Environ Monit Assess (2010) 167:473–491DOI 10.1007/s10661-009-1065-8

Abundances, distribution, and sources of trace metalsin Nakaumi–Honjo coastal lagoon sediments, Japan

Faruque Ahmed · M. Hawa Bibi · Koji Seto ·Hiroaki Ishiga · Takehiko Fukushima ·Barry P. Roser

Received: 15 May 2009 / Accepted: 30 June 2009 / Published online: 11 July 2009© Springer Science + Business Media B.V. 2009

Abstract Bottom sediments from Nakaumi La-goon and the Honjo Area in southwest Japan wereanalyzed to determine their geochemical composi-tions and to assess potential impacts by compari-son with sediment quality guidelines. Present-daywater quality was also assessed. Results showedthat the water quality of Nakaumi Lagoon andthe Honjo area contrasts between their upper andlower parts. Average abundances of As, Pb, Zn,Cu, Ni, and Cr in the Nakaumi sediments were12, 25, 135, 32, 21, and 46 ppm, respectively, com-pared to 10, 24, 110, 26, 20, and 38 ppm in the

F. Ahmed (B) · T. FukushimaGraduate School of Life and Environmental Sciences,University of Tsukuba, 1-1-1 Tennoudai,Tsukuba 305-8572, Japane-mail: frahmed2007@yahoo.com

M. H. BibiDepartment of Environmental Science andTechnology, Saitama University, 255 Shimo-okubo,Saitama 338-8570, Japan

K. SetoResearch Center for Coastal Lagoon Environments,Shimane University, Matsue 690-8504, Japan

H. Ishiga · B. P. RoserDepartment of Geoscience, Shimane University,Matsue 690-8504, Japan

Honjo area. All averages are greater than thoseof the upper continental crust. The elevated metalconcentrations are probably related to the fine-grained nature of the sediments, reducing bottomconditions produced by abundant organic mat-ter and possibly minor non-point anthropogenicsources. Trace metal contents are strongly corre-lated with Fe2O3, suggesting that Fe oxides play arole in controlling abundances. Metal concentra-tions exceed the NYSDEC lowest effect level andCCME interim sediment quality guidelines thatindicate moderate impact on aquatic organisms.Average abundances of As and Zn are compa-rable to the Coastal Ocean Sediment Databasethreshold, whereas maximum concentrations ex-ceed that value, indicating that the concentrationsof these metals are potentially toxic. These en-richments suggest that regular monitoring may bedesirable even where no point sources of metalpollution exist.

Keywords Coastal lagoon sediment ·Geochemistry · Trace metals · Environmentalguidelines · Southwest Japan

Introduction

Coastal lagoon and reservoir sediments are recog-nized as carriers and possible sources of contami-

474 Environ Monit Assess (2010) 167:473–491

nants in aquatic systems. Trace metals are amongthe most persistent of pollutants in the aquaticecosystem (Arnason and Fletcher 2003). Elevatedconcentrations of heavy metals are released intothe aquatic environment as a result of leachingfrom bedrocks and soils, water drainage, runofffrom banks, and discharge of urban and industrialwastewaters (Soares et al. 1999). Contaminationof aquatic ecosystems by heavy metals can beconfirmed in both waters and sediments (Alberinget al. 1999). However, measurements of pollu-tants in waters may not be conclusive due tofluctuations in water discharge and low residencetimes. In contrast, studies of sediments play animportant role because clastic detritus has a longresidence time (Singh et al. 1997). Sediments actas both sources and sinks of trace elements, andthe distribution of trace metals is dependent onbiogeochemical transformations that occur withinthem (Peltier et al. 2003). Lake and reservoirsediments thus provide records of natural water-shed conditions and of changes caused by humanactivities (Arnason and Fletcher 2003). In the pastfew decades, many geochemical and environmen-tal studies have been made of coastal and lakesediments worldwide in an effort to determine theextent of contamination from trace metals (e.g.,Rosales-Hoz et al. 2000; Marvin et al. 2004; Esenet al. 2009).

Coastal lagoons are typical estuarine environ-ments that receive the by-products of inlandhuman activities (Yamamuro and Kanai 2005).Human activity around coastal lagoons has in-creased considerably in recent years, and theimpact on these productive and economically im-portant environments has become a matter ofconcern (Yamamuro and Kanai 2005). The mod-ern industrial revolution in Japan started in theearly 1950s and continued through the 1970s(Yoshimura et al. 2005). However, the drainagebasins of lakes and lagoons in southwest Japanhave been affected by human activities over cen-turies (Sadakata 1985), and these could have re-sulted in anthropogenic trace element emissionsinto the atmosphere and deposition in the lakesystems (Matsunaga et al. 1999). Moreover, mod-ification of the river drainages at specific locationscould lead to changes in the chemical compositionof detritus. Such modification has occurred in the

past, with massive influx of granitoid waste fromhistoric tatara mining (Ortiz and Roser 2004).Ishiga et al. (2000a) reported that the large-scaleexploitation of residual iron sands in the catch-ments of Lake Shinji and Nakaumi Lagoon insouthwest Japan led to extensive deforestation inthe hinterland and resulted in the increased influxof clastic detritus.

In recent years, much attention has been paid tosedimentologic and organic geochemical studiesof Lake Nakaumi, a brackish coastal lagoon, andits sediments (e.g., Tokuoka et al. 1990; Sampeiet al. 1997; Yamamuro 2000; Sampei andMatsumoto 2001; Yamamuro and Kanai 2005;Ichikawa et al. 2007). However, these studieshave not considered the potential for ecologicalrisk associated with heavy metal concentrationsin the sediments, and as yet, very little is knownabout the concentrations and distributions of traceelements and heavy metals in the Nakaumi sed-iments. Nowadays, both public and governmentsectors have become increasingly interested incontrolling the water and sediment qualities ofLake Nakaumi. The US Environmental Protec-tion Agency recognizes that while ambient waterquality criteria are an important component inassuring a healthy aquatic environment, contam-inated sediments may be responsible for signifi-cant adverse biological effects, even though waterquality criteria may not be exceeded (NRC 1989).Therefore, assessment of metal concentrations inthe Nakaumi sediments is required.

