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An extended column adsorption study on arsenic (As(III)/As(V)) was conducted using the developed adsorbent iron-oxide-coated natural rock. We considered a column with a diameter of 2 cm and varying bed depths, including 10 , 15 , and 20 . The breakthrough (C/C0 = 0.016) times were 31.0, 49.0, and 63.0 h and the exhaust (C/C0 = 0.90) times were 60.0, 90.0, and 110.0 h, respectively for As(III). For As(V), those were found to be (breakthrough times corresponding toC/C0 = 0.0033) 5.0, 11.0, and 18.0 h and 20.0, 27.0, and 36.0 h, respectively. The up-flow rate was maintained at 8 mL min−1. The As(III) and As(V) concentrations were 0.6 and 3 mg L−1. Bohart and Adams sorption model was employed to determine the important column design parameters. The column was designed by the bed-depth-service-time model. The adsorption capacity (N0) and the adsorption rate constant (K) calculated were 295.30 mg L−1and 20.41 L mg−1 h−1, respectively, for As(III) and 599.82 mg L−1and 0.233 L mg−1 h−1, respectively, for As(V). The effects on the variation of initial concentrations and flow rates were also investigated. The 10-cm exhaust bed (As(III)) was regenerated with 1 M NaOH, and its performance was evaluated. An attempt has been made to minimize the As adsorbed exhausted sludge mixing with Portland cement and the prepared blocks were used for leaching tests in different inorganic mediums for 90 d; immobility was accounted fromDevalues. [ABSTRACT FROM PUBLISHER]

High arsenic (As) levels occur naturally in geothermal areas, potentially polluting downstream wetland ecosystems. The study was to determine the distribution of As among aqueous, solid, and plant phases in the Guandu Wetland of Taiwan. Chemical compounds (As, Fe, Mn, TOC, SO, and FeS) and isotopic compositions (δS) in water and soil samples were analyzed to characterize the As distribution. The sequential extraction of As and total As in plant samples wasanalyzed to estimate the bioconcentration factor (BCF) and translocation factor (TF; defined as the ratio of metal concentration in the shoots to those in the roots) of As in Kandelia obovata in aqueous and solid phases. The As concentrations in plants (23.69 mg/kg) were higher than in the surrounding water (0.0018 mg/L) and soils (17.24 mg/kg). Kandelia obovata have high As bioavailability and low TF, causing easy adaptation to grow in As-contaminated wetland ecosystems. BCF (13657.92) was higher than BCF (1.38). The uptake and bioaccumulation of As in Kandelia obovata are significant; therefore, Kandelia obovata is an As accumulator. The uptake As by the Kandelia obovata plant might depend on the oxidation of As-contained FeS in the aerial roots and/or adsorption of As on root surface. [ABSTRACT FROM AUTHOR]

