Intercalibration of benthic flux chambers I. Accuracy of flux measurements and influence of chamber...

Progress in
Oceanography
Progress in Oceanography 60 (2004) 1–28

www.elsevier.com/locate/pocean

Intercalibration of benthic flux chambers I. Accuracy offlux measurements and influence of chamber hydrodynamics

A. Tengberg a,*, H. Stahl a, G. Gust b, V. M€uller b, U. Arning b,H. Andersson a, P.O.J. Hall a

a Department Chemistry, G€oteborg University, SE-412 96 G€oteborg, Swedenb TUHH, Ocean Engineering 1, L€ammersieth 72, DE-22305 Hamburg, Germany

Received 30 January 2003; received in revised form 28 December 2003; accepted 7 January 2004

Abstract

The hydrodynamic properties and the capability to measure sediment–water solute fluxes, at assumed steady state

conditions, were compared for three radically different benthic chamber designs: the ‘‘Microcosm’’, the ‘‘Mississippi’’ and

the ‘‘G€oteborg’’ chambers. The hydrodynamic properties were characterized bymounting a PVCbottom in each chamber

and measuring mixing time, diffusive boundary layer thickness (DBL thickness) shear velocity ðu�Þ, and total pressure

created by the water mixing. The Microcosm had the most even distribution of DBL thickness and u�, but the highestdifferential pressure at high water mixing rates. The Mississippi chamber had low differential pressures at high u�. TheG€oteborg chamberwas in between the twoothers regarding these properties.DBL thickness and u� were found to correlateaccording to the following empirical formula: DBL ¼ 76:18ðu�Þ�0:933

. Multiple flux incubations with replicates of each of

the chamber typeswere carried out on homogenized,macrofauna-free sediments in four tanks. The degree of homogeneity

was determined by calculating solute fluxes (of oxygen, silicate, phosphate and ammonium) from porewater profiles and

by sampling for porosity, organic carbon andmeiofauna. All these results, except meiofauna, indicated that there were no

significant horizontal variations within the sediment in any of the parallel incubation experiments. The statistical eval-

uations also suggested that the occasional variations in meiofauna abundance did not have any influence on the measured

solute fluxes. Forty-three microelectrode profiles of oxygen in the DBL and porewater were evaluated with four different

procedures to calculate diffusive fluxes. The procedure presented byBerg,Risgaard-Petersen andRysgaard, 1989 [Limnol.

Oceanogr. 43, 1500] was found to be superior because of its ability to fit measured profiles accurately, and because it takes

into consideration vertical zonation with different oxygen consumption rates in the sediment. During the flux incubations,

the mixing in the chambers was replicated ranging from slow mixing to just noticeable sediment resuspension. In the

‘‘hydrodynamic characterizations’’ these mixing rates corresponded to average DBL thickness from 120 to 550 lm, to u�

from 0.12 to 0.68 cm/s, and to differential pressures from 0–3 Pa. Although not directly transferable, since the incubations

were done on a ‘‘real’’ sediment with a rougher surface while in the characterizations a PVC plate simulated the sediments

surface, these data give ideas about the prevailing hydrodynamic condition in the chambers during the incubations. The

variations in water mixing did not generate statistically significant differences between the chamber types for any of the

measured fluxes of oxygen or nutrients. Consequently it can be concluded that, for these non-permeable sediments and so

long as appropriate water mixing (within the ranges given above) is maintained, the type of stirring mechanism and

*Corresponding author. Tel.: +46-31-772-2776; fax: +46-31-772-2785.

E-mail addresses: [email protected] (A. Tengberg); [email protected] (P.O.J. Hall).

0079-6611/$ - see front matter � 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.pocean.2003.12.001

mail to: [email protected]

2 A. Tengberg et al. / Progress in Oceanography 60 (2004) 1–28

chamber design used were not critical for the magnitude of the measured fluxes. The average measured oxygen flux was

11.2� 2.7 (from 40 incubations), while the diffusive flux calculated (from 43 profiles using the Berg et al., 1989 [Limnol.

Oceanogr. 43, 1500] procedure) was 11.1� 3.0 mmol m�2 day�1. This strongly suggests that accurate oxygen flux

measurements were obtained with the three types of benthic chambers used and that the oxygen uptake is diffusive.

� 2004 Elsevier Ltd. All rights reserved.

Keywords: Benthic flux chambers, hydrodynamic properties, intercalibration, accuracy of flux measurements, repeatability of flux

measurements, porewater solute distributions, calculated solute fluxes, evaluation of procedures, Sweden, G€oteborg, G€oteborg

University

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2. Materials and methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Ack

Refe

2.1. Physical measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2. Comparative flux measurements and sediment sampling . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3. Evaluation of different procedures to predict fluxes from porewater profiles . . . . . . . . . . 9

2.4. Statistical evaluation of the results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3. Results and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.1. Hydrodynamic measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2. Sediment homogeneity and flux incubations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

nowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

rences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

1. Introduction

Several factors influence the decomposition of organic material in marine sediments such as deposition

rate (e.g. Canfield, 1993), chemical composition of the decomposing material (e.g. Kristensen, Ahmed, &Devol, 1995), availability of oxygen (e.g. Hulthe, Hulth, & Hall, 1998), temperature (e.g. Land�en & Hall,

1998) and biological reworking (e.g. Aller, 1982; Aller & Aller, 1998). Another factor is the hydrodynamic

conditions at the sediment–water interface (e.g. Boudreau & Guinasso, 1982). In general, higher water flow

velocities near the bottom will give higher bottom stresses s (friction velocities u� ¼ ðs=qÞ1=2) and thus a

thinner diffusive boundary layer (DBL) (Jørgensen & Des Marais, 1990). Enhanced activities of certain

groups of animals (e.g. Jumars, 1993; Vogel, 1981) may arise as well. Both processes may result in higher

sediment oxygen uptake rates (Hall, Anderson, Rutgers van der Loeff, Sundby, & Westerlund, 1989;

Jørgensen & Des Marais, 1990; Jørgensen & Revsbech, 1985). High bottom currents or water circulationabove permeable sediments with bedform roughness may also induce flow of porewater and advective

mixing of porewater with bottom water, influencing porewater solute distributions and sediment–water

exchange rates (Booij, Helder, & Sundby, 1991; Glud, Forster, & Huettel, 1996; Huettel & Gust, 1992b;

Huettel, Ziebis, & Forster, 1996).

Tools commonly used to study remineralization rates in sediments and to measure sediment–water

solute exchange include a variety of laboratory incubation systems (e.g. Booij, Sundby, & Helder, 1994;

Hall, Hulth, Hulthe, Land�en, & Tengberg, 1996; Hall, Hulth, Troell, & Faganeli, 1991; Silverberg et al.,

A. Tengberg et al. / Progress in Oceanography 60 (2004) 1–28 3

2000) and benthic-lander mounted in situ chambers (for a review of chamber and profiling landers, see

Tengberg et al., 1995). Different types of incubators employ different water mixing systems to prevent

gradient formation inside the chamber and to ‘‘mimic’’ the in situ hydrodynamic conditions. Several in-cubators and chambers have been studied and calibrated individually with focus on their hydrodynamic

properties and capabilities to measure benthic fluxes. Berelson, Hammond, and Cutter (1990) and Berelson

et al. (1990) studied benthic fluxes as a function of stirring speed in situ in the deep sea and did not find any

significant variations in the fluxes of oxygen, carbonate system species and nutrients. DBL thickness has

been measured directly with microelectrodes (e.g. Glud, Gundersen, Revsbech, Jørgensen, & Huettel,

1995), calculated from alabaster or hydroquinone dissolution (Opdyke, Gust, & Ledwell, 1987; Santschi,

Andersson, Fleisher, & Bowles, 1991; Vershinin, Gornizkij, Egorov, & Rozanov, 1994), or estimated from

uptake by the seabed of radiotracer (Dickinson & Sayles, 1992; Hall et al., 1989; Santschi, Nyffeler, �OHara,Buchhholtz-Ten-Brink, & Broecker, 1984; Sayles & Dickinson, 1991). Skin friction probes have been used

for direct shear stress measurements (e.g. Buchhholtz-ten-Brink, Gust, & Chavis, 1989; Gust, 1988), and

pressure gauges have been applied to measure differential pressures in chambers (e.g. Glud et al., 1996). The

capability of different field-going erosion chambers to create evenly distributed low and high bottom shear

stress was compared by Gust and M€uller (1997). Nicholson, Longmore, and Berelson (1999) compared the

capabilities of two chamber designs to measure fluxes of oxygen and nutrients in a shallow bay. Brostr€omand Nilsson (1999) coupled theoretically modelled hydrodynamic conditions in a chamber with the DBL

thickness, and Glud and Blackburn (2002) estimated through simulations the importance of using anappropriate chamber size when measuring fluxes in sediments with high macrofauna abundance.

Despite all these and other studies, there has not been any investigation directly coupling different

chamber designs and ensuing hydrodynamic properties with solute fluxes measured in the chambers for

impermeable homogenised sediments.

In this study we used measurements of the DBL thickness (with alabaster plates), shear stress (with skin

friction probes), total pressure (with a 10-channel pressure gauge) and mixing time to physically cha-

racterise three different benthic chamber designs. We then coupled these hydrodynamic properties, using

statistical methods, with replicate measurements of oxygen, phosphate, ammonium and silicate fluxes fromhomogenised sediments. The main goals of this study were to:

1. Compare the hydrodynamic performance characteristics of three different flux chamber types.

2. Establish if merely stirring is sufficient for flux experiments, or whether more ‘‘advanced’’ devices and

designs are needed to provide realistic hydrodynamic conditions for reliable and high-quality solute flux

measurements.