The present investigation of the surface wa-ter and bottom sediments of Lake Nakaumi inShimane and Tottori prefectures was undertakento evaluate its environment and to obtain a betterunderstanding of the present status of the lagoonenvironments in southwest Japan. The aims of thisreconnaissance study were to gain insight into: (1)water quality and the nature of the water columnin Nakaumi Lagoon and the semi-enclosed HonjoArea within it; (2) geochemical compositions ofthe bottom sediments, including major and traceelement concentrations, elemental distributions,and their sources; and (3) the potential toxicityof the metal concentrations on aquatic biota inthe study areas by comparison of abundances inthe upper continental crust and with reference tosediment quality guidelines.

Environ Monit Assess (2010) 167:473–491 475

Materials and methods

Geologic and hydrologic outlines of NakaumiLagoon and the Honjo area

Nakaumi Lagoon has an area of 87 km2 andis located in the central Japan Sea coast withinShimane and Tottori prefectures of southwestJapan (Fig. 1). It is representative of the highlyeutrophicated and strongly enclosed coastal es-tuarine systems in Japan and has been one ofthe largest brackish lakes in the country since thelast sea level rise in the Holocene (e.g., Nakada

et al. 1991; Umitsu 1991; Ichikawa et al. 2007).Nakaumi has an average water depth of 5.5 m.The eastern side of the lagoon has been semi-closed since 2400 years BP by the development ofYumigahama Peninsula, which was fed by detritusfrom the Hino River (Fig. 1). The Hino Riverdrains a watershed of about 865 km2 (Ortiz andRoser 2004) to the south and east of Nakaumiand empties into Miho Bay. Details of the geo-logical setting and development of Nakaumi aredescribed by Tokuoka et al. (1990).

The northwestern corner of Lake Nakaumi,known as the Honjo area (surface area 17 km2),

Fig. 1 Simplified basement geology and the locationsof Lake Nakaumi and Honjo area in Shimane andTottori prefectures. Inset, location in Japan. Geology based

on the 1:200,000 geological maps of Shimane prefecture(EBGMSP 1997); Chugoku area no. 3 (JICE 1984); andTakahashi (Teraoka et al. 1996)

476 Environ Monit Assess (2010) 167:473–491

was partially isolated by the Moriyama andOmisaki dikes in the 1980s as part of a reclamationscheme intended to create additional agriculturalland. The reclamation ultimately did not proceedand the scheme has now been abandoned, but thedikes remain. However, waters from the Honjoarea and Nakaumi proper are still exchangedthrough a western drainage channel.

At present, Lake Shinji and eastern LakeNakaumi are connected by the 8-km-long OhashiRiver. Lake Nakaumi is connected to the MihoBay and the Japan Sea through the narrowSakai Channel in the northeast (Mitsunashi andTokuoka 1988). The Sakai Channel was broad-ened and deepened to a depth of 10 m by dredg-ing. Dredging has also occurred within Nakaumiitself, in the east and the southeastern corner(Yonago Bay), increasing water depth there from5 to 10 m. A basin offshore the tip of YumigahamaPeninsula was also dredged to an average depth of7 m with a maximum of 17 m; this induced a strongcurrent in the bottom layer that flows back fromthe lower to the upper reaches (Ichikawa et al.2007). Because oxygen-rich water from Miho Bayis mainly consumed during this backflow, mostparts of the bottom water layer in Lake Nakaumiare characterized by oxygen depletion in the sum-mer (Sampei et al. 1997; Ichikawa et al. 2007).

Geologically, the southern part of LakeNakaumi is underlain by Cretaceous to Paleogenegranitic and volcanic rocks (Fig. 1). These arecovered by a complex sequence of Miocenesedimentary and volcanic rocks. Thick Miocenestrata occur beneath the Holocene lagoonsediments (Yamauchi et al. 1980). Nakaumireceives freshwater input from the Iinashi River(catchment area of ∼208 km2) in the south, low-salinity water from Lake Shinji and the OhashiRiver in the west, and seawater through the SakaiChannel. The salinity of the upper layer of thelagoon water is about 17‰, whereas that of thelower layer is about 27‰ (Sampei et al. 1997).The study area is characterized by a humidclimate, with average annual temperature ofabout 15◦C and average annual precipitation of alittle more than 2,000 mm.

The southeastern, eastern, and northern fringesof the lake are moderately urbanized (Yasugi

Town, Yonago City, and Sakaiminato Town, re-spectively), whereas the southwestern and west-ern margins are mostly forested, with a mixtureof native broadleaf species, plantation forests, andbamboo. The only major industry in the area isa Hitachi Metals Industries steel mill near thesoutheastern shore, along with light industrial orservice operations. Flatlands flanking the Iinashiand Ohashi Rivers are used for paddy cultivation,and Nakaumi thus receives wastewater from irri-gation. Uplands of the Iinashi and Ohashi Riversare forested, with the mix of vegetation describedabove.

Analytical procedures

Measurement of water quality

Water parameters including depth, temperature,electrical conductivity (EC), salinity, chlorophyll-a, turbidity, and dissolved oxygen (DO) con-centrations were measured in the field duringsediment sampling using a portable Horiba U-22multi-monitoring system (Horiba Co. Ltd.). Datawere collected from different depths at 21 loca-tions (Fig. 2) from Lake Nakaumi (n = 11) andthe Honjo area (n = 10).

Sediment sample collection and preparation

Fifty-nine sediment samples were collected fromNakaumi (n = 40) and the Honjo area (n = 19) inAugust 2006. Location of sample sites is given inFig. 2. Samples were collected when the weatherwas fine. The uppermost 2 cm of the bottomsediments was collected using an Ekman-BergeBottom Sampler (Rigo Co. Ltd., Japan). Compos-ite samples were taken from the surface portionof the catcher with a plastic spatula. Sedimentsamples weighing about 200 g were packed inZiploc® bags and stored in a cooler box at 4◦Cfor transport to the laboratory.

