Benthic Fluxes of Cadmium , Lead , Copper and Nitrogen Species in the Northern Adriatic Sea in Front of the River Po Outflow , Italy - Zago Et Al

.The Science of the Total Environment 246 2000 121]137

Benthic fluxes of cadmium, lead, copper and nitrogenspecies in the northern Adriatic Sea in front of the

River Po outflow, Italy

Cristina Zagoa,U, Gabriele Capodaglioa,b, Sergio Ceradinic,Giovanni Ciceric, Luisa Abelmoschid, Francesco Soggiad,

Paolo Cescona,b, Giuseppe Scarponie

aDipartimento Scienze Ambientali, Uniersita Ca Foscari di Venezia, Dorsoduro 2137, 30123 Venezia, Italy` `bCentro di Studio sulla Chimica e le Tecnologie per lAmbiente-CNR, Venezia, cro Uniersita Ca Foscari di Venezia,` `

Dorsoduro 2137, 30123 Venezia, ItalycENEL, SRI, Via Reggio Emilia 39, 20090 Segrate, Milano, Italy

dDipartimento di Chimica e Chimica Industriale, Sezione Chimica Analitica ed Ambientale, Via Dodecaneso 31, 16146Genoa, Italy

eInstituto di Sciente del mere, Uniersita di Ancona, Via Brecce Bianche, 60131 Ancona, Italy`

Received 1 June 1999; accepted 13 October 1999

Abstract

. .Trace heavy metal Cd, Pb and Cu and nitrogen species N-NO , N-NO and N-NH fluxes between sediment3 2 4and water were examined for approximately 4 days, in a coastal marine station located in the northern Adriatic Seain front of the River Po outflow. An in situ benthic chamber, equipped with electronic devices for monitoring andadjustment of oxygen and pH and with a temperature detector, was used. The benthic chamber experiment enabledstudy of the temporal trend of metals and nutrients when oxygen concentration varied in a controlled environment.Although particular care was devoted to chamber deposition and parameter control, sediment resuspension occurredat the beginning of the experiment and O fluctuations were observed during the course of the experiment. Pb2concentration was affected by both resuspension and oxic conditions in bottom water, which prevented determinationof any reasonable Pb flux value. Cd and Cu, not influenced by oxygen fluctuations, reached an equilibrium phase in a

. . y2 y1short period with initial positive fluxes from sediment of 0.68 S.D.s0.07 and 6.9 S.D.s5.6 pmol cm h ,respectively. With regard to nitrogen species, the highest positive flux was that of N-NH 10.5, S.D.s2.4, nmol4

y2 y1. cm h whose concentration increased in the chamber, while nitrate concentration initial flux of y5.7,y2 y1.S.D.s1.5, nmol cm h immediately decreased after the beginning of the experiment. Nitrite concentration was

U Corresponding author. Tel.: q39-0412578504; fax: q39-0412579549.

0048-9697r00r$ - see front matter Q 2000 Elsevier Science B.V. All rights reserved. .PII: S 0 0 4 8 - 9 6 9 7 9 9 0 0 4 2 1 - 0

( )C. Zago et al. r The Science of the Total Enironment 246 2000 121]137122

y2almost constant throughout the experiment and its flux was generally low initial flux 0.1, S.D.s0.9, nmol cmy1.h . Q 2000 Elsevier Science B.V. All rights reserved.

Keywords: Po River outflow; Metals; Nitrogen; Benthic fluxes

1. Introduction

The sediment]water interface of a marine basinis the site where gradients in chemical, physical,and biological properties are the greatest. Fluxesof constituents through this interface, called ben-thic fluxes, affect element concentrations in bothpore waters and overlying bottom waters; thusthey are important processes of the whole marine

biogeochemical cycles of many elements ValKlump and Martens, 1981; Santschi et al., 1990;Rivera Duarte and Flegal, 1994; Riedel et al.,

.1997 . Processes responsible for these benthicfluxes are usually the upward flow of pore watercaused by hydrostatic pressure, molecular diffu-

sion due to concentration gradients e.g. concen-trations in pore waters are generally higher than

.in overlying waters , and mixing of sediment andwater at the interface due to bioturbation and

water turbulence Santschi et al., 1990; Petersen.et al., 1997 .

In coastal areas, due to settling of particulatematerial, elevated amounts of pollutants are fre-quently accumulated in sediments, which indeedconstitute an enormous potential repository forcontinuing inputs, with capability of transferringaccumulated material to the coastal ecosystemeven after anthropogenic inputs have been re-duced or eliminated. For many chemical species,sediments constitute the final repository. How-ever, chemicals may be recycled many times acrossthe sediment]water interface before being per-

.manently buried Santschi et al., 1990 . Dia-genetic reactions contribute to this cycling, and,for example, metals temporarily stored in sedi-ments may dissolve in porewaters and diffuse tooverlying waters due to gradient concentrations.

Direct measurements of benthic fluxes can beobtained by using benthic chambers Ciceri et al.,

.1992; Giblin et al., 1997 . Benthic chambers arebased on a simple principle. A known sea watervolume and a known sediment surface are isolated

inside the chamber during the experiment period.Water samples are periodically collected andanalysed to monitor oxygen conditions inside thechamber and to follow the temporal trend ofstudied elements. Benthic fluxes are finally esti-mated from concentration changes in time. Dif-ferently from the case of large box core sampling,an in situ chamber allows a benthic environmentto be enclosed without its removal from the origi-nal place, and thus permits estimation of benthicfluxes with minimal perturbations. Diagnostic

parameters such as temperature, oxygen, pH,.Eh measured in the enclosed water trace impor-

tant changes inside the chamber. The rise ofanoxic conditions inside the chamber during theexperiment can produce fluxes which are much

higher than the real ones Hammond et al., 1985;.Sundby et al., 1986 . For this reason oxygen and

pH need to be kept almost constant throughoutthe experiment. External additions are generallyperformed to balance the effect of microbial de-composition of organic matter, which lowers oxy-gen and pH inside the chamber.

The use of a benthic chamber to determinefluxes at the sediment]water interface in an al-most anoxic environment is useful to understandwhat happens in metal and nutrient cycling whenlow oxygen concentrations are present in bottomwaters, a phenomenon that frequently occurs incoastal and organic rich waters. In the presentstudy, a highly anthropised coastal marine envi-ronment of the northern Adriatic, influenced bythe River Po outflow, was selected for the benthicfluxes experiment as anoxic conditions commonly

occur in late summer Spagnoli and Bergamini,.1997 . In summer, the circulation of waters in this

area is rather slow in winter a fast-moving cy-.clonic system prevails , with a horizontal stratifi-

cation in the water column Barbanti et al., 1995;.Spagnoli and Bergamini, 1997 . To quantify the

benthic fluxes in the anoxic period a benthic

( )C. Zago et al. r The Science of the Total Enironment 246 2000 121]137 123

chamber was located in early October 1996 byexpert scuba divers at a coastal site, at a depth of20 m. The benthic fluxes of some heavy metals . Cd, Pb, Cu and of nitrogen species N-NO ,3

.N-NO , N-NH were studied using an in situ2 4benthic chamber, fitted with an oxygen controldevice. Measurements were carried out in the

dissolved fraction of seawater filtrate from a.0.4-mm pore size filter . In the case of Pb, both

dissolved and particulate concentrations were de-termined due to the low amount of particulate

.matter only one metal could be determined .

