This article was downloaded by: [National Cheng Kung University]On: 31 August 2011, At: 22:44Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Journal of Environmental Science and Health, Part APublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/lesa20

Biogeochemical interactions among the arsenic, iron,humic substances, and microbes in mud volcanoes insouthern TaiwanChia-Chuan Liu a , Jyoti Prakash Maity a b , Jiin-Shuh Jean a , Ondra Sracek c d , Sandeep Kara , Zhaohui Li e , Jochen Bundschuh a f g , Chien-Yen Chen b & Hsueh-Yu Lu ba Department of Earth Sciences, National Cheng Kung University, Tainan, Taiwanb Department of Earth and Environmental Sciences, National Chung Cheng University, ChiayiCounty, Taiwanc Department of Geology, Faculty of Science, Palacký University, Olomouc, Czech Republicd OPV s.r.o. (Groundwater Protection Ltd), Praha, Czech Republice Department of Geosciences, University of Wisconsin–Parkside, Kenosha, Wisconsin, USAf Institute of Applied Research, Karlsruhe University of Applied Sciences, Karlsruhe, Germanyg KTH-International Groundwater Arsenic Research Group, Department of Land and WaterResources Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden

Available online: 31 Aug 2011

To cite this article: Chia-Chuan Liu, Jyoti Prakash Maity, Jiin-Shuh Jean, Ondra Sracek, Sandeep Kar, Zhaohui Li, JochenBundschuh, Chien-Yen Chen & Hsueh-Yu Lu (2011): Biogeochemical interactions among the arsenic, iron, humic substances,and microbes in mud volcanoes in southern Taiwan, Journal of Environmental Science and Health, Part A, 46:11, 1218-1230

To link to this article: http://dx.doi.org/10.1080/10934529.2011.598793

PLEASE SCROLL DOWN FOR ARTICLE

Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions

This article may be used for research, teaching and private study purposes. Any substantial or systematicreproduction, re-distribution, re-selling, loan, sub-licensing, systematic supply or distribution in any form toanyone is expressly forbidden.

The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses shouldbe independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.

Journal of Environmental Science and Health Part A (2011) 46, 1218–1230Copyright C© Taylor & Francis Group, LLCISSN: 1093-4529 (Print); 1532-4117 (Online)DOI: 10.1080/10934529.2011.598793

Biogeochemical interactions among the arsenic, iron,humic substances, and microbes in mud volcanoesin southern Taiwan

CHIA-CHUAN LIU1, JYOTI PRAKASH MAITY1,2, JIIN-SHUH JEAN1, ONDRA SRACEK3,4,SANDEEP KAR1, ZHAOHUI LI5, JOCHEN BUNDSCHUH1,6,7, CHIEN-YEN CHEN2 and HSUEH-YU LU2

1Department of Earth Sciences, National Cheng Kung University, Tainan, Taiwan2Department of Earth and Environmental Sciences, National Chung Cheng University, Chiayi County, Taiwan3Department of Geology, Faculty of Science, Palacky University, Olomouc, Czech Republic4OPV s.r.o. (Groundwater Protection Ltd), Praha, Czech Republic5Department of Geosciences, University of Wisconsin–Parkside, Kenosha, Wisconsin, USA6Institute of Applied Research, Karlsruhe University of Applied Sciences, Karlsruhe, Germany7KTH-International Groundwater Arsenic Research Group, Department of Land and Water Resources Engineering, Royal Instituteof Technology (KTH), Stockholm, Sweden

Fluid and mud samples collected from Hsiaokunshui (HKS), Wushanting (WST), Yenshuikeng (YSK), Kunshuiping (KSP), Liyushan(LYS), and Sinyangnyuhu (SYNH) mud volcanoes of southwestern Taiwan were characterized for major ions, humic substances (HS)and trace elements concentrations. The relationship between the release of arsenic (As) and activities of sulfate-reducing bacteria hasbeen assessed to understand relevant geochemical processes in the mud volcanoes. Arsenic (0.02–0.06 mg/L) and humic substances(4.13 × 10−4 to 1.64 × 10−3 mM) in the fluids of mud volcanoes showed a positive correlation (r = 0.99, p < 0.05) except in Liyushanmud volcano. Arsenic and iron in mud sediments formed two separate groups i) high As, but low Fe in HKS, WST, and SYNH; andii) low As, but high Fe in the YSK, KSP, and LYS mud volcanoes. The EhS.H.E. values of the mud volcano liquids were characterizedby mild to strongly reducing conditions. The HKS, SYNH, and WST mud volcanoes (near the Chishan Fault) belongs to strongreducing environment (−33 to −116 mV), whereas the LYS, YSK, and KSP mud volcanoes located near the coastal plain are undermild reducing environment (−11 to 172 mV). At low Eh values mud volcanoes, saturation index (SI) values of poorly crystallinephases such as amorphous ferric hydroxide indicate understaturation, whereas saturation is reached in relatively high EhS.H.E. valuesmud volcanoes. Arsenic contents in sediments are low, presumably due to its release to fluids (As/Fe ratio in YSK, KSP, and LYSsediment: 4.86 × 10−4−6.20 × 10−4). At low EhS.H.E. values (mild to strong reducing environment), arsenic may co-precipitate withsulfides as a consequence of sulfate reduction (As/Fe ratios in WST, HKS, and SYNH sediments: 0.42–0.69).

Keywords: Mud volcanoes, Taiwan, arsenic, humic substances, sulfate-reducing bacteria, biogeochemistry.

Introduction

By a strict definition, mud volcanoes refer to geologicalfeatures assembled in different areas concurrent with activecontinental plates and linked with mud and hydrocarbongas release.[1] They are located in many unstable geologicareas, such as onshore and offshore, and near active andpassive continental margins.[2–4] Mud volcanoes are linkedto structured channels caused by tectonic compression, de-

Address correspondence to Jiin-Shuh Jean, Department of EarthSciences, National Cheng Kung University, Tainan, Taiwan;E-mail: jiinshuh@mail.ncku.edu.tw

hydration of clay minerals, and speedy deposition of sed-iments associated with slumps or turbidites (e.g. faults orfractures).[5–8] Mixed materials which include liquid, mud,and gas are transported from deep geological sources tothe surface of the earth. Thus mud liquids and mud sed-iments are commonly studied to assess the effect of theirdeep sources on the surficial environment.[3, 9–14]

Many mud volcanoes studied in Taiwan include someoffshore[15,16] and onshore[17,18] mud volcano sites. Thereare a total of 64 active mud volcanoes in 17 areas with dif-ferent geomorphological features and tectonic conditionsin Taiwan.[17,18] Their activities created special sedimentarycharacteristics, e.g. fine-grained deposits including con-solidated mudstones.[19–21] The mud volcanoes are mostly

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011

Biogeochemical interactions in mud volcanoes in southern Taiwan 1219

located in southern Taiwan,[14] and are continuously re-leasing fluids,[13] sediments, and large volumes of methanegas.[22]

Almost all mud volcanoes in southern Taiwan arecharacterized by high salinity rich in Na+ and Cl−,which are the major components of mud liquids.[23]

Biogeochemical processes in mud volcanoes in Taiwancan influence the chemical characteristics of fluids andsediments in mud volcano areas.[24] A previous studyhas suggested that mud volcano fluids may be derivedfrom a deep accretionary complex.[25] Seawater is thoughtto be the source of mud volcano liquids in Taiwan.[22]

Few researchers have tried to link the geochemicalproperties of the mud volcanoes to their biogeochemicalprocesses.[24,26]

Humic substances (HS) may exist as a soluble and ab-sorbable form in liquid and soil environments. The com-plexation of arsenic with soluble humic acid (HA) has beenshown to bind approximately 40% and 15% of total arseniteand arsenate, respectively in the presence of bridging met-als.[27] The experiment by Ko et al.[27] was conducted in thelaboratory environment under shaking incubation (dark,at 25◦ and pH 6.8) for 48 hours with the initial concen-tration of arsenite and arsenate, each with 1000 µg/L.[27]

The HS can effectively compete with negatively chargedAs for sorption sites on hydrated ferric oxide surfacescausing desorption of arsenic from iron minerals and in-hibiting the adsorption of arsenic onto humic-coated ironoxides.[28]

Humic acid may facilitate the transport of arsenic inthe form of both free and organically complexed arsenicspecies in subsurface environments. Although As(V) canmore strongly bind with dissolved organic carbon (DOC)than As (III), under environmentally relevant conditionsabout 10% of total As(V) may be bound to dissolved or-ganic matter (DOM), whereas >10% of As(III) is bound toDOM at very low As/DOC ratios only.[29] Also, several hu-mic acids can enhance the reduction of arsenate to arsenitein the liquid phase.