Approximately 60 g of each sediment samplewas dried in an oven at 110◦C for 48 h. Thedried samples were then ground for 20 min inan automatic agate mortar and pestle grinder.The powdered samples were then compressed intobriquettes using a force of 200 kN for 60 s.

Environ Monit Assess (2010) 167:473–491 477

Fig. 2 Locations of water quality and sediment sample sites in Nakaumi Lagoon and the Honjo area in Shimane and Tottoriprefectures, SW Japan

XRF analysis

Selected major oxide [TiO2, Fe2O3∗ (total iron

expressed as Fe2O3∗, MnO, CaO, and P2O5], total

sulfur (TS), and trace element (As, Pb, Zn, Cu,Ni, Cr, V, and Sr) concentrations were determinedby X-ray fluorescence (XRF) at Shimane Uni-versity using a RIX-2000 spectrometer (RigakuDenki Co. Ltd.) equipped with a Rh-anode X-raytube. All analyses were made on pressed powderbriquettes following the method of Ogasawara(1987). Average errors for all elements are lessthan ±10% relative. Analytical results for USGeological Survey standard SCo-1 (Cody Shale)were acceptable compared to the proposed valuesof Potts et al. (1992).

Statistical analysis

In order to establish inter-element relationships,correlation coefficients for the 14 elements wereanalyzed. One-way analysis of variance was usedto test for differences between three groupsof data from Lake Nakaumi, Honjo area, andOhashi River. Significant differences betweengroup means were established by the least sig-nificant difference test (p < 0.05) using statisticalpackage StatView 5.0 (SAS Institute Inc.).

Spatial analysis

The trace metal concentrations were used as theinput data for a contouring map to study the

478 Environ Monit Assess (2010) 167:473–491

distribution of metals in the surface sediments. AGIS software (ArcView 9.2) was used to conductthe spatial analysis for the current study.

Results

Water quality and the nature of water column

Physicochemical properties (temperature, EC,salinity, chlorophyll-a, turbidity, and DO) of the

water bodies of Nakaumi Lagoon and the Honjoarea contrast between their upper and lower parts(Figs. 3 and 4). Temperature ranged from 23.7◦Cto 30.6◦C and 24.3◦C to 31.2◦C; EC, 18.9–48.3and 23.0–34.6 mS/cm; salinity, 10.0–31.1 and 12.5–21.1 practical salinity units (psu); chlorophyll-a,0.5–50.6 and 1.1–95.7 ppb; turbidity, 0.7–15.7 and1.1–17.8 formazin turbidity units (FTU); and DO,0.1–10.2 and 0.1–7.0 mg/l in Nakaumi and theHonjo area, respectively. Dissolved O2 concentra-tions show significant variation between the sur-

Fig. 3 a–b Verticalchanges of water qualityin Nakaumi Lagoon

Environ Monit Assess (2010) 167:473–491 479

Fig. 4 Vertical changesof water quality in theHonjo area

face (6 to 10 mg/l) and the bottom layers (0.1 mg/lwith some exceptions) of both water bodies. Thisis in agreement with previous reports (Sampeiet al. 1997) showing that the bottom water ofNakaumi–Honjo becomes anoxic or oxygen-poorin the summer. Kamiya et al. (1996) also foundthat dissolved O2 concentrations in the neighbor-ing Lake Shinji were less than 0.5 mg/l in thewater immediately above the bottom sediments.These patterns indicate that the surface watersof Nakaumi–Honjo were oxic, whereas the lowerwaters were under reducing conditions. Concen-trations of chlorophyll-a in the deeper parts ofNakaumi and Honjo (ranges, 1–51 and 1–96 ppb)were higher than those in the overlying waterlayers (ranges, 1–14 and 1–4 ppb). Eutrophic con-ditions allow the concentration of chlorophyll inthe waters (Yamamuro and Kanai 2005).

Temperature gradually increases and EC, salin-ity, and turbidity gradually decrease toward thesurface in the western part of Nakaumi (e.g.,Fig. 3a from N-16 site). All these parameters dis-play almost constant values in the deep water,whereas EC, salinity, and turbidity gradually de-crease in the surface water of the eastern partof Nakaumi (Yonago Bay; Ichikawa et al. 2007;e.g. Fig. 3b from N-59 site). Conversely, thesechemical parameters are almost constant in theupper part and gradually change in the lower part

of Honjo water (e.g., Fig. 4 from H-15 site). Theaverages EC of Nakaumi and the Honjo areawaters were 36.6 and 24.3 mS/cm, respectively.High EC values in both water bodies suggesthigher ionic concentrations due to leaching fromweathering profiles in their catchments. Salinityvalues in the deeper parts of Nakaumi and Honjo(ranges, 15–31 and 13–21 psu) were also greaterthan those in overlying water layers (ranges, 10–22 and 13–14 psu), as observed by Ichikawa et al.(2007) for Nakaumi water. According to them,the annual average salinity in the surface layer ofNakaumi Lagoon (1 m below water surface) liesin a lower level of about 12–16 psu, whereas in thebottom layer (1 m above the lake bottom), it isrelatively high at ∼25–30 psu. The lower parts ofthe waters in both study areas were more turbidthan the upper parts, with the Honjo area showingthe maximum turbidity of 17.8 FTU. Moreover,the turbidity values showed sharp peaks at themiddle part of the water in Yonago Bay and inthe lower waters in the Honjo area (Figs. 3 and 4).The water masses of Nakaumi and Honjo thusshow stratified conditions with respect to mea-sured water parameters at around 2–4 and 4–5 m,respectively.

Considering the above discussion, it seems thatthe water qualities of the study areas vary in thewestern part of Nakaumi, Yonago Bay, and the

480 Environ Monit Assess (2010) 167:473–491

Honjo area (Figs. 3 and 4), as suggested by abruptchanges in physicochemical parameters betweentheir upper and lower parts.

