Influence of Manila clam aquaculture on rates and partitioning of organic carbon oxidation in sediment of Keunso Bay, Yellow Sea

Abstract

We investigated the effects of Manila clam aquaculture on the rates and pathways of anaerobic organic carbon (OC) oxidation in highly bioturbated (HB) and poorly bioturbated (PB) sediment in Keunso Bay, Yellow Sea. Due to the labile organic matter supply via sediment reworking by Manila clams, the anaerobic OC oxidation rate in HB sediment (38.8 mmol m-2 d-1) was ~1.5 times higher than that in PB sediment (26.8 mmol m-2 d-1). Microbial Fe(III) reduction (FeR) dominated OC oxidation pathways in HB sediment, comprising 55 to 76% of anaerobic OC oxidation, whereas sulfate reduction (SR) was the dominant oxidation pathway in PB sediment, accounting for up to 92% of anaerobic OC oxidation. Despite higher anaerobic respiration rates at the HB site, concentrations of NH4+, PO43-, oxalate-extractable iron (Fe(II)(oxal)), and total reduced inorganic sulfur were 2 to 3 times lower in HB than in PB sediment. Conversely, the concentration of reactive Fe(III)(oxal) at the HB site (2243 mmol m-2) exceeded that at the PB site (1127 mmol m-2) by a factor of 2. These results indicate that bioturbation by Manila clams enhances the re-oxidation processes of reduced metabolites in the sediment, thereby prohibiting SR and promoting FeR. Overall, the results suggest that aquaculture activities of Manila clams shift the dominant OC oxidation pathways in sediment from SR to FeR, which generates relatively oxidized and less sulfidic environments.

Benthic Respiration and Heavy Metal Benthic Fluxes in Artificial Shihwa Lake: Approaching In Situ Measurement

“…The POC and TN content, as well as the stable carbon isotopic composition (δ13C), were analyzed using an elemental analyzer (EA; Vario PYROcube, Elementar, Langenselbold, Germany) in conjunction with an isotope ratio mass spectrometer (IRMS; Isoprime 100, Isoprime, Cheadle Hulme, UK) after acidification with 1N HCl fumes. The isotopic composition was expressed in the δ notation as δ 13 C (‰) = ((R sample /R reference ) − 1) × 1000, where R is the corresponding ratio 13 C/ 12 C. The isotopic reference for carbon was Vienna PeeDee Belemnite (VPDB).…”

“…Deposited OM is rapidly oxidized in the sediment via various electron acceptors, such as oxygen, nitrate, manganese oxide, iron oxide, and sulfate [12]. SOD can quantify the total oxidation rates of organic carbon (OC) because oxygen consumes the aerobic respiration of microorganisms and the reoxidation of reduced compounds via an anaerobic process [13,14]. Therefore, SOD has been used to assess the extent of OM enrichment in the sediment, which is an important proxy for determining the trophic state of the coastal ecosystem.…”

Iron Reduction Controls Carbon Mineralization in Aquaculture Shrimp Pond Sediments in Subtropical Estuaries

“…Although sulfate reduction and methanogenesis have been widely reported in aquaculture pond systems (Hyun et al., 2013; Nho et al., 2018; Zhou et al., 2022), few studies have focused on Fe(III) reduction and its role in carbon mineralization in aquaculture pond systems. Indeed, aquaculture pond sediments have comparable or higher Fe(III) content than other aquatic sediments (Kim et al., 2020; Lemonnier et al., 2021; Mok et al., 2021). It is therefore reasonable to expect that microbial Fe(III) reduction also plays an essential role in aquaculture pond sediments, although there is currently a lack of field data to support this hypothesis.…”