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.
The global impact on public health of elevated arsenic (As) in water supplies is highlighted by an increasing number of countries worldwide reporting high As concentrations in drinking water. In ...Latin America, the problem of As contamination in water is known in 14 out of 20 countries: Argentina, Bolivia, Brazil, Chile, Colombia, Cuba, Ecuador, El Salvador, Guatemala, Honduras, Mexico, Nicaragua, Peru and Uruguay. Considering the 10μg/L limit for As in drinking water established by international and several national agencies, the number of exposed people is estimated to be about 14million. Health effects of As exposure were identified for the first time already in the 1910s in Bellville (Córdoba province, Argentina). Nevertheless, contamination of As in waters has been detected in 10 Latin American countries only within the last 10 to 15years. Arsenic is mobilized predominantly from young volcanic rocks and their weathering products. In alluvial aquifers, which are water sources frequently used for water supply, desorption of As from metal oxyhydroxides at high pH (>8) is the predominant mobility control; redox conditions are moderate reducing to oxidizing and As(V) is the predominant species. In the Andes, the Middle American cordillera and the Transmexican Volcanic Belt, oxidation of sulfide minerals is the primary As mobilization process. Rivers that originate in the Andean mountains, transport As to more densely populated areas in the lowlands (e.g. Rímac river in Peru, Pilcomayo river in Bolivia/Argentina/Paraguay). In many parts of Latin America, As often occurs together with F and B; in the Chaco–Pampean plain As is found additionally with V, Mo and U whereas in areas with sulfide ore deposits As often occurs together with heavy metals. These co-occurrences and the anthropogenic activities in mining areas that enhance the mobilization of As and other pollutants make more dramatic the environmental problem.
► In Latin America, As of predominantly geogenic origin in water is known in 14 out of 20 countries. ► Considering the 10 μg/L limit for As in drinking water, the number of exposed people is estimated to be about 14 million. ► Although health effects were identified in the 1910s, As has been detected in most countries only in the last 10–15 years. ► Arsenic occurs naturally by mobilization from volcanic rocks and desorption from metal oxyhydroxides at high pH. ► Anthropogenic activities in mining areas enhance As mobilization and make more dramatic the environmental problem.
This study applied advanced multivariate methods and risk assessment to evaluate the characteristics of polycyclic aromatic hydrocarbons (PAHs) in the sediment of the severely polluted Erjen River in ...Taiwan. High-molecular-weight PAHs (HPAHs) dominated in the rainy season. The ecological risk of PAHs in the sediment was low, whereas the total health risk through ingestion and dermal contact was considerably high. The SOM (self-organizing map) analysis clustered the datasets of PAH-contaminated sediment into five groups with similar concentration levels. Factor analysis identified major factors, namely coal combustion, traffic, petrogenic, and petrochemical industry factors, accounting for 88.67% of the variance in the original datasets. The major tributary and the downstream of the river were identified as PAH-contamination hotspots. The PMF (positive matrix factorization) was combined with toxicity assessment to estimate the possible apportionment of sources and the associated toxicity. Spills of petroleum-related products, vehicle exhaust, coal combustion, and exhaust from a petrochemical industry complex constituted respectively 12%, 6%, 74%, and 86% of PAHs in the sediment, but contributed respectively 7%, 15%, 22%, and 56% of toxicity posed by PAHs in the sediment. To improve the sediment quality, best management practices should be adopted to eliminate nonpoint sources of PAHs flushed by storm water into the major tributary and the downstream of the Erjen River. The proposed methodologies and results provide useful information on remediating river PAH-contaminated sediment and may be applicable to other basins with similar properties that are experiencing resembled river environmental issues.
•High-molecular-weight PAHs from pyrogenic sources dominate in the rainy season.•Spatial similarity and dominating factors of PAHs in sediment identify hotspots.•Receptor model combined with risk assessment can locate critical PAH sources.•The toxicity from the biggest contributor to PAHs is not the most important.•Non-point sources should be eliminated for improving sediment quality.
•We analyzed 39 groundwater and 393 core samples of arsenic–affected aquifer in Yilan, Taiwan.•Factor analysis shows aqueous As closely associated with HCO3− and NH4+.•High As and Fe contents were ...correlated in marine formation.•As was adsorbed or co-precipitated with non-crystalline Fe oxyhydroxides and sulfides.