3. Compare and evaluate different procedures to calculate fluxes from solute profiles in the porewater of the

sediment.

4. Investigate how accurately fluxes can be measured and replicated with benthic chambers.

2. Materials and methods

Three chamber designs were compared in this study. The ‘‘Microcosm’’ is cylindrical with a diameter of 20

cm. For stirring it pumps fluid away from the center of the cylinder in combination with a rotating disk. This

chamber has been described previously by Gust (1990), Gust and M€uller (1997), Thomsen and Gust (2000).

The ‘‘G€oteborg chamber’’ used on the G€oteborg I lander (Tengberg, 1997; Tengberg et al., 1995) is cylin-drical and has a diameter of 15 cm. Its water is mixed by a relatively large paddle wheel mounted on a vertical

shaft placed off-centre in the chamber. Hydrodynamic complexity is added to the flow pattern by a large

oxygen electrode placed inside the chamber. The ‘‘Mississippi chamber’’, the largest of the three chambers, is

box-shaped (20� 20 cm). Stirring is achieved by a horizontal paddle wheel positioned centrally in the

chamber and extending over the full chamber width. This chamber is used on the G€oteborg Mini and


G€oteborg II landers (for recent work with the latter lander, see e.g. Rabouille et al., 2001; Ragueneau et al.,

2001; Tengberg, Almroth, & Hall, 2003). Detailed drawings of the three chambers and the locations of

hydrodynamic measurements made within them during this study are presented in Fig. 1.

2.1. Physical measurements

All the physical measurements were done by mounting a PVC plate in the chamber leaving 11 cm of

overlying water (Fig. 1). The same water height was also aimed for in the flux incubations. The physical

properties (e.g. roughness and topography) of the smooth PVC plate and the sediment are not the same.

Consequently, the results from the physical measurements only give indications about the prevailing hy-

drodynamic conditions in the chambers during the subsequent sediment incubations. A first mapping of thewater movement at different mixing rates was achieved by simple visualisation methods. Light reflecting

Fig. 1. Detailed scaled drawings of the three participating chambers and of the emplacement of pressure gauges, alabaster plates and

skin friction probes during the hydrodynamic assessment of each chamber. These sensors were mounted on temporarily glue-fixed PVC

plates inside the chambers. The positions of the skin friction probes are numbered (from 1 to 6). The type and number of sensors used

in each chamber are also listed along with the total chamber surface area.


aluminium particles (average size 40 lm) were mixed into the water and illuminated through a 10-mm wide

movable slit. Video recordings of the aluminium particle movement were used to decide on the location of

representative and ‘‘worst case’’ (highest total pressures, maximal shear stress, etc.) measurement positions.Total mixing time at different stirring rates was estimated by keeping the pH of the chamber water at the

transition point (colour change) for a phenolphthalein indicator and alternately injecting equivalent

amounts of base (giving pink colour) and acid (removing the colour). Injections were made through a hole

in the chamber lid by directing a base/acid filled automatic pipette towards the bottom and injecting 5 ml of

solution promptly. This resulted in the injection, which was slightly heavier than the chamber water, being

pushed to the bottom where it spread out and was mixed upwards into the water. The total mixing time was

then obtained, using a stop watch, by measuring the time for a complete (observed with the eye) colour

change in the chamber.Previous investigations of differential pressure in incubation chambers have been made with commer-

cially available, one-channel differential pressure gauges (e.g. Glud et al., 1995; Huettel & Gust, 1992a;

Huettel & Gust, 1992b). To enhance the measurement capabilities, a robust 10-channel instrument was

developed. It was based on commercially available, differential, piezo-resistive, air-pressure sensors from

Honeywell (mod. 142PC01G). Ten sensors were mounted with the necessary electronics (filters, amplifiers,

etc.) in a rigid, height-adjustable box. One opening, on each sensor, was left open to the air but well

protected inside the box. The other opening was connected to a 3-mm (inner diameter) 2.5 m long silicon

tube. The inner half of the tube was carefully filled with low viscosity silicon oil (Rhodorsil 47, Rhone-Poulenc, France). The other half was filled with distilled water and connected to holes of 3 mm diameter

drilled through the chamber bottom (see Fig. 2 for a description of the set-up and Fig. 1 for the location of

measurement spots in the chambers). Signals from each of the gauges were A/D converted (in a Biopac

Fig. 2. Schematic drawing of the 10-channel pressure gauge set-up that was constructed to map differential pressures at the bottom of

the chambers at different water mixing rates.


Model MP 100 A/D-converter) and collected at 4 Hz on a Macintosh computer using the software Acq-

Knowledge� 3.1.2. Before and after a set of measurements, each sensor was individually calibrated by

adding and removing a known volume of water with an automatic pipette. The system is capable ofmeasuring total pressures of 0–200 Pa with a repeatability of �0.03 Pa, and it has proven to be stable and

robust throughout a large number of experiments. Evaluation of each chamber at each stirring speed was

made during ten ‘‘stirring-on’’ and ten ‘‘stirring-off’’ cycles of 3 min each. The retained pressure at each on/

off interval was the mean value collected during the last minute. For verification of the influence of water

type (freshwater and seawater, 34 PSU) some of the measurements were made with both types of water. All

physical measurements made during the intercalibration are listed along with the number of replicates and

the temperature in Table 1.

We used the weight loss of 5 cm2 alabaster (CaSO4 � 2H2O) plates and the associated calcium increase inthe overlying water to estimate the diffusive boundary layer thickness (DBL thickness) in the chambers at

different water mixing rates. These methods have been described in detail in several previous laboratory and

in situ investigations (see e.g. Buchhholtz-ten-Brink et al., 1989; Opdyke et al., 1987; Santschi et al., 1991;

Santschi, Bower, Nyffeler, Azevedo, & Broecker, 1983). The chambers filled with freshwater were incubated

for about 10 h at constant temperature (18� 0.5 �C). Six samples (30 ml each) were taken sequentially from

the overlying water of each chamber and analysed for dissolved Ca2þ using an atomic absorption spec-

trophotometer (Perkin Elmer model #3110, analytical repeatability about 0.5% RSD). Replacement water

with an average Ca2þ-concentration of 1.6 lM was added. After the experiment, the plates were carefullyremoved from the embedding material present in depressions milled into the PVC bottom and allowed to

dry at room temperature until no additional weight loss between repeated weighings was observed. The

locations and number of plates used in each chamber are shown in Fig. 1.

Measurements of skin friction were executed concurrently at six different radial/diagonal positions in all

three chambers (Fig. 1) in time series of 5 min per value, permitting determination of the local instanta-

neous values collected at a sampling rate of 20 Hz per channel. Subsequent data processing with inclusion

of calibration coefficients provided mean values as well as variance, skewness and flatness of the bottom

stress s (or friction velocity u�). From these, spatially averaged values were calculated for each chamber andstirring rate. The measuring technique applied was constant-temperature hot-film anemometry, with sea-

water-resistant hot films as probes. Details of probe design, calibration features and performance are

presented in Gust and Weatherly (1985), Gust (1988), and Junglewitz, M€uller, and Gust (1997). The in-

vestigations were conducted at two different temperatures (8 and 18 �C) and calibration curves for the

probes were obtained prior to this work for stresses up to 0.4 N/m2 in a rotary calibration flume (a mi-

crocosm of 30 cm diameter). Temperature effects were fully compensated by a software-based algorithm

Table 1

Physical measurements made in each chamber during the intercalibration

Chamber 1 2 3 4

Mixing time Pressure DBL Shear velocity, u�

Number of experiments/

replication of each

experiment/temperature

(�C)


replication of each


(�C)


replication of each


(�C)


replication of each


(�C)

G€oteborg 5/10/18 5/10/18 2/4/18 4/10/18 4/10/8

Mississippi 6/10/18 6/10/18 of which 2/10/18 in

seawater

2/4/18 4/10/18 4/10/8

Microcosm 5/10/18 7/10/18 of which 3/10/18 in

seawater

4/3/18 7/10/18 7/10/8

The number of experiments, the replication of each experiment and the temperature and water type (freshwater and seawater) used

during the experiments are presented.


(Junglewitz et al., 1997). The relative error of the friction velocity due to the calibration and temperature

compensation methods applied is estimated at <4%.

2.2. Comparative flux measurements and sediment sampling

With an anchor dredge, 1.25 m3 of a silty sediment was collected at 34 m water depth (SE of Lillesk€ar inthe Koster Fjord, a coastal part of the Skagerrak, western Sweden) and sieved through 5 mm mesh-size

sieves. The sediment was split into two 0.62 m3 batches. The first, named finer sediment, was mixed with

industrial sand and bottom water (from the sampling site) to a volume ratio of 10:1:2 (sedi-

ment:sand:water). The second, called coarser sediment, was mixed to a volume ratio of 10:2:2 (sedi-

ment:sand:water). Both of the batches were thoroughly mixed for 3–4 h in a 6-m3 truck mixer (normallyused to mix cement at construction sites). Each of the homogenised batches was carefully filled into two 1

m� 0.75 m tanks (giving a total of four tanks) to an average sediment depth of 25 cm. On top of the

sediment, a 30 cm column of seawater (bottom water from the sampling site holding an approximate

temperature of 8 �C and a salinity of 26 ppt) was gently added. The four tanks were placed in dark con-

stant-temperature rooms (8.0� 0.6 �C) and left to settle for 20 days with air constantly bubbling in the

overlying water. In addition to oxygenating the overlying water, the air bubbling also created a slow water

circulation in the tanks. Eight days (190–192 h) before the flux incubations started in each tank, the

overlying water was exchanged with new water from the sampling site.Assessment of the sediment homogeneity was made through oxygen microelectrode (Revsbech, 1989)

measurements as well as sediment and porewater sampling. Each of the four tanks was divided into four

equal squares. In each square three oxygen microelectrode profiles (at a vertical resolution of 250 lm) were

obtained at random locations directly in the tank sediment before insertion of the chambers and start of the

incubations. After the incubations were finished, but before the chambers were retrieved, each square was

randomly sampled in triplicate (outside the chambers) for sediment by gently inserting 50-ml plastic sy-

ringes, from which the ends had been cut off and keeping the piston of the syringe in a steady position to

avoid compaction. The sediment was retrieved and sectioned into 10 mm slices. Known volumes, 2 ml, ofwet sediment from each slice were weighed, dried at 70 �C for at least 24 h, then weighed again. The po-

rosity was calculated from the water loss upon drying. For the calculations, a measured average solid phase

density of 2.7 kg dm�3and a water density of 1.02 kg dm�3 were used. The remaining sediment was put into

centrifuge tubes. Centrifugation for 30 min at 2100 rpm (and 8 �C) separated the porewater from solids.

