Assessment of the historical trace metal contamination of sediments in the Elizabeth River, Virginia

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Marine Pollution Bulletin 54 (2007) 385–395

Assessment of the historical trace metal contamination of sedimentsin the Elizabeth River, Virginia

Christine F. Conrad, David Fugate, Janice Daus, Catherine J. Chisholm-Brause,Steven A. Kuehl *

College of William and Mary, School of Marine Science, Virginia Institute of Marine Science, 1208 Greate Road, Gloucester Point, VA 23062, United States

Abstract

Two sediment cores (Southern Branch, PC-1, and Western Branch, WB-2) were taken from the highly industrialized Elizabeth River,Virginia. The concentrations of trace metals cadmium, cobalt, chromium, copper, nickel, lead and zinc, major elements iron, manganeseand aluminum, organic carbon content and the specific surface area of the sediments were determined in each of the cores. Down-corevariations in metals varied significantly in each core with maximum contamination events occurring at different times in different portionsof the river. In PC-1, maximum metal concentrations were seen after the appearance of 137Cs. In contrast, the highest levels in WB-2occurred well before the appearance of 137Cs. Although stricter environmental regulations have caused a decrease in metal concentra-tions since the 1980s, the concentrations in the surface sediments of many trace metals were elevated to levels 2–5 times higher thanthe levels at the bottom of the cores in both the Southern and Western Branches of the river.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Elizabeth River; Enrichment factor; Geochronology; Metals; Sediments

1. Introduction

The contamination of coastal systems through humanactivities has increased over the past years as populationdensity has increased. Significant monitoring and restora-tion efforts of these impacted systems have been developedto provide managers with the scientific information neededto implement effective controls for remediation. To fullyunderstand the anthropogenic impact on an ecosystem,long-term data from chemical, physical and biological indi-cators are needed. Carefully dated sediment cores can pro-vide chronologies of contaminant concentrations and arecord of the changes in concentrations of chemical indica-tors in the environment over time (Schropp et al., 1990;Hornberger et al., 1999). Because metals strongly associatewith the surface of particles, their transport and depositionin estuarine and coastal systems are often closely related to

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doi:10.1016/j.marpolbul.2006.11.005

* Corresponding author.E-mail address: [email protected] (S.A. Kuehl).

the transport and deposition of fine-grained sediments(Olsen et al., 1982; Dzombak and Morel, 1987; Davisand Hem, 1989; Scheidigger et al., 1997; Bertsch and Sea-man, 1999). In the absence of significant changes in sedi-ment texture, trace metal accumulation rates in sedimentcores can reflect variations in metal inputs in a given systemover long periods of time.

The commonly observed historical pattern of trace met-als in sediments distant from major sources of contamina-tion is the initial occurrence of increased heavy metalconcentrations in sediments beginning in the early 1800sfollowed by a larger increase in the 1900s. A sharp increasein metal concentrations is often seen between 1940 and1970 followed by decreasing metal concentrations in subse-quent decades (Owens and Cornwell, 1995; Ravichandranet al., 1995). This pattern reflects the onset and then steadyincrease in industrialization, with the recent decline reflect-ing the implementation of environmental laws such as theprohibition of lead as a gasoline additive. In the vicinityof direct sources of contamination, the historical variation

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386 C.F. Conrad et al. / Marine Pollution Bulletin 54 (2007) 385–395

in metals concentrations may be markedly different, reflect-ing the local influence of pollution sources.

The Elizabeth River is a tributary of the James Riverlocated in the southern portion of the Chesapeake Baywhose watershed includes the cities of Chesapeake, Nor-folk, Portsmouth and Virginia Beach (Fig. 1). It is a highlyindustrialized estuary with an estimated 600,000 peopleinhabiting the 777 km2 watershed. The entire river is sub-ject to tidal forcings with a gradient of decreasing salinityas distance upstream (away from the Chesapeake Bay)increases. Salinity is generally lowest in the surface watersand increases with depth with the highest values in thenear-bottom waters (Ewing et al., 1990). The morphologyof the river has been greatly altered over the years. Origi-nally a broad shallow estuary, the river channels have beendredged to 12–15 m, twice its normal depth, and its widthhas been decreased by 75% due to development of itsshores. Over 50% of the adjacent wetland areas have beenlost since WWII.

