| 1. |
- Hiroshiro, Y, et al.
(författare)
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Hydrogeochemical properties of a salinity-affected coastal aquifer in western Japan
- 2006
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Ingår i: Hydrological Processes. - : Wiley. - 1099-1085 .- 0885-6087. ; 20:6, s. 1425-1435
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Tidskriftsartikel (refereegranskat)abstract
- Coastal groundwater aquifers are often exposed to heavy pumping and consequently to risks of saltwater intrusion. In many cases, however, the observed increase in groundwater salinity can only be partly explained by actual saltwater intrusion from the sea. Other salinity-increasing processes may also significantly contribute to the total salt content of the groundwater. This paper describes a geochemical investigation that was carried out to investigate recent salinity increases in groundwater for the Motooka coastal area in Fukuoka, Japan. A strong increase in electrical conductivity at 15-20 m depth was observed, corresponding to the freshwater and saltwater interface. Oxidation-reduction potentials observed in deeper groundwater were low, indicating long residence time for the groundwater. These results, together with hydrogen-oxygen isotope ratio analysis, indicated that the deeper groundwater is affected by seawater. Consequently, observed tritium concentration in the shallow groundwater system was higher than that of the deeper groundwater system, and a C-14 isotope dating of shell samples collected at 2 m depth indicated an age of about 2000 years. The overall results suggest that the aquifer was originally below the current sea floor and that deeper saline groundwater is not mixed with the shallower fresh groundwater. The deeper groundwater is, therefore, mainly affected by old seawater. In other words, modern saltwater intrusion has not yet occurred even if some wells contain saline water. The study shows that, even though coastal aquifers are heavily pumped, the reason for the rise in groundwater salinity may not necessarily be due to seawater intrusion. Further geochemical and hydrological investigations will be necessary to identify the underlying mechanisms. Copyright (c) 2006 John Wiley & Sons, Ltd.
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| 2. |
- Jin, Y H, et al.
(författare)
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Detection of ENSO-influence on the monthly precipitation in South Korea
- 2005
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Ingår i: Hydrological Processes. - : Wiley. - 1099-1085 .- 0885-6087. ; 19:20, s. 4081-4092
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Tidskriftsartikel (refereegranskat)abstract
- During the latest several decades, there has been considerable interest in revealing the relationship between El Nino-southern oscillation (ENSO) and hydro-meteorological variables. The oscillation is characterized by a simple index, the southern oscillation index (SOI). However, thus far, there is little evidence for the influence of ENSO in Korea and Japan. The influence of ENSO has also been studied in South Korea, but the estimated results are still qualitative and show an indirect relationship between ENSO and hydro-meteorological variables. In this study we use simple approaches to reveal the quantitative and direct correlation between SOI and the monthly precipitation at five stations distributed over South Korea. The monthly precipitation data are transformed into nonexceedance probability time series because the data cannot be normally distributed by applying the usual transformations. The SOI is classified into five categories according to their values. Additionally, to detect the nonlinear relationship between categorized SOI and nonexceedance probability of the monthly precipitation, we use Kendall's tau, a nonparametric test. Significant correlations between the categorized SOI and the transformed precipitation are detected. Generally, the monthly precipitation is influenced by a La Nina event with a lag time of 4 months for southern coastal areas and a lag time of 5 months for middle to high regions in South Korea.
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| 3. |
- Nakagawa, K., et al.
(författare)
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Modelling reactive solute transport from groundwater to soil surface under evaporation
- 2010
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Ingår i: Hydrological Processes. - : Wiley. - 1099-1085 .- 0885-6087. ; 24:5, s. 608-617
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Tidskriftsartikel (refereegranskat)abstract
- Two-stage soil column experiments involving capillary rise and evaporation were conducted to improve understanding of salt and water movement from groundwater to soil surface. In total, 64 soil columns were placed in a tank partly filled with water in order to mimic the groundwater table in soil. Each soil column was analysed by dividing it into 27 segments to analyse pore water and ion distribution in both liquid and solid phases after prescribed time periods. The water and solute transport behaviour in the columns was simulated by a one-dimensional numerical model. The model considers the cation exchange of four cations (Ca2+, Mg2+, Na+ and K+) in both dissolved and exchangeable forms and anion retardation for one anion (SO42-). The Cl- is treated as a conservative solute without retardation. The numerical results of the cation distributions in both liquid and solid phases, anions in the liquid phase, and volumetric water contents were in relatively good agreement with the experimental results. To achieve a better model fit to these experimental results, a variable cation exchange capacity (CEC) distribution may be required. When a simple calculation scheme for evaporation intensity was applied, better predictions in terms of daily variation were achieved. The soil water profile displayed a steady state behaviour approximately 10 days after the start of the experiments. This was in agreement with numerical results and calculated distribution of velocity vectors. The final model includes cation exchange, anion retardation, and unsaturated water flow. Consequently, the model can be applied to study sequential irrigation effects on salt accumulation or reactive transport during major ion concentration changes in groundwater. Copyright (C) 2009 John Wiley & Sons, Ltd.