The porewater was analysed spectrophotometrically (according to Strickland & Parsons, 1968) for nutrient

concentrations (silicate, phosphate and ammonium) on a TRAACS auto-analyser (precision 2%, n ¼ 20).

The solid phase was dried, homogenised (with a mortar and pestle) and analysed for the content of organic

carbon after acid treatment to remove inorganic carbon. The analytical instrument was a Phison Instru-ments Elemental CHN analyser (mod. NA1500NC). Furthermore, three samples for meiofauna were taken

with 3.8 cm2 tubes to a depth of 5 cm in each square. These samples were gently washed with tap water on a

40-lm sieve. The animals retained on the sieve were separated from the sediment by centrifugation in

Ludox HS-40 (McIntyre & Warwick, 1984). Organisms were identified to the major taxa (nematodes,

foraminifers, copepods, kinorynchs, ostracods, bivalves, annelids, ophiures and arcariens) and counted

under a stereo-microscope. Other details relating to the tank samples are given in Table 2.

Flux incubations were started in each tank by gently inserting the ten chambers (four replicates of each

of the G€oteborg and Mississippi chambers and two of the Microcosm) into the sediment and closing theirlids. Each lid was equipped with two valves; one for collection of water samples and the other for entry of

replacement water from the tank. The aim was to keep the overlying water column at similar heights in all

chambers; in reality it varied between 11.1 and 13.8 cm. The height was measured with a ruler before and

after the incubations at a minimum of 10 locations in each chamber. In the tanks the sediment surface was

approximately flat and without any noticeable variations of topography. A total of forty incubations (10 in

Table 2

Detailed description of the incubations and sampling carried out in the four experimental tanks

Tank # and

temperature

(�C)

Sediment type

Sed:Sand:Wat

(volume ratio)

and measured

fluxes

Number of flux incubations,

chamber and shear velocity

ðu�Þ (cm/s)

Approximate

DBL

thickness

ðlmÞ

Maximal

differential

pressure

(Pa)

Number each of

the sediment

solute profiles

Diffusion

coefficientd Dsw

(10�5 cm2 s�1)

Type and number

of other sediment

samples

2 G€oteborg at 0.34 cm/s 210 0.4 Oxygen, 10b 1.40

2 G€oteborg at 0.24 cm/s 290 0.2 Silica, 12c 0.76

1 10:1:2 1 Mississippi at 0.41 cm/s 180 1 Phosphate, 12c 0.83e Porosity profiles, 4

8.3 O2 and nutrientsa 1 Mississippi at 0.17 cm/s 400 0 Ammonium, 12c 1.21 Org-C profiles, 11

2 Mississippi at 0.12 cm/s 550 0 Meiofauna, 12

2 Gust at 0.68 cm/s 120 3

Total 10 Total 58


Sandy 2 G€oteborg at 0.24 cm/s 290 0.2 Silica, 12c 0.75


7.7 O2 and nutrientsa 2 Mississippi at 0.14 cm/s 480 0 Ammonium, 12c 1.19 Meiofauna, 12

2 Gust at 0.29 cm/s 250 0.2

Total 10 Total 58


Sandy 2 G€oteborg at 0.24 cm/s 290 0.2 Silica, 12c 0.74



2 Gust at 0.29 cm/s 250 0.2

Total 10 Total 60


2 G€oteborg at 0.24 cm/s 290 0.2. Silica, 6c 0.75



2 Gust at 0.29 cm/s 250 0.2

Total 10 Total 35

The temperature and type of sediment (sandy and less sandy) are given. The incubations made with each chamber and the individual hydrodynamic settings during

each of them are listed. The number and type of samples taken and measurements made in the sediment are presented along with the diffusion coefficients used to

calculate sediment–water fluxes from porewater distributions.aNutrients measured during flux incubations are the same as for the sediment solute profiles.bUsed boundary conditions to calculate oxygen fluxes with the Berg, Risgaard-Petersen, and Rysgaard (1998) model: oxygen flux¼ 0 and concentration¼ 0 at the

bottom of the profile.cUsed boundary conditions to calculate nutrient fluxes with the Berg et al. (1998) model: measured concentrations at the top and at the bottom of the profile.d The free diffusion coefficient in seawater at a salinity of 35 PSU, a pressure of 1 bar and the given temperature was obtained from Boudreau (1997) for nutrients and

from Li and Gregory (1974) for oxygen.e For phosphate an equal amount of H2PO

�4 and HPO2�

4 was assumed when calculating Dsw.

8A.Tengberg

etal./Progress

inOcea

nography60(2004)1–28


each tank) were carried out. Each of them lasted for 38–56 h. All the obtained results assume that steady

state conditions were prevailing during the incubations, making it possible to compare results among

chambers. Throughout the incubations, six water samples were taken at regular time intervals from theoverlying water in each chamber. At every sampling occasion, one volume-calibrated 50-ml glass syringe

was used to sample for oxygen and one 50-ml polypropylene syringe for nutrients. Prior to analysis or

storage, the samples in the plastic syringes were filtered through cellulose acetate filters (0.45 lm). All filters

were rinsed with 100 ml of Milli-Q water before use. Determinations of oxygen (by Winkler titration with a

precision of 0.6%, n ¼ 20) were made immediately after each sampling occasion. Addition of the Winkler

reagents to the samples were made directly into the glass syringes (Hall et al., 1989). Samples for nutrients

were frozen for about two weeks before they were analysed on the ‘‘TRAACS’’ auto-analyser (see above).

The replacement water, entering the chamber from the tank at each sampling occasion, was analysed fornutrients and oxygen. When calculating the fluxes in each chamber, compensations were made for the

replacement water. Since the chamber volumes were large compared to the replaced water volumes, and the

entry/exit of the incoming/outgoing water were well separated, it was assumed that none of the incoming

water was taken out with the syringe at each sampling occasion. If instead an immediate complete mixing

was assumed in the worst case, that is for the smallest chamber, the difference in flux between the two

methods was modelled to be less than 0.2%. Sampling and incubations made in the tanks are listed in Table

2. Some typical examples of flux incubation results are shown in Figs. 3(a)–(c).

2.3. Evaluation of different procedures to predict fluxes from porewater profiles

Several procedures, especially for oxygen, can be used to calculate sediment–water exchange fluxes from

measured solute profiles in the porewater. Even if these are based on the same basic assumptions and

equations they do not all give the same result when applied to the same set of data. Some of the procedures

have been described, discussed and compared by Revsbech, Madsen, and Jørgensen (1986), Epping and

Helder (1997), Silverberg et al. (2000) and Elberling and Damgaard (2001). All those investigations above,

as well as others, were carried out at natural sites, with natural variability and patchiness, and none of themcompared calculated fluxes with flux measurements made on homogenised sediment. In this investigation

we have chosen to use the 43 porewater oxygen profiles to evaluate and compare four procedures to cal-

culate fluxes from the profiles. The fluxes calculated with the procedure that was judged most reliable were

then compared with the fluxes measured in the chambers.

Since the sediment was sieved and free from macrofauna, we assumed that there was no active solute

transport through bioirrigation (e.g. Rutgers van der Loeff et al., 1984). As the sediment was non-

permeable, we expected that molecular diffusion was the main transport mechanism for all sediment–

water fluxes, both the calculated and the measured ones. We also assumed that the system was atsteady state, which is a prerequisite for most models. In the procedures presented below the diffusion

coefficient for oxygen in free seawater (Dsw in cm2 s�1) is needed as an input parameter. It was obtained

for the given temperature and salinity from tables compiled by Ramsing and Gundersen (available at

http://www.unisense.com/). These investigators used Broecker and Peng (1974) to obtain D0 for distilled

water at 10 �C and corrected it for the given temperature and salinity according to Li and Gregory

(1974) (see Table 2 for all the diffusion coefficients used in this investigation). The diffusivities corrected

for tortuosity were calculated as DS ¼ DswU2 according to Ullman and Aller (1982), where U is the

porosity. The oxygen profiles were obtained with higher vertical resolution (0.25 mm) than the porosityprofiles (10 mm). Porosity in the top 2.5 mm, the oxygenated zone, therefore was estimated through

linear interpolation as an average value in the top 2.5-mm of the sediment in each tank (Fig. 4). When

calculating fluxes from the porewater nutrient profiles, which were obtained with the same vertical

resolution as the porosity profiles, we used the average measured porosity for the given tank and

sediment depth.

http://www.unisense.com/

100

150

200

250

300

350

0 10 20 30 40 50 60

O2

[µM

]

Miss. 1D

Gust 2A

Gbg 4B

Time [h] Time [h]

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 10 20 30 40 50 60

PO

4 [µ

M]

Miss. 1B

Gbg. 1B

Gust. 4A

Time [h]

14

16

18

20

22

24

26

28

30

32

0 10 20 30 40 50 60

Si[µ

M]

Gbg. 1C

Miss. 4D

Gust 3B

(c)

(b)(a)

Fig. 3. Examples of typical solute concentration changes with time during individual chamber incubations. Such plots were used to

calculate and compare sediment–water fluxes. In total, results from nine different incubations are shown. (a) gives three examples for

oxygen, (b) three examples for phosphate and (c) three examples for silicate. Each data point represents a discrete sample taken with a

syringe. A linear concentration change with time was used to calculate the fluxes which assumes prevailing steady-state conditions

during the incubations.