The Elizabeth River is the major deep-water port for theHampton Roads Area and one of the largest naval bases inthe United States. The most impacted section of the river isParadise Creek which is located in the Southern Branchand drains 7.6 km2 of the central portion of the City ofPortsmouth (Johnson and Villa, 1976; Conrad and Chis-holm-Brause, 2004). Land use along the shores of thisregion is primarily industrial and includes oil terminals,

James River

PC-1

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Norfolk NavaShipyard

St. Julian Naval Depot

Coal Transport RR Crossing

US

CoTraFac

Craney Island Dredge Disposal

Area

City of

Portsmouth

James River

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WB-2

Norfolk NavaShipyard

St. Julian Naval Depot

Coal Transport RR Crossing

US

CoTraFac

Craney Island Dredge Disposal

Area

City of

Portsmouth

Fig. 1. Map of the Elizabeth River subestuary system located in the Southerlocations of the two sediment cores, PC-1 and WB-2, are starred on the map.

shipyard installations, coal transloading facilities, petro-leum distribution and shipment operations, and woodtreatment facilities (Fig. 1). US Naval operations beganin this portion of the river in 1787 and dredging began in1900 (Fig. 2). This portion of the river is also more con-fined than other branches of the river leading to increasedresidence times of contaminants in this region (Ewing et al.,1990). In contrast, the Western Branch is primarily a resi-dential area that is readily flushed with little industrialactivity resulting in lower levels of both organic and metalcontaminants in its waters and sediments.

The historical industrial and commercial developmentalong the river has lead to increased contaminant loadsto the sediments (Fig. 2). Dangerous levels of metal andorganic contaminants in the sediments of the ElizabethRiver have lead to its designation as a toxic hot spot bythe Environmental Protection Agency. Metals concentra-tions in surface sediments from the Elizabeth River havebeen studied extensively over the years and have been doc-umented to be up to 10 times higher than baseline levels forthe lower Chesapeake Bay area (Sinex and Helz, 1981;Rule, 1986; Conrad and Chisholm-Brause, 2004). Specifi-cally, Cu, Pb and Zn are all found at elevated levels withinmost portions of the Mainstem and Southern Branch of theriver. However, the historical levels of contamination in theriver are not well known, and few studies have been carriedout in shallow estuaries that are highly industrialized

l

Naval Base

al nsloading ility

City of

Norfolk

l

Naval Base

al nsloading ility

City of

Norfolk

n Chesapeake Bay on the East coast of Mid-Atlantic United States. TheOther important sites throughout the system are also detailed.

1900 20001700 18001752

City of Portsmouth established

MaximumContamination in Southern Branch

(1970’s to 1980’s)

MaximumContamination in Western Branch

(late 1800’s to early 1900’s)

Norfolk Naval Shipyard (established 1787)

Norfolk Naval Hospital (1830)

Establishment of Coal Transport Facilities and Railroads (1838) (Cu, Zn, Cr, Pb, Cd)

Automobiles (Pb, Zn)

Wetlands Decline

Dredging Operations

Fig. 2. Timeline for the historical development of the Elizabeth River watershed and their association with maximum contaminant loads determined incores taken from the Western Branch and Southern Branch portions of the river.

C.F. Conrad et al. / Marine Pollution Bulletin 54 (2007) 385–395 387

(Ravichandran et al., 1995). The objective of this work is toexamine the historical record of trace metal contaminationin the highly industrialized Elizabeth River subestuary, Vir-ginia. Differences in the onset, duration and extent of con-tamination in an industrialized and non-industrializedportion of the river are compared. Changes in sedimentproperties (surface area, % organic carbon and major ele-ments Fe, Mn and Al) are used in conjunction with radio-chemical data to ascertain changes in depositional regimesthroughout the cores. Concentrations of metals that char-acterize Elizabeth River sediments prior to industrializa-tion will be established, metal concentrations throughoutthe cores will be compared to baseline values and metalconcentrations in modern sediments will be examined.

2. Materials and methods

2.1. Sample collection

Two sediment cores were collected in the ElizabethRiver in August 1998, one each from the Southern andWestern Branches (Fig. 1). The channel of the SouthernBranch is routinely dredged as it is part of the IntracoastalWaterway. The core from this portion of the river wastaken in the mouth of Paradise Creek near its confluencewith the Southern Branch (PC-1) and not in the main chan-nel itself. The second core (WB-2) was collected upstreamof the dredged portion of the Western Branch’s mainchannel. PC-1 is approximately 200 cm in depth and wascollected using a 7.62 cm diameter aluminum tube vibra-corer. WB-2 was collected using a 12.7 cm diameter gravitycore and is approximately 300 cm deep. Each core wastransported to the lab where they were sectioned, bagged

and stored at 4 �C until chemical analyses. PC-1 wassampled at intervals of 6–2 cm, and WB-2 was sampledat intervals of 2–4 cm. Deeper portions of WB-2 weresampled less frequently (every 5–0 cm).