2. Materials and methods

2.1. Laboratories, general equipment and materials

Clean chemistry laboratories with Class 100areas for the most critical procedures prepara-

tion and cleaning of sampling equipment andbottles, filtration and treatment of samples, vol-

.tammetric analysis were available both in theVenice University laboratory and on board.Laboratories, equipment and procedures have

been described elsewhere Ciceri et al., 1992;Capodaglio et al., 1994a; Scarponi et al., 1996;

.Zago, 1999 and the reader should refer to thisliterature for details.

2.2. Contamination control

Heavy metals dissolved in marine waters areusually present in very low concentrations nM or

.lower . For this reason it is of primary importanceto keep all materials and procedures involved incollecting, storing, and sample treatments andanalysis under rigorous contamination control inorder to prevent every possible sample contami-

.nation Mart, 1979a,b . In this work, careful at-tention with respect to any potential contributionto contamination was given to general laboratoryequipment, chemical reagents, materials used forsampling bottles, sampling equipment, storagebottles and their cleaning, on board laboratoriesand other facilities in the field, filtration devices

and procedures, storage conditions, pretreatmentof samples and final instrumental analysis see

.Scarponi et al., 1996 .Particular attention was devoted to cleaning

the FEP Teflon Fluorinated Ethylene Propylene,.Nalgene bottles, following the procedure de-

.scribed in Scarponi et al. 1996 which provides .for both HNO and HCl Merck, Suprapur acid3

treatments. On board, bottles were conditionedbefore use, filling them a few times with filtratedseawater collected on site.

All the materials used for sampling, filtrationand sample treatments followed similar acidcleaning procedures in order to obtain an ele-vated cleanness standard. Policarbonate filters

.were cleaned with diluted HCl Merck, Suprapur .Before use, filters was conditioned with filteredseawater.

2.3. Benthic chamber experiment

The experiment was carried out from 7 to 11October 1995 at a coastal site in front of theRiver Po outflow, 44844945.700N, 12827916.300E, .Fig. 1 . During chamber positioning, the scubadivers observed a high presence of particulateand colloidal material close to the bottom. The

Fig. 1. Map of the northern Adriatic Sea in front of the riverPo outflow showing the site of study. Cruise Prisma I .MURST , research vessel Urania, October 7]11, 1995, site .18 S1 .


chamber was carefully deposited on the bottomusing all precautions required to not disturb thesuperficial sediment.

An in situ benthic chamber of cylindrical shape .internal diameter 70 cm, height 32 cm and

.volume of approximately 120 l was used Fig. 2 .Probes for temperature, O and pH measure-2ments were mounted inside the chamber. Devicesfor O and pH adjustments were also available to2prevent anoxia and increasing acidity. External

.additions of O Chromatographic grade were2performed by the use of a diving bomb lower

y1 .non-intervention limit 1.2 mg l . Added oxygenvolumes were controlled by an electronic moni-toring device located on the water surface. Atirregular time steps, decided in the field by theoperator and related to oxygen concentrationsinside the chamber, but constrained by logistic

.feasibility, 30 or 60 ml atmospheric pressureoxygen aliquots were added. To prevent pH de-crease, 1.4-ml aliquots of a 0.1 M NaOH solutionwere automatically added when the pH inside thechamber passed from the original value of 7.9 to

7.8 lower non-intervention limit defined at the.beginning of the experiment . The NaOH solu-

tion used was previously purified in our cleanlaboratory using a Chelex-100 resin column.

To exclude any possible effects of metal con-tamination from gaseous oxygen and NaOH solu-

Fig. 2. Diagram of the in situ benthic chamber used for theexperiment.

Table 1 .Oxygen volumes at atmospheric pressure pumped inside the

benthic chamber to prevent anoxia during the experiment, atspecified times from the beginning of the experiment

.Time h Volume Time Volume . . .ml h ml

6 30 46.6 609 30 47.6 60

12 30 62.1 3015 30 65.1 3018 30 68.1 3021 30 71.1 3022.7 60 74.1 3023.3 60 77.2 3024.3 60 80.2 3025.3 60 83.2 3043.6 60 86.2 3044.6 60 89.2 3045.6 60 92.2 30

tion injected inside the chamber, tests were previ-ously performed in the laboratory. Two 2-l bottlesfilled with ultrapure water were insufflated every2 h with 45 ml of O for 30 and 60 h, respectively,2using the same oxygen bombs as those of thebenthic chamber experiment. The samples werethen analysed for Cd, Pb and Cu content. Thetests did not show any metal contamination in theinsufflated waters. Similarly, direct analysis of theNaOH solution showed no metal contamination.In Table 1 oxygen additions performed during theexperiments are reported. The NaOH additions .1.4 ml injected for 2 min every hour were per-formed starting from 16.5 h from the beginning ofthe experiment.

Approximately twice per day water samples for .determination of metals approx. 700 ml and

.nutrients approx. 300 ml were collected by aperistaltic pump connected with the benthic

chamber through a FEP sampling tube internal.diameter 6 mm . Samples were collected after

pumping approximately 400 ml of water deadvolume of the sampling tube connecting the ben-

.thic chamber with the sea surface . Water volumesextracted from the chamber were immediatelybalanced by drawing water from the outsidechamber environment through a pressure valvelocated in the benthic chamber walls. During the4 days of the experiment, nine samples were


. collected at the following times hours : 0 im-. mediately after deposition , 7, 12 only for nitro-

.gen compounds , 23, 33.5, 47, 57, 71, 81 and 95.The low volume of water collected from thechamber and replenished from the outside envi-ronment is considered irrelevant in comparison

with the total benthic chamber volume approx.0.8% of the total volume was sampled in eachdrawing and only approx. 10% in all the experi-

.ment .Filtration of samples was performed at the

.moment of sampling, using an FEP Fluorowareapparatus especially developed for on-line pres-sure filtration. The peristaltic pump was used to

apply a depression in the sampling bottle 2 l,.FEP and the sample was forced to pass through

the filter mounted in an in-line filter holder Flu-.oroware, Mod. 411 at the top of the bottle.

.Polycarbonate 0.4-mm filters Nuclepore wereused.

To preserve sample integrity with regard to the .total metal concentration Capodaglio et al., 1995

they were stored frozen at a temperature ofy208C without mineral acid treatment.

2.4. Voltammetric determination of Cd, Pb and Cuin seawater

The instrumentation assembly for voltammetricdeterminations of total dissolved Cd, Pb and Cuused in our laboratory consists of an elec-trochemical cell especially developed for ultra-

trace metal determination in seawater EG&G,. Model Rotel 2, Munich, Germany Mart et al.,

.1980 and of a voltammetric device with anodicstripping capability in the differential pulse mode,

DPASV EG&G, Polarographic Analyzer, Model.384B, Princeton, NJ, USA .