(1) The first procedure we used to calculate fluxes was described by Cai and Sayles (1996). They compiled

data from several studies and concluded that there is a simple relationship between oxygen penetration

depth (L in mm), benthic oxygen flux (J in mmol m�2 day�1) and bottom water oxygen concentration

((O2)BW in lM). The relationship is:

J ¼ 8640 � 2/Ds

ðO2ÞBWL

:

The multiplication by 8640 in the equations converts the flux data to units of mmol m�2 day�1. It was

shown that this relationship holds well for continental margin sediments in which the oxygen penetration is

a few mm to cm. In deeper areas where the oxygen penetration is more than 10 cm it was reported that this

procedure is less precise (Cai & Sayles, 1996). The main intention of this empirical procedure was not toestimate fluxes but to calculate oxygen penetration depth. However, since the oxygen flux is included in the

relationship this procedure has also been used for flux calculations and we therefore have chosen to include

it in this intercomparison.

(2) Procedure No. 2 used the linear concentration change (dCðxÞ=dx; C in lM and x in mm) in the DBL

above the sediment to calculate the flux using Fick’s first law:

-60

-50

-40

-30

-20

-10

0

0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

Porosity

Dep

th in

sed

imen

t [m

m]

Tank 1

Tank 2

Tank 3

Tank 4

Fig. 4. Average porosity profiles in each of the four tanks. Each data point is an average of four individually measured values. The

standard deviation is given only for one of the profiles, but its magnitude is representative for all the profiles.


J ¼ �86406 � /Ds

dCðxÞdx

:

This procedure has been used frequently and is described in many previous studies (e.g. Elberling &Damgaard, 2001; Epping & Helder, 1997, and references therein). It can be used to estimate the flux at the

sediment–water interface ðx ¼ 0Þ from the gradient in the sediment (normally in the top layer) or, as in this

study, in the overlying water (DBL). When used in the DBL it has the advantage that the porosity does not

have to be measured/estimated (U ¼ 1 in water) and consequently Ds ¼ Dsw (see above).

(3) The procedure presented by Bouldin (1968) is yet another, based on the same assumptions for es-

tablishing the surficial gradient as for the others. In this model, oxygen consumption is assumed to be

constant with depth throughout the oxic zone. The square root of the oxygen concentration (in lM) is

plotted versus depth in the sediment and should yield a straight line (Fig. 5). The intercept of this line at anoxygen concentration of 0 indicates the penetration depth (L in mm). The slope of the line is called k. Thefollowing formula is used to calculate the flux by the Bouldin procedure:

J ¼ 8640 � 2LDs

1

k

� �2

:

(4) The numerical model PROFILE described by Berg et al. (1998) is available to users as freely dis-

tributed software for calculations of the rate of net solute consumption as a function of depth in the

Tank 1, square 3, 3 profiles

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.51050 15 20

Dep

th (

mm

)

Sqrt (O2)

Fig. 5. Typical examples of distributions obtained when plotting the square root of the oxygen concentration against depth in the

sediment. The slope and intercept of these lines are used as input in the Bouldin (1968) model to calculate fluxes from porewater

distributions.


sediment. The procedure involves finding a series of least square fits to the measured concentration profile,

followed by comparisons of these fits through statistical F-testing. This approach leads to an objective

selection of the simplest consumption profile, one that reproduces the measured concentration profile.

From the calculated consumption profile the integrated O2 consumption at the sediment surface is esti-

mated. Detailed descriptions of the mathematics and the reasoning behind this procedure are given in Berg

et al. (1998).

2.4. Statistical evaluation of the results

The hydrodynamic investigations of the chambers, the flux incubations and the porewater profile cal-

culations resulted in two tables of raw data (not presented here), which were analysed statistically. One

table was created to assess the degree of homogeneity within a tank and between tanks. This table con-

tained 420 experimentally obtained values of porosity (at a depth of 5 mm), calculated fluxes of oxygen and

nutrients, and three types of meiofauna (nematodes, foraminifers and others).

Another table was created to compare and couple measured fluxes with each other and with chamber-specific parameters. This table contained 760 values and the data were organized into factors and response

variables. The factors are parameters that could have an influence on the result(s), that is, the response

variables, in this case the measured fluxes of oxygen and nutrients. The following factors were tested: tank

number (which takes into account the sequential timing of the four incubation runs), chamber type (Mi-

crocosm, Mississippi and G€oteborg chambers), sediment type (sandy or less sandy), incubation temperature

(it did not vary much), chamber shape (cylindrical or box), mixing time, exposed sediment area, chamber


water height, internal area (of chamber walls, stirring mechanism etc.), average DBL thickness, worst case

differential pressure, and average bottom stress.

To compare means of populations, one-way analysis of variance (ANOVA) was used with Student–Newman–Keuls multiple comparisons a posteriori (Underwood, 1997). To analyse relationships

between variables, simple linear regression was used to test if there was a statistically significant

relationship and how large the explained variance ðR2Þ was. In all cases a significance level of P ¼ 0:05was required.

3. Results and discussion

3.1. Hydrodynamic measurements

The flux incubations were carried out at 8 �C and in 26 ppt seawater, while most of the hydrodynamic

studies were made at 18 �C with freshwater in the chambers. As a verification of any temperature influence,

all friction velocity measurements were carried out at both 8 and 18 �C (Table 3). To compare the influence

of seawater versus freshwater, some of the pressure measurements were made in both water types (Table 3).

From these experiments we concluded that neither variations in temperature nor salinity had significant

influence on the major findings of this investigation, and we decided to consistently use uncompensated 18�C data when comparing hydrodynamic parameters with each other and with the measured fluxes. The

reason for choosing this data set was that it was more complete (see Table 3 for a summary of the hy-

drodynamic results).

Depending on the degree of permeability of natural sediments, either diffusion (non-permeable sedi-

ments) or advective fluid exchange (permeable sediments) may control the flux, which means that different

emphasis lies on bottom stress and pressure from one situation to another. For non-permeable sediments,

the flux control may be related to the bottom stress, while for permeable sediments it may be a combination

of bottom stress and horizontal pressure gradient. Our sediments can be regarded as non-permeable, andthey were macrofauna-free, so bioirrigation has not been considered.

Values of the DBL thickness were estimated both through weight loss of individual alabaster plates and

through the Ca2þ increase in the overlying water (Santschi et al., 1983). The two methods corresponded well

in obtaining average DBL thickness over the plates (Fig. 6) and further confirmed the reliability and

simplicity of this method.

At all water mixing rates the Microcosm exhibited a remarkably even horizontal distribution of shear

velocity ðu�Þ and DBL thickness (7A and 7B). Previous investigations and intercomparisons have given

similar indications (Gust & M€uller, 1997). It is clear that the Microcosm is the most suitable, among thethree presented here, to use when the aim is to create evenly distributed shear velocity and DBL thickness.

Such conditions are important when investigating, for example, at what shear velocity sediment will become

resuspended or when calibrating skin friction probes or methods to measure the DBL thickness. When

studying the influence of hydrodynamic conditions on benthic faunal activity, the Microcosm is probably

also the most suitable tool because of its ability to reproduce homogeneous hydrodynamic conditions over

almost the whole chamber surface. It is only in a small area in the center, where the water is sucked up in a

vortex by the pump, that the Microcosm showed a thinner DBL thickness, a higher shear stress and a larger

negative pressure. When comparing standard deviations of DBL thickness over the individual alabasterplates, the G€oteborg chamber gave 182� 25 lm, the Mississippi chamber 196� 34 lm and the Microcosm

130� 10 lm (after discarding the value from the centrally placed plate) for spatially averaged values for u�

of 0.48, 0.44 and 0.65 cm/s, respectively (Fig. 7).