Sediment characteristics

The bottom sediment samples (0–2 cm) collectedfrom Nakaumi Lagoon and Honjo area in thisstudy were mainly very soft, black, olive black orgreenish black, slightly silty, fine clays. The oliveand black colors indicate less oxidizing or reduc-ing conditions (Galasso et al. 2000). Fine sandsand silts were abundant in some samples, whichalso contained occasional marine shells or shellfragments, but most contained a high proportionof clays. The grain size of Nakaumi surface sed-iments is generally consistent, at approximately3–4 μm in diameter (Sampei and Matsumoto2001). The fine-grained sediments prevalent inboth water bodies are also enriched in organicmatter (Yamamuro 2000; Sampei and Matsumoto2001). Silt and clay contents of the sediments inthe neighboring Lake Shinji are greater than 90%at water depths of more than 3 m (Yamamuro andKoike 1998). The clay particles often appeared tobe coated with Fe(oxy)hydroxides, which can actas carriers of metallic pollutants by adsorption, asobserved by Galán et al. (2003) in the river sed-iments in Spain. The organic carbon contents ofthe bottom sediments in Lake Nakaumi are gen-erally 1–3 wt.% (Sampei and Matsumoto 2001).TS in Nakaumi sediments (1–2 wt.%) is primarilycontained in iron sulfide (pyrite and FeS; Sampeiet al. 1997).

Concentrations of elements in the sediments

Summary compositions of the Nakaumi andHonjo sediments are presented in Table 1. OhashiRiver (Figs. 1 and 2) stream sediment data fromsites above Lake Nakaumi (Ahmed et al., unpub-lished data, 2006) and average upper continentalcrust (UCC) from Taylor and McLennan (1985)are also included for comparison.

Abundances of trace metals in the Nakaumisediments are higher than in those from Honjoand the Ohashi River. The highest concentrationsof As, Pb, Zn, Cu, Ni, and Cr were all recordedin the Nakaumi sediments (Table 1). Vanadium T

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Environ Monit Assess (2010) 167:473–491 481

abundances range between 17 and 151 ppm; theaverage is also highest among the three samplesets. Nakaumi sediments contain the lowest andhighest Sr among the three water bodies. Thehighest average values of As, Pb, Zn, Cu, Ni,and Cr were also observed in Nakaumi. Overallconcentrations of TiO2, Fe2O3, MnO, and CaO inthe Nakaumi sediments range from 0.17 to 0.60,1.60 to 7.96, 0.07 to 1.09, and 1.03 to 15.85 wt.%,respectively.

On average, the Honjo sediments contain9.8 ppm As, 110.4 ppm Zn, 26.3 ppm Cu, and38.3 ppm Cr. Average concentrations of Pb, Ni,and V are similar to those in Nakaumi. The high-est concentration of V and the highest averagevalue of Sr occur in the Honjo Area. Abundancesof CaO show significant variation in Nakaumi andHonjo sediments. Ca and Sr have similar geo-chemical behavior in sediments, and therefore,both CaO and Sr are enriched in the surface

samples. Average concentrations of P2O5 are al-most identical in Nakaumi, Honjo and the OhashiRiver. However, Honjo sediments have slightlygreater contents of TiO2, Fe2O3, and CaO thanNakaumi; the contrast is much larger with OhashiRiver sediments.

The Ohashi River sediments contain less As,Pb, Cu, and Cr than in either the Nakaumi andHonjo sediments. Maximum and average concen-trations of Zn, Ni, V, and Sr differ significantlybetween the river and lake sediments, with levelsat least two to three times greater in the Nakaumiand Honjo sediments (Table 1). MnO contentsvary between 0.13 and 0.32 wt.% in the riversediments and yield the highest average value of0.21 wt.%. Abundances of other oxides in theOhashi River are relatively low. The lowest aver-age value of TS occurred in the river sediments.

The concentrations of As, Pb, Zn, Cu, Ni, andCr in the three sample sets are illustrated in Fig. 5.

Fig. 5 a–f Summary ofconcentrations of heavymetals in sediments inLake Nakaumi (LN), theHonjo area (HA), and theOhashi River (OR),Shimane and Tottoriprefectures, Japan.Ohashi River streamsediment data fromAhmed et al.(unpublished data, 2006).Horizontal lines give therange, excluding outliers(circles); boxes enclose50% of the data andillustrate the 25%quartile, median (verticalbar), and 75% quartile.Outliers are defined asthe upper or lowerquartile ±1.5 times theinterquartile difference

a

c

e f

b

d

482 Environ Monit Assess (2010) 167:473–491

Median, maximum, and mean levels of these met-als (except median level of Ni) are greatest in theNakaumi sediments. The highest median level ofNi was observed in the Honjo Area. Mean valuesof As, Zn, Cu, and Ni do not differ significantlybetween Nakaumi Lagoon and the Honjo Area,but levels in Nakaumi are double those in theOhashi River (Table 1).

Inter-element relationship

Table 2 shows the correlation matrix for ele-ments in the sediments. Strong positive relation-ships were observed between the concentrationsof Fe2O3 and As, Pb, Zn, Cu, Ni, Cr, V, and TiO2,between V and As, Pb, Zn, Cu, Ni, Cr, and TiO2,and also between TS and As, Pb, Zn, Cu, Ni, V,and Fe2O3 in Lake Nakaumi. In the Honjo area,Fe2O3 concentrations are strongly correlated withAs, Pb, Zn, Cu, Ni, Cr, V, and TiO2 and TS withAs, Pb, Zn, and Cu. Significant associations of Vand TiO2 with Zn, Cu, Ni, and Cr and of MnOwith As and Pb were also observed in the Honjosediments. Conversely, concentrations of Sr, CaO,and P2O5 in both areas show no relationships,reflecting the different behavior of these elements.