2.2. Sediment dating

210Pb (T1/2 = 22.3 yr) and 137Cs (T1/2 = 30.1 yr) wereused in this study to investigate changes in metals concen-trations on a decadal time scale. 210Pb is a naturally occur-ring radionuclide that strongly associates with particles,making it a useful tracer for the fate of particle-reactivecontaminants, such as trace metals (Alexander et al.,1993; Ravichandran et al., 1995; Hirschberg et al., 1996).210Pb and 137Cs are commonly used to determine sedimen-tation rates over the last 80–100 yr in coastal environments(Krishnaswami et al., 1971; Dukat and Kuehl, 1995; Del-lapenna et al., 2003) and recent studies have utilized thisgeochronological method to constrain the time of contam-inant deposition in industrialized areas (Macdonald et al.,1991; Smith and Schafer, 1999; van Geen and Luoma,1999). However, post-depositional mixing of sediments byphysical and biological processes often complicates use of210Pb in shallow estuarine environments. Bomb falloutradioisotopes such as 137Cs are also a common tool for dat-ing sediment cores. 137Cs was first introduced into the envi-ronment in significant amounts through atmosphericnuclear tests in 1954 and can provide an independent esti-mate of the sediment accumulation rate in cores (e.g., Alex-ander et al., 1993).

Alpha spectroscopy was used to measure 210Pb activitiesindirectly through its 210Po daughter following the methodsof Flynn (1968) and Nittrouer et al. (1983/1984). The pro-


cedure was modified as detailed in Dellapenna et al. (2003)and Kniskern and Kuehl (2003). In brief, samples (5–10 g)were oven-dried (60 �C), spiked with a 209Po standard, sub-jected to a partial acid leaching using HNO3 and HCL, andthe Po plated onto silver metal disks for counting. 137Csactivities were measured (at identical geometries) onhomogenized wet-packed samples using a semi-planarintrinsic germanium detector coupled with a multichannelanalyzer. Net areas of the 661.62 KeV photopeak for137Cs were used along with calibrated efficiency factors tocalculate sample activity, which was expressed in terms ofdry sample weight.

2.3. Sediment analysis

Sediments were analyzed for trace metals (Cd, Co, Cr,Cu, Ni, Pb and Zn) and major elements (Fe, Mn and Al)using a strong acid digestion technique. Sediments (2 gdry weight) were added to 10 mL concentrated trace metalgrade HNO3. The sediments were extracted for 20–24 h at70 �C. The samples were then centrifuged at 5000 rpm for30 min (IEC PR-7000M centrifuge, rotor #966). Theextracts were analyzed using a Thermo Jarrell Ash TraceScan inductively coupled plasma atomic emission spectro-photometer (ICP-AES). ICP sample measurements weremade in triplicate. Standards, prepared by dilution of com-mercially available ICP standards, and acid blanks wereanalyzed regularly to verify instrument stability. Sampleswith instrumental error greater than 2% were re-analyzed.Method recoveries were verified through the extraction ofa standard reference material, NIST SRM 1944-NewYork–New Jersey Waterway Sediment. The recoveries ofmost metals in the sediment standard were determinedwithin 10%, except for Cr, Cu and Ni which were 28%,30% and 25%, respectively.

Fig. 3. Distribution of excess 210Pb and 137Cs for PC-1 (a) and excess 210Pb andlevels were present to depths of 90–100 cm and 125 cm, respectively. Supportenor excess 210Pb levels were detected below 30 cm in WB-2. See text for a det

The specific surface area (SSA) and organic carbon con-tent (%OC) of the sediments were also determined. SSAwas determined by nitrogen adsorption using the Bru-nauer, Emmet, Teller (BET) N2-adsorption method (Webband Orr, 1997) on a Micromeritics Gemini 2375 surfacearea analyzer. A 5-point adsorption curve was used withrelative pressures ranging from 0.05 to 0.25. Organic car-bon concentrations were measured on dried, acidified sed-iment samples by high temperature combustion using aFisons 1108 Elemental Analyzer.

