Comparison of two methods of measuring the depth of the redox potential discontinuity in intertidal mudflat sediments

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. © Inter-Research 2013.