Takahiro Hosono

Sources of nitrate and ammonium contamination in groundwater under developing Asian megacities

The status of nitrate (NO(3)(-)), nitrite (NO(2)(-)) and ammonium (NH(4)(+)) contamination in the water systems, and the mechanisms controlling their sources, pathways, and distributions were investigated for the Southeast Asian cities of Metro Manila, Bangkok, and Jakarta. GIS-based monitoring and dual isotope approach (nitrate delta(15)N and delta(18)O) suggested that human waste via severe sewer leakage was the major source of nutrient contaminants in Metro Manila and Jakarta urban areas. Furthermore, the characteristics of the nutrient contamination differed depending on the agricultural land use pattern in the suburban areas: high nitrate contamination was observed in Jakarta (dry fields), and relatively lower nutrients consisting mainly of ammonium were detected in Bangkok (paddy fields). The exponential increase in NO(3)(-)-delta(15)N along with the NO(3)(-) reduction and clear delta(18)O/delta(15)N slopes of NO(3)(-) ( approximately 0.5) indicated the occurrence of denitrification. An anoxic subsurface system associated with the natural geological setting (e.g., the old tidal plain at Bangkok) and artificial pavement coverage served to buffer NO(3)(-) contamination via active denitrification and reduced nitrification. Our results showed that NO(3)(-) and NH(4)(+) contamination of the aquifers in Metro Manila, Bangkok, and Jakarta was not excessive, suggesting low risk of drinking groundwater to human health, at present. However, the increased nitrogen load and increased per capita gross domestic product (GDP) in these developing cities may increase this contamination in the very near future. Continuous monitoring and management of the groundwater system is needed to minimize groundwater pollution in these areas, and this information should be shared among adjacent countries with similar geographic and cultural settings.

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.

Effects of intensive urbanization on the intrusion of shallow groundwater into deep groundwater: examples from Bangkok and Jakarta.

Asian megacities have severe pollution problems in both coastal and urban areas. In addition, the groundwater potential has decreased and land subsidence has occurred because of intensive groundwater pumping in urban areas. To prevent the adverse effects of urbanization on groundwater quality, it is necessary to confirm the changes in groundwater flow and contaminant transport caused by urbanization. We examined the effects of urbanization on contaminant transport in groundwater. The research areas were located around Bangkok, Thailand, and Jakarta, Indonesia, cities with populations of approximately 8 and 12 million, respectively. Each metropolitan city is located on a river delta and is adjacent to a bay. We measured the water level and collected water samples at boreholes at multiple depths (100 to 200 m) in 2004 and 2006 in Bangkok and Jakarta, respectively. The current hydraulic potential is below sea level in both cities because of prior excess abstraction of groundwater. As a result, the direction of groundwater flow is now downward in the coastal area. The Cl(-) concentration and delta(18)O distributions in groundwater suggest that the decline in hydraulic potential has caused the intrusion of seawater and shallow groundwater into deep groundwater. Concentrations of Mn and NO3(-)-N in groundwater suggest the intrusion of these contaminants from shallow to deep aquifers with downward groundwater flow and implies an accumulation of contaminants in deep aquifers. Therefore, it is important to recognize the possibility of future contaminant transport with the discharge of deep groundwater into the sea after the recovery of groundwater potential in the coastal 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 HCO3 as major anion, and in 20%, NO3 is the major anion. Main water types in the study area are CaHCO3, CaMgHCO3, CaNaHCO3, and CaNaNO3ClHCO3. CO2-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 Ca2+, Mg2+ and HCO3− 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.

Human impacts on groundwater flow and contamination deduced by multiple isotopes in Seoul City, South Korea.

The influence of human activities on the flow system and contamination of groundwater were investigated in Seoul City, South Korea, one of the largest Asian cities, using a combination of isotopes (deltaD, T, delta15N, delta18O, delta34S, and 87Sr/86Sr). Eighteen representative groundwater and river water samples, which were collected over a wide area of the city, were compared with previously reported data. The distribution of stable isotopes (deltaD and delta18O) with groundwater potential data shows that recharged groundwater from either the surrounding mountainous area as well as the Han River and other surface streams discharged towards the northern-central part of the city, where a subway tunnel pumping station is located. It is suggested from T values (3.3 to 5.8 T.U.) that groundwater was recharged in the last 30 to 40 years. The delta34S and delta15N of SO4(2-) and NO3- data were efficiently used as indicators of contamination by human activities. These isotopes clarified that the contribution of anthropogenic contaminants i.e., industrial and household effluents, waste landfills, and fertilizers, are responsible for the enrichment by SO4(2-) (>30 ppm as SO4(2-)) and NO3- (>20 ppm as NO3-) of groundwater. The 87Sr/86Sr values of groundwater vary (0.71326 to 0.75058) in accordance with the host rocks of different origins. Mineral elements such as Ca are also suggested to be derived naturally from rocks. The groundwater under Seoul City is greatly affected by transportation of pollutants along the groundwater flow controlled by subway tunnel pumping, contributing to the degradation of water quality in urbanized areas.

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.

Sr-Nd-Pb isotopic compositions of volcanic rocks around the Hishikari gold deposit, southwest Japan: Implications for the contribution of a felsic lower crust

Abstract The Sr–Nd–Pb isotope compositions of Late Pliocene to Pleistocene volcanic rocks around the Hishikari mine in southern Kyusyu of Japan, one of the largest hydrothermal gold deposit in the circum-Pacific belt, were determined in order to elucidate their source characteristics and evolution and the characteristics of magma related to gold mineralization. The Hishikari volcanic rocks (HVR) are classified into the Kurosonsan group (2.4–1.0 Ma) in the northern area and the Shishimano group (1.7–0.5 Ma) in the southern area. Each group is composed of three subgroups of andesite and one subgroup of rhyodacite in a late-stage. In the Kurosonsan group, the 87Sr/86Sr, 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb increase, while the 143Nd/144Nd decrease with decreasing age. The evolution pattern is opposite to this in the Shishimano group. On the Sr–Nd and Pb isotope diagrams, the HVR show a mixing array between two isotopically homogeneous components: a depleted component with a MORB-like composition, and an enriched component with radiogenic Pb and Sr and unradiogenic Nd. Regional comparison of isotope data from the HVR with those of rocks in and around Japan indicates that (1) the depleted component originated from low-K and high-alumina basaltic magma upwelling from the mantle, whereas (2) the enriched component was derived from rocks in lower crust of granodioritic composition, which we considered to have developed in the eastern margin of the Eurasian subcontinental lithosphere. According to a model calculation, the assimilation of the lower crust into the HVR increased with time from 51% to 77% in the Kurosonsan group, whereas decreased from 68% to 57% in the Shishimano group. We suggest that the Shishimano rhyodacite, which crystallized in the later stages of the Shishimano group and is considered to have been responsible for gold mineralization, was formed by intense fractional crystallization from andesite magma with a depleted Sr, Nd and Pb isotopic signature.

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.

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.

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.