The dissolution-induced finger pattern in geological medium plays an important role in both geological processes and engineering practices. Numerical models have been developed to investigate the evolution of the chemical dissolution front within a fluid-saturated porous medium. In these models, several permeability-porosity relationships have been proposed and incorporated into the numerical model for describing simultaneous changes in permeability and porosity induced by mineral dissolution, but limited experimental data are available to justify one form superior to the other. This study investigates the effects of the permeability-porosity relationships on the morphological evolution of the chemical dissolution front. Three porosity-permeability relationships, namely, modified Fair-Hatch, Kozeny-Carman and Verma-Pruess (VP) models are incorporated into the numerical model. A series of numerical simulations are performed to evaluate the morphological evolution of reaction front, and the corresponding behaviour diagrams are constructed. Results shows that the morphological development are similar each other for modified Fair-Fatch and Kozeny-Carman model. The VP model yields a relative low primary and secondary critical upstream pressure gradient value owing to the flow-focusing effect enhanced by the stronger dependence of permeability on porosity. A comparison of behaviour diagrams of front morphology among three relationships show that the double-fingering front occurs under condition of lower upstream pressure gradient and smaller non-uniformity spacing for VP model. Our simulations demonstrate that the choice of the permeability-porosity function plays important roles on the evolution patterns of dissolution front. Therefore, an adequate description of the permeability-porosity relationship may lead to a more realistic simulation of field problems. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Groundwater supplies over 50 % of drinking water in Kinmen. Approximately 16.8 % of groundwater samples in Kinmen exceed the drinking water quality standard (DWQS) of NO-N (10 mg/L). The residents drinking high nitrate-polluted groundwater pose a potential risk to health. To formulate effective water quality management plan and assure a safe drinking water in Kinmen, the detailed spatial distribution of nitrate-N in groundwater is a prerequisite. The aim of this study is to develop an efficient scheme for evaluating spatial distribution of nitrate-N in residential well water using logistic regression (LR) model. A probability-based nitrate-N contamination map in Kinmen is constructed. The LR model predicted the binary occurrence probability of groundwater nitrate-N concentrations exceeding DWQS by simple measurement variables as independent variables, including sampling season, soil type, water table depth, pH, EC, DO, and Eh. The analyzed results reveal that three statistically significant explanatory variables, soil type, pH, and EC, are selected for the forward stepwise LR analysis. The total ratio of correct classification reaches 92.7 %. The highest probability of nitrate-N contamination map presents in the central zone, indicating that groundwater in the central zone should not be used for drinking purposes. Furthermore, a handy EC-pH-probability curve of nitrate-N exceeding the threshold of DWQS was developed. This curve can be used for preliminary screening of nitrate-N contamination in Kinmen groundwater. This study recommended that the local agency should implement the best management practice strategies to control nonpoint nitrogen sources and carry out a systematic monitoring of groundwater quality in residential wells of the high nitrate-N contamination zones. [ABSTRACT FROM AUTHOR]

Highlights: [•] Arsenic contaminated and humic-substance-enriched aquifers in the Chianan Plain were investigated. [•] Aqueous As was closely correlated with TOC, Alk, fluorescence intensity and Eh. [•] Arsenic species were under non-equilibrium chemical conditions. [•] Iron oxyhydroxides and sulfides contained the major portion of As. [•] As-rich black shale is the major source of As in the Chianan Plain. [ABSTRACT FROM AUTHOR]

Seafood farmed in arsenic (As)-contaminated areas is a major exposure pathway for the ingestion of inorganic As by individuals in the southwestern part of Taiwan. This study presents a probabilistic risk assessment using limited data for inorganic As intake through the consumption of the seafood by local residents in these areas. The As content and the consumption rate are both treated as probability distributions, taking into account the variability of the amount in the seafood and individual consumption habits. The Monte Carlo simulation technique is utilized to conduct an assessment of exposure due to the daily intake of inorganic As from As-contaminated seafood. Exposure is evaluated according to the provisional tolerable weekly intake (PTWI) established by the FAO/WHO and the target risk based on the US Environmental Protection Agency guidelines. The assessment results show that inorganic As intake from five types of fish (excluding mullet) and shellfish fall below the PTWI threshold values for the 95th percentiles, but exceed the target cancer risk of 10. The predicted 95th percentile for inorganic As intake and lifetime cancer risks obtained in the study are both markedly higher than those obtained in previous studies in which the consumption rate of seafood considered is a deterministic value. This study demonstrates the importance of the individual variability of seafood consumption when evaluating a high exposure sub-group of the population who eat higher amounts of fish and shellfish than the average Taiwanese. [ABSTRACT FROM AUTHOR]

In this article, we used the inverse distance weighting (IDW) method to estimate the rainfall distribution in the middle of Taiwan. We evaluated the relationship between interpolation accuracy and two critical parameters of IDW: power (α value), and a radius of influence (search radius). A total of 46 rainfall stations and rainfall data between 1981 and 2010 were used in this study, of which the 12 rainfall stations belonging to the Taichung Irrigation Association (TIA) were used for cross-validation. To obtain optimal interpolation data of rainfall, the value of the radius of influence, and the control parameter-α were determined by root mean squared error. The results show that the optimal parameters for IDW in interpolating rainfall data have a radius of influence up to 10-30 km in most cases. However, the optimal α values varied between zero and five. Rainfall data of interpolation using IDW can obtain more accurate results during the dry season than in the flood season. High correlation coefficient values of over 0.95 confirmed IDW as a suitable method of spatial interpolation to predict the probable rainfall data in the middle of Taiwan. [ABSTRACT FROM AUTHOR]