Previous studies have shown that Fe-oxides/hydroxidesand organic matter are important components with regardto the mobilization of As in the subsurface environment,which may be facilitated by anaerobic bacteria. Clostrid-ium spp. and Shewanella spp. are reported to be responsi-ble for the release of As under anaerobic conditions.[30,31]

Among them, Shewanella putrefaciens can reduce As(V)to As(III)[30] whereas Clostridium spp. can consume rox-arsone and release inorganic arsenic.[31] Significant SO4

2-

concentrations in mud volcano liquids is also conducive tothe activity of sulfate-reducing bacteria (SRB) in anaer-obic environments, which may affect As concentrationsin the liquid. The SRB reduce SO4

2− to S2−, which mayprecipitate as secondary sulfides in deep zones of mudvolcanoes. This study aims at linking different geochem-ical factors with microbial activities to explain correla-

tion and interaction between liquids and solids of mudvolcanoes.

Materials and methods

Study area description

Taiwan is located at the arc-continent boundary betweenthe Philippine Sea Plate and the Eurasian Plate in the EastAsia.[32] The geologic structure of the area can be dividedinto 5 major tectonic units by N-S oriented major thrustfaults. From west to east, the units are Coastal Plain, West-ern Foothills, Hsuehshan Range, Central Range, and theCoastal Range (Fig. 1). There are at least 17 active mudvolcanoes in southwestern Taiwan, mainly located withinthe Western Foothills Zone.[18] Along the axis of the Kut-ingkeng structural anticline, which is more or less parallelto the direction of the Chishan (CS) Fault, one of the ma-jor active faults in southwestern Taiwan,[14] at least 5 mudvolcanoes are located.[17]

Sampling collection and chemical analysis of mud liquids

Liquid and mud samples were collected from mud vol-canoes of three geological structures in southern Tai-wan.[13,14,24,26] The samples were collected at the eruptionvent of mud volcano. However, Yenshuikeng (YSK) hastwo eruption vents (Yenshuikeng-1 and Yenshuikeng-2 areabout 20 meters apart),[25] where the liquid and mud sam-ples were collected. Wushanting (WST) and Sinyangnyuhu(SYNH) mud volcanoes are located along the Chis-han (CS) Fault. Kunshuiping (KSP) and Liyushan (LYS)mud volcanoes are located in the coastal plain, whereasHsiaokunshui (HKS) and Yenshuikeng (YSK) are in theKutingkeng anticline between the CS fault and coastalplain (Fig. 1).

Specific conductivity (mS/cm), total dissolved solid(TDS), pH, temperature (◦C), and alkalinity were deter-mined in the field. A portable conductivity meter was usedto measure specific conductivity, salinity and TDS (Sun-tex; WTW, LF320, Germany). pH and temperature weremeasured using redox meter (SP701, Suntex, Kaohsiung,Taiwan). Alkalinity was measured using Microprocessor-Controlled Photometer-PC MultiDirect (Lovibond,Germany).

Triplicate samples were collected in 500 mL steril-ized dark bottles and were stored at 4◦C. The acidi-fied samples (with HNO3, pH = 2) were used for majorcations (Ca2+, Mg2+, Na+, K+), As and other trace el-ements analyses, whereas the non-acidified samples wereused for anion analyses. The mixed mud/liquids sampleswere centrifuged at 10,000 rpm for 10 min and filteredthrough a 0.45 µm filter membrane in HydrogeologyLaboratory at National Cheng Kung University, Tainan,

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011

1220 Liu et al.

Fig. 1. Study area of mud volcanoes in southern Taiwan.

Taiwan. The major ion concentrations in mud liquids weredetermined by repeated analyses with an Ion Chromato-graph (Dionex, CA, USA) (precision: ±5%) for majorions (Ca2+, Mg2+, Na+, K+, Cl−, SO4

2−). The trace ele-ment concentrations of the liquids were measured by In-ductively Coupled Plasma Mass Spectrometer (ICP-MS)(Hewlett-Packard, Yamanashi-Ken, Japan). The overallanalytical errors were less than 5% for major components.The anaerobic samples were collected with addition ofN2 gas for bacterial isolation and identification. Specia-tion calculations for mud volcano liquids were performedby PHREEQC[33] using combined databases (minteq.datand llnl.dat).

Extraction of exchangeable and/or soluble ions from muds

The oven-dried (∼50◦C) samples were extracted with 0.1MHCl[34] for determination of trace elements. After 24 h con-tinuous shaking on a shaker platform, the samples were cen-trifuged at 10,000 rpm for 10 min and filtered through the0.45 µm filter membrane. The trace element concentrationsof these filtered samples were measured by ICP-MS usingexternal calibration with certified multi-element standardmethod (accuracy: ±5% and precision: ±2%). The concen-trations of exchangeable ions were expressed in terms ofmg/kg of oven dried mud. Total organic carbon (TOC)analysis was performed on High-temperature combustion(HTC) TOC analyzer (Analytic Jena, Micro N/C modelHT 1300, Germany).

Fluorescence of humic substance in mud liquid

Mud samples collected at mud volcano areas were cen-trifuged at 10,000 rpm for 10 min and the supernatantswere filtered through a 0.45 µm filter membrane. The fluo-rescence intensity of humic substances (HS) in mud volcanoliquids was detected by a fluorescence spectrophotometer(Model F-4500, Hitachi, Japan), and the concentration ofHS was measured by quinic acid standard curve with theexcitation and absorption wavelengths of 347 and 445 nm,respectively.[35]

Bacterial extraction and physiological characteristics ofbacterial isolate

Hi-Media culture media (Mumbai, India)[36] were preparedand each 10 mL culture medium was injected into Hungatetube and autoclaved. Mud samples were added to culturemedium under anaerobic conditions and after 2–3 weeks,1mL of culture medium was taken and put into anotherfresh medium. After repeating the procedure three times,the medium was cultured on agar plate under anaerobicconditions.[37] The bacteria appraisal included DNA extrac-tion from bacteria and Polymerase Chain Reaction (PCR)amplification, nucleotide sequencing, sequence alignment,phylogenetic analysis, and sulfate reduction rate determi-nation.

