In situ organism-sediment interactions: Bioturbation and biogeochemistry in a highly depositional estuary

PLoS One. 2017 Nov 27;12(11):e0187800. doi: 10.1371/journal.pone.0187800. eCollection 2017.

Abstract

Organic matter (OM) production and degradation is important in coastal estuaries, and OM fate is strongly influenced by the coupled interactions of bioturbation and biogeochemistry. From April to September 2013 sediment cores and a benthic observing system, Wormcam, were used to investigate the in situ relationship of biogeochemistry and macrofauna bioturbation in Cape Lookout Bight North Carolina. Wormcam imagery provided a vivid depiction of macrofauna functioning in an environment not previously observed, and affirmed the importance of fine-scale temporal observations of the benthic environment in situ. Observation of macrofauna presence and bioturbation during the summer contradicted previous studies that found this area to be azoic during methane activity and sulfide build-up. Sulfate concentrations decreased while sulfide and dissolved inorganic carbon concentrations increased during the summer. This coincided with changes in the depth and rates of bioturbation. Summer burrow depths (~0.8 cm) and rates (~0.4 cm h-1) were significantly less than spring burrow depths (~3.0 cm) and rates (~1.0 cm h-1). While sulfate reduction and OM degradation increased with temperature at a microscopic level, macroscopic OM degradation was reduced. As a result, reduced conditions dominated and a thin aerobic sediment layer, a few millimeters in thickness, was visible at the sediment surface. Decreases in macrofauna burrow depth and rates diminishes the area of influence of bioturbators, limiting bioturbation and subsequently the important ecosystem functions these organisms provide.

MeSH terms

  • Animals
  • Ecosystem*
  • Estuaries*
  • Geography
  • Geologic Sediments / chemistry*
  • North Carolina

Grants and funding

This work was supported in part by the National Science Foundation funded OCE-PRF to SKS, Japan Student Service Organization to MSS, and Duke University Marine Lab funded Joseph S. Ramus Endowment to SKS and MSS. The authors have declared that no competing interests exist. Author SK Sturdivant is currently also employed by a commercial company: INSPIRE Environmental. During the time of this study SKS was not employed by INSPIRE Environmental. The commercial entity INSPIRE Environmental provided support in the form of a salary for author SKS, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the 'author contributions' section. Additional financial support from: Division of Ocean Sciences (1324294) to Dr. Samuel Kersey Sturdivant. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.