Microbial oxidation of manganese in a North Carolina estuary1

Abstract

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.

A dissolved cobalt plume in the oxygen minimum zone of the eastern tropical South Pacific

“…Holocene records from the Pearl River delta and shelf slope in the South China Sea ∼ 20 • N (Hu et al, 2012(Hu et al, , 2013 show mean Co / Al ratios of 2.2 and 2.1 × 10 −4 g g −1 , respectively, similar to sediments from the Gulf of Papua at 9 • S (2.3 × 10 −4 g g −1 , Alongi et al, 1996). Crustal Co / Al in these sedimentary systems implies that most of the Co provided from fluvial sediment delivery either does not dissolve or is quickly reburied by water column Mn oxidation, rates of which can be very high in estuaries and coastal seas (Moffett and Ho, 1996;Moffett, 1994;Sunda and Huntsman, 1987;Sunda and Huntsman, 1990).…”

Copper Concentration and CuII Activity in San Diego Bay

“…A sample of ocean beach water (La Jolla shore) was also included in the data set as being representative of water outside the bay. Copper activity values fall in the expected range for estuarine waters [14,[24][25][26]. pCu values greater than 11.6 (low copper concentration) are generally associated with water at the mouth of the harbor or outside of it.…”

Effects of photosynthesis on the accumulation of Mn and Fe by Phaeocystis colonies

“…The organic content of the mucus may facilitate the photoreduction of solid phase Fe(III) to soluble Fe(II). Similar mechanisms may also be involved in the case of Mn and make it available to phytoplankton (Sunda and Huntsman 1994).…”