DNA isolation. The Genomic DNA extraction kit (Vio-gene, Taipei, Taiwan) was used after the bacteria were

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011

Biogeochemical interactions in mud volcanoes in southern Taiwan 1221

sufficiently incubated. A detailed description of the proce-dure for DNA isolation is provided in its instruction man-ual. The culture medium was centrifuged at 7,500 rpm for10 min and then the supernatant was removed. The pel-let was extracted with 200 µL lysozyme reaction solution(20 mM Tris-HCl, pH = 8.0; 2 mM EDTA; 20 mg/mLlysozyme). The Eppendorf tubes were incubated horizon-tally at 37◦C for 30 min. Then 20 µL proteinase K and200 µL EX buffer were added and vortexed for 20 s withfurther incubation at 60◦C for 30 min. Furthermore, 210 µLisopropanol was added to each Eppendorf tube and mixedthoroughly. All liquids were transferred to genomic DNAmini-columns with an Eppendorf pipette and centrifugedat 7,500 rpm for 10 min. After removal of the supernatant,the pellets were treated two times with 500 µL WS bufferand centrifuged at 8,000 rpm for 2 min. The genomic DNAmini column was dried at room temperature and then wasdissolved in 50 µL TE buffer (10 mM Tris-Cl, 1 mM EDTA,pH 8.0).

Polymerase chain reaction (PCR) amplification. DNAsequences were reproduced with forward and reverseprimers, and the 16S 27F (forward): 5′–AGAGTTTGATCCTGGCTC AG-3′ (genomic positions 8–27, Escherichiacoli numbering) and 16S 1492R (reverse): 5′–GGTTACCTTGTTA CGACTT-3′ (genomic positions 1488–1511,Escherichia coli numbering) were identified in this study.[38]

Each 50 µL PCR reaction contained: 5 ng template DNA,5 µL 10X reaction buffer, 5 µL MgCl2 (25 mM), 5 µLdNTP mix (8 mM), 10 pmole of each primer, and 2U ofTaq polymerase (Promega, Madison, WI, USA). The PCRreaction was carried out on a MJ Thermal Cycler (GeneticResearch Instruments, Braintree, Essex, UK) programmedto have the sequence of (1) a first cycle of denaturation at95◦C for 2 min, (2) 30 cycles of denaturation at 94◦C for45′s, (3) annealing at 56◦C for 75 s; (4) extension at 72◦Cfor 90 s, (5) 72◦C stabilization for 10 min, and (6) storage at4◦C. After completion of the program, the PCR productswere identified by gel electrophoresis.

Nucleotide sequencing, sequence alignment and phylogeneticanalysis. The universal forward and reverse primers weresynthesized by Mission Biotech Co. Ltd. (Taipei, Taiwan).The gene sequencing was made from the PCR productthrough a gene sequencer (ABI 3730 XL DNA Analyzer,Applied Biosystems, CA, USA). These sequence fragments(∼1500 bp) were preformed by BLAST in GeneBank ofNCBI to compare the difference for nucleotide sequences ofthe bacteria. 16 S rDNA were aligned with the CLUSTALX 1.81 program.[39] Neighbor-joining (NJ) analysis basedon Kimura’s two-parameter distance was performed us-ing the software MEGA 2.0.[40,41] Confidence of the cladereconstruction was tested by bootstrapping[42] with 1000replicates using unweighted characters.

Sulfate reduction experiments. After identification of thebacteria type, single-culture bacteria were cultured un-der anaerobic environments in sulfate-reducing bacteria(SRB) medium for nearly one month, and the ionic con-centrations (SO4

2−, SO3−, S, NO3

−, NO2−) in the SRB

medium were determined by the Ion Chromatographand Microprocessor-Controlled Photometer-PC MultiDi-rect. The precipitate of sulfate-reducing medium (Hi-medium) in anaerobic conditions was analyzed usingan environmental scanning electron microscope (FEIQuanta 400 F, Netherlands) and energy-dispersive X-ray spectrometer (Genesis 4000, American) (ESEM/EDX)analyzer.

Results and discussion

Chemical characteristics of the mud liquids

The chemical characteristics of the mud volcano liquids areshown in Table 1 and Figure 2. The EhS.H.E. values (range:−116 to 172 mV) of the mud volcano liquids shows mild tostrong reducing conditions. The HKS, SYNH, and WSTmud volcanoes (near the Chishan fault) belongs to the mildto strong reducing environment (−33 to −116 mV), whereasthe LYS, YSK, and KSP mud volcanoes located near thecoastal plain are under mild reducing environment (−11to 172 mV). The pH values of mud volcano liquids wereslightly alkaline (7.3–8.0).

The salinity values of mud volcano liquids were in therange of 1.1–25.5�. NaCl was the major liquid type inmost of mud volcano liquids (Na+: 1045 ± 2.64 to 10583± 3.60 mg/L with median of 4250 mg/L; Cl−: 328 ± 0.55to 25607 ± 3.46 mg/L with median of 5230 mg/L). Na+and Cl− represent the dominant ions in the mud volcanoliquids (except LYS mud volcano), suggesting a marinesource (Fig. 2). The origin of salinity in mud volcano liq-uids could arise from connate water as the mud volcanoesare located at the active collision zone between oceanic(Philippine Sea Plate) and continental (Eurasian Plate)plates.

The Ca2+/Cl− and Mg2+/Cl− ratios of the liquids rangefrom 0.0015–0.015 and 0.00019–0.037, respectively (Ta-ble 1). These values were lower than those of seawater (0.019and 0.39, respectively), even though the Ca2+ and Mg2+concentrations were still significant. There is no correlationbetween As and Fe in liquids (r = −0.12, p > 0.05), but lowEhS.H.E. values correspond to higher As concentrations inmud liquids. The SO4

2−/Cl− molar ratios (0.0008–0.033)of mud volcano liquids were also lower than that of sea-water (0.05), which may be partially attributed to the ac-tivities of sulfate-reducing bacteria in the mud volcanoliquids.

The HS concentrations in the mud volcano liquids werein the range between 1.84 × 10−4 and 2.46 × 10−3 µM(Table 2). There is a significant correlation between As and

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011

1222 Liu et al.

Table 1. Chemical analysis result for each mud volcano liquid.

Yenshuikeng-1 Yenshuikeng-2 Liyushan Sinyangnyuhu Wushanting Hsiaokunshui Kunshuiping

Ca2+(mg/L)(mean ± SD) 17 ± 0.72 15 ± 0.88 4 ± 0.96 9 ± 0.95 26 ± 0.99 60 ± 2.10 8 ± 1.00Mg2+ (mg/L)(mean ± SD) 186 ± 4.92 195 ± 2.02 3 ± 0.2 8 ± 0.1 18 ± 0.95 102 ± 0.85 139 ± 1.05Na+ (mg/L)(mean ± SD) 4916 ± 3.00 4250 ± 1.73 1045 ± 2.64 2906 ± 2.87 3886 ± 3.7 10583 ± 3.60 4328 ± 3.60K+ (mg/L)(mean ± SD) 45 ± 1.05 47 ± 0.12 12 ± 0.17 17 ± 1.07 46. ± 0.8 130 ± 0.45 47 ± 0.60Alkalinity (mg/L)(mean ± SD) 890 ± 4.00 820 ± 2.55 560 ± 2.64 1750 ± 3.6 900 ± 3.6 940 ± 4.58 1060 ± 4.35SO4

2- (mg/L)(mea ± SD) 19 ± 1.11 15 ± 1.17 10 ± 0.35 105 ± 1.00 48 ± 1.28 21 ± 1.22 8 ± 0.10Cl− (mg/L)(mean ± SD) 5393 ± 3.60 5231 ± 3.00 327 ± 0.55 4241 ± 3.16 6663 ± 2.72 25607 ± 3.46 5020 ± 2.65TDS (mg/L) 9850.0 11700.0 1950.0 7900.0 16665.0 50000.0 11450.0Conductivity (mS/cm) 28.2 43.8 3.02 4.12 7.20 24.00 15.22pH 7.60 8.2 7.34 7.7 7.90 8.04 7.20Temperature (◦C) 33.7 33.6 27.1 38.1 20.6 22.9 31.1EhS.H.E. 162 133 172 −116 −62 −33 −11Salinity(�) 18.3 25.2 1.1 4.6 3.9 11.9 10.2Reference [25] [25] This Study This Study [54] [54] [54]