3. Results and discussion

3.1. Geochronology

Sediment profiles of 210Pb for both Paradise Creek andWestern Branch sites generally show logarithmic decreasein excess activity with depth (Fig. 3). As such, the profileswere initially modeled using the constant initial activ-ity:constant accumulation rate approach (Appleby andOldfield, 1992). In this case, a best fit curve is fitted tothe excess activity profile and the accumulation rate isderived from the slope of this curve and the 210Pb decayconstant, yielding apparent 210Pb accumulation rates of2.0 and 0.5 cm yr�1, respectively. The assumption of con-stant initial activity is reasonably well supported in estua-rine environments, where intense horizontal transportand tidal mixing would be expected to result in uniform210Pb concentrations on suspended sediments. The assump-tion of constant accumulation rate and potential influenceof diffusive (biological) mixing on the 210Pb rates are fur-ther explored below. For both cores, supported 210Pb levelswere calculated to be 1.0 ± 0.2.

For Paradise Creek, the sediment accumulation rate cal-culated from maximum penetration depth of 137Cs (first

137Cs for WB-2 (b) as a function of depth. In PC-1, 137Cs and excess 210Pbd 210Pb levels for both cores were calculated to be 1.0 ± 0.2. Neither 137Csailed description of the accumulation rate estimates based on these data.


appearance from global fallout in 1954) is consistent withthe apparent 210Pb accumulation rate. Using the maximumdepth of 137Cs penetration at 99 cm and time between firstappearance and sample collection (44 years) yields an aver-age accumulation rate of 2.3 cm yr�1, as compared with2.0 cm yr�1 calculated from the slope of the excess 210Pbactivity profile. There is a large, broad peak in 137Csroughly centered at �40 cm (spreading from �32 to2 cm) that is assumed to correspond to the 1963–64 maxi-mum fallout (Fig. 3). Using depth range over which maxi-mum fallout is observed, calculated rates range from 1.1 to1.5 cm yr�1. Hence, whereas the basic shape of the 137Csprofile is generally consistent with that expected fromatmospheric fallout under steady-state conditions (Wallingand He, 1992) the peak is somewhat broader and maximumactivities (1963–64) are much higher in the core than wouldbe predicted from the 210Pb accumulation rate. Sedimentmixing by bioturbation of the uppermost sediment layershas been shown to strongly affect tracer profiles (e.g., Guin-asso and Schink, 1975), however X-radiographs of this coreshow dominant physical stratification (Fig. 4a), which isnot consistent with such an effect. In addition, althoughbioturbation can cause significant peak broadening, it also

(a) Paradise Creek Vibracore

PC-1

Dep

th (

cm)

60

102

3

70

Fig. 4. X-radiographs of sections representative of (a) PC-1 and (b) WB-2. The2 X-radiograph shows the 35–70 cm portion of the core. Laminations can be seWB-2 core is extensively mixed as indicated by the mottling throughout the X

will depress the depth of maximum concentration, oppositeto what is observed for this core. Close inspection of the210Pb profile for Paradise Creek reveals that while theexcess activities generally decrease logarithmically, thereare changes in the slope of the profile with respect to depth,which could be the result of fluctuating accumulation ratesover time. Based on these data, we suggest that acceleratedsedimentation rate in the 40–85 cm interval influences thetracer profiles. This is supported by a nearly vertical slopeof the excess 210Pb activity profile in this section of thecore. Overall, while we are confident that the ParadiseCreek core indicates relatively high average sediment accu-mulation rates, the instantaneous rate almost certainly var-ies over time. Based on the above estimates from 137Cs and210Pb geochronology, the average accumulation rate in thisarea ranges between 1.1 and 2.3 cm yr�1.

In contrast with Paradise Creek, sediment geochronol-ogy of the Western Branch site indicates significantly loweraccumulation rates, and is likely strongly influenced by bio-turbation. The nearly complete absence of a fallout signa-ture in the 137Cs profile (i.e., subsurface maximum) forthis core coupled with the observed logarithmic decreasein 137Cs activity is strongly suggestive of biodiffusion. This

WB-2

(b) Western Branch Kasten Core

5

PC-1 X-radiograph shows the 60–102 cm portion of the core, and the WB-en throughout PC-1 indicating a lack of sediment mixing in this core. The-radiograph.


is also supported by the X-radiograph from this site, whichdisplays mottled structure characteristic of bioturbation,and little preserved physical stratification (Fig. 4b).Whereas other scenarios involving complex depositionaland/or erosional histories could be invoked to explain theobserved profiles, the data here are consistent with diffusivemixing. In any case, the accumulation rate, 0.5 cm yr�1,calculated from these data using the activity:constant accu-mulation rate approach described previously represents themaximum value and provide the most conservative estimateof sediment age. Any downward diffusion would only serveto increase apparent 210Pb rates leading to an underestima-tion of the age of the sediments in this core. We thereforeconclude that the Western Branch site has accumulatedat a slower rate, 60.5 cm yr�1, compared to the ParadiseCreek site with has an estimated accumulation ratebetween 1.1 and 2.3 cm yr�1. Based on this maximum rate,sediments in the deeper portions of the WB-2 core arelikely older than can be dated with the 210Pb method(>�100 years). Because of the complexities involved in dat-ing this core, the occurrence of contamination in this corewill be largely interpreted in terms of pre- and post-appear-ance of 137Cs.

