| 1. |
- Amano, Hiroki, et al.
(författare)
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Groundwater geochemistry of a nitrate-contaminated agricultural site
- 2016
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 75:15
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Tidskriftsartikel (refereegranskat)abstract
- Groundwater samples were collected from several soil depths down to 50 m below soil surface to investigate vertical profiles of NO3 − and hydrogeochemical characteristics of the experimental site. The experimental site is located in the Shimabara City, Nagasaki, Japan, where nitrate contamination in groundwater is severe due to intensive agricultural production. A transition zone regarding dissolved ions was found between specific depths caused by differences in the permeability of soil layers. Though NO3 − concentration decreased significantly in the transition zone, the entire soil depth exceeded permissible levels (50 mg L−1) for drinking purposes. Comparing the temporal NO3 − fluctuation above the transition zone with that of the below, distinct fluctuations were observed depending on sampling campaign. High rainfall amounts typically lead to initial decrease in NO3 − concentration for the shallow groundwater. After some time, however, increase in NO3 − concentration occurred due to leaching of accumulated NO3 − in the soil matrix. This indicated that temporal NO3 − fluctuation is mainly controlled by natural impact and occurring crop system. Results of principal component analysis suggested that application of chemical fertilizers [(NH4)2SO4, NH4NO3, and KCl], dissolution of minerals (feldspar, calcite, and dolomite), and ion exchange are the predominant factors resulting in the observed vertical groundwater chemistry. The relative magnitude of these three principal component scores changed across the transition zone. Below the transition zone, groundwater geochemistry reflected application of NH4NO3 and KCl fertilizer and dissolution of albite and orthoclase.
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| 2. |
- Amano, Hiroki, et al.
(författare)
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Surface water chemistry and nitrate pollution in Shimabara, Nagasaki, Japan
- 2018
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 77:9
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Tidskriftsartikel (refereegranskat)abstract
- Groundwater is a finite resource that is threatened by pollution all over the world. Shimabara City, Nagasaki, Japan, uses groundwater for its main water supply. During recent years, the city has experienced severe nitrate pollution in its groundwater. For better understanding of origin and impact of the pollution, chemical effects and surface–groundwater interactions need to be examined. For this purpose, we developed a methodology that builds on joint geochemical analyses and advanced statistical treatment. Water samples were collected at 42 sampling points in Shimabara including a part of Unzen City. Spatial distribution of water chemistry constituents was assessed by describing Stiff and Piper diagrams using major ions concentrations. The nitrate (NO3 + NO2–N) concentration in 45% of water samples exceeded permissible Japanese drinking level of 10 mg L− 1. Most of the samples showed Ca–HCO3 or Ca–(NO3 + SO4) water types. Some samples were classified into characteristic water types such as Na–Cl, (Na + K)–HCO3, (Na + K)–(SO4 + NO3), and Ca–Cl. Thus, results indicated salt water intrusion from the sea and anthropogenic pollution. At the upstream of Nishi River, although water chemistry was characterized as Ca–HCO3, ion concentrations were higher than those of other rivers. This is probably an effect of disinfection in livestock farming using slaked lime. Positive correlation between NO3 − and SO4 2−, Mg2+, Ca2+, Na+, K+, and Cl− (r = 0.32–0.64) is evidence that nitrate pollution sources are chemical fertilizers and livestock waste. Principal component analysis showed that chemistry of water samples can be explained by three main components (PCs). PC1 depicts general ion concentration. PC2 and PC3 share influence from chemical fertilizer and livestock waste. Cluster analyses grouped water samples into four main clusters. One of these is the general river chemistry mainly affected by PC1. The others reflect anthropogenic activities and are identified by the combination of the three PCs.
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| 3. |
- Nakagawa, Kei, et al.