Note: Mildly reducing: Eh S.H.E value = −100 to 200 mV; Strongly reducing: Eh S.H.E value<−100 mV.[55]

HS in the mud volcano liquids (r = 0.99, p < 0.05) (Fig. 3a),but no correlation between As and Fe (r = −0.05, p > 0.05)was observed (Fig. 3b). Dissolved organic carbon has beenestimated in mud liquids, which contain 141–530 mg/Lof organic carbon (Table 3). The presence of Ca2+ andMg2+ may facilitate ion bridge for complexation of As(V)

with humic substances in aquatic environments.[43] It hasbeen demonstrated that carboxyl and hydroxyl functionalgroups of humic acids (HA) and fulvic acids (FA) are ableto form very stable complexes with many metal cations orhydroxy metal cations in the order of Fe3+ >Al3+ >Pb2+>Ca2+ >Mn2+ >Mg2+.[44]

Fig. 2. Ionic status (Na+ and Cl−, K+, Mg2+, Ca2+, SO42−, HCO3

−) in the mud volcano liquid (n = 6).

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011

Biogeochemical interactions in mud volcanoes in southern Taiwan 1223

Table 2. Arsenic, Fe, and Humic substance (HS) concentrations in different mud volcanoes.

As Fe

Mud volcano Mud (mg/kg) Liquid (mg/L) Mud (mg/kg) Liquid (mg/L)As/Fe ratio

in mud EhS.H.E. (mV)

HSliquid (µM)

Hsiaokunshui 3.2 0.06 4.6 0.02 0.69 −33 2.93 × 10−3

Wushanting 2.1 0.02 4.6 0.01 0.45 −62 1.64 × 10−4

Yenshuikeng-1 0.59 0.02 951 0.14 6.2 × 10−4 162 4.13 × 10−4

Kunshuiping 0.55 0.06 1130 0.09 4.86 × 10−4 −11 2.96 × 10−3

Liyushan 0.65 29.8 1190 68.9 5.46 × 10−4 172 1.17 × 10−3

Sinyangnyuhu 2.2 0.02 5.2 0.05 0.42 −116 1.84 × 10−4

Geochemical characteristics of the muds

The trace element contents in the mud can be divided intotwo groups (Table 4). Higher amounts of Fe (951–1190mg/kg) and lower amounts of As (0.551–0.645 mg/kg)were found in YSK, KSP, and LYS samples (Fig. 1), buthigher amounts of As (2.1–3.2 mg/kg) and lower amountsof Fe (4.6–4.7 mg/kg) were found in HKS, WST, andSYNH samples (Fig. 1). High As in sediments is ob-served under strong reducing environments in mud vol-

Fig. 3. Correlations among As, HS, Fe in mud volcano liquids:(a) As vs. HS; (b) As vs. Fe.

canoes located in the Chishan (CS) Fault zone comparedto mud volcanoes located at the coastal plain. Total or-ganic carbon in muds was ranging between 12 and 22 g/Kg(Table 3).

Bacteria identification and culture in sulfate-reducingmedium

The isolated SRB include Gram positive Clostridium spp.and Gram-negative Shewanella spp. (Fig. 4). Anaerobicbacteria such as Shewanella spp. may play an importantrole in reducing geochemical species such as SO4

2−, caus-ing precipitation of sulfides from mud liquids that act as asink for As. The Clostridium spp. in a defined mixed culturewas stable and could produce around 1.5 mM H2S froman initial concentration of 20 mM sodium sulfate.[45] Theliquids in the studied mud volcanoes contain high concen-trations of H2S, which could be produced by Shewanellaputrefaciens.[46] In this process Shewanella putrefaciens uti-lizes Fe to produce considerable amounts of H2S.

A bacterial isolate (Shewanella spp.) was selected for cul-tivation in sulfate-reducing medium, and the ions S, SO3

−,SO4

2−, NO2−, NO3

− in the medium were determined. TheSO4

2− concentration in SRB medium was reduced from 394to 105 mg/L while SO3

− in SRB medium were reduced from4 mg/L to < 0.04 mg/L, and S concentrations increasedto 135 from 24 mg/L after 1 month incubation (Table 5and Fig. 5). This suggests that SRB activity affecting SO4

2-

concentrations might precipitate arsenic as sulfides, whichin turn, could reduce dissolved concentrations of As.

Table 3. Concentration of total organic carbon and dissolvedorganic carbon in mud volcano mud and liquids.

Concentration of totalorganic carbon Mud (g/Kg) Liquids (mg/L)

WST 15.73 254.90HKS 14.65 196.60SYNH 16.31 263.67GWP 15.16 233.67YSK 11.45 140.62LYS 22.06 530.03

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011

1224 Liu et al.

Table 4. Concentrations of trace elements in the mud volcano sediments in southwestern Taiwan.

Trace element contents in the mud sediments (mg/kg)

Mud volcano V Cr Mn Fe Ni Co Cu Zn As Se Rb Sr Mo Cd Ba Reference

Hsiaokunshui 2.7 1.2 1.4 4.6 2.1 1.6 1.7 7.7 3.2 0.1 0.3 ND ND ND 6.5 [54]

Wushanting 1.8 1.3 1.4 4.6 2.0 1.2 2.1 3.0 2.1 0.09 0.3 ND ND ND 20.6 [54]

Yenshuikeng-1 0.74 0.35 29.2 951 0.54 0.35 0.35 2.45 0.59 ND 0.09 6.72 0.005 0.002 6.24 This studyKunshuiping 1.33 0.69 26 1130 0.83 0.50 0.62 3.28 0.55 0.28 0.15 5.72 0.007 0.005 1.53 This studyLiyushan 0.75 0.39 28.6 1190 0.61 0.39 0.40 2.83 0.64 0.26 0.07 2.55 0.008 0.003 1.40 This studySinyangnyuhu 1.5 1.1 1.4 4.7 1.8 1.4 1.3 2.9 2.2 ND 0.2 ND ND ND 17.3 This study

Note: ND = not detected.

Fig. 4. Phylogenic relationships among the bacterial isolates in the liquids of different mud volcanoes.

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011

Biogeochemical interactions in mud volcanoes in southern Taiwan 1225

Table 5. The ion variation of bacteria culture by using liquidsulfate-reducing medium.

Time NO3− NO2

− SO42− SO3

− S(day) (mg/L) (mg/L) (mg/L) (mg/L) (mg/L)

0 7.8 1.88 393.5 4 <0.041 8.44 1.8 383.5 4.5 32 9.31 1.76 374.5 7.6 113 9.62 0.89 362.4 10 137 9.63 <0.1 220.3 20 208 9.64 <0.1 209.1 25 20

11 9.64 <0.1 125.8 103 1914 9.64 <0.1 117.3 110 1916 9.64 <0.1 110.3 133.3 2322 9.64 <0.1 105.3 134.5 24

Arsenic content in muds and liquids and geochemicalmodeling

Arsenic concentration in the Liyushan (LYS) mud vol-cano liquids and muds were found to be 29.8 mg/L and0.65 mg/kg, respectively (Table 2). This resulted in As dis-tribution coefficient of 0.02 L/kg. The other mud contentslisted in Table 4 were 0.55–3.2 mg/kg for As and 4.6–1190mg/kg for Fe. Concentrations of As and Fe in mud volcanoliquids (except LYS mud volcano) were 0.02–0.06 mg/L and0.01–0.14 mg/L, respectively (Table 2), with resulting Asdistribution coefficient of 9.16–110 L/kg. This implies thepresence of higher As in muds compared to liquids exceptLYS. The As concentrations in the liquids were all abovethe provisional WHO drinking water guideline value of10 µg/L.

