and the USSL classification, the spring waters are considered suitable for irrigation. Though there is wide spread use of chemical fertilizers and intense urban settlements at the lower flanks of the volcano, anthropogenic activities for now seem to have little impact on the spring water quality.

Evolution model of δ³4S and δ¹8O in dissolved sulfate in volcanic fan aquifers from recharge to coastal zone and through the Jakarta urban area, Indonesia.

The sources of sulfate in an aquifer system, and its formation/degradation via biogeochemical reactions, were investigated by determining sulfate isotope ratios (δ³4S(SO4) and δ¹8O(SO4) in dissolved sulfate in groundwater from the Jakarta Basin. The groundwater flow paths, water ages, and geochemical features are well known from previous studies, providing a framework for the groundwater chemical and isotopic data, which is supplemented with data for spring water, river water, hot spring water, seawater, detergents, and fertilizers within the basin. The sulfate isotope composition of groundwater samples varied widely from -2.9‰ to +33.4‰ for δ³4S(SO4) and +4.9‰ to +17.8‰ for δ¹8O(SO4) and changed systematically along its flow direction from the mountains north to the coastal area. The groundwater samples were classified into three groups showing (1) relatively low and narrow δ(34)S(SO4) (+2.3‰ to +7.6‰) with low and varied δ¹8O(SO4) (+4.9‰ to +12.9‰) compositions, (2) high and varied δ³4S(SO4) (+10.2‰ to +33.4‰) with high δ¹8O(SO4) (+12.4‰ to +17.3‰) compositions, and (3) low δ³4S(SO4) (< +6.1‰) with high δ¹8O(SO4) (up to +17.8‰) compositions. These three types of groundwater were observed in the terrestrial unconfined aquifer, the coastal unconfined and confined aquifers, and the terrestrial confined aquifer, respectively. A combination of field measurements, concentrations, and previously determined δ¹5N(NO3) data, showed that the observed isotopic heterogeneity was mainly the result of contributions of pollutants from domestic sewage in the rural area, mixing of seawater sulfate that had experienced previous bacterial sulfate reduction in the coastal area, and isotopic fractionation during the formation of sulfate through bacterial disproportionation of elemental sulfur. Our results clearly support the hypothesis that human impacts are important factors in understanding the sulfur cycle in present-day subsurface environments. A general model of sulfate isotopic evolution along with groundwater flow has rarely been proposed, due to the complicated hydrogeological research setting that causes varied isotope ratios, although its understanding has recently received great attention. This pioneer study on a simple volcanic fan aquifer system with a well-understood groundwater flow mechanism provides a useful model for future studies.

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.

Effects of environmental regulations on heavy metal pollution decline in core sediments from Manila Bay.

We investigated the high-resolution heavy metal pollution history of Manila Bay using heavy metal concentrations and Pb isotope ratios together with (210)Pb dating to find out the effects of environmental regulations after the 1990 s. Our results suggested that the rate of decline in heavy metal pollution increased dramatically from the end of the 1990 s due to stricter environmental regulations, Administrative Order No. 42, being enforced by the Philippines government. The presented data and methodology should form the basis for future monitoring, leading to pollution control, and to the generation of preventive measures at the pollution source for the maintenance of environmental quality in the coastal metropolitan city of Manila. Although this is the first report of a reduction in pollution in Asian developing country, our results suggest that we can expect to find similar signs of pollution decline in other parts of the world as well.