Yu-Hsuan Kao

Characterization and risk assessment of PAH-contaminated river sediment by using advanced multivariate methods

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.

Biogeochemical cycling of arsenic in coastal salinized aquifers: Evidence from sulfur isotope study.

Arsenic (As) contamination of groundwater, accompanied by critical salinization, occurs in the southwestern coastal area of Taiwan. Statistical analyses and geochemical calculations indicate that a possible source of aqueous arsenic is the reductive dissolution of As-bearing iron oxyhydroxides. There are few reports of the influence of sulfate-sulfide redox cycling on arsenic mobility in brackish groundwater. We evaluated the contribution of sulfate reduction and sulfide re-oxidation on As enrichment using δ(34)S([SO(4)]) and δ(18)O([SO(4)]) sulfur isotopic analyses of groundwater. Fifty-three groundwater samples were divided into groups of high-As content and salinized (Type A), low-As and non-salinized (Type B), and high-As and non-salinized (Type C) groundwaters, based on hydro-geochemical analysis. The relatively high enrichment of (34)S([SO(4)]) and (18)O([SO(4)]) present in Type A, caused by microbial-mediated reduction of sulfate, and high (18)O enrichment factor (ε([SO(4)-H(2)O])), suggests that sulfur disproportionation is an important process during the reductive dissolution of As-containing iron oxyhydroxides. Limited co-precipitation of ion-sulfide increased the rate of As liberation under anaerobic conditions. In contrast to this, Type B and Type C groundwater samples showed high δ(18)O([SO(4)]) and low δ(34)S([SO(4)]) values under mildly reducing conditions. Base on (18)O mass balance calculations, the oxide sources of sulfate are from infiltrated atmospheric O(2), caused by additional recharge of dissolved oxygen and sulfide re-oxidation. The anthropogenic influence of extensive pumping also promotes atmospheric oxygen entry into aquifers, altering redox conditions, and increasing the rate of As release into groundwater.

Investigating the interactive mechanisms between surface water and groundwater over the Jhuoshuei river basin in central Taiwan

In Taiwan, groundwater commonly becomes important water resources in dry periods, and/or areas lack of water storage facility due to its low cost, steady water supply and good water quality. However, improper groundwater development brings about serious decreases in groundwater levels and land subsidence which causes disasters, such as seawater intrusion or soil salination, accompanied with environmental and economic losses. It is critical to develop strategies for water resources conservation in mountainous areas. The complex heterogeneity of mountainous physiographic environment makes it challenging in the forecasts of groundwater level variations, particularly in mountainous areas. Artificial neural networks (ANNs) have been recognized as an effective modeling tool for complex nonlinear systems in the last two decades. This study aims to investigate the interactive mechanisms of groundwater at the mountainous areas of the Jhuoshuei river basin in central Taiwan through analyzing and modeling the groundwater level variations. Several issues are discussed in this study, which includes the correlation between groundwater level variation and rainfall as well as streamflow, the identification of groundwater recharge patterns and effective rainfall thresholds for estimating groundwater level variations. The results indicate: (1) the daily variation of groundwater level is closely correlated with river flow and one-day antecedent rainfall based on correlation analyses; (2) effective rainfall thresholds can be identified successfully; (3) groundwater level variations can be classified into four types for monitoring wells; and (4) the daily variations of groundwater level can be well estimated by constructed ANNs. The identified interactive mechanisms between surface water and groundwater can facilitate the mountainous water resource conservation strategy for better water management, especially irrigation water supply and for alleviating land subsidence in downstream areas in the future.

Assessment of nitrogen contamination of groundwater in paddy and upland fields

This study aims to assess the nitrogen contamination of groundwater in paddy and upland fields. A reactive chemical transport model PHREEQC and a variable saturated groundwater flow and transport model FEMWATER were used to evaluate the vertical transport of nitrogen compound in various soil types of paddy and upland. The shallow groundwater quality monitoring data of 2003, 2006, 2009 in the Choushui river alluvial fan, the major agriculture production area in Taiwan, were applied to support the validity of the numerical simulation findings. Results from PHREEQC and FEMWATER simulations showed that the organic-rich impermeable plow sole layer underneath the muddy layer of rice paddy can effectively reduce NO3− and N2 to NH4+ and retard the movement of NH4+. However, in the upland field which has no plow sole layer, the NH4+ can move easily to the shallow aquifer and contaminate the groundwater. The spatiotemporal distribution of NO3−–N and NH4+–N in the Choushui river alluvial fan revealed that high nitrate–N contamination areas were located mainly in the upland field of the proximal fan, where the granular unconfined aquifer was vulnerable to surface contaminants. Moreover, the unconfined nature of the aquifer allows the oxidization of NH4+ to NO3− and accelerates the plume movement. High ammonium–N concentration areas were mostly dispersed in the distal-fan area where upland planting and aquacultural farming were prevailed. The high NH4+–N found in the northern Choushui river alluvial fan was attributed to the alternative planting of rice and upland crops, and the plow sole layer was broken to maintain the quick drainage upland crop needs.

Dynamic column adsorption of As on iron-oxide-coated natural rock (IOCNR) and sludge management

AbstractAn 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 to C/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−1 and 20.41 L mg−1 h−1, respectively, for As(III) and 599.82 mg L−1 and 0.233 L mg−1 h−1, respectively, f...