Speciation calculations by PHREEQC revealed that mudvolcano liquids are undersaturated with respect to sulfate

Fig. 5. The ion variation of bacteria culture by using sulfate-reducing medium.

minerals such as gypsum and anhydrite (Table 6), but alsowith respect to sulfides minerals. However, redox status ofmud liquids based on the Eh values taken on surface is un-certain because samples were probably affected by mixingwith more oxidized liquids at shallow depth and contactwith atmosphere. Thus, SI values for sulfides minerals fordeep fluids may be different. All mud volcano liquids exceptLYS are supersaturated with respect to dolomite. Supersat-uration with respect to other carbonate minerals such ascalcite is also common.

In the LYS sample, supersaturation is reached withrespect to siderite. However, supersaturation does notnecessarily imply precipitation because precipitation canbe limited by slow reaction kinetics for minerals such assiderite. On the other hand, kinetics of sulfides mineralsprecipitation is relatively fast.[33,47] Values of calculated logPCO2 are very high, frequently >−2.0, presumably due tothe input of CO2 or decomposition of organic matter.

Mud volcano liquids are undersaturated with respectto all As-bearing minerals. On the other hand, super-saturation is reached for well-crystalline phases such asgoethite. Samples collected from SYNH, WST, and HKSclose to the Chishan Fault are undersaturated with re-spect to amorphous Fe(OH)3(a), suggesting that poorlycrystalline ferric phase may be dissolving, but the sam-ples in YSK, LYS, SYNH, WST, HKS, and KSP mudvolcanoes are supersaturated with respect to goethite(Table 6).

Spatial variations of major ions in mud liquids

The samples for spatial variations of major ions in mud liq-uids were collected from January to April (pre-monsoon).

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011

1226 Liu et al.

Table 6. Saturation indices for selected mineral phases in the mud volcano liquids calculated using PHREEQC.

Mud volcanoes

Mineral phases Yenshuikeng-1 Liyushan Sinyangnyuhu Wushanting Hsiaokunshui Kunshuiping

Sulfate mineralsAnhydrite −3.93 −4.18 −3.26 −3.27 −3.63 −4.59Gypsum −3.75 −3.97 −3.11 −3.04 −3.42 −4.41

Carbonate mineralsAragonite −0.19 −1.03 0.04 0.15 0.51 −0.85Calcite −0.05 −0.90 0.18 0.30 0.66 −0.72Dolomite 1.40 −1.60 0.78 0.77 1.93 0.27Siderite −0.39 2.32 −0.16 −1.09 −0.81 −0.57Log PCO2 −1.74 −1.67 −1.48 −2.10 −2.29 −1.26

Arsenic-bearing mineralsArsenolite −59.1 −39.9 −24.7 −45.9 −34.1 −26.4Realgar −76.7 −69.1 −26.8 −57.9 −43.3 −37.5Claudetite −58.9 −39.7 −24.4 −45.1 −33.8 −26.1

Iron oxides/hydroxidesGoethite (α-FeOOH) 7.39 9.60 2.95 4.97 4.10 3.25Fe(OH)3(a) 1.20 3.64 −3.39 −0.76 −1.73 2.86

The F-values of the cations (Na+, K+, Mg2+, Ca2+) andanions (Cl−, alkalinity, SO4

2−) concentrations in mudvolcano liquids showed high spatial variations (p < 0.05)(Table 7). This suggests varied geochemical behavior anddifferent source components for mud volcanoes. There aredifferent groups of mud volcano fields in Taiwan depend-ing on their chemical constituents.[26] The composition ofmud volcano liquids may consist of connate water mixedwith circulatory meteoric water which was affected bywater–rock interaction and biogeochemical processes.[24]

Sulfate concentrations were higher in Chishan (CS)Fault (48.8–105.7 mg/L) than in Kutingkeng anticline(15.0–21.2 mg/L) and coastal plain (8.0–11.0 mg/L). Thissupports the presence of higher sulfate in mildly to stronglyreduced fluids (Eh: −62 to −116 mV), whereas lowersulfate was observed in mildly reduced fluids (Eh: −33 to172 mV).

The concentrations of cations (Na+, K2+, Mg2+, Ca2+)and anions (Cl−) in mud volcano liquids did not showsignificant difference among three geological domains ex-cept for LYS. LYS mud volcano shows comparatively lowerionic constituents than the other mud volcanoes. Thehigh concentration of sulfate in brine makes it a dom-inant electron acceptor,[48] and sulfate-reducing bacteriamay reduce sulfate to sulfide. The Scheffe’s test shows thatconcentration of most ions in liquids are significantly dif-ferent (p < 0.05) in all mud volcanoes (Table 7). Onlyfew ions are not significantly different (e.g., Mg2+ con-centrations in the LYS and SYNH mud volcanoes, andalkalinity values in YSK1 and WST mud volcanoes). Allof mud volcano liquids have spatial variations in Na+and Cl−. These results suggest that the ions concentra-tions in mud volcano liquids can be affected by mudsources.

Conceptual model of arsenic mobilization in mudvolcanoes

The probable processes of arsenic mobilization in mud vol-canoes are shown in Figure 6. High correlation between As

Fig. 6. Hypothetical models of arsenic mobilization in mud vol-cano areas.

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011

Tab

le7.

The

spat

ialv

aria

tion

ofm

ajor

ions

inm

udliq

uids

atY

ensh

uike

ng(Y

SK),

Liy

usha

n(L

YS)

,Sin

yang

nyuh

u(S

YN

H),

Wus

hant

ing

(WST

),H

siao

kuns

hui(

HK

S),

and

Kun

shui

ping

(KSP

)m

udvo

lcan

oes.

Dif

fere

ntm

udvo

lcan

oes

Sam

plin

gar

eas

YS

K1

(1)

YS

K2

(2)

LYS

(3)

SY

NH

(4)

WS

T(5

)H

KS

(6)

KS

P(7

)

Na+

Mea

n(m

g/L

)49

1642

5010

4529

06.7

738

86.3

1058

343

28SD

3.0

1.73

2.64

2.87

3.7

3.6

3.6

F-v

alue

3078

233.

0∗∗∗

Sche

ffe’

ste

st(1

,2)∗∗

∗ ,(1,

3)∗∗

∗ ,(1,

4)∗∗

∗ ,(1,

5)∗∗

∗ ,(1,

6)∗∗

∗(1

,7)∗∗

∗ ,(2,

3)∗∗

∗ ,(2,

4)∗∗

∗ ,(2,

5)∗∗

∗ ,(2,

6)∗∗

∗ ,(2,

7)∗∗

∗ ,(3,

4)∗∗

∗ ,(3,

5)∗∗

∗ ,(3,

6)∗∗

∗ ,(3

,7)∗∗

∗ ,(4,

5)∗∗

∗ ,(4,

6)∗∗

∗ ,(4,

7)∗∗

∗ ,(5,

6)∗∗

∗ ,(5,

7)∗∗

∗ ,(6,

7)∗∗

∗

K+

Mea

n(m

g/L

)45

47.0

312

.217

.17

46.0

130

47.0

0SD

1.05

0.12

0.17

1.07

0.8

0.45

0.6

F-v

alue

8880

.9∗∗

∗

Sche

ffe’

ste

st(1

,3)∗∗

∗ ,(1,

4)∗∗

∗ ,(1,

7)∗∗

∗ ,(2,

3)∗∗

∗ ,(2,

4)∗∗

∗ ,(2,

6)∗∗

∗ ,(3,

4)∗∗

∗ ,(3,

5)∗∗

∗ ,(3,

6)∗∗

∗ ,(3,

7)∗∗

∗ ,(4,

5)∗∗

∗ ,(4,

6)∗∗

∗ ,(4,

7)∗∗

∗ ,(5,

6)∗∗

∗ ,(6,

7)∗∗

∗

Mg2+

Mea

n(m

g/L

)18

6.0

195

3.1

8.1

18.8

102.