.The electrochemical cell Teflon, PTFE isequipped with a rotating glassy carbon disk elec-

.trode, RGCDE, and an AgrAgCl, KCl sat.reference electrode to which all potentials arereferred. A Pt wire was used as an auxiliaryelectrode. The auxiliary electrode is inserted in-side small FEP tubes, filled with saturated KClsolution, and fitted with porous Vycor tips. ATeflon cap covers the cell and separates it fromthe Plexiglas box holding the electrode motor and

the cell controller. The cleanness obtained by thiselectrochemical cell makes it possible to ensure alow detection limit of DPASV of approximately

y1 .0.2 ng l for Cd and Pb Scarponi et al., 1997y1 .and 1 ng l for Cu Capodaglio et al., 1994b .

The working electrode was a preformed thin .mercury film electrode TMFE deposited on the

surface of the RGCDE just before beginning themeasurement. This technique, avoiding any exter-nal preconcentration, allows a high sensitivity anda low contamination risk.

To prepare the RGCDE for film deposition, itwas rotated at 1000 rev. miny1 and the smoothsurface was polished with wetted alumina powder .0.075 mm grain size or lower using a filter paper.The electrode was then rinsed for 5 min with1:200 diluted ultrapure HCl and then two orthree times with ultrapure water. The Hg film wasplated by controlled potential electrolysis of

.Hg II nitrate solution. The electrolytic solution isy2 . y4made 2.5=10 M in KCl ultrapure and 10

.M Hg NO and purged with N for at least 203 2 2 .min; Hg NO is prepared by oxidising hexadis-3 2

.tilled Hg with HNO NIST . Deposition was car-3ried out at y1.0 V for 20 min while the electrodewas rotating at 4000 rev. miny1. A quiescentperiod of 30 s follows and then a differentialpulse potential scan was carried out in the posi-tive direction until a potential of y0.18 V isreached with a scan rate of 10 mV sy1, a pulseheight of 50 mV and a pulse frequency of 5 sy1.

If the voltammogram obtained did not showany appreciable peak and the base current is

.sufficiently low 300]500 nA , then it was possibleto carry on the analysis of the samples; otherwisethe Hg film was destroyed and another prepared.The electrochemical assembly was rinsed by onealiquot of degassed sample before starting themeasurements.

Total dissolved metal concentration measure- .ments were carried out on UV digested pHf2

samples. In fact, due to the large amount oforganic matter expected in bottom water samplesof coastal areas, acid digestion alone was not

sufficient to release the metals completely espe-.cially in the case of Cu due to very strong bind-

ing of macromolecular ligands Scarponi et al.,.1996 . For acid digestion, 100 ml of 32% HCl


Ultrapure, NIST National Institute of Standards.and Technology, USA was added to 50 ml of

.sample Nurnberg et al., 1976 . The metal con-centrations introduced into the samples by this

y1HCl addition certification shows 0.014 ng l ofy1 .Cd and 0.006 ng l of Pb are lower than the

detection limits reported above Scarponi et al.,.1996 . UV irradiation of acidified samples was

.performed by high-power Hg lamp 1.2 kW for 4h.

Separate determinations of Cd and Pb on oneside, and Cu on the other were then performedaccording to the following procedure. Approxi-

mately 50 ml of digested sample precise volume.measured at the end of analysis is transferred

into the electrochemical vessel in the degassingposition of the cell assembly and purged for 20min with N . The vessel was then rapidly trans-2ferred in the measurement position of the cellwhere the TMFE has already been prepared,tested and rinsed. The metal deposition was then

carried out by constant potential electrolysis Cdand Pb determination:y0.95 V, 20 min; Cu de-

.termination:y 0.85 V, 10 min with electrode ro-tating at 4000 rev. miny1. After a quiescent pe-riod of 30 s a pulsed potential scan was applied inthe positive direction from the deposition poten-

tial to the final potential y0.18 V for Cd and Pb.and y0.15 V for Cu and the voltammogram

.recorded stripping step . At the end of the scan y1 .the rotation was restarted 4000 rev. min and

the potential held at y0.18 V for 5 min to cleanthe electrode of the residual amalgamated metals.To test electrode stability and repeatability of thevoltammogram, a second measurement was per-formed on the sample solution. Three standardadditions are used for quantification, each ableapproximately to double the peak obtained by the

sample deposition 20%50 ml of Cd and Pb stan-dard solutions of 100 mg ly1, 20 ml of Cu stan-

y1 .dard solutions of 600 mg l . After each additionthe voltammetric measurement is repeated. Thevolume of the sample is finally measured using agraduated cylinder and the working electrode isprepared for a new determination starting frompolishing.

The accuracy of laboratory measurements was .periodically verified generally every 2 weeks by

determining the metal content of the NASS-4seawater reference material National Research

.Council of Canada, Ottawa, Canada . The resultswere reported on a control chart, and typical

examples have already been reported see e.g..Scarponi et al., 1996; Zago, 1999 . Measurements

on samples were carried out only in the case ofvalues included in the certified tolerance interval.Otherwise, checks of the overall procedure andstandard concentrations were performed to re-store accuracy before running new measure-ments.

As regards repeatability, it is to be noted thatfor each sample measurements were repeated

.three times see below and the relative pooledstandard deviations were approximately 5.5%,8.4% and 4.8% for Cd, Pb and Cu, respectively.

2.5. Other determinations

Nitrate, nitrite and ammonium in filtrated sea-water were determined by colorimetric methods .Parson et al., 1984 . The nitrate concentration

.was determined by flow injection analysis FIA ,using a Lachat Quickchem Automatic Flow Injec-tion Ion Analyzer. The method is based on thereduction of nitrate to nitrite in a cadmium cop-perised column followed by a spectrophotometricdetermination of nitrite after diazotisation reac-

.tion with sulphanilamide by N- 1-naftil ethylene-diamine ?2 HCl. Nitrite was determined using thesecond step of the previous procedure. The detec-tion limits are 2 and 0.1 mg ly1 for nitrate andnitrite, respectively. The ammonium determina-tion was also performed by FIA using the colori-metric method based on the Berthelot reaction .Solorzano, 1969 . The detection limit of thistechnique is 1 mg ly1.

Temperature, oxygen concentration and pHwere measured in situ during the benthic cham-ber experiment, using a multiparametric probe .Idronaut, Mod. 316 modified for trace metalanalysis. The probe was also used to control thedevices for oxygen and pH adjustment inside thebenthic chamber.

Due to the low water volume collected for eachsample, the particulate amount in filters allowedthe analysis of only one metal with the technique.


Lead was selected due to its known affinity withparticulate material Turekian, 1977; Rivera.Duarte and Flegal, 1994 .