High arsenic concentrations (average 0.1 mg/L) of groundwater were found in Lanyang plain of Taiwan. In this study, 39 groundwater samples from 23 wells were collected and 14 hydro-geochemical parameters were analyzed. Factor analysis was applied to determine major influence factors of the arsenic enriched groundwater quality, and PHREEQC was used to calculate the distribution of aqueous species and saturation index of which affected the hydrogeochemistry of groundwater. 393 geological core samples from 9 drilling wells were collected and analyzed the contents of total arsenic and iron. Moreover, core samples associated with high arsenic concentration groundwater were selected, mineralogical phases were analyzed using X-ray fluorescence (XRF), high resolution X-ray photoelectron (XPS) and scanning electron microscope and energy dispersive spectrometer (SEM-EDS). Results of the arsenic enrichment factor determined by factor analysis indicated that infiltration of the organic and nitrogen pollutants from anthropogenic activities to shallow groundwater, and the reductive dissolution from iron oxyhydroxides in the deep aquifer were the main processes of arsenic release to groundwater from the sediment. Total arsenic and iron contents of the core samples were well correlated in marine sequences. The presence of clay layer within the subsurface may increase in the As contamination in groundwater aquifer. However the time for As release from clay layer to lower aquifer may require tens or hundreds years to complete under natural environment condition. Surface analyses of core sample performed by XPS showed that arsenic was adsorbed or co-precipitated with non-crystalline iron oxyhdroxides and sulfides. After a long term burial of sediment, microbial metabolism of organic matter creates a more reducing environment, arsenic may then be gradually released from iron oxyhydroxides by reductive dissolution or desorption to aqueous phase. The framboidal-diagenetic type phase was identified by XPS and the groundwater is supersaturated with respect to pyrite and orpiment determined by PHREEQC are suggesting sulfide minerals co-precipitate As. Arsenic in sediments is released into groundwater primarily by the reductive dissolution of As-bearing Fe-oxyhydroxides in reducing environment in the Lanyang plain.
River discharge is one of the important hydraulic data to evaluate and manage the regional water resources. Estimating river discharge is generally based on field measurements. The measurement data ...are then applied to construct water level-discharge rating curves. However, it is sometimes difficult to obtain accurate discharge data due to the high uncertainty of flow. A commonly used technique is the propeller-type flowmeters (PTF), which average the results of 1-, 2-, or 3-point methods to obtain a vertical mean velocity. In this study, three types of flowmeters were employed to compare the accuracy of flow measured. The devices were calibrated using a tow tank testing: PTF, acoustic Doppler profiler (ADP), and radar surface velocimeter (RSV). To assess the applicability of the non-contact observation method, a series of 16 experiments in channels were conducted. Surface velocity measurement using the RSV was compared with the measurements obtained by PTF. The relationship between measured surface velocity of RSV and measured vertical mean velocity of PTF was established. The results show that the RSV can effectively estimate the river discharge in the open channel flow.
The movement of high-arsenic (As)-concentration Beitou geothermal spring water up to 4600 μg/L from the upstream area may affect the downstream Guandu plain and Guandu wetland. The major As pathway ...is via the subsurface flow. The study assesses the fate and transport of As-enriched geothermal spring water in the Beitou-Guandu area. The groundwater head and flow field velocity are first simulated by using HYDROGEOCHEM—fluid flow model. The steady state flow field is well-calibrated with root mean square error 1.73 m and
R
2
= 0.992. The spatial–temporal distributions of As in the Beitou-Guandu area are simulated by the HYDROGEOCHEM reactive transport model using the calibrated steady state flow field. The results show that high As concentration (250 μg/L) in groundwater of Guandu plain was caused by the movement of high As concentration from the Beitou geothermal spring water. In contrast, the low As concentration (5–50 μg/L) in Guandu wetland was mitigated by the tidal water dilution. The simulated As concentrations increase in the first 3 years, and then gradually decrease due to the adsorption of As on the iron oxide minerals ferrihydrite and iron sulfide minerals pyrite. Furthermore, the hydrogeochemical transport model is applied to assess the effect of bioaccumulation of As by the mangrove plants of Guandu wetland. The dominant mangrove plants,
Kandelia obovata
, can reduce about 5–30 μg/L As concentration in groundwater. It may be one of sinks of As in Guandu wetland. The inclusion of
K. obovata
can uptake the aqueous As and allow the simulated As concentration further close to the field measurement in the Guandu wetland. The study successfully models the reactive chemical transport of As by considering both geochemical reactions and biochemical uptakes in the Beitou-Guandu area. The result demonstrates that the complex biogeochemical transport can be quantified by the sophisticated HYDROGEOCHEM model. Moreover, the salient features of the biogeochemical reactions can be recovered and elucidated through a series of systematic simulation.