(författare)
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Analysis of earthquake-induced groundwater level change using self-organizing maps
- 2019
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 78:15
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Tidskriftsartikel (refereegranskat)abstract
- For a better understanding of possible physical links between geophysical observables and earthquake characteristics, it is important to analyze statistical spatiotemporal patterns in nature related to such events. For this purpose, characteristic changes in groundwater level (GWL) were observed before and after the 2016 Kumamoto earthquake in Japan. Previous research has shown that self-organizing maps (SOM) can be used to classify complex patterns of GWL-change during different parts of the earthquake sequence. In this study, we used before and after earthquake GWL data as input vectors to SOM. In total, 64 observed GWLs were classified into 12 different clusters. Most shallow wells displayed GWL difference that was small during the foreshock (first earthquake) and large during the main-shock (second earthquake). Upstream deep wells showed relatively large difference in water level from 1 to 2 days after the earthquakes. The GWL rapidly increased just after the earthquake, then tended to gradually decrease from September. Most of the shallow wells in the unconfined aquifer rapidly recovered to initial GWLs within several hours to several days, because of hydrostatic pressure. However, most of the deep wells in the confined aquifer needed longer time to recover, in some cases several weeks to several months. These findings are important for the physical understanding of earthquake effects on the groundwater environment, disaster prevention, and possibility for development of earthquake precursors.
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| 4. |
- Nakagawa, Kei, et al.
(författare)
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Distribution of heavy metals and related health risks through soil ingestion in rural areas of western Japan
- 2022
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Ingår i: Chemosphere. - : Elsevier BV. - 1879-1298 .- 0045-6535. ; 290
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of heavy metal concentrations and related human health risks were investigated for Shimabara City, Nagasaki Prefecture. The purpose was to clarify the potential for heavy metal contamination in an area already known to be affected by nitrate pollution. A total of 188 soil samples was collected at 47 sites. The heavy metal content of the soil was measured in laboratory using an X-ray analyzer. The highest contents of heavy metals exceeded common background concentration in Japanese soils. The highest concentrations of Cu and Zn appear to be related to application of livestock waste in agriculture. Principal component and cluster analyses were performed to classify the sampling sites based on soil content of heavy metals. Three principal components (PCs) were extracted with the first PC explaining crustal constituents, the second explaining application of livestock waste, and the third explaining other types of anthropogenic pollutants. The cluster analysis resulted in 5 groups regarding the sampling locations. In total, 44% of sampling locations belonged to Group 1 and 46% to Group 2, distributed over the agricultural land in the northern part of the city and the urban area in the southern part of the city, respectively. There is a potential temporal health risk for the Pb content at specific locations in the area.
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| 5. |
- Nakagawa, Kei, et al.
(författare)
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Spatial trends of nitrate pollution and groundwater chemistry in Shimabara, Nagasaki, Japan
- 2016
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 75:3, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- Groundwater contamination by nitrate is a common problem in many parts of the world. The agriculturally important Shimabara district in Nagasaki, Japan, is experiencing this problem. The general source of drinking water of the study area is groundwater and consequently the nitrate contamination is a significant problem. For this reason, a groundwater investigation was performed and water samples were collected at 40 locations including residential areas, public water supply wells, springs, and rivers from August 2011 to November 2013. Results showed that nitrate nitrogen (NO3-N) concentration is exceeding the Japanese drinking water quality standards (10 mg L−1) at 15 locations. Maximum NO3-N concentration was 26.6 mg L−1. Nitrate ($${\text{NO}}_{3}^{ - }$$NO3-) was strongly correlated with Cl− (r = 0.96), K+ (r = 0.68), $${\text{SO}}_{4}^{2 - }$$SO42- (r = 0.66), and Ca2+ (r = 0.59), respectively. The high correlations with Cl− and K+ are related to livestock waste. Corresponding correlation with $${\text{SO}}_{4}^{2 - }$$SO42- is related to chemical fertilizers and Ca2+ to calcareous material to neutralize acidic soil. Both the first and second components in principal component analysis reflect ion dissolution from aquifer matrix during groundwater flow along the mountain side towards the lower reaches of the alluvial fan. Using hierarchical cluster analysis, chemical characteristics of groundwater were classified into four clusters. One cluster is strongly related to the nitrate contaminated groundwater and the other clusters reflect the origin of the major ions in the groundwater.
