Shin-ichi Onodera

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.

Anthropogenic effects on the subsurface thermal and groundwater environments in Osaka, Japan and Bangkok, Thailand

Anthropogenic effects in both Osaka and Bangkok were evaluated to compare the relationships between subsurface environment and the development stage of both cities. Subsurface thermal anomalies due to heat island effects were found in both cities. The Surface Warming Index (SWI), the departure depth from the steady geothermal gradient, was used as an indicator of the heat island effect. SWI increases (deeper) with the magnitude of heat island effect and the elapsed time starting from the surface warming. Distributions of subsurface thermal anomalies due to the heat island effect agreed well with the distribution of changes in air temperature due to the same process, which is described by the distribution of population density in both Osaka and Bangkok. Different time lags between groundwater depression and subsidence in the two cities was found. This is attributed to differences in hydrogeologic characters, such as porosity and hydraulic conductivity. We find that differences in subsurface degradations in Osaka and Bangkok, including subsurface thermal anomalies, groundwater depression, and land subsidence, depends on the difference of the development stage of urbanization and hydrogeological characters.

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.

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.

An overview of the effects of urbanization on the quantity and quality of groundwater in South Asian megacities

One of the challenges facing megacities in South Asian developing countries in their attempts to realize so-called urban rejuvenation is groundwater conditioned by canal seepage and immense sewage loads. To understand the connection between groundwater pollutants and urbanization, numerous studies were reviewed, and data obtained from a variety of national and international organizations were analyzed. In Delhi and Dhaka, urbanization has lowered the groundwater level as a result of severe overextraction, and its dense population makes Delhi particularly vulnerable to groundwater pollution. In the coastal areas of Karachi and Mumbai, such pollution is magnified by the proximity of seawater as well as the increasing populations of these areas. Among the groundwater pollutants associated with urbanization, chlorides and nitrates are the chief anthropogenic toxins; thus, they are examined in this study. This paper concludes with policy recommendations for minimizing the impact of urbanization on groundwater.

Comparative study of bedload sediment yield processes in small mountainous catchments covered by secondary and disturbed forests, western Japan

To clarify the sediment yield processes following a disturbance by a forest fire in a mountainous catchment, and considering the hydrological and geomorphological processes in the headwater, we measured bedload sediment yield at rainfall events in disturbed and secondary forest catchments in the western part of Japan. The three catchments were under different hydrogeological conditions. The IK, TB and TY catchments were disturbed by forest fires in 2000, 1994, and 1978, respectively. In the IK catchment, although runoff response to rainfall was fastest with high peak flows, the catchment also had the highest base flow. Moreover, the annual sediment yield there was about ten times as high as in the other two catchments, and it was found that there was a steep linear curve in the relationship between precipitation and bedload sediment yield. This is thought to be caused by overland flow generation following water repellency on the slopes, and by the accumulated sediment that forms the thick soil layer on the valley bottom. On the other hand, in the TB catchment runoff experienced high peak flows at rainfall events and low base flows, and there was a gradual linear curve in the precipitation–sediment yield relationship. This might be the result of there being a thin soil layer on the hillslope and on the valley bottom because of successive erosion after the fire. In the TY catchment, runoff had a low peak flow at rainfall events and a high base flow; and the bedload sediment yield increased exponentially with increasing precipitation. Therefore, sediment yield in the TB catchment was more than that in the TY during storm events with precipitation of less than 100 mm, whereas it was the opposite during heavier rainfalls. It indicates that there is a thick soil layer on the slope and a thin soil layer on the valley bottom in the TY catchment following the recovering of vegetation, and that the sediment yield process predominates only during big rainfall events, only then does subsurface flow generate.

Effect of Forest Fires on Hydrology and Biogeochemistry of Watersheds

Forest fire generally includes both natural wildfire and human-induced fire (e.g., slash-and-burn agriculture and accidental fire). Areas burned by forest fire are relatively widespread across the world (Table 30.1), but vary substantially across continents. For example, burned areas account for about two thirds of the total area in Africa, yet only approximately 1% in North America (Roy et al. 2008). Wildfire occurrence is primarily related to drought intensity, whereas agricultural demands oftentimes drive human-induced fires, particularly slash-and-burn cultivation. Because the controlling factors of both fire types have increased recently, global burned areas have also increased. In the Amazon catchment alone, burned area has expanded to encompass more than ten times its pre-1980 area (Peres et al. 2006). These increases in forest fire frequency and intensity have enhanced its role in, and contribution to, total global deforestation (Roy et al. 2008).

Sediment Yield Variation in Small Catchments with Different Bedrock in a Humid Temperate Region

Sediment yield in mountainous catchments is closely associated with habitat stability of ecosystems in floodplain or valley bottom. The results of this study provide potential scenarios of future changes in sediment yield as a result of increasing rainfall due to climatic warming. We monitored stream discharge and sediment yield at four small catchments with different bedrock types and stream orders in a subalpine environment in central Japan. The results showed that bedload materials were yielded continuously in the granitic rock area, but only intermittently during the strong storm runoff in the sedimentary rock area. Our results indicate that future increase in the amount of bedload yield in sedimentary rock area will be proportional to rainfall in the granitic catchments, but may be variable in the sedimentary catchment depending on the sediment availability. The amount of bedload had no linear relation with catchment size. In the longterm, however, the impact on habitat stability can be substantial in both types of catchments, because annual amount of bedload will increase from year-to-year. Nevertheless, out results indicate that an improvement of the existing methods for predicting the trends of bedload yield is needed for the appropriate management and conservation of mountainous watersheds.

Vertical distribution of sediment phosphorus in Lake Hachirogata related to the effect of land reclamation on phosphorus accumulation

The focus of this work is the change in sediment properties and chemical characteristics that occur after land reclamation projects. The results indicate a higher sedimentation rate in Lake Hachirogata after reclamation, with the rate increasing with proximity to the agricultural zone. In the west-side water samples, higher levels of dissolved total nitrogen and dissolved total phosphorus (DTP) were found in both surface and bottom waters. The increase in P (39–80%) was generally greater than that for N (12–16%), regarding the nutrient supply from reclaimed farmland in the western part of the lake. In the eastern part of the lake, the pore-water Cl− profile showed a decreasing vertical gradient in the sediment core. This indicates desalination of the lake water after construction of a sluice gate in 1961. In the western sediment-core sample, a uniform Cl− profile indicates the mixing of lake water and pore water after reclamation. Considering the sedimentation of P in the last 100 years, there is a trend of increasing accumulation of P and P-activities after the reclamation project. This appears to be an impact from change in the lake environment as a result of increased agricultural nutrients, desalination, and residence. A large amount of mobile phosphorus (42–72% of TP in the western core sample) trapped in sediment increases the risk of phosphorus release and intensification of algal blooms. High sediment phosphorus and phosphorus mobility should be considered a source of pollution in the coastal environment.