713

9.0

SD4.

922.

020.

20.

10.

950.

851.

05F

-val

ue43

13.7

∗∗∗

Sche

ffe’

ste

st(1

,2)∗∗

∗ ,(1,

3)∗∗

∗ ,(1,

4)∗∗

∗ ,(1,

5)∗∗

∗ ,(1,

6)∗∗

∗ ,(1,

7)∗∗

∗ ,(2,

3)∗∗

∗ ,(2,

4)∗∗

∗ ,(2,

5)∗∗

∗ ,(2,

6)∗∗

∗ ,(2,

7)∗∗

∗ ,(3,

5)∗∗

∗ ,(3,

6)∗∗

∗ ,(3,

7)∗∗

∗ ,(4

,5)∗∗

∗ ,(4,

6)∗∗

∗ ,(4,

7)∗∗

∗ ,(5,

6)∗∗

∗ ,(5,

7)∗∗

∗ ,(6,

7)∗∗

∗

Ca2+

Mea

n(m

g/L

)17

.015

.04.

869.

4726

.560

.83

8.0

SD0.

720.

880.

960.

950.

992.

11.

0F

-val

ue80

0.9∗∗

∗

Sche

ffe’

ste

st(1

,3)∗∗

∗ ,(1,

4)∗∗

∗ ,(1,

5)∗∗

∗ ,(1,

6)∗∗

∗(1

,7)∗∗

∗ ,(2,

3)∗∗

∗ ,(2,

4)∗∗

∗ ,(2,

5)∗∗

∗ ,(2,

6)∗∗

∗ ,(2,

7)∗∗

∗ ,(3,

4)∗∗

∗ ,(3,

5)∗∗

∗ ,(3,

6)∗∗

∗ ,(4,

5)∗∗

∗ ,(4

,6)∗∗

∗ ,(5,

6)∗∗

∗ ,(5,

7)∗∗

∗ ,(6,

7)∗∗

∗

Cl−

Mea

n(m

g/L

)53

9352

3032

7.9

4241

.57

6663

.325

607.

050

20.0

SD3.

63.

00.

553.

162.

723.

462.

65F

-val

ue23

5709

04.5

∗∗∗

Sche

ffe’

ste

st(1

,2)∗∗

∗ ,(1,

3)∗∗

∗ ,(1,

4)∗∗

∗ ,(1,

5)∗∗

∗ ,(1,

6)∗∗

∗(1

,7)∗∗

∗ ,(2,

3)∗∗

∗ ,(2,

4)∗∗

∗ ,(2,

5)∗∗

∗ ,(2,

6)∗∗

∗ ,(2,

7)∗∗

∗ ,(3,

4)∗∗

∗ ,(3,

5)∗∗

∗ ,(3,

6)∗∗

∗ ,(3

,7)∗∗

∗ ,(4,

5)∗∗

∗ ,(4,

6)∗∗

∗ ,(4,

7)∗∗

∗ ,(5,

6)∗∗

∗ ,(5,

7)∗∗

∗ ,(6,

7)∗∗

∗

Alk

alin

ity

Mea

n(m

g/L

)89

0.0

819.

9756

0.0

1750

.090

0.0

940.

010

60.0

SD4.

02.

552.

643.

63.

64.

584.

35F

-val

ue31

035.

7∗∗∗

Sche

ffe’

ste

st(1

,2)∗∗

∗ ,(1,

3)∗∗

∗ ,(1,

4)∗∗

∗ ,(1,

6)∗∗

∗(1

,7)∗∗

∗ ,(2,

3)∗∗

∗ ,(2,

4)∗∗

∗ ,(2,

5)∗∗

∗ ,(2,

6)∗∗

∗ ,(2,

7)∗∗

∗ ,(3,

4)∗∗

∗ ,(3,

5)∗∗

∗ ,(3,

6)∗∗

∗ ,(3,

7)∗∗

∗ ,(4,

5)∗∗

∗ ,(4

,6)∗∗

∗ ,(4,

7)∗∗

∗ ,(5,

6)∗∗

∗ ,(5,

7)∗∗

∗ ,(6,

7)∗∗

∗

SO4

2−M

ean(

mg/

L)

19.0

15.0

11.0

105.

748

.821

.28.

0SD

1.11

1.17

0.35

1.0

1.28

1.22

0.1

F-v

alue

3331

.3∗∗

∗

Sche

ffe’

ste

st(1

,2)∗∗

∗ ,(1,

3)∗∗

∗ ,(1,

4)∗∗

∗ ,(1,

5)∗∗

∗ ,(1,

7)∗∗

∗ ,(2,

3)∗∗

∗ ,(2,

4)∗∗

∗ ,(2,

5)∗∗

∗ ,(2,

6)∗∗

∗ ,(2,

7)∗∗

∗ ,(3,

4)∗∗

∗ ,(3,

5)∗∗

∗ ,(3,

6)∗∗

∗ ,(4,

5)∗∗

∗ ,(4

,6)∗∗

∗ ,(4,

7)∗∗

∗ ,(5,

6)∗∗

∗ ,(5,

7)∗∗

∗ ,(6,

7)∗∗

∗

1227

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011

1228 Liu et al.

Fig. 7. ESEM-EDX analysis of As, Fe and S precipitates afterculturing in sulfate-reducing medium in this study: (a) black colorprecipitate; (b) ESEM image; (c) EDX result (the sample wascoated with Au) (color figure available online).

and HS in the presence of sulfate-reducing bacteria in mudfluid suggests that HS be redox-active and can also changethe redox state of arsenic during reaction.[49] It is clear thatnatural organic matter (NOM) is abundant in the subsur-face environment particularly in mud volcano areas. Some-times they influence the mobility of elements like arsenic.[29]

Microbial degradation of organic matter can enhance thereductive dissolution of As-coated iron oxy(hydr)oxides.[50]

Dissolved organic matter (DOM) also can compete withAs for binding onto different mineral surfaces.[51,52]

The SRB are active in reducing environments, making theSO4

2−/Cl− molar ratios (0.0008–0.033) of mud volcano liq-uids lower than that of seawater (0.05). In-vitro experimentresults (Fig. 5) are consistent with field data because SO4

2−was reduced to S2−. Sulfate-reducing bacteria can reduceSO4

2− to S2−, which may precipitate as secondary sulfidessuch as mackinawite (FeS) in deep zone of mud volcanoes,disturbing correlation between arsenic and iron in mud vol-canoes liquids.[41,42] Sulfide (H2S or HS−) in liquid phaseat considerable concentration acts as a strong reductant inreduced environments.[53] SRB can reduce SO4

2− to S, andinduce the precipitation of sulfides.

The EDX results of the As, Fe and S precipitates formedduring bacterial activity in sulfate-reducing medium (Hi-medium) are shown in Figure 7. Secondary sulfide mineralscan act as a sink for arsenic in mud volcano fluids. Fur-

thermore, precipitated sulfide minerals such as FeS may becoating Fe(III) phases, limiting their further dissolution[47]

and they may also incorporate some released arsenic. Anapparent discrepancy between EhS.H.E. values and assumedsulfate reduction may be caused by redox disequilibriumand mixing with oxidized water in shallow zone of mudvolcanoes.