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| 6. |
- Nakagawa, Kei, et al.
(författare)
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Temporal characteristics of groundwater chemistry affected by the 2016 Kumamoto earthquake using self-organizing maps
- 2020
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694. ; 582
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Tidskriftsartikel (refereegranskat)abstract
- Possibilities to perform pre- and post-seismic groundwater chemical comparisons on regional groundwater flow systems are rare due to lack of data and observations. The Kumamoto earthquake provides an unusual opportunity to improve the knowledge on earthquake hydrology and earthquake effects on hydrochemistry of groundwater due to a wealth of pre- and post-quake observations. We analyzed 12 physiochemical parameters (SiO2, (NO3 – + NO2 –)-N, Fetotal, Mntotal, pH, F−, Cl−, SO4 2−, Na+, K+, Ca2+, and Mg2+) using self-organizing maps (SOM) combined with hydrological and geological characteristics to improve the understanding of changes in groundwater chemistry after a major earthquake. The results indicate that the earthquake induced hydrological and environmental change via fault forming (Suizenji fault systems), liquefaction, rock fracturing, and ground shaking. These geological processes created rock fresh reactive surfaces, rock loosening, and enhancement of hydraulic conductivity. In turn, this lead to secondary processes in groundwater chemistry by advection, dilution, and chemical reaction. The most obvious indicator of hydrological and environmental change was from the increased dissolved silica content stemming from fracturing and Si-O bond cleavage in silicate rocks. Besides this, decreasing concentration of common ions (Cl−, F−, Na+, K+, Ca2+) was found due to dilution from mountain-side water release. Increase in (NO3 – + NO2 –)-N, SO4 2−, and Mg2+ concentration occurred locally due to soil leaching of contaminants or agricultural fertilizers through surface ruptures in recharge areas. Increase of SO4 2− content also originated from leaching of marine clay in coastal areas and possibly sporadic deep crustal fluid upwelling. Increase in (NO3 – + NO2 –)-N and Cl− content occurred from sewage water pipe breaks in the Suizenji fault formation in urban areas. Decrease of pH occurred in a few wells due to mixing of river water and different types of aquifer groundwater. Increase of Fetotal and Mntotal concentration possibly originated from leaching of marine clay by liquefaction in coastal areas. However, in most cases the water chemistry changes were subtle, thus not resulting in any groundwater quality deterioration of water supplies.
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| 7. |
- Nakagawa, Kei, et al.
(författare)
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Use of sterols to monitor surface water quality change and nitrate pollution source
- 2019
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Ingår i: Ecological Indicators. - : Elsevier BV. - 1470-160X. ; 107
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Tidskriftsartikel (refereegranskat)abstract
- Coprostanol was tested as ecological indicator to trace domestic and manure effluents and to investigate possible pollution sources in surface water. Pollution assessment was performed by analysing NO3 −, NO2 −, coprostanol (5β(H)-Cholestan-3β-ol), and cholestanol (5α(H)-Cholestan-3β-ol) in water samples from 42 sites along rivers in Shimabara and Unzen City, Japan. NO2-N concentration exceeded 0.04 mg L−1 at 2 sampling sites during winter and 6 sampling sites during summer. NO3 + NO2-N concentration exceeded 10 mg L−1 at 19 sampling sites during winter and 7 sampling sites during in summer. The highest concentration was 82.4 mg L−1 in summer. Detectable NO3-N concentration was observed in northern parts of the study area. Coprostanol concentration exceeded 700 ng L−1 (Australian Drinking Water Standard) at 8 sampling points during winter and 6 sampling sites during summer. At 10 and 5% of the sampling sites, both nitrate and coprostanol concentration exceeded drinking water standard during winter and summer, respectively. The percentage of sampling sites where either concentration was above drinking water standard was 45% during winter and 22% during summer season. However, depending on sampling site, the relationships between nitrate and coprostanol concentrations showed different patterns. The sterol ratio exceeded 0.5 at 17 sampling sites during winter and 14 sampling sites during summer. Thus, it was confirmed that fecal pollution is present in the studied surface water. A method to distinguish between principal pollution sources was developed by separating four areas in a nitrate concentration and sterol ratio plot. Results show that sampled data could be reasonably classified into appropriate polluted/non-polluted groups. Thus, coprostanol and sterol ratio can be used as indicators to distinguish between different nitrate pollution sources in surface water.