3.2. Sediment properties

The physical and chemical properties of the sediments(SSA, %OC, Fe, Mn and Al) in each core were examinedto determine changes in sediment input over time(Fig. 5). In PC-1, Fe and Mn concentrations generallyincrease from the surface to �50 cm, followed by a period

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% OC

Fig. 5. Depth profiles of Fe, Mn, % organic carbon and specific surface area, oleft, and the scale for WB-2 is shown on the right. The dashed horizontal line i

of higher, more variable concentrations ranging from �50to 125 cm. Aluminum concentrations also increase to�50 cm, but there is a subsequent period of relativelylow, constant levels from �50 to 125 cm. Below 125 cm,Fe, Mn and Al concentrations decrease back to those seennear the surface of the core and remain fairly constant. Theorganic carbon content of the sediments generallydecreases to �50 cm and subsequently increase and remainrelatively constant (Fig. 5d). The changes in Fe, Mn and%OC with depth in PC-1 are reflected in the SSA measure-ments. In the �50–125 cm region, SSA is elevated andsomewhat variable indicating the presence of smaller,finer-grained sediments. Outside of this region, SSAremains fairly constant (Fig. 5e). Because concentrationsof Fe, Mn and %OC are inversely proportional to thegrain-size of sediments (p 6 0.05), it is likely that thevariability in their profiles stems from this increase infine-grained sediments being deposited �50–125 cm. Incontrast, the Al concentrations are relatively stable in thisportion of the core indicating that Al has a geochemicalbehavior unique from Fe and Mn (Fig. 5c). Using a spear-man correlation, only %OC was found to significantlydecrease in with increasing depth (Table 1).

Sediment properties measured in WB-2 were compara-ble in concentration to those in PC-1 but, with the excep-tion of Al, were much more constant than the measuredparticle property values in PC-1. In WB-2, Fe and Mn lev-els are generally unchanging with depth with the exceptionof a large decrease in the concentrations of both Fe andMn at �150 cm. This decrease in concentration can beexplained by a significant decrease in the surface area of

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g-1 ) % Al

SSA (m2 g-1 )

f sediments in PC-1 (O) and WB-2 (�). The scale for PC-1 is shown on thendicates the depth of the first appearance of 137Cs (i.e., the 1954 horizon).

Table 1Spearman correlation coefficients for sediment properties with depth inWB-2 and PC-1

Western branch (WB-2) Paradise creek (PC-1)

Sedimentproperty

Correlationcoefficient

Sedimentproperty

Correlationcoefficient

Al �0.363* Al �0.274Fe 0.108 Fe �0.312Mn 0.042 Mn 0.060SSA 0.038 SSA �0.132% OC �0.908* % OC �0.544*

Correlations are considered statistically significant at the 95% confidenceinterval (p < 0.05) and are marked with an *. Positive correlations indicatethat measured values increase with increasing depth, while negative cor-relations indicate a decrease in measured value with increasing depth.

Table 2Mean metal concentrations (lg metal g�1 sediment) of modern sediments(post first appearance of 137Cs) from PC-1 and WB-2

Metal PC-1 WB-2 PC-1/WB-2

Cd 1.48 ± 1.08 1.45 ± 1.47 1.02(0.40–3.21) (0.56–3.84)

Co 30.36 ± 21.93 9.09 ± 0.81 3.34(15.48–95.38) (8.10–10.88)

Cr 78.03 ± 58.39 41.99 ± 15.05 1.86(40.23–236.40) (31.58–78.27)

Cu 145.89 ± 77.15 78.56 ± 31.04 1.86(54.76–248.70) (56.32–146.07)

Ni 35.74 ± 18.76 15.56 ± 2.22 2.30(21.73–90.46) (11.64–17.25)

Pb 146.99 ± 69.66 109.14 ± 30.23 1.35(72.94–256.25) (84.55–181.64)

Zn 320.87 ± 144.42 563.29 ± 255.19 0.57(156.26–499.15) (420.27–1094.95)