Lead in particulate matter was determined byatomic absorption spectrophotometry GFAAS,

SpectrAA 400 Plus, Varian, equipped with.graphite furnace GTA96 after microwave diges-

.tion CEM Corporation, MDS-2000, 630 Watt inTeflon containers with pressure control Ad-

.vanced Computed Vessel, ACV . Filters weredried and weighted in a laminar flow hood Class

.100 . They were brought to constant weight andmicrowave acid digested with 3 ml of 8 M nitric

.acid Merck, Suprapur . The following programwas used: 0.5 min at 30% of microwave power, 0.5min at 40% and 1 min at 50%. The solution wasthen adjusted to 5 ml by adding ultrapure water .Millipore, Milli-Q . Filters were again dried inlaminar flow and brought to constant weight todetermine, by difference, the amount of solu-bilized particulate material. Lead determinationwas performed in the digested solution by thestandard additions method.

2.6. Calculation of benthic fluxes

The benthic flux of a chemical species at thesediment]water interface is defined as the massof that species flowing per unit of sediment sur-face and per unit of time. Considering the generictime interval between observations i and iq1

.carried out during the experiment with is1 ,n ,and defining the time interval as D t s t y t ,i iq1 ithe corresponding mass gradient measured in wa-ter as Dm sm ym and S the surface of thei iq1 isediment]water interface in the benthic chamber,the mean benthic flux in the considered timeinterval, F , can be computed using the equation:i

D mi .F s 1i S D ti

Usually S is given in cm2, D t in hours and theiunits of flux depend on units of Dm which, initurn, are related to the concentration units. De-noting DC sC yC as the concentration gra-i iq 1 i

y1dient in the considered time interval in nmol l ,

i.e. pmol cmy3, for trace metals, and in mmol ly1,y3 .i.e. nmol cm , for nitrogen species , V as the

3.volume of the benthic chamber in cm and H .the chamber height in cm , then

.Dm sDC V 2i i

and

.SsVrH 3

.can be substituted in Eq. 1 , giving the followingfinal equation for flux:

DC Hi .F s 4i D ti

with F expressed as pmol cmy2 hy1, for traceimetals, and as nmol cmy2 hy1 for nitrogenspecies, respectively.

Positive fluxes result when concentrations in-crease with time. In this event material releasefrom sediment andror from particulate matter tothe water phase is inferred. On the contrary,negative fluxes result when concentrations in wa-ter decrease with time. This last is the case oftransport toward the sediment or the particulate.It is to be remarked that in some cases, chemicaltransformations between different chemical formsof the same element present in the water phasecan also simulate benthic fluxes. Moreover, con-comitant processes occurring in both directions atthe sediment]water interface can occur. In bothcases apparent fluxes are observed from mea-surements carried out only in water, representingthe overall result of all possible processes. Due to

the general non-linear temporal profiles except.for N-NH natural fluxes were calculated from4

concentration gradients determined between thestart of the experiment and the subsequent obser-

w . xvation Eq. 4 for is1 . In the case of N-NH4linearity was observed within the first 33.5 h ofthe experiment, thus natural flux was computedas the average of individual values measured upto this time.


3. Results and discussion

3.1. General characteristics of the enclosure duringthe experiment

Temperature, oxygen, pH and particulate mat-ter changes during the experiment are shown inFig. 3. Temperature was almost constant through-out the experiment with a very slight decrease intime. At the beginning, low oxygen concentration,

y1 approximately 1.3 mg l close to anoxia and toy1 .the intervention limit of 1.2 mg l , was mea-

sured inside the chamber. Similar conditions arefrequently found, at the end of the summer pe-riod, in the bottom waters of many estuaries andcoastal areas due to seasonal stratification of wa-

ter masses Officer et al., 1984; Selinger et al.,.1985 . In spite of the oxygen additions performed

inside the chamber when the intervention limitwas reached 6 h from the beginning of the exper-

.iment and continuing every 3 h, see Table 1 ,oxygen concentration decreased continuously. Af-

.ter 21 h it decreased Fig. 3 to the lower accept- y1 .able level 0.12 mg l decided as the point of

further intervention to prevent strongly anoxicconditions occurring inside the chamber. Then,the oxygen flow pumped into the benthic chamber

was temporarily enhanced both in quantity from. 30 to 60 ml and in frequency pumping every ;1

.h , the first time from 22.7 to 35.3 h, and the .second from 43.6 to 47.6 h Table 1 . The original .programme of O additions 30 ml every 3 h was2

restored after 62.1 h and continued until the endof the experiment. The fluctuations in oxygen

concentration measured inside the chamber Fig..3 are consequences of these changes in oxygen

fluxes.The pH inside the chamber ranged between

.7.90 and 7.67 throughout the experiment Fig. 3 .The reduced variation allowed us to consider pHalmost constant.

Although the chamber was carefully depositedon the bottom, as already described, a smallamount of resuspension occurred. The particulatematerial inside the benthic chamber increasedconsiderably at the beginning of the experiment

suggesting a sediment and consequently pore.water resuspension due to chamber placement

Fig. 3. Temporal trends of temperature, oxygen, pH and par-ticulate material inside the benthic chamber.

.Fig. 3 . The low value of particulate matter mea-sured at time zero refers to the sample collectedfrom the top of the chamber, before resuspensionaffected this part of the enclosure. For this rea-son it represents the original particulate content

in the site under study. Subsequently after thefirst 7 h, the particulate matter inside the cham-ber strongly decreased due to particulate settlingand the system reached approximately the initialconditions after approximately 60 h. In the caseof resuspension, the concentrations of elementswith high affinity with particulate, e.g. Fe, Mn and


Table 2Cd, Pb and Cu concentrations determined in seawater sam-ples collected during the experiment

y1 . .Time h Metal concentrations nmol l

.Repetitions Mean R.S.D. %

Cadmium0 0.26, 0.17, 0.21 0.21 217 ], ], ] ] ]

23 0.73, 0.69, 0.69 0.70 3.333.5 0.70, 0.64, 0.58 0.64 9.447 0.69, 0.67, 0.66 0.67 2.357 0.62, 0.64, ] 0.63 2.271 0.63, 0.67, 0.72 0.67 6.781 0.66, 0.60, 0.65 0.64 5.095 0.18, 0.27, 0.25 0.23 20

Lead0 0.26, 0.33, 0.34 0.31 147 0.71, 0.72, 0.62 0.68 8.1

23 0.09, 0.11, 0.10 0.10 1033.5 0.50, 0.49, 0.49 0.49 1.247 0.15, 0.14, 0.14 0.14 4.057 0.19, 0.19, ] 0.19 0.071 0.11, 0.12, 0.11 0.11 5.181 ], 0.08, 0.06 0.07 2095 0.04, 0.05, 0.06 0.05 20

Copper0 9.1, 9.2, 8.5 8.9 4.27 10.0, 9.5, 11.7 10.4 11

23 9.6, 8.8, 9.2 9.2 4.333.5 9.0, 9.6, 9.7 9.4 4.047 9.2, 9.7, 10.4 9.8 6.257 9.6, 10.0, 10.7 10.1 5.571 10.5, 10.6, 10.6 10.6 0.581 10.6, ], 9.9 10.2 4.895 4.0, ], 3.9 4.0 1.8

Pb, may artificially change in both water andsuspended matter, with consequent modifications

of the original benthic fluxes Turekian, 1977;Forstner and Wittman, 1979; Rivera Duarte and

.Flegal, 1994 .