Conclusions

This study deals with geochemical interactions in sevenmud volcanoes of SW Taiwan with special reference toAs, Fe, S and humic substances (HS). The Na+ and Cl−concentrations in the mud volcano liquids indicate a paleo-marine source modified by mixing with meteoric waters.Mild to strong reducing conditions support occurrences ofbacterial reduction processes especially by SRB leading toprecipitation of sulfides. Geochemical modeling showingprecipitated crystalline Fe(III) phase supports higher Feand As in muds and their association. The experimentalresults showed that As, Fe and S precipitates were formedafter culturing in sulfate-reducing medium and SO4

2− wasreduced to S. The behavior of As, SO4

2−, and Fe in mudvolcano liquids seems to be affected by the biogeochemicalinteractions. The reducing bacteria such as Shewanella spp.are found to be responsible for reducing SO4

2−, causingprecipitation of sulfides from mud liquids and act as a sinkfor As. This study suggests that biogeochemical processeswith participation of bacterial consortium, especially SRB,may affect arsenic behavior in mud volcanoes of southernTaiwan.

Acknowledgment

This work was supported by the National Science Councilof Taiwan (Grant number NSC 98-2627-M-006-004). Theauthors are grateful to the support and assistance of Mr.Jiann-Hong Liu during field surveys.

References

[1] Dimitrov, L.I. Mud volcanoes—the most important pathway fordegassing deeply buried sediments. Earth Sci Rev. 2002, 59, 49–76.

[2] Kholodov, V.N. Mud volcanoes: Distribution regularities and gen-esis (Communication 2. Geological–Geochemical peculiarities andformation model). Lithol. Miner. Resour. 2002, 37, 293–310.

[3] Milkov, A.V. Worldwide distribution of submarine mud volcanoesand associated gas hydrates. Mar. Geol. 2000, 167, 29–42.

[4] Yassir, N.A. Mud volcanoes: Evidence of neotectonic activity. Mem.Geol. Soc. China 1987, 9, 513–524.

[5] Kohl, B.; Roberts, H.H. Fossil foraminifera from four active mudvolcanoes in the Gulf of Mexico. Geo-Mar. Lett. 1994, 14, 126–134.

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011

Biogeochemical interactions in mud volcanoes in southern Taiwan 1229

[6] Vogt, P.R.; Gardner, J.; Crane, K. The Norwegian-Barents-Svalbard(NBS) continental margin: Introducing a natural laboratory of masswasting, hydrates and ascent of sediment pore water and methane.Geo-Mar. Lett. 1999, 19, 2–21.

[7] Kopf, A.J. Significance of mud volcanism. Rev. Geophys. 2002, 40,1005, doi:10.1029/2000RG000093.

[8] Huguen, C.; Mascle, J.; Chaumillon, E.; Kopf, A.J.; Woodside, J.;Zitter, T. Structural setting and tectonic control of mud volcanoesfrom the Central Mediterranean Ridge (Eastern Mediterranean).Mar. Geol. 2004, 209, 245–263.

[9] Pimenov, N.V.; Savvichev, A.S.; Rusanov, I.I.; Lein, A.Y.; Ivanov,M.V. Microbiological processes of the carbon and sulfur cycles atcold methane seeps of the North Atlantic. Microbiology 2000, 69,709–720.

[10] Fleischer, P.; Orsi, T.H.; Richardson, M.D.; Anderson, A.L. Distri-bution of free gas in marine sediments: a global overview. Geo-Mar.Lett. 2001, 21, 103–122.

[11] Milkov, A.V.; Sassen, R.; Apanasovich, T.V.; Dadashev, F.G. Globalgas flux from mud volcanoes: A significant source of fossil methanein the atmosphere and the ocean. Geophys. Res. Lett. 2003, 30,1037.

[12] Milkov, A.V.; Vogt, P.R.; Crane, K.; Lein, A.Y.; Sassen, R.;Cherkashev, G.A. Geological, geochemical, and microbial pro-cesses at the hydrate-bearing Haakon Mosby mud volcano: a review.Chem. Geol. 2004, 205, 347–366.

[13] Yeh, G.H.; Yang, T.F.; Chen, J.C.; Chen, Y.G.; Song, S.R. Fluid geo-chemistry of mud volcanoes in Taiwan. In: Martinelli, G.; Panahi,B.; Eds; NATO Science Series: IV: Earth and Environmental Sci-ences, 2004, 51, 227–237.

[14] You, C.F.; Gieskes, J.M.; Lee, T.; Yui, T.-F.; Chen, H.-W. Geochem-istry of mud volcano liquids in the Taiwan accretionary prism. Appl.Geochem. 2004, 19, 695–707.

[15] Liu, C.S.; Huang, I.L.; Teng, L.S. Structural features off southwest-ern Taiwan. Mar. Geol. 1997, 137, 305–319.

[16] Chow, J.; Lee, J.S.; Liu, C.S.; Lee, B.D.; Watkins, J.S. A submarinecanyon as the cause of a mud volcano: Liuchieuyu Island in Taiwan.Mar. Geol. 2001, 176, 55–63.

[17] Shih, T.T. A survey of the active mud volcanoes in Taiwan and astudy of their types and the character of the mud. Petrol. Geol.Taiwan 1967, 5, 259–311.

[18] Wang, S.; Shu, M.; Yang, C. Morphological study of mud volcanoeson land in Taiwan. J. National Taiwan Museum 1988, 31, 31–49.

[19] Cita, M.B.; Ryan, W.B.F.; Paggi, L. Prometheus mud breccia. Anexample of shale diapirism in the Western Mediterrranean Ridge.Ann. Geol. Des Pays Hell. 1981, 30, 543–569.

[20] Barber, A.J.; Tjokrosapoetro, S.; Charlton, T.R. Mud volcanoes,shale diapirs, wrench fault and melanges in accretionary com-plexes, eastern Indonesia. Am. Assoc. Petrol. Geol. Bull. 1986, 70,1729–1741.

[21] Hovland, M.; Hill, A.; Stokes, D. The structure and geomorphologyof the Dashgil mud volcano, Azerbaijan. Geomorphology 1997, 21,1–15.

[22] Yang, T.-F.; Yeh, G.-H.; Fu, C.-C.; Wang, C.-C.; Lan, T.-F.; Lee,H.-F.; Chen, C.-H.; Walia, V.; Sung, Q.-C. Composition and exha-lation flux of gases from mud volcanoes in Taiwan. Environ. Geol.2004, 46, 1003–1011.

[23] Yakimov, M.M.; Giuliano, L.; Crisafi, E.; Chernikova, T.N.; Tim-mis, K.N.; Golyshin, P.N. Microbial community of a saline mudvolcano at San Biagio-Belpasso, Mt. Etna (Italy). Environ. Micro-biol. 2002, 4, 249–256.

[24] Liu, C.-C.; Jean, J.-S.; Nath, B.; Lee, M.-K.; Hor, L.-I.; Lin,K.-H.; Maity, J.P. Geochemical characterization of the fluids andmud from two southern Taiwan mud volcanoes: Implications forwater-sediment interaction and groundwater As enrichment. Appl.Geochem. 2009, 24, 1793–1802.

[25] Gieskes, J.M.; You, C.-F.; Lee, T.; Yui, T.F.; Chen, H.W. Hydrogeo-chemistry of mud volcanoes in Taiwan. Acta Geol. Taiwan 1992,30, 79–88.

[26] Nath, B.; Jean, J.-S.; Lee, M.-K.; Yang, H.-J.; Liu, C.-C. Geochem-istry of high arsenic groundwater in Chia-Nan plain, SouthwesternTaiwan: possible sources and reactive transport of arsenic. J. Con-tam. Hydrol. 2008, 99, 85–96.

