Stig Westerlund

The effect of oxygen on release and uptake of cobalt, manganese, iron and phosphate at the sediment-water interface

The porewater of a sediment core taken at 6 m depth in Gullmarsfjorden, Sweden, was enriched in Fe, Mn, Co, and phosphate compared to the overlying bottom water. Yet, in situ measurements with a benthic flux-chamber, in which dissolved oxygen and pH were maintained near ambient values (regulated flux-chamber), showed that the sediment did not release any of these ions but instead removed Co, Mn, and Fe from the overlying water. In a parallel experiment, where dissolved oxygen and pH were not maintained but allowed to decrease as a result of benthic respiration, Co, Mn, Fe, and PO4 were released from the sediment. An accidental interruption of the stirring in the regulated chamber caused a pulse of dissolved Co, Mn, Fe, and PO4 to be released from the sediment. When the stirring was resumed, all four ions were again removed. The kinetics of the removal process was apparent first order with half-removal times of 3–5 days, similar to the removal kinetics of the radioactive tracers 59Fe and 54Mn from the water in a smaller chamber, run in parallel. The critical variable which controls the reactions at the sediment-water interface is the flux of oxygen from the water column into the sediment. When benthic chambers are used to measure fluxes of redox-sensitive ions, the oxygen flux must be maintained as close as possible to the actual in situ flux. If not, the measured fluxes may vary greatly in magnitude and even change direction.

Trace metal determinations in estuarine waters by electrothermal atomic absorption spectrometry after extraction of dithiocarbamate complexes into freon

Cadmium, copper, iron, lead, nickel and zinc are determined. The dithiocarbamate complexes of the metals are extracted into Freon-TF and back-extracted into dilute nitric acid solution. Portions of the back-extracts are injected into a graphite furnace. The method gives complete separation from the matrix irrespective of salinity. It is therefore useful throughout the full salinity range of an estuary, 0–35‰.The effect of high iron concentrations on the extraction is eliminated by using a mixed acetate buffercomplexing agent solution.

Benthic fluxes of cadmium, copper, nickel, zinc and lead in the coastal environment

Fluxes of trace metals across the sediment-water interface were measured in situ at 6 m depth in Gullmarsfjorden, Sweden, using diver-operated stirred benthic flux-chambers. These were equipped so that dissolved oxygen and pH could be maintained near ambient seawater values (regulated chamber) or be allowed to change in response to benthic respiration (unregulated chamber). In the regulated chamber, Cd, Cu, Ni, and Zn were released from the sediment at constant rates both during a winter experiment (water temperature −1 °C) and during a fall experiment (+ 10°C). During the fall experiment, fluxes (in nmol m−2 d−1) of 13 (Cd), 118 (Cu), 209 (Ni), and 1400 (Zn) were measured. In winter, the release rates were lower by factors of 5 and 10 for Cu and Ni but not significantly different for Cd and Zn. Neither release nor uptake by the sediment could be demonstrated for Pb. The pore-water in a diver-collected core was depleted in Cd, Cu, and Zn and slightly enriched in Ni and Pb, relative to the ambient seawater. There was no correspondence between fluxes calculated from porewater profiles and actually measured fluxes; nor could the fluxes be directly related to the degradation rate of organic matter. In the unregulated chamber, initial trace metal release rates were lower than in the regulated chamber. As the oxygen concentration decreased, the metal fluxes decreased as well and were ultimately reversed as sulfide began to appear in the water. The fluxes of trace metals are sensitive to the oxygen regime in the flux chamber because the solubilization of these metals, which takes place in a thin oxic layer near the sediment surface, depends on the oxygen flux across the sediment-water interface.