3.2. Trace metals

The Cd, Pb and Cu concentrations in sea watersamples and the Pb concentration in particulate

matter referred to both weight of particulate,y1 y1.nmol g , and volume of water, nmol l ,

together with their mean values and analytical

Table 3Particulate Pb concentration during the experiment referredboth to particulate mass and to seawater volume

.Time h Particulate Pb concentration


y1nmol g0 47, 47, 49 48 2.47 155, 154, 159 156 1.7

23 127, 123, 127 126 1.833.5 77, 74, 71 74 4.147 28, 29, 29 29 2.057 28, 28, 29 28 2.0

a a71 111, 110, 110 110 0.581 57, 57, 59 58 2.095 41, 41, 42 41 1.4

y1nmol l0 0.25, 0.25, 0.26 0.25 2.37 4.00, 3.96, 4.09 4.02 1.7

23 2.18, 2.12, 2.19 2.16 1.833.5 0.99, 0.95, 0.92 0.95 3.747 0.34, 0.35, 0.34 0.34 1.757 0.26, 0.26, 0.26 0.26 0.0

a a71 1.15, 1.14, 1.14 1.14 0.581 0.49, 0.49, 0.50 0.49 1.295 0.40, 0.40, 0.41 0.40 1.4

a Contaminated sample.

repeatabilities, are reported in Tables 2 and 3.The sample collected for particulate Pb at 71 hproved to be contaminated and the correspondingoutlying value was not considered in furtherelaborations. The different behaviours observedfor Pb, on one side, and Cd and Cu, on the other,suggest to describe metals results in this twometal grouping.

3.2.1. LeadFig. 4 shows the concentration trends of Pb in

the particulate fractions during the experiment.Data on particulate content are also shown.

The particulate fraction of the total lead con-centration in seawater particulate lead in nmol

y1 .l shows a very similar trend to that of theparticulate amount, both with an initial substan-tial increase, followed by a gradual decrease dur-ing the experiment, initially more rapid and then

.rather slow. Indeed, a good correlation rs0.96is observed. This result confirms the occurrenceof sediment resuspension at the beginning of the


y1 . y1 .Fig. 4. Particulate Pb expressed in nmol g dashed line , and nmol l small dotted line measured inside the benthic chamber .during the experiment. The content of particulate matter is also reported continuous line . Error bars "1 S.D.

experiment as observed through the Pb be-haviour. As regards the lead content in particu-late matter expressed in nmol gy1, it is less af-fected by resuspension than the previous variable,and the correlation with the amount of particu-late matter is reduced to 0.88. However, an in-crease of lead content in particulate matter from

y1 . the initial value 47 nmol g to 7 h later 155y1 .nmol g was observed, and it corresponds to

the maximum particulate content inside thechamber. Thus, Pb concentration in suspendedmatter ranged between the value of the originalparticulate matter, in the case of no resuspension .beginning of the experiment , and that of sedi-ment when resuspended matter predominates inthe particulate. By this result, it is reasonable toconclude that Pb concentrations in superficialsediments were higher than those of the originalparticulate material. After 47 h, Pb concentra-

y1 .tions expressed in nmol g in Fig. 4 againshowed values similar to the initial ones, meaningthat resuspended material, presumably composedby particles with larger mass grains and with ahigher sedimentation rate, had sank into the sedi-

.ment Forstner and Wittman, 1979 .The Pb concentration in the dissolved fraction

shows a temporal trend which highlights the in-fluence of both resuspension and oxygen concen-

.tration Fig. 5 . Indeed the trend of soluble leadconcentration in time shows a temporary initial

.increase observed after 7 h of experiment fol-lowed by a general decrease during the experi-ment, related to the sediment resuspension, withsuperimposed fluctuations corresponding to thoseof oxygen content.

The fluctuations of Pb concentration during theexperiment should not be attributed to possibleexternal contamination caused by oxygen inflowfor two reasons. First of all, as explained in theexperimental part, the oxygen inflated from thediving bomb was tested for metal contaminationbefore the experiment and proved uncontami-nated. Secondly, the relationship stressed hereregards the O concentration in water and not2the volume of O added, which has a very differ-2

.ent pattern see Table 1 .The observed relationship between dissolved

.lead and oxygen concentrations rs0.61, Fig. 5suggests that the detected increase of dissolvedlead concentration could be due to oxidation oforganic matter, caused by increased fluxes of oxy-gen pumped inside the chamber. The oxidation oforganic matter seems to induce Pb release fromsuperficial sediment but not from particulate ma-terial toward the dissolved phase; practically noPb decrease, related to the oxygen increase, is

.evident in the particulate matter Fig. 4 . More-over, oxidation of unstable sulphides present insuperficial sediments could cause upward diffu-

.sion fluxes from pore waters. Petersen et al. 1997


Fig. 5. Cd, Pb and Cu dissolved concentrations measuredinside the benthic chamber during the experiment. For com-parison the oxygen trend is also reported. Error bars "1 S.D.

studied the impact of microbial activity on therelease of trace elements by parallel incubation ofsediment suspensions under different conditions.The authors found that trace elements can bereleased during the reoxidation of anoxic sedi-ments and that this release is strongly affected bymicrobial processes. At a temperature of 208C,similar to the temperature measured inside the

.benthic chamber, Petersen et al. 1997 foundthat the sediment suspension in oxygenated watercaused an immediate reoxidation of sulphides tosulphates, which increase in solution. Their inves-tigations illustrated that biological activity had asignificant effect on sulphate release. These re-sults should support the hypotheses that the oxi-

dation of unstable sulphides increased Pb concen-trations inside the chamber when oxygen addi-tions were increased.

3.2.2. Cadmium and copperThe temporal trends of Cd and Cu concentra-

.tions proved similar to each other Fig. 5 . Theconcentrations of these two metals initially in-creased, until they reached an equilibrium periodwith stable values after 7]20 h from the begin-ning of the experiment. After approximately 80 h,when oxygen concentration inside the chamberdecreased for a relatively long period, Cd and Cuconcentrations decreased consistently, probablydue to precipitation processes toward the sedi-ment phase. Due to the particular temporal trendof Cd and Cu concentrations, which did not fol-

low the particulate trend see, e.g. the period of.stable concentrations , it is reasonable to suppose

that these metals were not affected by sedimentresuspension due to benthic chamber placement.However, the increase of Cd from 0.2 to 0.7 nmolly1 was probably due to porewater release fromsediment due to the increased pressure appliedon sediment during chamber positioning. On thecontrary, an increase of Cu did not occur. Ifporewater release from sediment occurred, theincrease of Cd and not of Cu suggests an enrich-ment of Cd and a higher CdrCu ratio in pore-water than in overlying waters.

Cd and Cu concentrations were not influencedby the observed oxygen fluctuations, with theexclusion of the final part of the experiment,when strictly anoxic conditions were present in-side the benthic chamber for relatively long time .Fig. 5 . In anoxic conditions, sulphates are re-duced to sulphides and metals such as Cd andparticularly Cu commonly precipitate as metal

sulphides in superficial sediments Westerlund etal., 1986; van der Sloot et al., 1990; Brugmann et

.al., 1992 .

