Behaviour of manganese in the Rhine and Scheldt estuaries

124

Experiments were conducted with 54Mn(II) to determine the kinetics of particulate manganese formation in seawater from the lower Newport River estuary, North Carolina. Dissolved Mn was rapidly converted into particles at constant rates that ranged from 0.36 to 6.2% h-r (0.62-3.5 nmol liter-l h-l), yielding turnover times of the dissolved manganese pool of 0.7-l 1 d. Dissolved Mn turnover rates increased with temperature (Q10 = 2) up to a maximum at 25"-35°C and also increased with the ratio of particulate to dissolved Mn. These two factors explained most of the variation in the observed turnover rates.Sample deoxygenation reduced the formation of particulate 54Mn by 94% and virtually all the particulate 54Mn formed in natural oxygen-containing samples could be dissolved by 10 PM ascorbic acid, a strong reducing agent. These results indicated that the formation of particulate 54Mn resulted primarily from the oxidation of Mn(I1) to manganese oxides (MnO,). The oxidation rates, however, were much too rapid to be accounted for by abiotic mechanisms, and the rate was reduced by 97% following heat sterilization of the seawater. In addition, the rates conformed to the Michaclis-Menten enzyme kinetics model with V,,, equal to 1.2 x lO-8 mol liter-' h-' and K, equal to 1.9 x lo-' M. These findings provide strong evidence that oxidation of Mn in the estuarine samples is microbially catalyzed. This catalysis appears to be instrumental in the rapid redox cycling of Mn and in the scavenging of dissolved Mn onto particles in aquatic systems.

“…data). Evidence also has been reported for microbial mediation of Mn oxidation in two other estuaries (Wollast et al 1979;Vojak et al 1985) and in a freshwater lake (Chapnick et al 1982 …”

Section: Discussionmentioning

confidence: 71%

Section: -B 35omentioning

confidence: 96%

Section: -B 35omentioning

confidence: 99%

See 1 more Smart Citation

Microbial oxidation of manganese in a North Carolina estuary1

Sunda

Huntsman

1987

124

“…Dissolved manganese concentrations can be as low as 0.3 nmol liter-' in some surface waters of the Pacific Ocean (Klinkhammer and Bender 1980) and can approach 10,000 nmol liter-' in riverine and estuarine waters (Wollast et al 1979). In the North Carolina estuary from which our Chlamydomonas sp.…”

Section: A)mentioning

confidence: 99%

Regulation of cellular manganese and manganese transport rates in the unicellular alga Chlamydomonas1

Sunda

Huntsman

1985

The cellular accumulation and uptake kinetics of manganese by Chlamya'omonas sp. were studied in model chelate buffer systems. Cellular manganese concentrations and uptake rates were related to the computed free manganese ion concentration and were independent of the total or chelated manganese concentration.Cellular manganese was constant at about 1 mmol liter-' of cellular volume at free manganese ion concentrations of 1 O-7.b-l O-6.3 mol liter-l and decreased below this range. Manganese uptake rates followed saturation kinetics and V,,,, but not KS (1 Om7.0 mol liter-l), varied with the fret manganese ion concentration in the growth medium. V.,, appeared to be under negative feedback control and increased with decreasing manganese ion concentration.

“…Several studies of manganese oxidation by such geochemical approaches have led to the conclusion that biological catalysis must be occurring (Emerson et al 1979;Wollast et al 1979). Further studies by a combined microbiological and geochemical approach (Emerson et al 1982) confirmed 1247 that the rates observed in nature were due to bacterial activity.…”

mentioning

confidence: 96%

Microbial mediation of Mn(II) and Co(II) precipitation at the O₂/H₂S interfaces in two anoxic fjords1

Tebo

Nealson

Emerson

et al. 1984

144

We studied the potential for bacterial catalysis of Mn(II), Co(H), and Fe(III) precipitation at the 02/H2S interfaces in Saanich Inlet, British Columbia, and in Framvaren Fjord, Norway. In Saanich Inlet the interface is below the photic zone, but in Framvaren Fjord it is within the region of significant light penetration. Biological catalysis of metal removal was measured as the binding of radioactive isotopes as a function of time in the presence and absence of poisons which do not measurably interfere with the solution chemistry of manganese. In a region just above the oxic/ anoxic interface in Saanich Inlet, the binding of Co(I1) and Mn(I1) was inhibited by the bacterial poisons, but Fe(III) precipitation was not. Measurements of the oxidation state of the particulate material indicated a slightly higher Mn(IV):Mn(II) ratio in the region of dissolved Mn(B) precipitation, confirming that manganese was being oxidized and not simply bound, In both fjords, binding was either stronger or more rapid under air saturation than under conditions of oxygen limitation, suggesting that O2 is the electron acceptor during manganese oxidation. In Framvaren