The averages are shown with the standard deviations and the range ofconcentrations (minimum to maximum) in parentheses below.


the sediments in this portion of the core. Aluminum con-centrations are extremely variable (Fig. 5c) but show a sig-nificant decrease in concentration with increasing depth(Table 1). The variability in the Al concentrations withdepth is likely due to known anthropogenic inputs of Alto this portion of the river (Goldberg et al., 1978; Sinexand Helz, 1981; Tessier et al., 1985). Organic carbon ishighest at the surface, and steadily decreases with depthuntil it reaches a constant level of 1.5% at �50 cm. Thisdecrease was also found to be statistically significant withdepth (Table 1). The % carbon in the surface sedimentsof WB-2 are �2.5% compared to �4% in PC-1. The SSAof the sediments in WB-2 are fairly constant from the sur-face to �125 cm, with one region of variable SSAs rangingfrom �25 to 50 cm. The sediments below 125 cm havemuch lower surface areas indicating the presence of larger,coarser-grained particles.

3.3. Trace metal normalization

Normalization of trace metal concentrations to grainsize, specific surface area and reactive surface phases suchas Fe and Al is a common technique to remove artifactsin the data due to differences in depositional environments(Horowitz and Elrick, 1987; Daskalaskis and O’Connor,1995; Ravichandran et al., 1995; Rubio et al., 2000). Thisallows for a direct comparison to be made between con-tamination levels of samples taken from different locations.One of the most common normalization techniques is con-verting trace metal concentrations to enrichment factors(EFs) by normalizing metals concentrations to a commonelement (usually Al or Fe) and comparing the normalizedconcentration to average crustal abundance data (Taylor,1964; Rule, 1986; Windom et al., 1989; Schiff and Weis-berg, 1999; Summers et al., 1996). The enrichment factor(EF) for a given trace metal (Me) is therefore defined asfollows (after Rule, 1986):

EF ¼ ð½Mes�=½Fes�Þ=ð½Mecr�=½Fecr�Þ ð1Þ

where the subscripts s and cr denote the concentrations atthe experimental stations and crustal abundances (fromTaylor, 1964), respectively.

For this study, we chose to Fe as the normalizing ele-ment. The natural concentrations of Fe in the core sedi-ments are more uniform than the Al concentrations. Femay be a better predictor than Al for background tracemetal levels due to the similarities in the geochemistry ofFe and many trace metals in both oxic and anoxic condi-tions (Schiff and Weisberg, 1999). Also, documentedanthropogenic inputs of Al due to industrial activities inthe Elizabeth River would result in an underestimation ofEFs (Goldberg et al., 1996; Sinex and Helz, 1981; Tessieret al., 1985). The variable behavior of Al and the lack ofcorrelations with other particle properties suggest that thegeochemical behavior of this element is unique from theother metals in the system.

3.4. Core comparison

All metals in PC-1 are quite variable with standard devi-ations ranging from 53% to 95% of the mean concentra-tion. The metals in WB-2 similarly have large standarddeviations in their mean concentrations. The exceptionsare Ni and Co which have standard deviations below15% of the mean concentration. The overall rank of highestto lowest metal concentrations in PC-1 is: Zn > Pb > Cu >Cr > Ni > Co > Cd. The rank of metals concentrationsin WB-2 yields the same result. The average metal concen-trations in PC-1 and WB-2 can be compared to assessdifferences in the overall contaminant loading of each sam-pling site (Table 2). To eliminate the different time periodscovered by each core and to compare only the residential(WB-2) vs. the industrial site (PC-1), the averages of themetal concentrations in modern sediments, or those beingdeposited after the first appearance of 137Cs have beenused. Comparing the ratio of the mean of the modern

Table 3Spearman correlation coefficients for metals concentrations with depth inWB-2 and PC-1

Western branch (WB-2) Paradise creek (PC-1)

Metal Correlation coefficient Metal Correlation coefficient

Cd 0.424* Cd �0.823*

Co �0.007 Co �0.644*

Cr �0.241 Cr �0.840*

Cu �0.189 Cu �0.875*

Ni �0.332* Ni �0.525*

Pb �0.154 Pb �0.819*

Zn �0.161 Zn �0.872*

Correlations are considered statistically significant at the 95% confidenceinterval (p < 0.05) and are marked with an *. Positive correlations indicatethat metals concentrations increase with increasing depth, while negativecorrelations indicate that metals concentrations decrease with increasingdepth.


metals concentrations in PC-1 to WB-2 it is seen that onlyZn is lower in PC-1 (ratio of mean concentrations = 0.57).Mean concentrations of Cd and Pb are somewhat similar inthe two cores (ratio = 1.02 and 1.35, respectively), and Co,Cr, Cu and Ni are all distinctly elevated in the industrialarea as compared to the residential core site (Table 2).