3.3. Nitrogen species

Table 4 reports the nitrogen species concentra-tion in the collected seawater samples. The outly-ing value obtained for N-NO at 57 h is not3considered further. Note that the temporal trends


Table 4N-NO , N-NO and N-NH concentrations determined in3 2 4seawater samples collected during the experiment

y1 . .Time h Concentration mmol l


N-NO30 3.41, 3.73, 3.31 3.48 6.37 2.04, 2.15, 2.53 2.24 11.5

12 1.84, 1.72, 2.24 1.93 14.123 2.01, 1.83, 2.10 1.98 6.933.5 1.63, 1.32, 1.35 1.43 11.947 1.98, 2.19, 1.95 2.04 6.4

a57 3.67, 4.11, 3.79 3.86 5.971 2.64, 2.29, 2.33 2.42 7.981 2.01, 2.29, 2.24 2.18 6.995 2.25, 2.37, 2.23 2.28 3.3

N-NO20 1.33, 1.34, 1.57 1.41 9.67 1.61, 1.34, 1.36 1.44 10.5

12 1.45, 1.59, 1.34 1.46 8.623 0.80, 1.08, 0.91 0.93 15.233.5 1.01, 0.93, 1.16 1.03 11.347 1.34, 1.34, 1.28 1.32 2.657 1.17, 1.15, 1.05 1.12 5.771 1.89, 1.64, 1.65 1.73 8.281 1.73, 1.54, 1.67 1.65 5.995 1.12, 0.92, 1.04 1.03 9.8

N-NH40 8.3, 7.7, 7.7 7.9 4.47 9.5, 9.8, 9.5 9.6 1.812 12.1, 11.4, 11.5 11.7 3.223 14.9, 15.4, 14.8 15.0 2.133.5 19.0, 18.6, 18.4 18.7 1.647 19.6, 19.3, 19.8 19.6 1.357 18.3, 19.8, 18.8 19.0 4.071 21.7, 21.0, 21.1 21.3 1.881 22.4, 22.7, 22.7 22.6 0.895 24.3, 23.4, 23.3 23.7 2.3

a Contaminated sample.

.of these species Fig. 6 do not show any associa- .tion with the particulate matter Fig. 3 denoting

that resuspension apparently did not influencenitrogen species concentrations.

During the experiment, the N-NO concentra-3tion inside the benthic chamber initially de-creased and then it settled at an equilibriumvalue approximately 40% lower than the initial

.value Fig. 6 . A comparison between the nitrateand oxygen temporal trends shows that O fluc-2

Fig. 6. Temporal trends of nitrogen species inside the benthicchamber. For comparison the oxygen trend is also reported.Error bars "1 S.D.

tuations did not affect N-NO concentration.3Indeed laboratory experiments carried out by

.Petersen et al. 1997 showed that, due to thegrowing time required by populations of nitrifyingbacteria, nitrate concentration increased in solu-

tion only after longer periods approx. 170 h in.their incubation experiment than that observed

here during oxygen fluctuation. Probably for thisreason, in our experiment nitrate concentrationwas not influenced by oxygen fluctuations. Theinitial decrease can be interpreted in terms ofboth transport toward the sediment andror ni-

.trate reduction anaerobic conditions to ammo- .nia Santschi et al., 1990; Overnell et al., 1995 .

The N-NO concentration was almost constant2throughout the experiment, although some small


Table 5aBenthic fluxes obtained by benthic chamber

y2 y1 y2 y1 . . .Time h Flux pmol cm h Flux nmol cm h

Cd Cu N-NO N-NO N-NH3 2 4

. . . .7 ] 6.9 5.6 y5.7 1.5 q0.1 0.9 q7.8 1.8 . . .12 ] ] y2.0 2.4 q0.1 1.2 q13.4 2.7

. . . . .23 q0.68 0.07 y2.4 2.4 q0.1 0.9 y1.5 0.5 q9.6 1.4 . . . . .33.5 y0.18 0.19 q0.6 1.7 y1.7 0.7 q0.3 0.6 q11.3 1.3 . . . . .47 q0.07 0.15 q0.9 1.7 q1.4 0.5 q0.7 0.3 q2.1 0.9 . . . .57 q0.13 0.07 q0.13 2.6 ] y0.6 0.2 y1.9 2.6 . . . . .71 q0.09 0.11 q1.1 1.3 q0.5 0.3 q1.4 0.4 q5.3 1.9 . . . . .81 y0.10 0.18 y1.0 1.6 y0.8 0.8 y0.3 0.5 q4.2 1.3 . . . . .95 y0.94 0.13 y14.4 1.1 q0.2 0.4 y1.4 0.3 q2.5 1.3

a Values are associated with the upper limits of the observation periods. Standard deviations in parentheses.

fluctuations, apparently inversely related to oxy-gen changes, were observed. However, thesefluctuations are almost within the experimental

.errors see error bars in Fig. 6 .The N-NH concentration increased almost4

continuously with time, as usually found in anoxic .environments Santschi et al., 1990 . During am-

monification, organic macromolecules present inthe superficial sediment andror in waters both

.in dissolved and particulate phases are hydrol-ysed, and organically bound nitrogen, mostly inthe form of aminoacids, is brought into solution.By deamination of aminoacids ammonium is re-

.leased into solution Santschi et al., 1990 . Morethan this, in anaerobic environments, nitrate re-

duction to ammonia frequently occurs Santschi.et al., 1990; Overnell et al., 1995 ; this possibly

happened at the beginning of the experiment seethe N-NO concentration decrease from the ini-3

.tial sample .

3.4. Benthic fluxes

Benthic fluxes were computed according to Eq. .4 , with is1, for all the species measured in thiswork. Results are reported in Table 5. Fluxes ofPb were not considered because, as reportedabove, this metal showed strong effects from sedi-ment resuspension and oxygen fluctuations.

Fig. 7. Cd and Cu benthic fluxes measured by the benthicchamber experiment. Flux values are associated with the up-per limits of the observation period. Error bars "1 S.D.

3.4.1. Metal speciesThe temporal trends of Cd and Cu fluxes inside

the chamber are shown in Fig. 7. For both metalsthe flux, after an initial positive value release

.from sediment or particulate , reduces rapidly toalmost zero and it remains negligible until 80 hwhen a negative flux is measured. This negativeflux is presumably related to the strictly anoxic

.conditions observed in this period see Fig. 3 and


Fig. 8. Nitrogen species benthic fluxes measured by the ben-thic chamber experiment. Flux values are associated with theupper limits of the observation period. Error bars "1 S.D.

the consequent metal sulphide precipitation insuperficial sediments.

3.4.2. Nitrogen species .Fluxes of nitrogen species Table 5 are shown

in Fig. 8. To allow a direct, quantitative compar-ison between fluxes of the three nitrogen species,the same scale was used in the graphs.