Factor analysis is applied to 28 groundwater samples collected from wells in the coastal blackfoot disease area of Yun-Lin, Taiwan. Correlations among 13 hydrochemical parameters are statistically ...examined. A two-factor model is suggested and explains over 77.8% of the total groundwater quality variation. Factor 1 (seawater salinization) includes concentrations of EC, TDS, Cl
−, SO
4
2−, Na
+, K
+ and Mg
2+, and Factor 2 (arsenic pollutant) includes concentrations of Alk, TOC and arsenic. Maps are drawn to show the geographical distribution of the factors. These maps delineate high salinity and arsenic concentrations. The geographical distribution of the factor scores at individual wells does not reveal the sources of the constituents, which are instead, deduced from geological and hydrological evidence. The areas of high seawater salinization and arsenic pollution correspond well to the groundwater over-pumping area. Over-pumping of the local groundwater causes land subsidence and gradual salinization by seawater. The over-pumping also introduces excess dissolved oxygen that oxidizes the immobile minerals, releases arsenic by reductive dissolution of arsenic-rich iron oxyhydroxides and increases the arsenic concentration in water. The over-extraction of groundwater is the major cause of groundwater salinization and arsenic pollution in the coastal area of Yun-Lin, Taiwan.
This study characterized the sediment quality of the severely contaminated Erjen River in Taiwan by using multivariate analysis methods—including factor analysis (FA), self-organizing maps (SOMs), ...and positive matrix factorization (PMF)—and health risk assessment. The SOMs classified the dataset with similar heavy-metal-contaminated sediment into five groups. FA extracted three major factors—traditional electroplating and metal-surface processing factor, nontraditional heavy-metal-industry factor, and natural geological factor—which accounted for 80.8% of the variance. The SOMs and FA revealed the heavy-metal-contaminated-sediment hotspots in the middle and upper reaches of the major tributary in the dry season. The hazardous index value for health risk via ingestion was 0.302. PMF further qualified the source apportionment, indicating that traditional electroplating and metal-surface-processing industries comprised 47% of the health risk posed by heavy-metal-contaminated sediment. Contaminants discharged from traditional electroplating and metal-surface-processing industries in the middle and upper reaches of the major tributary must be eliminated first to improve the sediment quality in Erjen River. The proposed assessment framework for heavy-metal-contaminated sediment can be applied to contaminated-sediment river sites in other regions.
•Sediment quality was assessed by FA, SOM, PMF, and health risk assessment.•The contaminated hotspots were identified by using FA and SOM.•PMF estimated that the electroplating and metal-surface-processing industries comprised the major health risk.
•Effects of permeability anisotropy on chemical dissolution fronts.•Permeability anisotropy modified flow-focusing effect.•Permeability anisotropy influences morphologies of dissolution ...fronts.•Effects of permeability anisotropy decrease when upstream pressure gradient increases.
The morphological evolutions of chemical dissolution fronts have attracted increasing interest in the field of the geological sciences and in industrial applications. Extensive research based on numerical simulations has been conducted to understand how various mechanisms and processes influence the morphological evolution of chemical dissolution fronts within geological media. Most researchers in previous studies have assumed the medium permeability to be isotropic for developing numerical models, despite isotropic geological media being uncommon in the real world. This study investigates the effect of medium permeability anisotropy on the morphological evolutions of two non-uniformities with higher permeability in a geochemical dissolution system. A series of numerical simulations are performed to evaluate the effect of medium permeability anisotropy on the morphological evolution of a chemical dissolution front. The simulation results indicate that the patterns of the dissolution reaction front are substantially affected by medium permeability anisotropy. An increase in the permeability anisotropy ratio, which is defined as the ratio of the permeability in the transverse direction to that in the longitudinal direction, enhances the dominance of the flow-focusing effect over the stabilizing or merging effect induced by diffusion/dispersion mechanism. Therefore, an increase in the permeability anisotropy ratio can increase the fingering length of the dissolution front or cause the dissolution front to have a more unstable pattern. By contrast, a reduction in the permeability anisotropy ratio will weaken the flow-focusing effect, thereby reducing the fingering length of the dissolution front or changing the front morphology such that it has a more stable status. The effect of the permeability anisotropy ratio on the morphological evolution tends to decrease when the Zhao number (negative dimensionless upstream pressure gradient) of the system increases. The consideration of medium permeability anisotropy in the geochemical dissolution model renders the simulation of the morphological evolutions of dissolution reaction fronts more realistic.
PDF