Summary: Multi-species advective–dispersive transport equations sequentially coupled with first-order decay reactions are widely used to describe the transport and fate of the decay chain contaminants such as radionuclide, chlorinated solvents, and nitrogen. Although researchers attempted to present various types of methods for analytically solving this transport equation system, the currently available solutions are mostly limited to an infinite or a semi-infinite domain. A generalized analytical solution for the coupled multi-species transport problem in a finite domain associated with an arbitrary time-dependent source boundary is not available in the published literature. In this study, we first derive generalized analytical solutions for this transport problem in a finite domain involving arbitrary number of species subject to an arbitrary time-dependent source boundary. Subsequently, we adopt these derived generalized analytical solutions to obtain explicit analytical solutions for a special-case transport scenario involving an exponentially decaying Bateman type time-dependent source boundary. We test the derived special-case solutions against the previously published coupled 4-species transport solution and the corresponding numerical solution with coupled 10-species transport to conduct the solution verification. Finally, we compare the new analytical solutions derived for a finite domain against the published analytical solutions derived for a semi-infinite domain to illustrate the effect of the exit boundary condition on coupled multi-species transport with an exponential decaying source boundary. The results show noticeable discrepancies between the breakthrough curves of all the species in the immediate vicinity of the exit boundary obtained from the analytical solutions for a finite domain and a semi-infinite domain for the dispersion-dominated condition. [ABSTRACT FROM AUTHOR]

Abstract: The study assesses the effects of event rainfall on the soil erosion in terraced paddy fields under rice cropping, fallow, and green manure planting. A 0.75-ha terraced rice field was used to investigate the soil erosion under the regular cultivation of rice in 2005, fallow in 2006, and planting with green manure in 2007. The results show that infiltration rates significantly increase when a terraced paddy field is under fallow or is planted with green manure; the paddy is more vulnerable to embankment collapse and increased the rates of soil erosion. In an experimental field, suspended solid in run-off samples reached the maximal concentrations of 1700mg/l for fallow in 2006, and 3400mg/l for manure planted field in 2007, during heavy rainfall events. These values were significantly greater than the erosion rate of 500mg/l recorded for rice cropped field during 2005. The estimated annual erosion rate was 4.15tonha−1 yr−1 for green manure planted field, which was significantly higher than that of the rice-planted terraced paddy (0.77tonha−1 yr−1). Moreover, terraced paddy runoff significantly increased when planted with green manure. Soil erosion rates calculated by the Universal Soil Loss Equation (USLE) from the optimal available data were considerably higher than the field-measured values. The comparison revealed that soil conservation using rice-planted terraced paddy was more effective than that resulting from other uses. The government should formulate effective measures and maintain sustainable rice planting in the terraced paddies. [Copyright &y& Elsevier]

High arsenic (As) concentration in groundwater potentially poses a serious threat to the health of local residents in southwestern Taiwan. Although the As release to groundwater is responsible for the reducing bacteria-mediated reductive dissolution of As-rich Fe hydroxides, the influences of FeRB and different organic substrates on As and Fe mobility and transformation were rarely discussed. An experiment that involved As-adsorbed synthetic amorphous Fe(III) hydroxide (HFO) and the inoculation of in situ Fe-reducing bacteria (FeRB) was performed to evaluate the contribution of FeRB to the As mobility and transformation. The batched experiment of As-free HFO showed that the reducing bacteria rapidly induced the reduction of amorphous Fe oxyhydroxide to Fe(II) by reductive dissolution of HFO and formation of Fe-citrate complexation. For aqueous As(V) reduction experiment, arsenate was effectively reduced to As(III) by the facultative anaerobic bacterium in the cultured FeRB. In the experiment of As-containing HFO reduction, the aqueous As(V) acts as an electron acceptor and reduced to As(III) after the reductive dissolution of Fe(III) on HFO. However, the increase in the As(III) concentrations with time for various organic substrates in the As-adsorbed HFO-reducing experiment differ from the rates of As(V) reduction with various organic substrates in the As(V)-reducing experiment. The decrease in sorption sites by coupled reductive dissolution of HFO and the competitive desorption of small molecular organic carbon is apparently the important factor of As mobility. For large molecular organic carbon (i.e., citrate), the significant contribution of citrate on As mobility is the complexation of iron citrate. A working hypothesis model of As biogeochemical cycling is proposed to illustrate the relevant processes in the groundwater aquitard of southwestern Taiwan. [ABSTRACT FROM AUTHOR]