Plotting spatially averaged u� (for a u� between 0.3 and 1.7 cm/s) against DBL thickness from all

chambers and operational settings (Fig. 8) gave the following empirical relationship:

Table 3

Summary of the individual chamber results from the hydrodynamic measurements

Chamber # Stirring speed/

pump flow

Mixing time (s) Pressure Average shear

stress, u� 18�/8�(cm/s)

DBL

Max differential pressure

fresh watera/sea watera

(Pa)

Distance between

max and min

pressure (mm)

Average DBL

from Ca increasea

(lm)

Average DBL

from platesa

(lm)

13 rpm 150 <0.2 No data 0.26/0.26 279 (5) 274 (14)

G€oteborg 26 rpm 59 0.6 (0.2) 42 0.48/0.49 172 (16) 186 (6)

64 rpm 34 3.2 (1.1) 70 1.03/1.06

120 rpm 6 10.2 (5.9) 70 1.58/1.45

214 rpm 3 60.2 (14.4) 42

13 rpm >3600 <0.2 No data

Mississippi 27 rpm 662 0.4 (0.2) 50 0.18/0.15 361 (18) 335 (18)

65 rpm 46 0.6 (0.1)/ 1.0 (0.4) 55 0.47/0.40 193 (16) 197 (19)

128 rpm 18 4.2 (1.4) 110 0.81/0.72

185 rpm 6 8.6 (3.8)/6.4 (3.7) 110 1.12/0.91

280 rpm 3 15.7 (6.2) 110

0.2 cm/s 288 <0.2/<0.2 No data 0.26/0.29 221 (32) 230 (10)

Microcosm 0.5 cm/s 94 2.8 (0.1)/ 3.0 (0.5) 85 0.62/0.68 110 (16) 124 (6)

0.7 cm/s 25 7.8 (0.3) 85 0.83/0.91

1.0 cm/s 20 25.1 (1.6)/ 24.0 (2.0) 85 1.12/1.23 56 (4) 65 (18)

1.2 cm/s 20 47.8 (3.6) 90 1.31/1.43

1.5 cm/s 106.4 (10.4) 90 1.58/1.73 40 (5) 48 (8)

2.0 cm/s 150.7 (2.7) 85 2.05/2.24

For most water mixing rates, values are presented of mixing time, differential pressure together with the distance between the spots over which this pressure occurred,

shear stress and diffusive boundary layer thickness.a Values within parentheses gives the standard deviation for replicate measurements.

14

A.Tengberg

etal./Progress

inOcea

nography60(2004)1–28

y= 0.90x + 20.52

R2= 0.99

0

50

100

150

200

250

300

350

400

100500 150 200 250 300 350 400DBL from Ca increase [µm]

DB

L f

rom

wei

ght

loss

[µm

]

Fig. 6. Plots of average measured diffusive boundary layer thickness (DBL thickness) obtained from weight loss of individual alabaster

plates versus DBL thickness obtained from linear Ca2þ increase in the chamber water resulting from dissolution of the alabaster plates.


DBL ¼ 76:18ðu�Þ�0:933

(with a correlation coefficient r2 of 0.97). This relationship corresponds well with results presented inBuchhholtz-ten-Brink et al. (1989).

While the Microcosm is suitable to create evenly distributed DBL thickness and shear stress, it dem-

onstrated the highest differential pressures, at equal stirring rates, of the three chambers. Advective

porewater transport as a result of differential pressure has been shown, both in flume and chamber studies,

to increase benthic exchange rates in permeable sediments (Glud et al., 1996; Glud et al., 1995; Huettel &

Gust, 1992a, 1992b). The relation between shear stress and the maximal differential pressure gradient

(pressure difference over the distance that the pressure difference occurs) is presented in Fig. 9 for the three

chambers. While the Microcosm produced a rapidly increasing pressure/distance ratio with increasingaverage shear stress, the G€oteborg and Mississippi chambers showed small increases. At even higher

stirring rates, for which shear stress data are not available, the creation of a vortex in the G€oteborgchamber also created higher differential pressures (at a stirring of 214 RPM the pressure/distance ratio was

14 Pa/cm). This was not the case for the Mississippi chamber in which the pressure/distance ratio never

exceeded 1.4 Pa/cm (Table 3). Consequently, if there is a desire to keep the influence of differential pressure

as low as possible regardless of the water mixing rate and the spatial bottom stress distribution, a stirrer of

Mississippi type may be favorable. It must also be noted from these investigations that the relative standard

deviations of pressure and shear stress measurements for the two paddle wheel stirred chambers (G€oteborgand Mississippi) were higher than for the more smoothly stirred Microcosm (Table 3). This has been noted

before and is related to the pulsing of stirrers with impellers or bars (Buchhholtz-ten-Brink et al., 1989;

Gust & M€uller, 1997).

3.2. Sediment homogeneity and flux incubations

Out of the 48 measured O2 profiles, 43 were retained as usable. The other five were discarded due to too

noisy or broken electrodes. Profile data from the four tanks are presented in Fig. 10 as average profiles foreach tank.

The four different procedures described above were used to calculate oxygen fluxes from the porewater

profiles. These results were subsequently compared with the chamber-measured fluxes (Fig. 11). As can be

seen there are considerable differences in the calculated fluxes depending on the procedure used.

Fig. 7. (a) Examples of isopleths of the DBL thickness, obtained from alabaster plate observations. For the given examples the average

shear velocity ðu�Þ in the chambers were 0.48 cm/s for the G€oteborg chamber, 0.44 cm/s for the Mississippi chamber and 0.65 cm/s for

the Microcosm. (b) Examples of isopleths of u� (obtained with skin friction probes) for the different chambers. The distribution of DBL

thickness and u� look more irregular than they are in reality, since the data were collected with a discrete and limited number of probes

(for their location see Fig. 1).


The oxygen flux at the sediment–water interface is a reflection of the integrated consumption in the

multilayered aerobic zone of the sediment below. It has frequently been shown that the oxygen con-sumption rate is not constant within the aerobic zone, but that there are several zones with different

consumption rates (e.g. Revsbech & Jørgensen, 1986; Revsbech et al., 1986). Thus, it has been recom-

mended to assume at least two consumption zones to fit accurately a set of measured data points with a

modelled profile (e.g. Berg et al., 1998; Epping & Helder, 1997). Procedure No. 3, the model of Bouldin

(1968), assumes only one consumption zone. This model was not able to accurately fit in situ measured

profile data from the Adriatic Sea (Epping & Helder, 1997). Since the profile shapes and oxygen penetration

depths in that study were similar to the profiles measured here it was assumed likely that the Bouldin

procedure will not be able to describe our data as well.The original intention of Procedure No. 1 was to estimate oxygen penetration depth with input of the

flux and the bottom water concentration of oxygen. This procedure has however also been used for flux

y = 76.18x-0.93

R2

= 0.97

00.0 0.5 1.0 1.5 2.0

50

100

150

200

250

300

350

400

450

u* [cm/s]

DB

L [

µm]

Fig. 8. Shear velocity ðu�Þ plotted versus all data collected for DBL thickness in this study.

00.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

2

4

6

8

10

12

14

u* [cm/s]

Pre

ssur

e/di

stan

ce [

Pa/

cm]

Microcosm

Göteborg

Mississippi

Fig. 9. Shear velocity ðu�Þ plotted versus the pressure/distance ratio for the three chambers.


calculations, when the oxygen penetration depth was known. It is a simple and fast procedure to estimate

oxygen fluxes, but it does not take into account the actual shape of the oxygen profile or how the con-

sumption rate varies within the aerobic zone. Cai and Sayles (1996) also caution about the value of their

model when the oxygen penetration depth is only a few mm.

Use of the linear concentration change in the DBL is an attractive procedure, since there is no need for

input of porosity data. Previous comparisons between this procedure and the Berg et al. (1998) model havegiven almost perfect agreement (e.g. Elberling & Damgaard, 2001). Such an agreement should be expected,

since there is no consumption or production of oxygen in the DBL, and the DBL gradient should be di-

rectly related to consumption rates in the sediment below. The DBL procedure has, however, experimental

uncertainties, since the exact position of the sediment–water interface is not always obvious and sometimes

has to be guessed. This procedure also requires a high vertical resolution (about 50 lm) of the profile in the

DBL to obtain a string of data points within the zone of linear concentration change.

Procedure No. 4 uses all data points to fit a modelled profile. It assumes a number (up to 12) of different

consumption zones, which allows fitting a measured profile, even if it includes different consumption zones.All our measured data, both for oxygen and nutrients, were fitted using this procedure (see Fig. 12 for some

examples). When comparing calculated oxygen fluxes, using the Berg et al. procedure, with measured

oxygen fluxes the results agreed well (Fig. 11). Procedures 1 and 2 gave calculated fluxes that were 1.5–2

Fig. 11. Average calculated oxygen fluxes with the four different methods compared with each other and with the measured incubation

fluxes in the four tanks. Each calculated flux bar is based on the evaluation of 10–12 individual oxygen profiles. Each measured flux bar

is an average of four (for the G€oteborg and Mississippi chambers) or two (for the Microcosm) flux incubations. The standard error

bars are given for each bar.

-3.00

-2.50

-2.00

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

0 50 100 150 200 250 300 350

Ox

Tank 1

Tank 2

Tank 3

Tank 4

-3.00

-2.50

-2.00

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

0 50 100 150 200 250 300 350

Oxygen conc. [µM]

Dep

th in

sed

imen

t [m

m]

Tank 1

Tank 2

Tank 3

Tank 4

Fig. 10. Average oxygen profiles in each of the four tanks. Each data point is an average of 10–12 individually measured values. The

standard deviation is given only for one of the profiles, but its magnitude is representative for all the profiles.


-3.00

-2.75

-2.50

-2.25

-2.00

-1.75

-1.50

-1.25

-1.00

-0.75

-0.50

-0.25

0.00

0.25

0.50

0.75100500 150 200 250 300 350

Oxygen conc. [µM]

Dep

th in

sed

imen

t [m

m]

Mod

Mod

Mod

Mod

T1C2

T2C3

T3C1

T4B1

Fig. 12. Four measured oxygen profiles fitted with a modelled profile using the method of Berg et al. (1998). Measured data are

represented by spots and modelled by continuous lines.


times higher. The DBL-calculated fluxes agreed with the measured fluxes in tank 1, but in the other tanks

the calculation gave higher values. This procedure also gave the highest standard deviation of the four. A

higher vertical resolution of the measured profiles (e.g. 50 lm) would most likely have improved the end

results obtained with this procedure.