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| 8. |
- Yu, Zhi Qiang, et al.
(författare)
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Groundwater nitrogen response to regional land-use management in South Japan
- 2021
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 80:18
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Tidskriftsartikel (refereegranskat)abstract
- For a better understanding of the effects of regional groundwater management for different land-use types on nitrogen content in groundwater, we investigated the Miyakonojo River Basin in south of Japan where the Nitrate Directive Plan has been in practice since 2004. For this purpose, we used nitrogen concentrations from 420 wells between 2000 and 2017 together with 8 different land-use categorizations. The data were analyzed using self-organizing maps (SOM) and results showed that forest recharge areas have lowest mean nitrogen concentrations of about 2.9 mg/L. Urban areas displayed a mean nitrogen concentration of about 4.4 mg/L. Agricultural land such as paddy fields had a mean nitrogen concentration of about 5.1 mg/L. Groundwater discharge and residential areas had mean groundwater nitrogen concentrations of 8.2 and 7.1 mg/L, respectively. Intensive agricultural land-use and wastewater discharge from urban areas caused the main groundwater nitrogen contamination in these areas. About 70% of the wells had a decreasing trend of groundwater nitrogen concentration (p < 0.05, p ≥ 0.05) during the period 2009–2017. About 20% of the wells displayed a trend reversal from 2000–2008 (increasing) to 2009–2017 (decreasing). In general, the Nitrate Directive Plan appears to have had positive effects for mitigating groundwater nitrogen problems. However, 30% of the wells still do not display a decreasing trend and some wells exceed maximum permissive level for drinking water. Thus, management needs to continue to improve groundwater conditions regarding nitrogen content.
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| 9. |
- Yu, Zhi Qiang, et al.
(författare)
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Hydrogeochemical evolution of groundwater in a Quaternary sediment and Cretaceous sandstone unconfined aquifer in Northwestern China
- 2018
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 77:18
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Tidskriftsartikel (refereegranskat)abstract
- A better understanding of the hydrogeochemical evolution of groundwater in vulnerable aquifers is important for the protection of water resources. To assess groundwater chemistry, groundwater sampling was performed from different representative aquifers in 2012–2013. A Piper trilinear diagram showed that the groundwater types can be classified into Na–SO4 and Na–Cl types. Only one groundwater sample was Na–HCO3 type. The dominant cations for all samples were Na+. However, the dominant anions varied from HCO3 − to SO4 2−, and as well Cl−. The mean total dissolved solid (TDS) content of groundwater in the region was 1889 mg/L. Thus, only 20% of groundwater samples meet Chinese drinking water standards (< 1000 mg/L). Principal component analysis (PCA) combined with hierarchical cluster analysis (HCA) and self-organizing maps (SOM) were applied for the classification of the groundwater geochemistry. The three first principal components explained 58, 20, and 16% of the variance, respectively. The first component reflects sulfate minerals (gypsum, anhydrite) and halite dissolution, and/or evaporation in the shallow aquifer. The second and third components are interpreted as carbonate rock dissolution. The reason for two factors is that the different aquifers give rise to different degree of hydrogeochemical evolution (different travel distances and travel times). Identified clusters for evolution characteristic and influencing factors were confirmed by the PCA–HCA methods. Using information from eight ion components and SOM, formation mechanisms and influencing factors for the present groundwater quality were determined.
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