Ecological Engineering 37 (2011) 989993

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Ecological Engineering

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Benthic wefrom a

Hieu VanSchool of Envir , Gwa

a r t i c l

Article history:Received 18 AReceived in reAccepted 23 JaAvailable onlin

Keywords:Benthic uxMercuryMonomethylmElemental merWetlandOrganic matte

xic cos from. Eachsedisewauppend ach sr coneasin

1. Introduction

Riverinespecies and(Trebitz et ametals canprocesses iphytes, ads2010; Sasmto be domi1996; Walkfactors affetant for preheavy meta

Monomethat bioaccIn stagnantlands, mostanoxic sediular, sulfateHg(II) into Mmal compo1994). Give

CorresponE-mail add

populations, wetland sediments can be major sources of MMHgfor downstream river water. Indeed, the proportion of wetland

0925-8574/$ doi:10.1016/j.and coastal wetlands are rich in oral and faunalprovide nourishing habitats for aquatic ecosystems

l., 2009). In wetland habitats, pollutants such as heavybe removed from surface waters by several differentncluding particle sedimentation, ltration by macro-orption, and biological assimilation (El-Sheikh et al.,az et al., 2008).Of theseprocesses, sedimentation seemsnant with respect to metal removal (Lung and Light,er and Hurl, 2002). Therefore, understanding the keycting metal transfer from sediment to water is impor-diction of the remobilization and bioaccumulation ofls deposited in wetland sediments.thylmercury (MMHg) is a toxic form of mercury (Hg)

umulates and biomagnies within aquatic food webs.freshwater environments, such as at banks or wet-MMHg is produced by biotic processes occurring in

ments (Gilmour et al., 1992; King et al., 2002). In partic--reducing bacteria are capable of converting inorganicMHg using methyltransferase enzymes that are nor-

nents of the acetate metabolic pathway (Choi et al.,n the high biological activities of wetland microbial

ding author. Tel.: +82 62 715 2438; fax: +82 62 715 2434.ress: shan@gist.ac.kr (S. Han).

area within a drainage basin has been shown to correlate withMMHg levels in downstream lakes and streams (Driscoll et al.,1994; Guentzel, 2009; Warner et al., 2005).

At the sediment surface, divalent Hg is reduced to elementalmercury (Hg0), which is then released back to the water columnor adsorbed onto sediment particles. Although Hg0 may play a keyrole in the exchange of Hg at the sediment-water interface, themechanismresponsible for the reductionof divalentHg in freshwa-ter sediments is largely unknown (Bouffard and Amyot, 2009; Shiet al., 2005). Possible reduction processes include Hg reduction byUV near the sediment surface (Horvth and Vogler, 1998; Lalondeet al., 2001), bacterial Hg detoxication using the mer operon(Andra and Edmar, 2003), and Hg reduction by organic matter,magnetite, and dissimilatory metal-reducing bacteria (Allard andArsenie, 1991; Wiatrowski et al., 2006, 2009). Recently, Bouffardand Amyot (2009) reported that Hg0 constitutes a signicant por-tion (728%) of the total Hg (THg) in lake sediments, and that Hg0

adsorption to sediment is a fast reaction associated with the solidorganic matter content of the sediment. Nevertheless, the domi-nant Hg reduction processes in wetland sediments and the role ofhypoxic conditions of the water column have not yet been fullyestablished.

In the present study, we examined the sediment proles of THg,Hg0, andMMHg in cores collected fromwetland sediments close toa sewage outfall in the Damyang Riverine Wetland. Our aim was to

see front matter 2011 Elsevier B.V. All rights reserved.ecoleng.2011.01.011munication

transfer and speciation of mercury insewage outfall

Duong, Seunghee Han

onmental Science and Engineering, Gwangju Institute of Science and Technology (GIST)

e i n f o

ugust 2010vised form 6 January 2011nuary 2011e 4 March 2011

ercurycury

r

a b s t r a c t

In order to evaluate the role of hypotion of Hg, we analyzed sediment corethe Damyang Riverine Wetland, Korea(MMHg), and elemental Hg (Hg0) fromditions of the overlying water near thethe lowest production of MMHg, in theestimated at 1302109ngm2 day1 afrom sediment to overlying water at ement, but was highest in hypoxic watein wetland water is important for decr/ locate /eco leng

tland sediments downstream

ngju 500-712, Republic of Korea

nditions of overlying water in the benthic ux and specia-hypoxic or oxic sites downstream from a sewage outfall incore was analyzed for total Hg (THg), monomethylmercury

ment, and for THg and MMHg from pore water. Hypoxic con-ge outfall were associated with a peak production of Hg0, butr 2 cm sediments. The benthic uxes of THg and MMHg were

12 to 260ngm2 day1, respectively. The order of MMHg uxite did not follow the order of MMHg concentration in sedi-ditions. The results suggest that maintaining oxic conditionsg the transfer of MMHg from sediment into overlying water.