Nitrate flux proved negative at the beginning ofthe experiment the mean value obtained between

y2 y1.0 and 7 h is y5.7 nmol cm h after which itreduces to negligible values within approximately15 h.

Nitrite flux was generally the lowest of thenitrogen species. It does not show a clear tem-

poral trend and a few changes apparently in-

.versely related to oxygen fluctuations are only alittle higher than the experimental error see

.error bars in Fig. 8 .Ammonium flux presents higher values than

those of nitrate and nitrite. It assumes the highestpositive values within the first ;30 h of experi-

y2 y1.ment means10.5, S.D.s2.4 nmol cm h , it .remains low or negligible between ;30 h and

;60 h, after which it increases to values around5 nmol cmy2 hy1 until ;80 h, and finally itreduces again.

3.5. Comparison with literature data

To summarise, our best estimates of benthic y2 y1fluxes are the following in pmol cm h and

nmol cmy2 hy1 for metal and nitrogen species,.respectively : Cd 0.68, Cu 7.8, N-NO y5.7, N-3

NH 10.5. No values could be determined for Pb4due to the influence of sediment resuspension,whereas for N-NO results were not significant2with respect to measurement errors. Thus, exceptfor nitrate, apparent fluxes from sediment to wa-ter have been detected.

In Table 6 metal and nitrogen benthic fluxesmeasured in different coastal environments arecompared with our results. The table does notreport N-NO data because no reference was2found in the literature. Fluxes obtained in thepresent study in the northern Adriatic Sea infront of the River Po outflow were generally ofthe same order of magnitude as values found inthe literature, except for nitrate. The negativenitrate fluxes and positive ammonium fluxesobserved in our experiment indicate that possibly,at the beginning of the experiment, nitrate re-duces to ammonium as usually found in anoxic

environments Santschi et al., 1990; Overnell et.al., 1995 . This usually happens in coastal waters

when, due to summer water stratification, anoxicconditions frequently occur close to the bottom.However, N-NO reduction accounts for only part3of the apparent N-NH flux from sediment. In-4deed, N-NH can be released from the sediment,4in anoxic conditions, without oxidation at thesediment]water interface due to reduction of the

oxic barrier Val Klump and Martens, 1981; Balzer.et al., 1987 . As in our results, Bertuzzi et al.


Table 6 .Benthic fluxes measured in different coastal environments standard deviations in parentheses

y2 y1. y2 y1 .Site Flux pmol cm h Fluxes nmol cm h Reference

Cd Cu N-NO N-NH3 4

. . . .Po Estuary, north Adriatic Sea, Italy 0.68 0.07 6.9 5.6 y5.7 1.5 7.8 2.4 Present study .Ansedonia Bay, Tirrenian Sea, Italy 1.4 7.1 ] ] Ciceri et al. 1992

.Bang Pakong Estuary, Thailand 0.01%0.03 3.8%8.6 ] ] Cheevaporn et al. 1995 . .Gullmarsfjorden, Sweden Fall, winter 0.046%0.054 0.11%0.49 ] ] Westerlund et al. 1986

.Kalix River Estuary, Sweden ] 0.33%1.02 ] ] Widerlund 1996 .Chesapeake Bay, USA ] 1.24%3.21 ] ] Riedel et al. 1997

.Boston Harbor, MA, USA ] 1.2%10 ] ] Zago et al. submittedCape Lookout Bight, NC, USA ] ] ] 2%120 Val Klump and Martens

.1981 .Boston Harbor, MA, USA ] ] 0.4%54 0.4%50 Giblin et al. 1997

. . .Gulf of Trieste, north Adriatic Sea, Italy ] ] 0.7 3.0 3.3 2.9 Bertuzzi et al. 1997

.1997 obtained the greatest negative nitrate fluxin late summer, when they registered oxygen de-pletion in bottom waters.

4. Conclusions

Although subsurface sediment may be the sinkfor trace metals and nitrogen species, the presentobservations with benthic chamber showed that atthe beginning of the experiment the surface sedi-ment is a net source to the overlying water forCd, Cu and NH . Under almost anoxic conditions4metals such as Cu and Cd in a reducing environ-ment can be mobilised from sediment and diffusefrom pore waters to the water column, androrthey can also be removed from the water column

by sulphide precipitation Westerlund et al., 1986;.van der Sloot et al., 1990; Brugmann et al., 1992 .

The equal occurrence of both these processes ispresumably the reason why, approximately 20 hinto the experiment, after an initial flux fromsediment to water, Cd and Cu reached an equilib-rium phase where release and precipitationprocesses were balanced. When strictly anoxicconditions occurred inside the chamber, Cd andCu presumably precipitated as sulphides andfluxes proved to be negative. Cd and Cu are infact known for their high affinity with sulphides toform a mineral phase in anoxic conditions .Forstner and Wittman, 1979 . As regards Pb,concentrations were affected both by lead resus-

pension from surface sediments and pore waterdue to the chamber positioning and by oxic condi-tions inside the chamber. In spite of this, thebenthic chamber experiment proved useful tostudy the geochemical behaviour of lead whenoxygen concentration changed in an almost anoxicenvironment. In this respect Pb showed a com-pletely different geochemical behaviour to that ofCd and Cu.

As regards nitrogen species, ammonium showedthe highest positive fluxes. Negative values are

observed for nitrate and negligible fluxes with.respect to the measurement error are estimated

for nitrite. The total apparent nitrogen flux atthe sediment]water interface sum of the differ-

.ent nitrogen species fluxes were positive. Thismeans that during the sampling period sedimentacted as a source of nitrogen to the overlyingwater.

The benthic chamber experiment showed thatin the coastal area in front of the River Po at theend of the summer period the apparent flux ofCd, Cu and N-NH moves from the sediment4

towards the water column positive net flux values.only at the beginning of the experiment , for

N-NO it is in the reverse direction, and for3N-NO it shows negligible values.2

Acknowledgements

This work was supported by the PRISMA1


Project of the MURST. We would like to thankDr Clara Turetta for her helpful comments onthe manuscript and for assistance in the labora-tory activities. Financial support was provided toCristina Zago by the MAS3 CT95 0021 Project ofthe European Union.

References

Balzer W, Erlenkeuser H, Hartmann M, Muller PJ, PollehneF. Diagenesis and exchange processes at the benthicboundary. Seawater]sediment interactions in coastal wa-ters, Lecture Notes on Coastal and Estuarine Studies, chap.4. Berlin: Springler-Verlag, 1987:112]158.

Barbanti A, Bergamini MC, Frascari F, Miserocchi S, RattaM, Rosso G. Diagenetic processes and nutrient fluxes atthe sediment]water interface, northern Adriatic Sea, Italy.Mar Freshwater Res 1995;46:55]67.

Bertuzzi A, Faganeli J, Welker C, Brambati A. Benthic fluxesof dissolved inorganic carbon, nutrients and oxygen in the

.Gulf of Trieste northern Adriatic . Water Air Soil Pollut1997;99:305]314.

Brugmann L, Bernard PC, van Grieken R. Geochemistry ofsuspended matter from the Baltic Sea 2. Results of bulktrace metals analysis by AAS. Mar Chem 1992;38:303]323.

