Rapid organic matter mineralization coupled to iron cycling in intertidal mud flats of the Han River estuary, Yellow Sea

Abstract

Organic matter oxidation represents a transfer of elements to inorganic nutrients that support biological productivity and food web processes. Therefore, quantiWcation of the controls of organic matter mineralization is crucial to understanding the carbon cycle and biogeochemical dynamics in coastal marine environments. We investigated the rates and pathways of anaerobic carbon (C) oxidation in an unvegetated mud Xat (UMF) and a vegetated mud Xat (VMF) of the Ganghwa intertidal zone of the macro-tidal Han River estuary, Yellow Sea. Analyses of geochemical constituents revealed relatively oxidized conditions and high reactive Fe(III) concentrations (40-100 mol cm ¡3 ) in the sediments. A pronounced depth stratiWcation in Fe(III) was observed at the VMF site likely due to the lower number of infaunal burrows along with dense root formation by the macrophytes, Suaeda japonica. Depth-integrated rates of anaerobic C mineralization as well as sulfate-and Fe(III) reduction at the VMF were consistently higher than those at the UMF, likely driven by the dense vegetation that supplied organic C substrates and electron acceptors to the rhizosphere. Sediment inventories revealed that solid Fe(III) was up to 17 times more abundant than pore water sulfate, and direct rate measurements showed that microbial Fe(III) reduction comprised an equal or larger percentage of C oxidation (36-66 %) in comparison to sulfate reduction (36-40 %) at both sites studied. Time-course experiments indicated that sulfate reduction rates were likely underestimated, especially in the VMF rhizosphere, due to the reoxidation of reduced S in the presence of high Fe(III). The high rates of C mineralization suggest that the Ganghwa intertidal mud Xats are a signiWcant sink against the external loading of organic compounds, and organic matter mineralization is enhanced by chemical exchange regulated by extreme tidal Xushing and macro-microorganisms interactions.

Iron dynamics in a subtropical estuarine tidal marsh: effect of season and vegetation

“…Our results also suggest that the presence of plants increases the competitiveness of FeR% and lowers SR%, which is in accordance with that found in other studies, including mangrove mesocosms in North Queensland, Australia (Kristensen & Alongi 2006), tidal marshes on Sapelo Island, USA (Kostka et al 2002a) and Skidaway Island, USA (Hyun et al 2007), Han River estuary, Korea (Hyun et al 2009), Patuxent River, USA (Neubauer et al 2005), and mangrove forests on Phuket Island, Thailand (Kristensen et al 2000).…”

“…The unexplained proportion may have been caused by underestimated SR% in both types of mesocosm, but particularly for the vegetated mesocosms due to rapid sulfide reoxidation (Luo et al 2016). The unexplained proportion might also have been caused by CO 2 formation via fermentation (Jørgensen 2000, Hyun et al 2009 or by other terminal electronaccepting processes, such as denitrification and manganese (Mn) reduction. However, the contributions of NO 3 − and Mn(IV) to organic C mineralization may have been small, because their concentrations are much lower than concentrations of SO 4 2− and Fe(III) in sediments of the Min River estuary tidal marsh (Luo et al 2014).…”

Manganese and iron reduction dominate organic carbon oxidation in surface sediments of the deep Ulleung Basin, East Sea

“…Microbial Fe reduction has been quantified directly in sediments of various coastal oceans (Gribsholt et al, 2003;Kostka et al, 2002a, b;Hyun et al, 2007Hyun et al, , 2009b and indirectly in deeper continental margins (Thamdrup and Canfield, 1996;Jensen et al, 2003;Kostka et al, 1999). Earlier estimation from 16 different continental margin sediments indicated that Fe(III) reduction contributed 22 % on average to anaerobic carbon oxidation .…”

“…However, in sediments where manganese and iron oxides are abundant or rapidly recycled, microbial reduction of manganese and iron can be the dominant electron-accepting processes over sulfate reduction (Sørensen and Jørgensen, 1987;Aller, 1990;Canfield et al, 1993b). The significance of dissimilatory iron reduction for C org oxidation is well established in the sediments of various continental margins and coastal wetlands Thamdrup and Canfield, 1996;Jensen et al, 2003;Kostka et al, 2002a, b;Vandieken et al, 2006;Hyun et al, 2007Hyun et al, , 2009b. However, only a few locations such as the Panama Basin (Aller, 1990), the coastal Norwegian trough in Skagerrak and an adjacent fjord (Canfield et al, 1993a, b;Vandieken et al, 2014), the Black Sea shelf , and the continental shelf of the northern Barents Sea (Vandieken et al, 2006;Nickel et al, 2008) are known where microbial manganese reduction significantly contributes to carbon mineralization.…”

Sulfate Reduction and Sulfur Cycles at Two Seagrass Beds Inhabited by Cold Affinity Zostera marina and Warm Affinity Halophila nipponica in Temperate Coastal Waters

“…Due to the high sulfate concentration (28 mM) in seawater, sulfate reduction is considered to be among the most important anaerobic C org mineralization pathways in marine sediments (Blackburn et al 1994;Holmer and Nielsen 1997;Holmer et al 2001;Hyun et al 2007Hyun et al , 2009). …”