The influence of coring method on the preservation of sedimentary and biogeochemical features when sampling soft-bottom, shallow coastal environments.

It is frequently assumed that taking samples of soft marine sediments using surface-based gravity coring equipment causes minimal disruption to their sedimentological, biogeochemical, and biological condition. This assumption was evaluated by examining the potential disturbances caused when obtaining soft-sediment samples either by SCUBA or Craib-coring, comparing sediment oxygen microprofiles, benthic oxygen flux rates and sediment solid phase analyses (chlorophyll a (Chl a), organic carbon, and porosity) between both methods and against reference values measured in situ by benthic lander.

The two sampling methodologies were tested in shallow coastal environments on the west coast of Scotland and generally the results obtained from cores collected using SCUBA exhibited values closest to those observed in situ. Oxygen penetration depth was significantly shallower in cores obtained by Craib-corer compared with the SCUBA cores. Craib cores also produced higher oxygen uptake rates which could be caused by greater levels of sediment disturbance during sampling. In addition, more homogenous levels of Chl a in the top 1 cm of the Craib cores, compared with the SCUBA samples, may indicate either resuspension or compression during gravity coring. Using SCUBA for shallow-water soft-sediment sampling permits steady and controlled core-tube insertion and extraction, and more measured retrieval of the cores to the surface; this probably accounts for the observed differences.

Whereas benthic lander-based in situ measurement would be the preferred method for analyzing sediment parameters in detail in this type of environment, SCUBA-based sampling offers a more accurate alternative to surface-based gravity coring.

Authors:

Mogg, A.O.M., Attard, K.M., Stahl, H., Brand, T., Turnewitsch, R. and Sayer, M.D.J.

Limnology and Oceanography Methods
09, 28, 2017
Pages:
DOI: 10.1002/lom3.10211