Cadmium, copper, iron, nickel and zinc in the north-east Atlantic Ocean

Abstract The concentrations of cadmium, copper, iron, nickel and zinc have been determined on 105 water samples from the north-east Atlantic Ocean. Three rather different areas were sampled in this investigation. The first area is the Norwegian Sea, the birthplace for North Atlantic Deep Water (NADW), bordering the Arctic. Second, the relatively shallow Iceland-Faroe Ridge area where the newly formed deep water spills over into the northeast Atlantic. The third area sampled is the north-east Atlantic, further south, with less pronounced seasonal variations in temperature and light conditions. In the Norwegian Sea no surface depletion was found for cadmium, copper, nickel or zinc. The mean concentrations were (for unfiltered samples): Cd, 0.20 nM (22 ng l −1 ); Cu, 1.4 nM (90 ng l −1 ); Ni, 3.5 nM (200 ng l −1 ); and Zn, 1.5 nM (130 ng l −1 ). For iron the concentration in the surface water was 4.4 nM (250 ng l −1 ), with a slight increase towards the bottom. In the warm surface waters of the north-east Atlantic a depletion of cadmium and nickel was found for the surface waters that could be correlated to a depletion of nutrients. For copper and zinc the slight depletion found could not be correlated with any of the nutrients. In the deep waters of the north-east Atlantic, higher concentrations of cadmium, copper, nickel and zinc were found than at similar depths in the Norwegian sea. For iron, on the other hand, the concentrations were higher in the Norwegian Sea.

Trace metals in the water columns of the Black Sea and Framvaren Fjord

Abstract The trace metals cadmium, copper, nickel, lead, zinc, cobalt, iron and manganese from the oxic and anoxic water columns of the Black Sea and Framvaren Fjord are reported. The importance of particulate metal analysis is shown by data for Framvaren Fjord, which acts as a trap for trace metals. The input of trace metals is calculated based on data on the inflowing water.

Cadmium, copper, cobalt, nickel, lead, and zinc in the water column of the Weddell Sea, Antarctica

Abstract This paper presents results from the first complete investigation of the dissolved and suspended trace metals cadmium, copper, cobalt, nickel, lead, and zinc in the water column of the Weddell Sea, Antarctica. A total of 35 stations was covered in the central Weddell Sea and the shelf areas around the Filchner depression and Dronning Mauds Land. Snow samples were collected from the sea ice and from the Antarctic continent to evaluate the importance of the fresh water influence on the Weddell Sea. Oceanographic data, i.e., salinity, temperature, and nutrients, are used to link the trace metal results to the different water masses. The general range found is for cadmium, 0.5–0.8 nM; copper, 2.0–2.9 nM; cobalt, 20–40 nM; nickel, 6–7 nM; lead, 10 pM; zinc, 3–7 nM. The suspended trace metals are a small fraction, but considerably higher than in other oceans. The lowest concentrations of cadmium, copper, and zinc are found in the surface layer and in the whole water column at the Filchner Depression. Cobalt shows an increase in the surface water compared to the deep water. This is suggested to be generated by the terrogent material from the Antarctic continent from the melting of the ice. No evidence of anthropogenic lead can be seen in the lead profile. Nutrient trace metal relations found show poor statistical correlation in contrast to what is found in other oceans. This assumes that cadmium, copper, and zinc are not directly linked to the bioproduction cycle. However, the nutrient trace metal ratios found support the theory that the Weddell Sea is the ultimate source for generation of the nutrient trace metal ratios in the Pacific Ocean.

The solution chemistry of iron(II) in Framvaren Fjord

A vertical profile of soluble (< 0.4 μm) Fe(II) from Framvaren Fjord, Norway, was determined using an improved Ferrozine colorimetric method. Reduced iron concentrations increased dramatically below the O2/H2S interface (20m), reaching a maximum of 890 nM at 30m. The Fe(II) concentrations then decreased quasi-exponentially to near the detection limit (⩽ 18 nM) from 110m to the bottom (183m). Equilibrium calculations including dissolved iron-bisulfide complexes and five iron-sulfide solid phases indicate that dissolved Fe(II) does not form soluble bisulfide complexes in the deep anoxic waters. The total dissolved Fe(II) concentrations below 24m appear to be controlled by mackinawite (FeS) or greigite (Fe3S4) solubility. Changes in the relative rates of vertical diffusive mixing and upwelling due to episodic intermediate water renewal are clearly visible when comparing the dissolved Fe(II) profile from February, 1985 with older profiles. However, the total iron inventory (dissolved plus particulate) in the fjord has changed only slightly since 1981 (106 000 moles in 1981; 97 600 moles in 1983; and 91 600 moles in 1985). The residence time for dissolved Fe(II) in the anoxic waters of the main basin of Framvaren Fjord was calculated assuming that anoxic sediments collect only in the deeper portions of the basin, yielding a value of five years.