Relationships among the geochemical datashow that metallic elements are strongly corre-lated with total Fe (Table 2), suggesting thatFe2O3 may exert a major role in controlling themetal concentrations in the Nakaumi–Honjo sedi-ments, as discussed by Singh et al. (2005) for riversediments in India. The strong positive correlationmatrices of a suite of metals (As, Pb, Zn, Cu, Ni,and Cr in Nakaumi; Zn, Cu, Ni, and Cr in Honjo)with V suggest the possibility of formation of com-plexes with organic matter. The significant associ-ations of As, Pb, Zn, Cu, Ni, V, and Fe2O3 with TSin Lake Nakaumi and As, Pb, Zn, and Cu with TSin Honjo indicate that their concentrations may berelated to pyritization, as reported by Jones andManning (1994) for sediments in the UK. The neg-ative or poor correlations of Sr, CaO, and P2O5 inthe study areas reflect a different control for theseelements. Strong positive correlations between Srand CaO were found in Nakaumi and the Honjoarea and are most likely related to their similargeochemical behavior and association with shellmaterial. The overall interrelationships between

As, Pb, Zn, Cu, Ni, and Cr show that all aresignificantly correlated with each other, indicatinga common source of these metals and a similarenrichment mechanism in the bottom sediments.

Spatial variability of metal concentrations

Geochemical maps for As, Pb, Zn, Cu, Ni, and Crwere constructed using a GIS software (ArcView9.2) to examine their spatial distributions in thebottom sediments (Fig. 6). In general, several ar-eas of high metal concentrations were identifiedin the geochemical maps. In these maps, concen-trations of Ni and Cr are elevated in Yonago Bayrelative to the western part of Lake Nakaumi andthe Honjo Area. Yonago Bay lies on the outskirtsof Yonago City, and anthropogenic material fromurban sources may have influenced the elevatedconcentrations of these metals in the bottom sed-iments. However, the high Ni and Cr values alsocorrespond with a dredged area in which C/S ra-tios are high due to an accumulation of organicsapropel (Kurakado et al. 1998). The stronglyreducing conditions which prevail in the dredgedarea in Yonago Bay are thus also likely to havefavored Ni and Cr enrichment in the sediments.Similar spatial distribution patterns of As, Pb, Zn,and Cu are seen in the western and central parts ofNakaumi (Fig. 6). This provides a refinement andconfirmation of the results from the correlationanalysis (Table 2) in which strong associationswere found among these metals. Morphologically,the west–central part of Nakaumi and YonagoBay are deeper parts of the lagoon, sites that favorthe accumulation of the finest grains (Abraham1998). These areas are also enriched in organicmatter (Sampei et al. 1997; Kurakado et al. 1998;Yamamuro 2000). Thus, the highest concentra-tions of trace metals are present in the areas wherecarbon-rich clay-sized sediments dominate.

Discussion

Sources of metals in the sediments

The major lithogenic sources of metals are weath-ering of rocks and soils and water drainage andrunoff, whereas discharge of urban and indus-

Environ Monit Assess (2010) 167:473–491 483

Tab

le2

Cor

rela

tion

sbe

twee

nth

eel

emen

tsin

sedi

men

tsof

Lak

eN

akau

mia

ndH

onjo

area

As

Pb

Zn

Cu

Ni

Cr

VSr

TiO

2F

e 2O

3M

nOC

aOP

2O

5T

S

Lak

eN

akau

mi(

n=

40)

As

1.00

0.94

0.92

0.93

0.76

0.74

0.92

−0.7

30.

770.

930.

36−0

.52

0.20

0.77

Pb

1.00

0.97

0.96

0.72

0.69

0.95

−0.8

20.

830.

950.

29−0

.48

0.26

0.78

Zn

1.00

0.95

0.70

0.63

0.91

−0.7

40.

760.

910.

23−0

.37

0.26

0.86

Cu

1.00

0.67

0.66

0.89

−0.7

10.

720.

910.

36−0

.37

0.26

0.77

Ni

1.00

0.92

0.81

−0.5

60.

620.

740.

08−0

.52

0.26

0.71

Cr

1.00

0.80

−0.5

20.

590.

740.

16−0

.53

0.29

0.60

V1.

00−0

.75

0.89

0.98

0.22

−0. 5

70.

210.

76Sr

1.00

−0.7

1−0

.72

−0.1

80.

63−0

.35

−0.6

3T

iO2

1.00

0.89

0.15

−0.6

10.

030.

57F

e 2O

31.

000.

31−0

.57

0.18

0.70

MnO

1.00

−0.1

40.

44−0

.04

CaO

1.00

−0.0

3−0

.32

P2O

51.

000.

22T

S1.

00H

onjo

area

(n=

19)

As

1.00

0.96

0.92

0.86

0.83

0.47

0.59

−0.8

40.

600.

750.

75−0

.68

0.06

0.69

Pb

1.00

0.91

0.85

0.73

0.34

0.50

−0.8

30.

500.

660.

71−0

.65

−0.0

20.

73Z

n1.

000.

980.

850.

590.

70−0

.90

0.70

0.80

0.64

−0.5

50.

270.

80C

u1.

000.

830.

620.

72−0

.88

0.71

0.80

0.59

−0.5

10.

360.

74N

i1.

000.

830.

87−0

.89

0.87

0.91

0.46

−0.7

70.

080.

51C

r1.

000.

94−0

.74

0.95

0.88

0.14

−0.5

70.

130.

19V

1.00

−0.8

60.

990.

950.

18−0

.62

0.03

0.29

Sr1.

00−0

.87

−0.9

1−0

.45

0.76

0.02

−0.6

2T

iO2

1.00

0.96

0.21

−0.6

40.

060.

33F

e 2O

31.

000.

45−0

.68

0.06

0.38

MnO

1.00

−0.3

60.

250.

46C

aO1.

000.

45−0

.22

P2O

51.

000.

37T

S1.