The statistical evaluations (see Table 4 for a summary of significant results) revealed that, in spite of

different designs and different hydrodynamic settings, there was no significant difference between parallel

(from the same tank at the same time) chamber incubations for any of the measured solute fluxes (Figs. 11and 13). For each of the tanks, the intra-chamber difference was larger than the difference between the

average flux measured in each of the three chamber types. When comparing nutrient fluxes measured in

the different tanks there were, in some cases, significant differences (Table 4). This is not surprising since the

incubations started in tank 1 and were finished about a week later in tank 4. Tanks 2 and 3 also contained

sandier sediments.

A major experimental criterion for this study was to keep the degree of sediment homogeneity the same

everywhere inside a tank. Fluxes calculated from porewater profiles (Table 2) did not vary significantly

within the same tank, confirming that the sediment mixing process indeed had created fairly homogenoussediments.

For oxygen there was no significant difference between measured and calculated fluxes, and no difference

between the different tanks within the given standard deviations. This confirms the earlier assumption of

prevailing steady-state conditions both within a tank and between tanks. The average measured oxygen flux

(from 40 incubations with the three chamber types) was 11.2� 2.7 and that calculated by procedure # 4

(from 43 profiles) was 11.1� 3.0 mmol m�2 day�1, suggesting excellent agreement between these two

Table 4

Summary of statistically significant results from the data evaluation

Table type: variation inside tanks and between tanks, test of sediment homogeneity (total 420 values)

Table content: for each tank (1–4), square (1–4) and profile (1–3) experimental values of: porosity at 5 mm; oxygen penetration;

number of foraminifers, nematodes and other meiofauna; calculated fluxes (method Berg et al. (1998)) of: oxygen, silicate,

phosphate, and ammonium.

Variable p-value Degree of

significance

Comments

Comparison between squares in tanks

Tank 1

Nematodes 0.018 Low Nonhomogenous distribution in this tank

Foraminifers 0.035 Low Nonhomogenous distribution in this tank

Tank 3

Foraminifers 0.041 Low Nonhomogenous distribution in this tank

Comparison between tanks

Silicate 0.0088 Medium Significant difference but it is not possible to distinguish which is

higher

Ammonium <0.001 High Tank 2 higher than 1, 3 and 4

Nematodes 0.0017 Medium Significant difference but it is not possible to distinguish which is

higher

Foraminifers 0.0102 Low Significant difference but it is not possible to distinguish which is

higher

Table type: coupling between measured fluxes, hydrodynamics and chamber design (total 760 values)

Table content: for each tank (1–4), sediment type (low sand, high sand), chamber (G€oteborg, Gust and Mississippi), shape (round,

box) and stirring experimental values of: temperature; mixing time; exposed sediment area; water height; internal area (of chamber

walls, stirring mechanism, etc.); average DEL; worst case differential pressure and average shear stress

Comparison between chamber fluxes

Phosphate <0.001 High Tank 2 lower than 3 and 4 which were lower than 1

Silicate <0.001 High Tank 1 higher than 2 which was higher than 3 and 4

Interdependency of chamber fluxes

Phosphate and silicate 0.02 Low Higher phosphate gives higher silicate, r2 ¼ 0:227

Silicate and oxygen 0.017 Low Higher silicate gives higher oxygen, r2 ¼ 0:141

The level of significance was 0.05.


independent methods to obtain benthic fluxes of oxygen in macrofauna-free sediment. This excellent

agreement also strongly suggests that the three chamber types had the capability to measure benthic oxygen

fluxes accurately, and that the repeatability of these chambers to measure fluxes was similar to that ob-

tained when calculating fluxes from porewater gradients.

For nutrients, calculated fluxes did not agree with the measured ones, see Fig. 14 for nutrient porewater

data. For silicate the difference between calculated and measured fluxes was less pronounced than for the

other nutrients, but it was still statistically significant (Fig. 13). For phosphate the calculated fluxes were1.5–6 times higher and for ammonium about 10–20 times higher than the measured fluxes. It is usually

assumed that gradient-calculated and measured nutrient fluxes seldom agree due to processes close to the

sediment–water interface, such as adsorption, nitrification and bacterial assimilation (e.g. Blackburn, Hall,

Hulth, & Land�en, 1996; Sundby et al., 1986).

Apparently, in this study chamber hydrodynamics and design did not significantly influence any of the

measured fluxes for the selected settings. Such results could be expected for non-permeable sediments in

which the ongoing processes are controlled by integrated reaction rates in the sediment, as shown in the-

oretical models by Boudreau and Scott (1978) and by Reimers, Jahnke, and Thomsen (2001). In such

Fig. 13. Average calculated and measured fluxes of silicate (a), phosphate (b), and ammonium (c) in the four tanks. Each measured

flux bar represents an average of four (for the G€oteborg and Mississippi chambers) or two (for the Microcosm, except for the am-

monium fluxes in tanks 2 and 3 for which only data from one incubation was obtained) flux incubations. The standard error bars are

given for each bar.


sediments changes in the fluxes occur on longer time scales (days-weeks), and rapid changes in the hy-drodynamic conditions above the sediment are not expected to give any rapid changes in the measured

fluxes. Jørgensen and Des Marais (1990) showed that on a microbial mat, where most of the processes are

taking place close to the surface. The DBL thickness was limiting the oxygen flux, and upon decreasing the

DBL thickness from 590 to 160 lm the oxygen uptake rates increased rapidly from 49 to 135

mmol m�2 day�1. In this study the average chamber DBL thickness, obtained with the ‘‘alabaster method’’

using a chamber mounted PVC bottom, varied from approximately 550 to 120 lm (Table 2) without any

noticeable influence on the measured oxygen fluxes (Fig. 15(b)). Thus, the chamber-averaged DBL thick-

ness was apparently not a limiting factor with oxygen fluxes of about 11 mmol O2 m�2 day�1, which is a

typical magnitude of oxygen fluxes for many coastal, shelf and slope sediments (e.g. Andersson et al., 2002;

Archer & Devol, 1992; Hall et al., 1989; Hulth, Blackburn, & Hall, 1994; Rasmussen & Jørgensen, 1992). In

the deep sea, oxygen fluxes are typically lower, often around 0.5–1 mmol m�2 day�1 (e.g. Berelson et al.,

1990; Berelson, Hammond, O’Neill, Xu, & Zukin, 1990; Smith et al., 1997), and consequently, it is less

critical to simulate accurately the in situ hydrodynamic conditions.

-60

-50

-40

-30

-20

-10

0

0 50 100 150 200 250

Si conc.[µM]

Dep

th in

sed

imen

t [m

m]

Dep

th in

sed

imen

t [m

m]

Dep

th in

sed

imen

t [m

m]

Tank 1

Tank 2

Tank 3

Tank 4

-60

-50

-40

-30

-20

-10

00 20 40 60 80 100 120

Phosphate conc.[µM]

Tank 1

Tank 2

Tank 3

Tank 4

-60

-50

-40

-30

-20

-10

0

0 400 800 1200 1600 2000 2400 2800

NH4 conc.[µM]

Tank 1

Tank 2

Tank 3

Tank 4

(c)

(b)(a)

Fig. 14. Average silicate (a), phosphate (b) and ammonium (c) profiles in each of the four tanks. Each data point is an average of 12

individually measured values in tanks 1–3, and of six individually measured values in tank 4. The standard deviation is given only for

one of the profiles in each plot, but its magnitude is representative for all the profiles.


T1T1

T1

T1

T1

T1

T1

T1

T1

T1 T2T2

T2

T2 T2

T2

T2

T2

T2

T2

T3

T3

T3

T3

T3

T3 T3

T3

T3

T3 T4

T4

T4

T4 T4

T4

T4

T4

T4

T4

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80

Average U* [cm/s]

Oxy

gen

flux

[m

mol

m-2

d-1

]Göteborg

Microcosm

Mississippi

T1T1

T1

T1

T1

T1

T1

T1

T1

T1T2 T2

T2

T2T2

T2

T2

T2

T2

T2

T3

T3

T3

T3

T3

T3T3

T3

T3

T3T4

T4

T4

T4T4

T4

T4

T4

T4

T4

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

0 50 100 150 200 250 300 350 400

Average DBL [ m]

Oxy

gen

flux

[m

mol

m-2

d-1]

Göteborg

Microcosm

Mississippi

µ

(a)

(b)

Fig. 15. (a) Average friction velocity (u� in cm/s) plotted versus chamber-measured oxygen-uptake rates (assuming steady state). (b)

Average boundary layer thickness (in lm) plotted versus chamber-measured oxygen uptake rates. The data labels T1–T4 refers to the

tank incubation from which the data point originated.


The differences among the chambers, and between measured and calculated fluxes, might have been

significant if the oxygen fluxes were higher. There would possibly also have been a clear difference between

the chambers, and between measured and calculated fluxes, if the sediment were more permeable, uneven,

and/or contained burrowing and pumping fauna. For such situations, changes in hydrodynamic conditions


might influence both the faunal activity and create porewater advection. In sediments with abundant fauna,

flux incubations and newly developed two-dimensional planar optodes for in situ measurements of pore-

water solute distributions (Glud et al., 2001) are expected to give more representative solute flux estimatesthan those calculated from one-dimensional porewater distributions (e.g. Glud, Gundersen, Jørgensen,

Revsbech, & Schulz, 1994; Rutgers van der Loeff et al., 1984).

Meiofauna have been suggested to influence benthic solute fluxes and processes in the uppermost aerobic

zone of sediments (e.g. Aller & Aller, 1992). Meiofauna abundance was the only parameter that indicated

sediment heterogeneity (in two of the four tanks; Table 4). In tank 1 there were significant variations

between the squares for Nematodes and Foraminifers, and in tank 3 there were significant variations for

Foraminifers. There were also variations among the tanks (Fig. 16) with a decreasing trend from tank 1 to

Fig. 16. (a) Meiofauna abundance in each of the four incubation tanks. Each value is an average of 11–12 samples. The standard error

bars are given for each bar. (b) Variations between the 12 individual samples in tank 1. There was a significant difference between the

different samples.


tank 4. Apparently the variations in meiofaunal abundance did not influence the measured and calculated

fluxes in our study.

