The rates and pathways of carbon oxidation in bioturbated saltmarsh sediments

Abstract

This study was carried out to quantify the effects of higher organisms, invertebrate macrofauna, and macrophyte plants on the rates and pathways of microbial respiration coupled to organic matter oxidation in saltmarsh sediments. Sediment geochemistry, rates of microbial metabolism, and the abundance of anaerobic respiratory bacteria were determined at sites differing in the abundance of fiddler crab (Uca pugnax) burrows and vegetation (Spartina alterniflora) coverage. Solid-phase Fe(III) concentrations were 50 to 100 times higher, and solid sulfide concentrations were eight times lower in bioturbated, vegetated sediments (BVL) as compared to nonbioturbated, unvegetated (NUC) sediments. Integrated sulfate reduction rates were 10 times lower in BVL (2 mmol m Ϫ2 d Ϫ2 ) as compared to NUC sediments (20 mmol m Ϫ2 d Ϫ1 ). Directly measured Fe(III) reduction rates were high at the BVL site, whereas no Fe(III) reduction was detected at NUC or in killed sediment treatments. Molybdate, a specific inhibitor of sulfate reduction, inhibited 70% of carbon oxidation when added to NUC sediment but showed no effect on Fe(III) reduction or C oxidation in BVL sediments. Counts of Fe(III)-reducing bacteria (FeRB) were two orders of magnitude higher in BVL sediments (10 7 cells g Ϫ1 ) in comparison to NUC sediments (10 5 cells g Ϫ1 ). Fe(III) respiration comprised up to 100% of carbon oxidation in BVL sediments, whereas sulfate reduction was the dominant respiration process (Ն70% of C oxidation) at NUC. We provide strong evidence to show that macroorganisms stimulate FeRB to outcompete sulfate-reducing bacteria in saltmarsh sediments by supplying an abundance of reactive Fe(III) through reoxidation processes.

Biodiversity of benthic microbial communities in bioturbated coastal sediments is controlled by geochemical microniches

“…Although it has been known that burrowing organisms affect sediment biogeochemistry, the interactions are often complex and detailed investigations on the effect of geochemical microzonations on microbial diversity are scarce (Kostka et al, 2002;Lucas et al, 2003;Matsui et al, 2004;Papaspyrou et al, 2006). This is not surprising because studies on microbial diversity in marine sediments have also only just begun (Mu mann et al, 2005;Wilms et al, 2006;Wu et al, 2008).…”

“…Their burrows have been acknowledged as important conduits for chemical exchange between the water column and the sediment, linking the activity of these crustaceans to nutrient recycling, organic matter degradation and primary productivity (for example, Kostka et al, 2002;Papaspyrou et al, 2005). In this study, we examined the impact of the bioturbation activity of the ghost shrimp Neotrypaea californiensis and the fiddler crab Uca crenulata on microbial community compositions in the sediment.…”

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.…”

Anaerobic Metabolism: Linkages to Trace Gases and Aerobic Processes

“…Yet, Fe(III)-reducing bacteria are abundant in marine soils and sediments (Lowe et al, 2000;Kostka et al, 2002c), and several workers have noted that Fe(II) continues to accumulate when H 2 S production is blocked by molybdate, apparently because of enzymatic Fe(III) reduction (Canfield, 1989;Canfield et al, 1993b;Mines et al, 1997;Jacobson, 1994;Joye et al, 1996;Kostka et al, 2002c;S0rensen, 1982).…”