Capodaglio G, Toscano G, Cescon P, Scarponi G, Muntau H.Collaborative sampling error assessment of trace metaldetermination in seawater. Ann Chim 1994a;84:329]345.

Capodaglio G, Toscano G, Scarponi G, Cescon P. Coppercomplexation in the surface seawater of Terra Nova Bay .Antartica . Int J Environ Anal Chem 1994b;55:129]1128.

Capodaglio G, Scarponi G, Toscano G, Barbante C, Cescon P.Speciation of trace metals in seawater by anodic strippingvoltammetry: Critical analytical steps. Fresenius J AnalChem 1995;351:386]392.

Cheevaporn V, Jacinto GS, San Diego-McGlone ML. Heavymetal fluxes in Bang Pakong River Estuary, Thailand:sedimentary vs diffusive fluxes. Mar Pollut Bull1995;31:290]294.

Ciceri G, Maran S, Martinotti W, Quierazza G. Geochemicalcycling of heavy metals in a marine coastal area: benthicflux determination from porewater profiles and in situmeasurements using benthic chamber. Hydrobiologia1992;235r236:501]517.

Forstner U, Wittman GTW. Metal pollution in the aquaticenvironment. Heidelberg: Springler-Verlag, 1979:473.

Giblin AE, Hopkinson CS, Tucker J. Benthic metabolism andnutrient cycling in Boston Harbor, Massachusetts. Estuar-

.ies 1997;20 2 :346]364.Hammond DE, Fuller C, Harmon D, Hartman B, Korosek M,

Miller LG, Rea R, Warren S, Berelson W, Hager SW.Benthic fluxes in San Francisco Bay. Hydrobiologia1985;129:69]90.

Mart L. Prevention of contamination and other accuracy risksin voltammetric trace metal analysis of natural waters. Part

I. Preparatory steps, filtration and storage of water sam-ples. Fresenius Z Anal Chem 1979a;296:350]357.

Mart L. Prevention of contamination and other accuracy risksin voltammetric trace metal analysis of natural waters. PartII. Collection of surface water samples. Fresenius Z AnalChem 1979b;299:79]1022.

Mart L, Nurnberg HW, Valenta P. Prevention of contamina-tion and other accuracy risks in voltammetric trace metalanalysis of natural waters. Part III. Voltammetric ultratraceanalysis with a multicell system designed for clean benchworking. Fresenius Z Anal Chem 1980;300:350]362.

Nurnberg HW, Valenta P, Mart L, Raspor B, Sipos L. Appli-cations of polarography and voltammetry to marine andaquatic chemistry. II. The polarographic approach to thedetermination and speciation of toxic trace metals in themarine environment. Fresenius Z Anal Chem 1976;282:357]368.

Officer CB, Biggs RB, Taft JL, Cronin LE, Tyler MA, Boyn-ton WR. Chesapeake Bay anoxia: origin, development andsignificance. Science 1984;223:22]27.

Overnell J, Edwards A, Grantham BE, Harvey SM, Jones KJ,Leftley JW, Smallman DJ. Sediment]water column cou-pling and the fate of the spring phytoplankton bloom inLoch Linhe, a Scottish Fjordic Sea-loch. Sediment processesand sediment]water fluxes. Estuar Coast Schelf Sci1995;40:1]17.

Parson T, Maita Y, Lolli CM. A manual for chemical andbiological methods for seawater analysis. Oxford: Perga-mon Press, 1984.

Petersen W, Willer E, Willamowski C. Remobilization of traceelements from polluted anoxic sediments after resuspen-sion in oxic water. Water Air Soil Pollut 1997;99:515]522.

Riedel GF, Sanders JG, Osman RW. Biogeochemical controlon the flux of trace elements from estuarine sediments:water column oxygen concentrations and benthic infauna.Estuar Coast Schelf Sci 1997;44:23]38.

Rivera Duarte I, Flegal AR. Benthic lead fluxes in San Fran-cisco Bay, California, USA. Geochim Cosmochim Acta

.1994;58 15 :3307]3313.Santschi P, Hohener P, Benoit G, Buchholtz-ten Brink M.

Chemical processes at the sediment]water interface. MarChem 1990;30:269]315.

Scarponi G, Capodaglio G, Barbante C, Cescon P. The anodicstripping voltammetric titration procedure for study of tracemetal complexation in sea water. In: Caroli S, editor.Element speciation in bioinorganic chemistry, chemicalanalysis series, vol. 135, chap. 11, 1996:363]418.

Scarponi G, Capodaglio G, Turetta C, Barbante C, CecchiniM, Cescon P. Evolution of cadmium and lead contents inAntarctic coastal seawater during the austral summer. Int JEnviron Anal Chem 1997;66:23]49.

Selinger HH, Boggs J, Biggley WH. Catastrofic anoxia in theChesapeake Bay in 1984. Science 1985;228:70]73.

Solorzano L. Determination of ammonia in natural waters byphenol-hydroclorite method. Limnol Oceanogr 1969;14:799]801.


Spagnoli F, Bergamini MC. Water]sediment exchange ofnutrients during early diagenesis and resuspension of anoxicsediments from the northern Adriatic Sea shelf. Water AirSoil Pollut 1997;99:541]556.

Sundby B, Anderson LG, Hall PO, Iverfelt MM, van der LoeffR, Westerlund SF. The effect of oxygen on release anduptake of cobalt, manganese, iron and phosphate at thesediment]water interface. Geochim Cosmochim Acta1986;50:1281]1288.

Turekian KK. The state of metals in the ocean. GeochimCosmochim Acta 1977;41:1131]1144.

Val Klump J, Martens CS. Biogeochemical cycling in anorganic rich coastal marine basin-II. Nutrientsediment]water exchange processes. Geochim Cosmochim

.Acta 1981;45 1 :101]121.van der Sloot HA, Hoede D, Hamburg G, Woitties JRW, van

der Weijden CH. Trace elements in suspended matter fromthe anoxic hypersaline Tyro and Bannock Basins eastern

.Mediterranean . Mar Chem 1990;31:187]203.Westerlund SFG, Anderson LG, Hall POJ, Iverfeldt A, van

der Loeff RMM, Sundy B. Benthic fluxes of cadmium,copper, nickel, zinc and lead in the coastal environment.Geochim Cosmochim Acta 1986;50:1289]1296.

Widerlund A. Early diagenetic remobilization of copper innear-shore marine sediments: a quantitative pore-watermodel. 1996;54:41]53.

Zago C, Giblin AE, Bergamasco A. Changes in the metalcontent of surficial sediments of Boston Harbor since thecessation of sludge discharge. Mar Environ Res, submitted.

Zago C. Benthic fluxes and transport processes of trace ele-ments in sea water. Ph.D. thesis. XI Cycle. Ferrara Univer-sity, 1999.

Documents

Benthic Fluxes of Cadmium , Lead , Copper and Nitrogen Species in the Northern Adriatic Sea in Front of the River Po Outflow , Italy - Zago Et Al