2011 Elsevier B.V. All rights reserved.

990 H.V. Duong, S. Han / Ecological Engineering 37 (2011) 989993

elucidate the effects of hypoxic conditions of the water column onthebenthic speciationofHg. Inaddition, THgandMMHgconcentra-tions in the overlying and the surface pore waters were measuredto determinbenthic tran

2. Materia

2.1. Study a

The Damis located inwhich belolargest rive(NWC, 2010bed slope osedimentatThe geomorlands, oodsite was Na1265715

that has a tSedimen

2009. Becausampling seated with aat a locationsites (A, B, Csewage trea6200m3 daupstream olocated closstream. Theand C, weresites was aincluding c(Acorus), gring duringperennial gtance fromplant populdant benthsites.

2.2. Sedime

Sedimenacid-cleaneThe cores winto segmement surfacwater was ethe cores hof each lteanalysis of dstored freezwas approxsegments: 0

Surfaceand at a sewtocol (Gill adepth of apcleaned Te(0.45m p

were double-bagged and transported to the laboratory in a cooler.In the laboratory, the surface water samples were acidied to 0.4%(v/v) HCl solution and stored at 4 C until analysis.

alys

theachlutioHCl

is, apvernHN

tecte; ChandM-Cs cerRM

matrimematrrcennt w

rcuryds denomeg) wamL omL owasase unt eeousatogrCVAE46spiklicat= 7) a

alys

ter q, andusingmentnt saightrelatestabnlesrd de

ults

gani

al Hggg1

(Tabe ba.4nge the effects of hypoxia of the overlying water on thesfer of THg and MMHg.

ls and methods

rea

yang Riverine Wetland (DRW), total area of 0.98km2,the upper stream area of the Yeongsan River in Korea,

ngs to Damyang-gun in Chollanam-do. The DRW is ther marsh in Korea inhabited by protected wild animals). Compared to other major rivers in Korea, the averagef the Yeongsan River is very gentle (0.0011); therefore,ion is active even in upstreamareas, including theDRW.phic landscape of this area consists of streambed wet-plains, and piedmont hills (NWC, 2010). The samplingmsan Wetland (from 351745 to 351856 and fromto 1265809), one of six sub-wetlands in the DRW,

otal area of 0.26km2 (NWC, 2010).t and overlying water were sampled on November 11,se Korea is in the Asian Monsoon Climate region, theason was a dry season (late autumn to spring) associ-relatively low ow rate of 179,000m3 day1, measuredlose to the sampling sites (KWRC, 2010). The sampling, B1, and C1)were located downstreamof the Damyangtment plant (STP), which has a sewage outow rate ofy1. The control site was located approximately 1kmf the STP. Among the ve sampling sites, Site A wasest to the STP (

H.V. Duong, S. Han / Ecological Engineering 37 (2011) 989993 991

Table 1Concentrations of THg, loss on ignition (LOI), MMHg, %MMHg/THg, Hg0, and %Hg0/THg in sediment cores from the Damyang Riverine Wetlands. Temperature of the overlyingwater was 17 C.

D MMHg/THg (%) Hg0 (ngg1) Hg0/THg (%)

A

0 0.028 985 682 0.015 269 864 0.044 80.8 676 0.11 201 618 0.032 32.4 19

B

0 0.17 28.8 262 0.43 15.4 114 0.024 591 866 0.054 62.3 348 0.12 7.80 6.9

C

0 0.84 2.90 2.92 0.52 0.700 0.834 0.19 38.0 276 0.040 34.1 578 0.033 11.9 36

B1

0 0.32 45.5 312 0.45 3.30 2.34 0.56 3.30 4.96 0.15 94.5 528 0.046 55.4 48

C10 1.1 26.4 402 0.45 3.70 9.3

inKorea (5sured nearof sedimenties (5008sediment csuggestingthe discharg1999.

In generwith depthments, andof the sediSite B1 alsoLOI was higagreementsand, B andtion). Organdistributionorganic ma2009). Indelinear relatiA showed hfrom the %Ldepths, no s(r2 =0.11, p

3.2. Enhancconditions

Due to thA, overlyingDO concent240M (B12cm of sedhighest MMthest downwas detectetion. Accordnot the mament, whicthe sedime

Hg proles were typical of wetland sediments: higher atface and subsurface, and decreasing with depth (King et al.,

he upg/TH

th thA (Taypox

%Mthylaal., 2tratisedimsitu

ur ethen

5epth (cm) THg (ngg1) LOI (%) MMHg (pgg1)