00

Bol

dte

xthi

ghlig

hts

stro

ngco

rrel

atio

ns

484 Environ Monit Assess (2010) 167:473–491

Fig. 6 Geochemical maps of As, Pb, Zn, Cu, Ni, and Cr concentrations in bottom sediments of Lake Nakaumi and theHonjo area

trial wastewaters and waste disposals (includingdumping) are known major anthropogenic pol-lution sources (Pardo et al. 1990; Klavins et al.2000; Upadhyay et al. 2006). Besides environ-mental geochemical factors, common correlationsbetween elements are caused by physicochemi-

cal features of the elements and by geochemi-cal processes (Zhang and Selinus 1998). Kojimaet al. (2003) suggested that near the sediment–water interface and under anoxic conditions, Aswas released from sediments to the pore waterin Lake Biwa, Japan. The reported average con-

Environ Monit Assess (2010) 167:473–491 485

centrations of total organic carbon, total nitrogen,and total phosphorus in Nakaumi bottom sedi-ments were 3.2, 0.37, and 0.58 wt.%, respectively(Yamamuro 2000). According to Akimoto et al.(2004), changes in the reducing condition of thesediments were due to the accumulation of or-ganic matter (e.g., nutrients). Oxygen concentra-tions in Lake Shinji sediments at water depthsgreater than 3 m decrease to 0 mg/l within only0.5–3 mm from the sediment–water interface evenwhen the overlying water is saturated with O2

(Nakamura et al. 1996, cited from Yamamuroand Kanai 2005). Elevated As concentrations inthe Nakaumi and Honjo sediments are thus morelikely to be the product of burial of organic muddeposited under reducing conditions. Moreover,a strong positive relationship exists between Asand Fe2O3 (r2 = 0.83, p < 0.0001, n = 59; Fig. 7a)

in the bottom samples, also suggesting an asso-ciation with authigenic Fe oxides coatings in thesediments.

Chandrajith et al. (1995) and Ishiga et al.(2000b) noted that Pb concentrations in thebottom sediments of Lake Jinzai and LakeJaike in Shimane prefecture were associated withFe-bearing phases, most probably Fe oxides, oxy-hydroxides, and sulfides, depending on the ex-isting oxidation-reduction conditions. Ortiz andRoser (2006a) found that abundances of Pb inKando River sediments in Shimane were notprone to major disturbances from anthropogenicsources, and there was thus no clear evidenceof influence from human activity. The Pb abun-dances observed in Nakaumi and Honjo area thusprimarily reflect those of the source rock typesand of the soils developed on them. The higher Pb

0

5

10

15

20

0 2 4 6 8 10

r2 = 0.83

LN

HA

As

(pp

m)

Fe2O

3 (wt%)

a

0

10

20

30

40

0 2 4 6 8 10

r2 = 0.87

LN

HA

Pb

(p

pm

)

Fe2O

3 (wt%)

b

0

50

100

150

200

250

0 2 4 6 8 10

r2 = 0.80

LN

HA

Zn

(p

pm

)

Fe2O

3 (wt%)

c

0

15

30

45

60

0 2 4 6 8 10

r2 = 0.80

LN

HA

Cu

(p

pm

)

Fe2O

3 (wt%)

d

Fig. 7 a–d Correlations between Fe2O3 and As, Pb, Zn, and Cu in Lake Nakaumi and the Honjo area (excluding oneoutlier; n = 59). LN Lake Nakaumi, HA Honjo area

486 Environ Monit Assess (2010) 167:473–491

concentrations also likely reflect the fine-grainednature of the sediment prevalent in both areas(Graney and Eriksen 2004) and seasonal rain-falls in the hinterland which produce increasedsuspended sediment load (Ruiz-Fernández et al.2003). Furthermore, post-depositional diageneticremobilization can influence Pb migration to-ward the sediment–water interface and scaveng-ing onto organic matter or Fe oxy-hydroxides(Ruiz-Fernández et al. 2003), as suggested by thesignificant relationship of Pb with Fe2O3 (r2 =0.87, p < 0.0001, n = 59; Fig. 7b) in the Nakaumiand Honjo sediments and their elevated carboncontents (Sampei et al. 1997; Kurakado et al.1998).

Tessier et al. (1994), Tribovillard et al. (1994),and Singh et al. (2005) observed that Cu, Ni,and Zn have strong affinity with organic matter,Fe oxides, and clay minerals and may be fixedin sediments as authigenic sulfide minerals. Oneof the main sources of Zn pollution is the usein agriculture of liquid manure, composed ma-terials, and agrochemicals such as fertilizers andpesticides. Intensive use and discharge of Cu canlead to the widespread accumulation of Cu insediments where it often remains in surface layers.Enrichment of Zn and Cu concentrations (226and 41 ppm) near the sediment–water interfacein Lake Jinzai in Shimane prefecture has beenlinked to human activity, especially heavy use ofagrochemicals (Chandrajith et al. 1995). Signifi-cant positive correlations between Fe2O3 and Zn(r2 = 0.80, p < 0.0001, n = 59; Fig. 7c) and Cu(r2 = 0.80, p = 0.0001, n = 59; Fig. 7d) wereobserved in Nakaumi and the Honjo area, suggest-ing that Zn and Cu have similar behavior to Fein the sedimentary processes. These metals werethus most probably adsorbed onto Fe oxide orsulfide (Fe phase)-coated grains in the sediments,as proposed by other studies (e.g., Chandrajithet al. 1995) of lake sediments in southwest Japan.However, the high organic carbon contents of theNakaumi–Honjo sediments (Sampei et al. 1997;Kurakado et al. 1998) are also likely to be a sig-nificant factor in Cu and Zn enrichment.

The greater concentrations of Ni and Cr inNakaumi sediments (Table 1) are most probablyrelated to natural sources and also to domestic andagricultural wastes, as proposed by Chandrajith

et al. (1995) for Lake Jinzai in Shimane prefecture.Table 2 shows that Ni–Fe2O3 and Cr–Fe2O3 areclosely linked, with correlation coefficients of 0.74and 0.74 in Nakaumi and 0.91 and 0.88 in theHonjo sediments, respectively. Zn–MnO and Ni–MnO also show strong relationships in the Honjoarea, with correlation coefficients of 0.64 and 0.46,respectively. Nickel is often co-precipitated withFe and Mn oxides, and Zn and Ni are both en-riched in sediments and show good correlationwith Fe and Mn oxides (Tribovillard et al. 1994;Singh et al. 2005). All these features indicate thatthe sources of these elements are closely relatedto the sediments of the study areas.