Summary: The purpose of the study is to assess the applicability in estimating the mountain block recharge (MBR) to the downstream alluvial aquifers in the sub-tropical area using baseflow separation and rainfall infiltration methods. The Choushui-Wu River basin, the largest groundwater region in Taiwan was the study area. The high slope mountainous catchment located in the upstream of Choushui-Wu River basin, act as an important conduit in conveying surface and subsurface runoff to the recharge of the downstream alluvial aquifers. Geographic Information Systems (GISs) was applied to facilitate the estimation processes. The estimated MBR using the baseflow separation method was 1.08×109 m3/year of which Wu River and Choushui River basins comprised 0.27×109 m3/year (25.2%) and 0.81×109 m3/year (74.8%), respectively. These results are similar to the previous O18 isotopic study indicating that 22% and 78% were from the Wu River and Choushui River basins, respectively. Moreover, the estimated amount of lateral flow using C14 technique from the upstream of Choushui River basin was 0.83×109 m3/year, which is close to the result (0.81×109 m3/year) of this study. For comparison, groundwater recharged by rainfall infiltration in the mountainous catchment was derived from the precipitation, evapotranspiration, land use and soil types of the region. The estimated MBR by the rainfall infiltration method is 1.06×109 m3/year, which is close to 1.08×109 m3/year determined by the baseflow separation method. These results are also similar to the groundwater hydrograph analysis. The proposed methods show simple and efficient computation and do not require complex hydrological modeling and detailed knowledge of soil characteristics. They can reasonably estimate the lateral boundary influx contributing from the MBR and are thus applicable to estimate the MBRs in other sub-tropical regions. [Copyright &y& Elsevier]

Jang, Cheng-Shin, Chen-Wuing Liu, Shih-Kai Chen, and Wen-Sheng Lin, 2011. Using a Mass Balance Model to Evaluate Groundwater Budget of Seawater-Intruded Island Aquifers. Journal of the American Water Resources Association (JAWRA) 48(1): 61-73. DOI: 10.1111/j.1752-1688.2011.00593.x Abstract: The study developed a mass balance model to evaluate the groundwater budget of seawater-intruded island aquifers using limited available data. The Penghu islands were selected as a study area. As sparse observed data were available in the islands, methods of combining water and chloride balances were used to determine the amounts of groundwater pumping, seawater intrusion, aquifer storages, and safe yields in the shallow and deep aquifers. The groundwater budget shows that seawater intrusion to freshwater aquifers was 1.38 × 106 and 0.29 × 106 m3/year in the shallow and deep aquifers, respectively, indicating that the seawater intrusion is severe in the both aquifers. The safe yield of the shallow aquifer was 14.56 × 106 m3/year in 2005 which was four times higher than that of the deep aquifer (3.70 × 106 m3/year). However, the annual pumping amounts in the shallow and deep aquifers were 4.77 × 106 and 3.63 × 106 m3/year, respectively. Although the safe yield of the shallow aquifer is enough for all water resources demands, only 55% of exploitation amount was extracted from the shallow aquifer due to its poor water quality. Groundwater exploitation in the deep aquifer should be significantly reduced and regulated by a dynamic management of pumping scheme because the annual pumping amounts are close to the safe yield and seawater intrusion occurs continually. Additionally, to alleviate further aquifer salination, at least half of the current annual groundwater abstraction should be reduced. [ABSTRACT FROM AUTHOR]