The metals in the Elizabeth River cores vary markedly,and show distinct differences in regions of elevated concen-trations (Fig. 6). In WB-2, metal concentrations are lowand nearly constant below 100 cm, and it seems that back-ground metal concentrations are reached. Spearman corre-lations were used to assess the statistical trends in metalconcentrations with depth in both cores (Table 3). Whilemost metals in WB-2 showed a general decrease in concen-tration with increasing depth, only Ni showed a statisticallysignificant trend. In contrast, Cd significantly increased inconcentration with increasing depth suggesting that theremay have been a historical source of Cd to this portionof the river. Metals concentrations in PC-1 also show amarked decrease downcore, with low, relatively constantlevels for all metals (150–175 cm) (Fig. 6). Using the spear-man correlation, all metals in this core showed a significanttrend of decreasing metal concentrations with increasingdepth (Table 3). Although the concentrations at the bottomof PC-1 represent more modern contamination than thatseen at the bottom of WB-2, these concentrations may wellbe background levels for the metals measured. However, itis possible that there is another peak in metals concentra-

0 10 20 30 400

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CoCd

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Fig. 6. Depth profiles of trace metal concentrations (ppm) for PC-1 (O) and Wshown on the right. The dashed horizontal line indicates the depth of the first

tions deeper in the sediments that was not sampled by thiscore. The maximum level of metals in PC-1 occurs insediments above the 1954 maximum depth of 137Cs pene-tration (90–100 cm) while the maximum metal concentra-tions in WB-2 occur deeper in the core below the 137Cshorizon indicating different periods of contaminant loadingin the different portions of the river. The contaminantinputs to the industrialized Southern Branch are muchmore modern than the inputs to the predominantly residen-tial Western Branch.

on (ppm)

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B-2 (�). The scale for PC-1 is shown on the left, and the scale for WB-2 isappearance of 137Cs (i.e., the 1954 horizon).


3.5. Trace metal profiles

The depth profiles of metals in PC-1 can be divided intotwo general groups. The first group consists of Co, Cr, andNi. These metals show relatively low EFs leading up to the137Cs maximum, a sharp peak at 48 cm with maximum EFs< 4, and a rapid decrease towards the surface where theEFs return to those seen at the bottom of the core. The sec-ond group includes Cd, Cu, Pb and Zn (Fig. 7). Inputs ofthese metals are primarily derived from the fossil fuel oper-ations along the banks of the river and from automotivesources. The profiles for these metals exhibit a muchbroader maximum in EFs, from 48 cm to 12 cm belowthe surface in some cases. The EFs of the surface sedimentsare 14, 4.5, 14.4 and 6.5 for Cd, Cu, Pb and Zn, respec-tively, and the EFs of the main peaks are 25, 8.3, 30 and13. Based on the geochronology of this core, the peak at48 cm occurs after 1954. The upper limit of the peak inthe second group of metals (12 cm) occurs in more modernsediments well after the implementation of more stringentenvironmental regulations that were introduced in the late1960s and early 1970s.

The metals profiles for WB-2 can be grouped into threegeneral categories (Fig. 7). The first group consists of Coand Ni. The EFs for both of these metals are fairly con-stant throughout the length of the core and are actuallydepleted with respect to natural crustal abundance concen-trations (EF < 1). The second group contains Cd, Pb andZn again reflecting the impact of fossil fuel and automotivecontaminant sources in this portion of the river (Fig. 7).The profiles of these metals are characterized by a very

PC-1 Group I 0 1 2 3 4

Dep

th (

cm)

0

25

50

75

100

125

150

175

CoCrNi

0

25

50

75

100

125

150

175

WB-2 Group I0.0 0.2 0.4 0.6 0.8 1.0

Dep

th (

cm)

0

50

100

150

200

250

CoNi

WB-2 Gro0 25 50 75

Fig. 7. Trace metal enrichment factor profiles showing similar trends with depconcentrations (see Eq. (1) in text). Metals were grouped based on the position

broad peak from 44 cm to 78–88 cm below the surface,with Pb extending the deepest and Cd being the shallowestand elevated metals at the surface. The highest enrichmentof these metals is seen at 58–63 cm below the surface, wellbefore the 1954 137Cs horizon. The EFs of these metals inthe main peak are 243, 78 and 71 for Cd, Zn and Pb,respectively. The EFs at the surface for these metals are5.6, 14.6 and 11.7. Note that the EF for Cd in the bottomsediments of the core is 6.5, meaning that Cd levels areactually depleted in the surface sediments of this core.The third group of metals contains Cr and Cu (Fig. 7).These metals show a defined peak in their profiles, but theirEFs are much lower than the metals in group 2. The high-est EF for Cr is 2.5 and the highest EF for Cu is 7.2, andthe surface sediments are only slightly enriched in thesemetals in WB-2 (EFs < 2).