2 1450 2.0 4074 314 0.72 46.96 123 1.1 53.98 331 1.1 35210 174 0.74 56.32 111 2.8 1864 138 1.7 5946 684 1.4 1638 180 1.3 96.610 114 1.7 1332 98.9 2.2 8284 83.7 2.2 4326 139 1.3 2638 59.2 0.96 23.810 33.2 0.27 11.12 144 4.6 4544 139 3.5 6236 65.2 2.0 3648 182 1.4 27410 115 0.89 53.02 65.9 1.0 7574 39.9 0.80 181

0ngg1, Park et al., 2009). The THg concentrationmea-the STP discharge point (Site A) was similar to thatts contaminated with Hg from anthropogenic activi-000ngg1; Biester et al., 2002; Gray et al., 2006). Theoncentrations of THg at Site A showed a surface peak,higher Hg deposition in recent years, which agrees withe record of the STP: the STP began releasing sewage in

al, the LOI concentrations showed a decreasing trend(Table 1), which is typical for LOI in freshwater sedi-indicates active carbon mineralization near the surfacement (Bouffard and Amyot, 2009). While the LOI for

decreased with depth, the surface concentration ofher at Site B1 than at Sites A, B, C, or C1 which is inwith the sediment composition at each site (A and C1:C: silty sand, and B1: sandy silt; Shepards classica-ic matter content is known to inuence the surfaceof sediment THg due to a strong association between

tter and THg (Warner et al., 2005; Delongchamp et al.,ed, the surface distribution of THg showed a positive

the MMthe sur2001).

In t(%MMHSTP,wiat Sitewith hthe lowHg meHan etconcengladesfrom in(Gilmonoted wonship with %LOI for Sites B, C, B1 and C1 (Fig. 1). Siteigher THg concentration (1450ngg1) than expectedOI (2.0%) due to the treated sewage discharge. For otherignicant correlationwas found between THg and %LOI=0.14).

ed %MMHg/THg in sediment under oxic water

e treated sewage discharges from the STP close to Sitewaters at this site were hypoxic on the sampling date:rations were 51M (Site A), 250M (B), 260M (C),), and 240M (C1). Monomethylmercury in the upperiment ranged from 186 to 828pgg1 (Table 1). TheHg content was detected at the Site C, which was fur-stream from the STP, and the lowest MMHg contentd at Site B, which is in contrast to the THg distribu-ing to this order, MMHg discharged from the STP is

jor source of the MMHg deposited in the surface sedi-h indicates the importance of in situ production withinnt (Gilmour et al., 1998; King et al., 2002). Vertically,

0

%L

OI

0

1

2

3

4

Fig. 1. RelatioSites A, B, C, B1 2.2) includesper 2 cm of sediment, the proportion of MMHg in THgg) showed an increasing trend with distance from the

ehighestmeasurements at SiteC andC1, and the lowestble 1). The lowest %MMHg/THg at Site A was associatedic conditions of the overlying water A. It is possible thatMHg/THg at Site A is caused by sulde inhibition oftion potential (Benoit et al., 2001; Drott et al., 2007;007, 2008). An inverse correlation between the suldeon andHgmethylation rates has been observed in Ever-ents (FL, USA), which indicated that sulde producedsulfate reduction inhibited microbial Hg methylational., 1998). Indeed, a strong hydrogen sulde odor waswe sliced core A.THg (ng g -1)

20018016014012010080604020

0-2cm

2-4cm

4-6cm

6-8cm

8-10cm

r2=0.99

p

992 H.V. Duong, S. Han / Ecological Engineering 37 (2011) 989993

0

Hg

0(n

g g

-1)

0

100

200

300

400

500

600

700

A

B

Fig. 2. LinearC, B1, and C1 (

3.3. Enhancconditions

ElementsignicantlThe range(2.9045.5niments (66concentratiTexas (GrayHg0 and THTHg loadingcontent in w

The sedtions: meanSites C andpristine lakless similarThe highestciated withA. Recentlyof Hg(II) tomixed valetion of Hg(Ito the oxidincreased wresults, togHg0 producassociated w

3.4. Increasconditions

In the apore water

F = Dw2

where F (n(ng L1) atity ( = (Mwwater loss tdensity, and

enthic

ies wat ca

on cossa,r MMna

m2

n 79B1 are l41,0thangmhic with(42007

ghesty ofe geal., 1orgate; ttedn be

rlyinTHg (ng g-1

)

1000800600400200

B1

C

C1

r2=0.95

p

H.V. Duong, S. Han / Ecological Engineering 37 (2011) 989993 993

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Benthic transfer and speciation of mercury in wetland sediments downstream from a sewage outfallIntroductionMaterials and methodsStudy areaSediment core and surface-water samplingAnalysis of THg and MMHgAnalysis of ancillary parameters

Results and discussionOrganic matter content controls the sediment distribution of THgEnhanced %MMHg/THg in sediment under oxic water conditionsEnhanced %Hg0/THg in sediment under hypoxic water conditionsIncreased diffusion flux of MMHg under hypoxic water conditions

AcknowledgmentsReferences