Relationship between apparent redox potential discontinuity (aRPD) depth and environmental variables in soft-sediment habitats

Abstract

As global temperatures increase and dissolved oxygen (DO) content decreases in marine systems, indices assessing sediment DO content in benthic habitats are becoming increasingly useful. One such measure is the depth to the apparent redox potential discontinuity (aRPD), a transition of sediment color that serves as a relative measure of sediment DO content. We examined spatiotemporal variation of aRPD depth, and the nature of the relationships between aRPD depth and biotic (infauna and epibenthic predators) and abiotic variables (sediment properties), as well as the availability of resources (chlorophyll a concentration, and organic matter content) in the intertidal mudflats of the Bay of Fundy, Canada. aRPD depth varied significantly through space and time, and a combination of biotic (sessile and errant infauna, as well as epibenthic predators), and abiotic (exposure time of a plot, sediment particle size, penetrability, and water content) variables, as well as the availability of resources (sediment organic matter content, and chlorophyll a concentration) were correlated with aRPD depth. As such, knowledge of both biotic and abiotic variables are required for a holistic understanding of sediment DO conditions. Abiotic variables likely dictate a suite of potential aRPD depth conditions, while biota and resource availability, via bioturbation and respiration, strongly influence the observed aRPD depth. As DO conditions in marine systems will continue to change due to global climate change, elucidating these relationships are a key first step in predicting the influence decreasing DO content may have upon marine benthos.