Samples were also collected from tank 1 to determine organic carbon in the sediment solid phase. Theorganic carbon content did not change much with depth in the sediment, but there was horizontal variability

(data not shown). This variability was of similar magnitude as the variations in the flux measurements.

In this study the hydrodynamic features of three radically different benthic chamber designs were first

assessed. Multiple replicates of these chambers were then incubated, at different hydrodynamic settings, on

homogenised non-permeable sediments. There was no significant difference between the oxygen and nu-

trient fluxes measured with the chambers leading to the conclusion that the chamber design and hydro-

dynamic setting were of minor or no importance to the fluxes measured, so long as re-suspension is not

created and the mixing is sufficient to prevent the formation of gradients in the chamber.The degree of sediment homogenisation was studied by making l-electrode profiles with oxygen sensors

and by collecting and analysing sediment samples. The oxygen l-electrode profiles also gave the oppor-

tunity to compare different procedures for calculating fluxes from an oxygen gradient in the sediment or in

the DBL. Although all the procedures spring from the same basic assumptions only the procedure that took

into consideration multilayered consumption/production zones in the sediment gave consistent results. The

calculated oxygen fluxes were almost identical to the chamber measured fluxes.

Acknowledgements

Special thanks to the staff at Tj€arn€o Marine Biological Laboratory who assisted and helped us to carry

out this study. Alison Miles and Kristina Sundb€ack at Marine Botany are acknowledged in particular for

lending us their oxygen microelectrode equipment and showing us how to use it. We thank H. Millqvist for

constructing experimental equipment, P. Engstr€om and S. Agrenius for meiofauna analysis and H. Olsson

for nutrient and sedimentary organic C analyses. Funding for this study was provided by the European

Union MAST-III project ALIPOR (Contract No. CT950010) and by the Swedish Foundation for StrategicEnvironmental Research (MISTRA) through the MARE project.

References

Aller, R. C. (1982). The effect of macrobenthos on chemical properties of marine sediment and overlying water. In P. L. McCall & M.

J. S. Tevesz (Eds.), Animal–sediment relations (pp. 53–102). New York: Plenum.

Aller, R. C., & Aller, J. Y. (1992). Meiofauna and solute transport in marine muds. Limnology and Oceanography, 37, 1018–1033.

Aller, R. C., & Aller, J. Y. (1998). The effects of biogenic irrigation intensity and solute exchange on diagenetic reaction rates in marine

sediments. Journal of Marine Research, 56(4), 905–936.

Andersson, J. H., Wijsman, J. W. M., Herman, P. M. J., Middelburg, J. J., Soetaert, K., & Heip, C. (2002). Respiration patterns in the

ocean. Global Biogeochemical Cycles (submitted).

Archer, D., & Devol, A. (1992). Benthic oxygen fluxes on the Washington shelf and slope: A comparison of in-situ microelectrode and

chamber flux measurements. Limnology and Oceanography, 37, 614–629.

Berelson, W. M., Hammond, D. E., & Cutter, G. A. (1990). In situ measurements of calcium carbonate dissolution rates in deep-sea

sediments. Geochimica et Cosmochimica Acta, 54, 3013–3020.

Berelson, W. M., Hammond, D. E., O’Neill, -M., Xu, C., & Zukin, J. (1990). Benthic fluxes and pore water studies from sediments of

the central equatorial north Pacific: Nutrient diagenesis. Geochimica et Cosmochimica Acta, 54, 3001–3012.

Berg, P., Risgaard-Petersen, N., & Rysgaard, S. (1998). Interpretation of measured concentration profiles in sediment pore water.

Limnology and Oceanography, 43, 1500–1510.

Blackburn, T. H., Hall, P., Hulth, S., & Land�en, A. (1996). Organic-N loss by efflux and burial associated with a low efflux of

inorganic-N and with nitrate assimilation in Arctic sediments (Svalbard). Marine Ecology Progress Series, 141, 283–293.

Booij, K., Helder, W., & Sundby, B. (1991). Rapid redistribution of oxygen in sandy sediment induced by changes in the flow velocity

of the overlying water. Netherlands Journal of Sea Research, 28, 149–165.


Booij, K., Sundby, B., & Helder, W. (1994). Measuring the flux of oxygen to a muddy sediment with a cylindrical microcosm.

Netherlands Journal of Sea Research, 32, 1–11.

Boudreau, B. P. (1997). Diagenetic models and their implementation: Modelling transport and reactions in aquatic sediments (414 pp).

Berlin, Heidelberg, New York: Springer.

Boudreau, B. P., & Guinasso, N. L., Jr. (1982). The influence of a diffusive sublayer on accretion, dissolution, and diagenesis at the sea

floor. In K. A. Fanning & F. T. Manheim (Eds.), The dynamic environment at the ocean floor (pp. 115–145), Lexington, MA.

Boudreau, B. P., & Scott, M. R. (1978). A model for the diffusion controlled growth of deep-sea manganese nodules. American Journal

of Science, 278, 903–929.

Bouldin, D. R. (1968). Models for describing the diffusion of oxygen and other mobile constituents across the mud–water interface.

Journal of Ecology, 56, 77–87.

Broecker, W. S., & Peng, T.-H. (1974). Gas exchange rates between air and sea. Tellus, 26, 21–35.

Brostr€om, G., & Nilsson, J. (1999). A theoretical investigation of the diffusive boundary layer in benthic flux chamber experiments.

Journal of Sea Research, 42, 179–189.

Buchhholtz-ten-Brink, M. R., Gust, G., & Chavis, C. (1989). Calibration and performance of a stirred benthic chamber. Deep-Sea

Research, 36, 1083–1101.

Cai, W.-J., & Sayles, F. L. (1996). Oxygen penetration depths and fluxes in marine sediments. Marine Chemistry, 52, 123–131.

Canfield, D. E. (1993). Organic matter oxidation in marine sediments. In R. Wollast, V. MacKenzie, & L. Chou (Eds.), NATO ASI

Series: 14. Interactions of C, N, P and S biogeochemical cycles and global change (pp. 333–363). Berlin: Springer.

Dickinson, W., & Sayles, F. L. (1992). A benthic chamber with electric stirrer mixing. Technical Report WHOI-92-09, Woods Hole

Oceanographic Institution, USA, 17 pp.

Elberling, B., & Damgaard, L. R. (2001). Microscale measurements of oxygen diffusion and consumption in subaqueous sulfide

tailings. Geochimia et Cosmochimia Acta, 65, 1897–1905.

Epping, E. H. G., & Helder, W. (1997). Oxygen budgets calculated from in situ oxygen microprofiles for Northern Adriatic sediments.

Continental Shelf Research, 17, 1737–1764.

Glud, R. N., & Blackburn, N. (2002). The effects of chamber size on benthic oxygen uptake measurements: A simulation study.

Ophelia, 56, 23–31.

Glud, R. N., Forster, S., & Huettel, M. (1996). Influence of radial pressure gradients on solute exchange in stirred benthic chambers.

Marine Ecology Progress Series, 141, 303–311.

Glud, R. N., Gundersen, J. K., Revsbech, N. P., Jørgensen, B. B., & Huettel, M. (1995). Calibration and performance of the stirred

flux chamber from the benthic lander ELINOR. Deep-Sea Research, 42, 1021–1092.

Glud, R. N., Gundersen, J. K., Jørgensen, B. B., Revsbech, N. P., & Schulz, H. D. (1994). Diffusive and total oxygen uptake of

deep-sea sediments in the eastern South Atlantic Ocean: In situ and laboratory measurements. Deep-Sea Research, 41, 1767–

1788.

Glud, R. N., Tengberg, A., K€uhl, M., Hall, P., Klimant, I., & Holst, G. (2001). An in situ instrument for planar O2 optode

measurements at benthic interfaces. Limnology and Oceanography, 46, 2073–2080.

Gust, G. (1988). Skin friction probes for field applications. Journal of Geophysical Research, 93, 121–132.

Gust, G. (1990). Method of generating precisely-defined wall shearing stresses. US Patent Number: 4,973,165,1990.

Gust, G., & M€uller, V. (1997). Interfacial hydrodynamics and entrainment functions of currently used erosion devices. In N. Burt, R.

Parker, & J. Watts (Eds.), Cohesive sediments – Proc. 4th nearshore and estuarine cohesive sediment transport conference

INTERCOH ’94, Wallingford, 1994. (pp. 149–174). Chichester, UK: Wiley.

Gust, G., & Weatherly, G. L. (1985). Velocities, turbulence, and skin friction in a deep-sea logarithmic layer. Journal of Geophysical

Research, 90, 4779–4792.

Hall, P. O. J., Anderson, L. G., Rutgers van der Loeff, M. M., Sundby, B., & Westerlund, S. F. G. (1989). Oxygen uptake kinetics in

the benthic boundary layer. Limnology and Oceanography, 34, 734–746.

Hall, P. O. J., Hulth, S., Hulthe, G., Land�en, A., & Tengberg, A. (1996). Benthic nutrient fluxes on a basin-wide scale in the Skagerrak

(north-eastern North Sea). Journal of Sea Research, 35, 123–137.

Hall, P. O. J., Hulth, S., Troell, M., & Faganeli, J. (1991). Input and recycling of biogenic debris at the sediment–water interface in the

Gullmar Fjord, western Sweden. In P. Wassman, A.-S. Heiskanen, & O. Lindahl (Eds.), Sediment trap studies in the Nordic

countries (Vol. 2, pp. 235–254). Numiprint, Nurmij€arvi, Finland.