Early diagenetic production and sediment-water exchange of fluorescent dissolved organic matter in the coastal environment

Abstract Fluorescence at wavelengths characteristic of humic substances (excitation 350 nm, emission 450 nm) have been used in this study to approximate concentrations of fluorescent dissolved organic material (FDOM). In situ regulated and unregulated benthic chambers, sediment cores, and laboratory tank incubations were used to study early diagenesis of FDOM in coastal marine sediments of the Gullmar Fjord, western Sweden. In the regulated in situ chambers, pH and oxygen were kept at relatively stable levels, while in the unregulated in situ chambers, pH and oxygen were left to decrease as a result of biological activity. FDOM porewater distributions and correlation between FDOM and parameters indicating mineralization showed that FDOM was formed in the sediment and should flux across the sediment-water interface. A substantial flux of FDOM was also observed during winter and spring conditions and during anoxic conditions fall. However, no flux was observed during oxic conditions fall. Modeling indicated that oxygen penetration depth was deeper during winter than during fall, i.e., the oxygen penetration depth increased during fall towards winter values. We suggest that as FeOOH was formed when oxygen penetration depths increased, FROM was sorbed to newly formed FeOOH, inhibiting FDOM flux over the sediment-water interface. In addition, at onset of anoxic conditions in the sediment surface layer in fall incubations, FDOM flux from sediment to overlying water increased substantially. Increases in anoxic FDOM fluxes were accompanied by increases in Fe and phosphate fluxes. We suggest that reductively dissolved FeOOH released sorbed FDOM. FDOM released from FeOOH by anoxic conditions was not resorbed when oxic conditions were resumed. This could be an effect of higher pH in overlying water as compared with porewater, inhibiting FeOOH sorption of FDOM.

Iron in the water column of the Weddell Sea

Abstract Total, dissolved and suspended iron has been determined in the water column of the Weddell Sea area during the austral summer 1988–1989. Some data are also presented for dissolved manganese, suspended manganese and suspended aluminium. The average value for dissolved iron was found to be 1.2 nM, with somewhat higher values at the Filchner Ice Shelf. The total iron was found to be considerably higher, with a range between 1 and 6 nM in the central Weddell Sea and 1 and 25 nM at the shelves. Transport of iron from the shelves into the Weddell Sea basin is demonstrated. This is observed both for total and dissolved iron.

Trace metals in the Göta river estuary

Abstract The concentrations of the trace metals Cd, Cu, Fe, Ni, Pb and Zn in the Gota River estuary have been investigated. The following metal fractions have been determined: acid-leachable, dissolved, labile and particulate. The estuary represents a salt wedge type estuary and is situated in a densely populated region of Sweden. The metal concentrations found for the dissolved fraction is in the range of what can be considered as background levels for freshwater. It is difficult to evaluate any estuarine processes other than conservative mixing for Cd, Cu, Ni and Zn. The dissolved levels in the freshwater end member are Cd, 9–25 ngl −1 ; Cu, 1·1–1·4 μgl −1 ; Fe, 20–75 μg l −1 : Ni, 0·7–0·9 μg l −1 : Pb 0·09–0·2 μg l −1 ; and Zn, 6–7 μg l −1 : The results from the acid-leachable fraction show that at high suspended load the particles sediment in the river mouth. The trace metal levels in this fraction are subject to large variations.