[27] Ko, I.; Kim, J.Y.; Kim, K.W. Arsenic speciation and sorption ki-netics in the As–hematite–humic acid system. Coll. Surf. A: Physic-ochem. Eng. Aspects 2004, 234, 43–50.

[28] Davis, C.C.; Knocke, W.R.; Edwards, M. Implications of aqueoussilica sorption to iron hydroxide: Mobilization of iron colloids andinterference with sorption of arsenate and humic substances. Envi-ron. Sci. Technol. 2001, 35, 3158–3162.

[29] Buschmann, J.; Kappeler, A.; Lindauer, U.; Kistler, D.; Berg, M.;Sigg, L. Arsenite and arsenate binding to dissolved humic acids:Influence of pH, type of humic acid, and aluminum. Environ. Sci.Technol. 2006, 40, 6015–6020.

[30] Ona-Nguema, G.; Morin, G.; Wang, Y.; Menguy, N.; Juillot, F.;Olivi, L.; Aquilanti, G.; Abdelmoula, M.; Ruby, C.; Bargar, J.R.;Guyot, F.; Calas, G.; Brown, Jr, G.E. Arsenite sequestration atthe surface of nano-Fe(OH)2, ferrous-carbonate hydroxide, andgreen-rust after bioreduction of arsenic-sorbed lepidocrocite byShewanella putrefaciens. Geochim. Cosmochim. Acta 2009, 73,1359–1381.

[31] Stolz, J.F.; Perera, E.; Kilonzo, B.; Crable, B.; Fisher, E.;Ranganathan, M.; Wormer, L.; Basu, P. Biotransformation of 3-Nitro-4-hydroxybenzene Arsonic Acid (Roxarsone) and Release ofInorganic Arsenic by Clostridium Species. Environ. Sci. Technol.2007, 41, 818–823.

[32] Li, Y.H. Denudation of Taiwan island since Pliocene epoch. Geol-ogy 1976, 4, 105–106.

[33] Parkhurst, D.L.; Appelo, C.A.J. User’s guide to PHREEQC: Acomputer program for speciation, reaction-path, 1-D transport, andinverse geochemical calculations, US Geol. Surv. Water Resour.Invest. 1999, Rep. 99-4259.

[34] Klute, A. Methods of Soil Analysis, Part 1: Physical and Mineralogi-cal Methods. American Society of Agronomy, Madison, Wisconsin,USA, 1986; 23–40.

[35] EPA(R.O.C.), Standard Method of Water Analysis—Humicsubstance intensity in nature water by using fluorescencespectrophotometer-I. 1994, NIEA W940.50T.

[36] George, J.; Purushothaman, C.S.; Shouche, Y.S. Isolation and char-acterization of sulphate-reducing bacteria Desulfovibrio vulgarisfrom Vajreshwari thermal springs in Maharashtra, India. WorldJ. Micro. Biotech. 2008, 24, 681–685.

[37] Dubey, R.C.; Maheshwari, D.K. Practical microbiology. 1st ed.(reprint). S. Chand and Company Ltd., New Delhi, 2005; 10–25.

[38] Heleen, P.G.; Henricus, T.S.B.; Alfons, J.M.S.; Theo, A.H. Isolationof thermophilic Desulfotomaculum strains with methanol and sulfitefrom solfataric mud pools, and characterization of Desulfotomac-ulum solfataricum sp. nov. Int. J. System. Evolut. Microbiol. 2003,53, 1223–1229.

[39] Thompson, J.D.; Gibson, T.J.; Plewniak, F.; Jeanmougin, F.;Higgins, D.G. The Clustal X windows interface: flexible strategiesfor multiple sequence alignment aided by quality analysis tools.Nucl. Acid Res. 1997, 24, 4876–4882.

[40] Kimura, M. A simple method for estimating evolutionary rates ofbase substitutions through comparative studies of nucleotide se-quences. J. Mol. Evol. 1980, 16, 111–120.

[41] Kumar, S.; Tamura, K.; Jakobsen, I.B.; Nei, M. 2001 MEGA2:molecular evolutionary genetics analysis software. Bioinformatics2001, 17, 1244–1245.

[42] Felsenstein, J. Confidence limits on phylogenies: an approach usingthe bootstrap. Evolution 1985, 39, 783–791.

[43] Lin, H.T.; Wang, M.C.; Li, G.C. Complexation of arsenate withhumic substance in water extract of compost. Chemosphere 2004,56, 1105–1112.

[44] Gu, B.; Schmitt, J.; Chen, Z.; Liang, L.; McCarthy, J.F. Adsorptionand desorption of natural organic matter on iron oxide: mechanismsand models. Environ. Sci. Technol. 1994, 28, 38–46.

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011

1230 Liu et al.

[45] Ahmed, S.; Alexander, S. Anaerobic and aerobic degradation ofcyanophycin by the denitrifying bacterium Pseudomonas alcaligenesstrain DIP1 and role of three other coisolates in a mixed bacterialconsortium. Appl. Environ. Microbiol. 2008, 74, 3434–3443.

[46] Bonneville, S.; Behrends, T.; Van Cappellen, P.; Hyacinthe, C.;Roling, W.F.M. Reduction of Fe(III) colloids by Shewanella pu-trefaciens: A kinetic model. Geochim. Cosmochim. Acta 2006, 70,5842–5854.

[47] Vencelides, Z.; Sracek, O.; Prommer, H. Modelling of iron cyclingand its impact on the electron balance at a petroleum hydrocarboncontaminated site in Hnevice, Czech Republic. J. Contam. Hydrol.2007, 89, 270–294.

[48] Henrichs, S.M.; Reeburgh, W.S. Anaerobic mineralization of sedi-ment organic matter: A new estimate of the role of anaerobic pro-cesses in the oceanic carbon economy. Geomicrobiol. J. 1987, 5,191–237.

[49] Jie, J.; Iris, B.; Andre, P.; Andreas, K. Arsenic redox changes bymicrobially and chemically formed semiquinone radicals and hy-droquinones in a humic substance model quinine. Environ. Sci.Technol. 2009, 43, 3639–3645.

[50] McArthur, J.M.; Ravenscroft, P.; Safiulla, S.; Thirlwall, M.F. Ar-senic in groundwater: Testing pollution mechanisms for sedimen-tary aquifers in Bangladesh. Water Resour. Res. 2001, 37, 109–117.

[51] Redman, A.D.; Macalady, D.L.; Ahmann, D. Natural organic mat-ter affects arsenic speciation and sorption onto hematite. Environ.Sci. Technol. 2002, 36, 2889–2896.

[52] Bauer, M.; Blodau, C. Mobilization of arsenic by dissolved organicmatter from iron oxides, soils and sediments. Sci. Total Environ.2006, 354, 179–190.

[53] Rochette, E.A.; Bostick, B.C.; Li, G.; Fendorf, S. Kinetics of arsen-ate reduction by dissolved sulfide. Environ. Sci. Technol. 2000, 34,4714–4720.

[54] Liu, C.-C.; Maity, J.P.; Jean, J.-S.; Lee, M.-K.; Li, Z.; Nath, B.; Lin,K.-H. Chemical characteristics of mud volcano fluids in southwest-ern Taiwan and their linkage to elevated arsenic concentration ingroundwater. Environ. Earth Sci. 2011. (under revision)

[55] Hu, Q., Smith, D.K. Field-Scale Migration of 99Tc and 129I at theNevada Test Site. 2004 Materials Research Society Spring MeetingSan Francisco, CA, USA, April 12–16, 2004.

Dow

nloa

ded

by [

Nat

iona

l Che

ng K

ung

Uni

vers

ity]

at 2

2:44

31

Aug

ust 2

011