MEPS 487:7-13 (2013)  -  DOI: https://doi.org/10.3354/meps10407

ABSTRACT: Measurements of the depth of the redox potential discontinuity (RPD) are becoming progressively more important as a promising variable to evaluate the ecological status of many benthic environments. Two methods are commonly used to measure depth of the RPD in intertidal habitats: (1) visually, often by digital imaging (aRPD); or (2) with redox potential electrodes coupled to a millivolt meter. However, since both measurements of RPD may focus on different attributes of the sediment, it remains uncertain whether they yield comparable results, especially in dynamic intertidal sediments. We used a paired design to compare RPD values derived from the 2 methods on 9 intertidal mudflats in the Bay of Fundy, Canada, over 2 yr. When all samples were examined together, there was a highly significant difference between the 2 methods. Furthermore, this difference was not consistent over space and time. Our findings clearly demonstrate that aRPD and RPD measurements cannot be compared directly, hampering between-study comparison.

KEY WORDS: Redox potential · Apparent redox potential discontinuity · Sediment colour change · Redox potential discontinuity · Intertidal mudflats · Bay of Fundy