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| 4. |
- Wang, Xin-Ping, et al.
(författare)
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Effects of surface characteristics on infiltration patterns in an arid shrub desert
- 2007
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Ingår i: Hydrological Processes. - : Wiley. - 1099-1085 .- 0885-6087. ; 21:1, s. 72-79
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Tidskriftsartikel (refereegranskat)abstract
- Precipitation is often the sole source of water replenishment in arid and semi-arid areas and, thus, plays a pertinent role in sustaining desert ecosystems. Revegetation over 40 years using mainly Artemisia ordosica and Caragana korshinskii at Shapotou Desert Experimental Research Station near Lanzhou, China, has established a dwarf-shrub and microbiotic soil crust cover on the stabilized sand dunes. The redistribution of infiltrated moisture through percolation, root extraction, and evapotranspiration pathways was investigated. Three sets of time-domain reflectometry (TDR) probes were inserted horizontally at 5, 10, 15, 20, 30 and 40 cm depths below the ground surface in a soil pit. The three sets of TDR probes were installed in dwarf-shrub sites of A. ordosica and C. korshinskii community with and without a microbiotic soil crust cover, and an additional set was placed in a bare sand dune area that had neither vegetation nor a microbiotic soil crust present. Volumetric soil moisture content was recorded at hourly intervals and used in the assessment of infiltration for the different surface covers. Infiltration varied greatly, from 7.5 cm to more than 45 cm, depending upon rainfall quantity and soil surface conditions. In the shrub community area without microbiotic soil crust cover, infiltration increased due to preferential flow associated with root tunnels. The microbiotic soil crust cover had a significant negative influence on the infiltration for small rainfall events (similar10 mm), restricting the infiltration depth to less than 20 cm and increasing soil moisture content just beneath the soil profile of 10 cm, whereas it was not as strong or clear for larger rainfall events (similar60 mm). For small rainfall events, the wetting front depth for the three kinds of surface cover was as follows: shrub community without microbiotic soil crust > bare area > shrub community with microbiotic soil crust. In contrast, for large rainfall events, infiltration was similar in shrub communities with and without microbiotic soil crust cover, but significantly higher than measured in the bare area. Soil water extraction by roots associated with evapotranspiration restricted the wetting front penetration after 1 to 3 h of rainfall. Copyright © 2006 John Wiley & Sons, Ltd.
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| 5. |
- Yasuda, H, et al.
(författare)
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Prediction of Chinese Loess Plateau summer rainfall using Pacific Ocean spring sea surface temperature
- 2009
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Ingår i: Hydrological Processes. - : Wiley. - 1099-1085 .- 0885-6087. ; 23:5, s. 719-729
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Tidskriftsartikel (refereegranskat)abstract
- The Loess Plateau in China constitutes in important source area for both water and sediments to the Yellow River. Thus, improved prediction techniques of rainfall may lead to better estimation of discharge and sediment content for the Yellow River. Consequently. the objective of this study was to establish better links between rainfall of the Loess Plateau in China and sea surface temperature (SST) in the Pacific Ocean. Results showed that there is a strong lagged correlation between and SST and rainfall. The SST for Micronesia and areas South of the Aleutian Islands showed significant correlations (s.f. < 0.001: 99.9%) with rainfall over the dryer region of the Loess Plateau for a lag of 4 to 6 months. The SST over the equator On the cast Pacific Ocean also showed significant negative correlation with rainfall. Low and middle latitude areas (S10-20 degrees and around 30 degrees) of the south-east Pacific Ocean displayed significant positive and negative correlation with rainfall on the semiarid Loess Plateau. The differenced SST values (positive SST minus negative SST) increased these correlation,, with rainfall. An artificial neural network (ANN) model was used to predict Summer rainfall from the differenced SST during, the spring period. The correlation between predicted and observed months), rainfall was in general larger than 0.7. This indicates that major annual rainfall (during summer season) can be predicted with good accuracy using the suggested approach. Copyright (D 2008 John Wiley & Sons. Ltd.
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