Huettel, M., & Gust, G. (1992a). Solute release mechanisms from confined sediment cores in stirred benthic chambers and flume flows.

Marine Ecology Progress Series, 82, 187–197.

Huettel, M., & Gust, G. (1992b). Impact of bioroughness on interfacial solute exchange in permeable sediments. Marine Ecology

Progress Series, 89, 253–267.

Huettel, M., Ziebis, W., & Forster, S. (1996). Flow-induced uptake of particulate matter in permeable sediments. Limnology and

Oceanography, 41, 309–322.

Hulth, S., Blackburn, T. H., & Hall, P. O. J. (1994). Arctic sediments (Svalbard): Consumption and microdistribution of oxygen.

Marine Chemistry, 46, 293–316.


Hulthe, G., Hulth, S., & Hall, P. O. J. (1998). Effect of oxygen on degradation rate of refractory and labile organic matter in

continental margin sediments. Geochimica et Cosmochimica Acta, 62, 1319–1328.

Jumars, P. A. (1993). Concepts in biological oceanography. An interdisciplinary primer. Oxford University Press: Oxford.

Junglewitz, A., M€uller, V., & Gust, G. (1997). Calibration of a hot film sensor for application in turbulent ship model testing. In 1997

ASME Fluids Engineering Division Summer Meeting (FED SM97), paper 3468 (CD-Rom), Vancouver, Canada.

Jørgensen, B. B., & Des Marais, D. J. (1990). The diffusive boundary layer of sediments: Oxygen microgradients over a microbial mat.

Limnology and Oceanography, 35, 1343–1355.

Jørgensen, B. B., & Revsbech, N. P. (1985). Diffusive boundary layers and the oxygen uptake of sediments and detritus. Limnology and

Oceanography, 30, 111–122.

Kristensen, E., Ahmed, S. I., & Devol, A. H. (1995). Aerobic and anaerobic decomposition of organic matter in marine sediment:

Which is fastest. Limnology and Oceanography, 40, 1430–1437.

Land�en, A., & Hall, P. (1998). Seasonal variation of dissolved and adsorbed amino acids and ammonium in a near-shore marine

sediment. Marine Ecology Progress Series, 170, 67–84.

Li, Y.-H., & Gregory, S. (1974). Diffusion of ions in sea water and in deep-sea sediments. Geochimica et Cosmochimica Acta, 38, 703–

714.

McIntyre, A. D., & Warwick, K. M. (1984). Meiofauna techniques. In N. A. Holme & A. D. McIntyre (Eds.), Methods for the study of

marine benthos (pp. 217–244). Oxford: Blackwell.

Nicholson, G. J., Longmore, A. R., & Berelson, W. M. (1999). Nutrient fluxes measured by two types of benthic chamber. Marine &

Freshwater Research, 50, 567–572.

Opdyke, B. N., Gust, G., & Ledwell, J. R. (1987). Mass transfer from smooth alabaster surfaces in turbulent flows. Geophysical

Research Letters, 14, 1131–1134.

Rabouille, C., Stahl, H., Bassinot, F., Tengberg, A., Brunnegard, J., Hall, P., Kiriakoulakis, K., Reyss, J.-L., Dezileau, L., Crassous,

P., Roos, P., & Lampitt, R. S. (2001). Imbalance in the carbonate budget of surficial sediments in the North Atlantic Ocean:

variations over the last millenium? Progress in Oceanography, 50, 201–221.

Ragueneau, O., Gallinari, M., Corrin, L., Grandel, S., Hall, P., Hauvespre, A., Lampitt, R. S., Rickert, D., Stahl, H., Tengberg, A., &

Witbaard, R. (2001). The benthic silica cycle in the Northeast Atlantic: Annual mass balance, seasonality, and importance of non-

steady-state processes for the early diagenesis of biogenic opal in deep-sea sediments. Progress in Oceanography, 50, 171–200.

Rasmussen, H., & Jørgensen, B. B. (1992). Microelectrode studies of seasonal oxygen uptake in a coastal sediment: Role of molecular

diffusion. Marine Ecology Progress Series, 81, 289–303.

Reimers, C. E., Jahnke, R. A., & Thomsen, L. (2001). In-situ boundary layer measurements. In Boudreau & Jørgensen (Eds.), The

benthic boundary layer (pp. 245–268). Oxford: Oxford University Press.

Revsbech, N. P. (1989). An oxygen microsensor with a guard cathode. Limnology and Oceanography, 34, 474–478.

Revsbech, N. P., & Jørgensen, B. B. (1986). Microelectrodes: Their use in microbial ecology. Advances in Microbial Ecology, 9, 293–

352.

Revsbech, N. P., Madsen, B., & Jørgensen, B. B. (1986). Oxygen production and consumption in sediments determined at high spatial

resolution by computer simulation of oxygen microelectrode data. Limnology and Oceanography, 31, 293–304.

Rutgers van der Loeff, M. M., Anderson, L. G., Hall, P. O. J., Iverfeldt, �A., Josefson, A. B., Sundby, B., & Westerlund, S. F. G. (1984).

The asphyxiation technique: An approach to distinguishing between molecular diffusion and biologically mediated transport at the

sediment–water interface. Limnology and Oceanography, 29, 675–686.

Santschi, P. H., Andersson, R. F., Fleisher, M. Q., & Bowles, W. (1991). Measurements of diffusive sublayer thickness in the ocean by

alabaster dissolution, and their implications for the measurements of benthic fluxes. Journal of Geophysical Research, 96, 10641–

10657.

Santschi, P. H., Bower, P., Nyffeler, U. P., Azevedo, A., & Broecker, W. S. (1983). Estimates of the resistance to chemical transport

posed by the deep-sea boundary layer. Limnology and Oceanography, 28, 899–912.

Santschi, P. H., Nyffeler, U. P., �OHara, P., Buchhholtz-Ten-Brink, M. R., & Broecker, W. S. (1984). Radiotracer uptake on the sea

floor: Results from the MANOP chamber deployments in the eastern Pacific. Deep-Sea Research, 31, 451–468.

Sayles, F. L., & Dickinson, W. H. (1991). The ROLAI2D lander: A benthic lander for the study of exchange across the sediment–water

interface. Deep-Sea Research, 38, 505–529.

Silverberg, N., Sundby, B., Mucci, A., Zhong, S., Arakaki, T., Hall, P., Land�en, A., & Tengberg, A. (2000). Remineralization of

organic carbon in eastern Canadian continental margin sediments. Deep-Sea Research, 47, 699–731.

Smith, K. L, Jr., Glatts, R. C., Baldwin, R. J., Beaulieu, S. E., Uhlman, A. H., Horn, R. C., & Reimers, C. E. (1997). An autonomous,

bottom-transecting vehicle for making long time-series measurements of sediment community oxygen consumption to abyssal

depths. Limnology and Oceanography, 42, 1601–1612.

Strickland, J. D. N., & Parsons, T. R. (1968). A practical hand-book of seawater analysis. Bulletin of Fish Research Border Canada,

167, 311.

Sundby, B., Anderson, L., Hall, P., Iverfeldt,�A., Rutgers van der Loeff,M., &Westerlund, S. (1986). The effect of oxygen on release and

uptake of cobalt, manganese, iron and phosphate at the sediment–water interface. Geochimica et Cosmochimica Acta, 50, 1281–1288.


Tengberg, A., Almroth, E., & Hall, P. (2003). Resuspension and its effect on organic carbon recycling and nutrient exchange in coastal

sediments: In-situ measurements using new sensor technology. Journal of Experimental Marine Biology and Ecology, 285–286, 119–

142.

Tengberg, A. (1997). Free-vehicle benthic lander technology for the study of biogeochemical processes in marine sediments. Ph.D.

thesis, Chalmers University of Technology, G€oteborg, Sweden, pp. 48 and 6 appendices.

Tengberg, A., de Bov�ee, F., Hall, P., Berelson, W., Chadwick, B., Ciceri, G., Crassous, P., Devol, A., Emerson, S., Gage, J., Glud, R.,

Graziottin, F., Gundersen, J., Hammond, D., Helder, W., Hinga, K., Holby, O., Jahnke, R., Khripounoff, A., Lieberman, H.,

Nuppenau, V., Pfannkuche, O., Reimers, C., Rowe, G., Sahami, A., Sayles, F., Schurter, M., Smallman, D., Wehrli, B., & de

Wilde, P. (1995). Benthic chamber and profiling landers in oceanography – A review of design, technical solutions and functioning.

Progress in Oceanography, 35, 253–294.

Thomsen, L., & Gust, G. (2000). Sediment stability and characteristics of resuspended aggregates of the western European continental

margin. Deep-Sea Research, 47, 1881–1897.

Ullman, W. J., & Aller, R. C. (1982). Diffusion coefficients in near shore marine sediments. Limnology and Oceanography, 27, 552–556.

Underwood, A. J. (1997). Experiments in ecology, their logical design and interpretation using analysis of variance. Cambridge:

Cambridge University Press.

Vershinin, A. V., Gornizkij, A. B., Egorov, A. V., & Rozanov, A. G. (1994). The method of investigation of chemical exchange across

the water–sediment interface in open sea-bottom systems. Okeanologia, 34, 139–145.

Vogel, S. (1981). Life in moving fluids: the physical biology of flow. Boston, USA: Willard Grant.

Intercalibration of benthic flux chambers I. Accuracy of flux measurements and influence of chamber...

Documents

Transcript of Intercalibration of benthic flux chambers I. Accuracy of flux measurements and influence of chamber...