Summary: Because of potential impacts of global warming on the occurrence of increasing drought events, this work was to determine locations for groundwater emergency utilization in the Taipei Basin subject to conditions of groundwater quality and quantity. Multivariate indicator kriging was first used to probabilistically define regions with pristine groundwater quality which complies with the drinking water quality standard in Taiwan. Then, the groundwater flow model, MODFLOW, was adopted to simulate groundwater drawdown for specified pumping rates arranged in determined candidate zones with pristine groundwater quality during a six-month drought period. To reduce impacts on land subsidence by pumping, zones of pristine groundwater quality with minimizing pumping drawdown were the optimal locations to extract groundwater for domestic uses. Finally, a feasible scheme of groundwater emergency utilization during drought was proposed based on locations of current water supply plants and land-use. The analyzed results of combining groundwater quality and quantity reveal that two regions, the southern and eastern Taipei Basins, are feasible locations to pump groundwater during drought owing to characteristics of excellent groundwater quality and low pumping drawdown. After considering existent conditions of water supply plants and land-use, the southern Taipei Basin is recommended to extract groundwater for domestic uses, whereas groundwater in the eastern Taipei Basin is only limited for non-drinking purposes. [ABSTRACT FROM AUTHOR]

This study was performed to characterize hydrochemical properties of springs based on their geological origins in Taiwan. Stepwise discriminant analysis (DA) was used to establish a linear classification model of springs using hydrochemical parameters. Two hydrochemical datasets-ion concentrations and relative proportions of equivalents per liter of major ions-were included to perform prediction of the geological origins of springs. Analyzed results reveal that DA using relative proportions of equivalents per liter of major ions yields a 95.6% right assignation, which is superior to DA using ion concentrations. This result indicates that relative proportions of equivalents of major hydrochemical parameters in spring water are more highly associated with the geological origins than ion concentrations do. Low percentages of Na equivalents are common properties of springs emerging from acid-sulfate and neutral-sulfate igneous rock. Springs emerging from metamorphic rock show low percentages of Cl equivalents and high percentages of HCO $_{3}^{-}$ equivalents, and springs emerging from sedimentary rock exhibit high Cl/SO $_{4}^{2-}$ ratios. [ABSTRACT FROM AUTHOR]

The study compares the prediction performances of evapotranspiration by the FAO56 Penman-Monteith method and the pan evaporation method using the artificial neural network. A backpropagation neural network was adopted to determine the relationship between meteorological factors and evapotranspiration or evaporation. The evapotranspiration in the ChiaNan irrigated area of Tainan was considered. Weather data compiled by Irrigation Experiment Station of ChiaNan Irrigation Association were the input layer variables, including (1) the highest temperature, (2) the lowest temperature, (3) the average temperature, (4) the relative humidity, (5) the wind speed, (6) hours of sunlight, (7) amount of solar radiation, (8) the dew point, (9) morning ground temperature and (10) afternoon ground temperature. The importance of the ten weather factors was ranked by the general influence (GI) factor. Results show that the correlation coefficient between the evapotranspiration in 2004 calculated by FAO56 Penman-Monteith method and the one predicted by the neural network model with a hidden layer of ten nodes is 0.993. The actual evapotranspiration is 911.6 cm, and value prediction by the neural network is 896.4 cm, between which two values the error is 1.67%. The results reveal that the backpropagation neural network based on the FAO56 Penman-Monteith method can accurately predict evapotranspiration. However, the correlation coefficient between the actual evaporation in 2004 and the value prediction by the neural network with a hidden layer of ten nodes and an output layer with the pan evaporation as its target output is 0.708. The pan evaporation is 1,673.1 cm, while the value predicted by the backpropagation neural network is 1,451.7 cm, between which values the error is 13.23%. The backpropagation neural networks with pan evaporation as target outputs predict the evaporation with large errors. Moreover, the use of four agricultural weather factors (determined by the GI) including wind speed, average temperature, dew point and maximum temperature as input variables, and a hidden layer of three nodes in the backpropagation neural network model can successfully predict evapotranspiration based on the FAO56 Penman-Monteith method ( R = 0.98, error = 1.35%). [ABSTRACT FROM AUTHOR]