In addition to the main peak seen for the metals ingroups 2 and 3, Cr, Cu, Pb and Zn display a secondarymaximum at 28–34 cm. The EFs of the metals in these sed-iments are 4.7, 24 and 25, for Cu, Pb and Zn, respectively.This peak corresponds to the increase in SSA of the sedi-ments in this portion of the core (Fig. 5e), indicating a pos-sible change in sediment sources to this region of the riverduring this time. Additional peaks occurring prior to themaximum enrichment were seen in Cu and Pb profiles at�90 cm. The Pb peak is relatively small compared to themain peak, while the peak in Cu enrichment is nearly aslarge as the shallower maximum enrichment peak.

Chromium, Co and Ni are often thought to be associ-ated primarily with the mineral matrix of the sediment.Thus, the EFs for these elements should be relatively

PC-1 Group II0 5 10 15 20 25 30 35

CdCuPbZn

up II100 250

CdPbZn

WB-2 Group III0 2 4 6 8

CrCu

th in the PC-1 and WB-2 cores. Enrichment factors are normalized to Feand shape of the contaminant enriched peak(s) of the downcore profiles.


constant assuming that the primary mineral composition ofthe sediments has not changed over time. There is one datapoint in the profiles of these metals that causes the peak at48 cm. This point is probably not due to instrumental oranalytical error, as it is seen in three of the metals profiles.Rather, there may have been an impurity in this samplethat could account for this peak.

4. Conclusions

The historical sources of contaminant metals to the Eliz-abeth River are primarily derived from the extensive fossilfuel industry developed early in the 1800s. Secondarysources of pollutants are likely due to shipbuilding opera-tions and increases in automotive emissions during the1900s. While the sources of contamination are similar ineach portion of the river, the enrichment factor profilesindicate that the maximum input of metals in occurred atseparate points in time in the two areas sampled. In theWestern Branch, the maximum pulse of contaminationoccurred well before the 1954 137Cs horizon with a second-ary event for Cu, Pb and Zn occurring closer to, but stillprior to the horizon. The main peak in metals in the South-ern Branch at Paradise Creek occurred after 1954, muchlater than the pulse seen in the Western Branch sediments.Metals concentrations in both cores have markedlydecreased in recent years most likely due to the implemen-tation of stricter environmental controls. Despite theseefforts, the levels of contamination in the surface sedimentsof both cores are still enriched for many metals (Cu, Pb,Zn, and Cd). The surface concentrations are affected notonly by the timing and magnitude of the contamination,but also by sedimentary processes. X-radiographs for PC-1 were dominated by physical sedimentation processes asevidenced by the laminations in the sediments. This, cou-pled with the rapid decrease in metal concentrationstowards the surface suggests that the sediments are effec-tively sequestering the metals in this portion of the river.However, industrial and commercial activities in the South-ern Branch continue to introduce pollutants into the sedi-ments causing enrichment of many metals in thesesediments (Conrad and Chisholm-Brause, 2004). Althoughthe contamination occurred earlier in the Western Branchand is deeper in the sediments, some surface concentrationsare nearly as high as those seen in Paradise Creek eventhough the level of industrialization is much lower in thisportion of the river. The mottled features in the X-radio-graph indicate that there is extensive mixing throughoutthe upper portion of the Western Branch core, which couldresult the cycling of contaminated sediments back to thesurface.

Acknowledgement

The authors thank Linda Meneghini for her technicalsupport on this project. This work is funded by the Na-tional Sea Grant College Program of the National Oceanic

and Atmospheric Administration, US Department ofCommerce, the Virginia Marine Science Consortium andthe Virginia Sea Grant College Program. This paper is con-tribution number (to be inserted prior to publication) fromthe Virginia Institute of Marine Science, The College ofWilliam & Mary.

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Assessment of the historical trace metal contamination of sediments in the Elizabeth River, Virginia