As noted above, the Hitachi steel mill on theshore of Nakaumi is the main industrial site inthe study area. However, stringent regulations formanagement of industrial wastes and effluents areapplied in Japan to control environmental quality.Therefore, our study sites are unlikely to havebeen influenced by point sources. As there areno other major industries in the watersheds ofNakaumi Lagoon or the Honjo area and no knownpoint sources for metal enrichment, it is thereforelikely that the metal abundances observed aremainly sequestered in the clastic sediment frac-tion (e.g., inherited from bedrock), with additionalmodification depending on the redox conditions ofthe sediments, enrichment in organic matter, non-point anthropogenic sources (e.g., road runoff),and surface soil erosion.

Comparison of metal concentrationswith sediment quality guidelines

In order to evaluate if metal concentrations inthe Nakaumi sediments are present at conta-minant levels, their As, Pb, Zn, Cu, Ni, andCr contents were compared with three sedimentbenchmarks. The benchmarks used were estab-lished by the US National Oceanographic and At-mospheric Administration (Jones et al. 1997, citedin Ruiz-Fernández et al. 2003) and the New YorkState Department of Environmental Conserva-tion (NYSDEC 1999). The three benchmarks ap-plied were the Coastal Ocean Sediment Database(COSED), the lowest effect level (LEL), and thesevere effect level (SEL; Table 3). The COSEDvalues are indicative of metal contamination and

Environ Monit Assess (2010) 167:473–491 487

Table 3 Sediment quality criteria and metal concentrations (ppm) in lake sediments

Metals UCCa COSEDb LELc SELd ISQGe PELf LN HA

As 2 13 6 33 7 42 12 10Pb 20 45 31 110 30 112 25 24Zn 71 135 120 270 124 271 135 110Cu 25 42 16 110 19 108 32 26Ni 20 42 16 50 na na 21 20Cr 35 125 26 110 52 160 46 38

LN Lake Nakaumi, HA Honjo area, na not availableaUpper continental crust (UCC; Taylor and McLennan 1985)bCoastal Ocean Sediment Database (COSED; Daskalakis and O’Connor 1995)cLowest effect level (LEL; NYSDEC 1999)dSevere effect level (SEL; NYSDEC 1999)eInterim Sediment Quality Guideline (ISQG; SAIC 2002)fProbable effect level (PEL; SAIC 2002)

are used to quantify degradation of sediment qual-ity in estuarine and marine ecosystems (Ruiz-Fernández et al. 2003). If both LEL and SEL cri-teria are exceeded, the metal may severely impactbiota health. If only the LEL criterion is exceeded,the metal may moderately impact biota health(NYSDEC 1999; Graney and Eriksen 2004).

The metal concentrations from the study ar-eas were also compared with the Canadian Sedi-ment Quality Guidelines (CSedQGs) adopted bythe Canadian Council of Ministers of the Envi-ronment (CCME 1998). The CSedQGs presentvalues for individual chemicals or elements inboth freshwater and marine (including estuarine)sediments for the protection of aquatic life andwere developed from the available scientific in-formation on the biological effects of sediment-associated chemicals (SAIC 2002). The guidelineshave identified two numerical limits: (1) the lesserlimit is termed the interim sediment quality guide-line (ISQG) value and (2) the greater limit iscalled the probable effect level (PEL; CSMWG2003). Sediment chemical concentrations belowthe ISQG values are unlikely to be associatedwith adverse biological effects, whereas concen-trations above the PEL are expected to be fre-quently associated with adverse biological effects.Adverse effects are occasionally observed in sed-iments which have metal concentrations betweenthe two threshold values (CSMWG 2003). InterimSQGs and PELs for estuarine and marine sedi-ments have been derived for a number of metals,including As, Pb, Zn, Cu, and Cr (Table 3; SAIC2002).

The results of the present study show that As,Pb, Zn, Cu, Ni, and Cr concentrations in theNakaumi and Honjo sediments are greater thanthose of upper continental crust. The Nakaumiand Honjo bottom sediments are also significantlyenriched in As (Table 1) compared with UCC(2 ppm As from Taylor and McLennan 1985;5 ppm As from Rudnick 2005) and Japanesegranitoids (4 ppm As; n = 310; Terashima andIshihara 1986), representatives of which occupy alarge proportion of the Iinashi River catchment.The average As values in Nakaumi and Honjo aretwo to fivefold greater, suggesting that additionalAs has been contributed to the sedimentary en-vironment or that significant concentration of Ashas occurred due to geological and geochemicalprocesses. The average As concentrations in bothareas exceed the LEL limit from the NYSDEC(1999) and ISQG limit from the CCME (1998).The maximum values observed in Nakaumi andHonjo sediments are similar to or exceed theCOSED for As (Tables 1 and 3). This is of particu-lar significance, as such concentrations of As couldbe detrimental to the majority of benthic species.

Sediments at Nakaumi and Honjo have Pbconcentrations slightly higher than those reportedfrom Lakes Jinzai and Jaike in Shimane prefec-ture (average 16 and 22 ppm; Chandrajith et al.1995; Ishiga et al. 2000b). They are also higherthan abundances in <180 μm fractions of streamsediments from the Kando and Hino Rivers, alsoin Shimane (average 15 and 17 ppm; Ortiz andRoser 2006a, b). Pb abundances in Nakaumi andHonjo are thus a little greater than in the crustal

488 Environ Monit Assess (2010) 167:473–491

Table 4 Concentrations of heavy metals (ppm) in bot-tom sediments from Lakes Ontario (Marvin et al. 2004),Eijsden (Albering et al. 1999), Gulshan (Ahmed et al.

2005), Chapala (Rosales-Hoz et al. 2000), Banryoko andHamahara (Bibi et al. 2007), and Nakaumi and Honjo area(this study)

Metals Ontario Eijsden Gulshan Chapala Banryoko Hamahara Nakaumi Honjo

Pb 5–200 39–191 34–44 73–100 26–39 15–47 12–35 13–34Zn 11–1300 149–970 143–410 97–150 62–122 40–239 42–208 41–167Cu 4–110 29–115 39–50 25–34 16–39 4–36 8–51 9–39Ni na na 75–102 33–49 15–35 3–62 7–50 6–31Cr na na 112–122 52–83 32–59 20–78 24–94 18–70

na not available

background (20 ppm) and the local stream sed-iments (15–17 ppm). The maximum Pb contentsobserved in both Nakaumi and Honjo exceed theLEL and ISQG values (Tables 1 and 3), reflectingmoderate Pb enrichment in some samples. Over-all, however, Pb does not greatly exceed the envi-ronmental guidelines. Zinc concentrations in bothNakaumi and Honjo are considerably greater thanUCC. Average concentration of Zn in Nakaumiexceeds the LEL and the ISQG and is similar tothe COSED value, suggesting moderate concen-tration of Zn in the bottom sediments. Maximumabundances of Zn in both Nakaumi and Honjofall between the Canadian ISQG and PEL lim-its that likely reflect a potential impact on biotahealth.

Average Cu abundances are elevated relativeto UCC at both Nakaumi and Honjo, but arelower than those reported by Chandrajith et al.(1995) and Ishiga et al. (2000b) from Lakes Jinzaiand Jaike (41 and 40 ppm, respectively). Maxi-mum concentrations of Cu in Nakaumi and Honjosediments are broadly similar to the COSED limit.However, the SEL and PEL are much greaterthan those observed here. Average concentrationsof Cu in both water bodies exceed the NYSDEClowest effect level and the CCME interim SQGvalue. Therefore, Cu concentrations in the studyareas fall in the low to intermediate level. Aver-age abundances of Ni in Lake Nakaumi and theHonjo area are similar to UCC (Tables 1 and 3),and averages in <180 μm fractions of stream sed-iments from the Kando and Hino Rivers (average19 and 20 ppm, respectively; Ortiz and Roser2006a, b). Compared to the COSED, maximumconcentrations of Ni are slightly elevated in theNakaumi sediments and depleted in the Honjosediments. Average Ni concentrations in both

areas exceed the LEL for the protection of aquaticlife. Average concentrations of Cr in both areasare elevated relative to UCC. Maximum Cr con-centrations found in both areas are below thevalue in COSED, whereas they exceed the LELand ISQG levels that have moderate impact onbenthic organisms.

Table 4 compares the results for Nakaumi La-goon and the Honjo Area from this work withother studies conducted by Marvin et al. (2004)in Lake Ontario, Canada, Albering et al. (1999)in Lake Eijsden, The Netherlands, Ahmed et al.(2005) in Gulshan Lake, Bangladesh, Rosales-Hoz et al. (2000) in Lake Chapala, Mexico,and Bibi et al. (2007) in Lake Banryoko andLake Hamahara, southwest Japan. The maximumPb and Zn contents found in the Ontario andEijsden sediments are far greater than those fromthe study sites. The metal concentrations in ourstudy areas are also below the SEL and PELfor aquatic sediments, following the guidelines ofNYSDEC (1999) and CCME (1998). However,with the exception of a few values, the results ofthis study show that the concentration ranges ofa suite of metals (As, Pb, Zn, Cu, Ni, and Cr) inthe sediments are well above the established LELand ISQG. The average As and Zn concentrationsin both areas are comparable to COSED, whereasmaximum concentrations of As, Zn, Cu, and Niin Nakaumi Lagoon exceed this value, indicatingthat metal enrichments have occurred in bothNakaumi and the Honjo area.

Conclusions

The results show that the water masses ofNakaumi Lagoon and the Honjo area were strati-

Environ Monit Assess (2010) 167:473–491 489

fied with respect to measured water parameters ataround 2–4 and 4–5 m, respectively. Consideringthe physicochemical properties (temperature, EC,salinity, and turbidity), the water bodies of thestudy areas show variations among the westernpart of Nakaumi, Yonago Bay, and the Honjoarea. However, more detailed monitoring is re-quired to characterize the water qualities in thestudy areas. Abundances of As, Pb, Zn, Cu, Ni,and Cr in the sediments are greater than aver-age upper continental crust, indicating that metalconcentration has occurred in both coastal areas.Increases in the abundances of these metals arelikely related to the very fine-grained nature ofthe sediments, redox conditions in the bottomsediments, Fe oxide and oxy-hydroxide content,enrichment in organic matter, and possibly a mi-nor contribution from non-point anthropogenicsources. Significant positive relationships betweenFe2O3 and As, Pb, Zn, Cu, Ni, and Cr were foundin the sediments, suggesting that these metals maybe adsorbed on Fe oxides. Concentrations of sometrace metals in the sediments exceed internationalthreshold values. Based on the NYSDEC andCCME guidelines, Nakaumi and Honjo sedimentsare moderately contaminated with respect to As,Zn, and Cr and are slightly contaminated withPb, Cu, and Ni. Average As and Zn abundancesin both coastal areas are also comparable toCOSED, while the maximum concentrations ex-ceed this value, indicating that these metals havepotential impact on biota health. According to theenvironmental quality criteria for sediments, it isdesirable that routine monitoring for heavy metalconcentrations should be instituted, even thoughthe enrichments observed arise mainly from nat-ural processes rather than from anthropogenicinputs.

Acknowledgements Our thanks to Professor YoshihiroSawada for access to the XRF facilities; to Dr. HiroyukiTakata, Dr. Kengo Kurata, Keiko Yamaguchi, HirokiOgusa, Hajime Yanagitani, and Kosei Noda for their helpwith sampling; to Dr. Edwin Ortiz for his help with Fig. 1;and to Daham Taranga Jayawardana for his assistancewith Fig. 6. This work was carried out under the PriorityResearch Project on Estuarine and Coastal Lagoon Envi-ronment, Shimane University, Japan.

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