Topographic controls on the distribution of bioturbation in an intertidal sandflat

Abstract

Intertidal environments are highly dynamic and exhibit both regular and periodic fluctuations in environmental parameters. The interplay of these parameters controls the distribution and abundance of infaunal organisms resulting in sporadic bioturbation distributions that are well‐documented but not fully understood. This study investigates topographic controls on infaunal distributions at East Beach in White Rock, British Columbia, Canada. East Beach is a sandy intertidal flat characterized by sand dunes that give rise to two alternating shore‐parallel subenvironments: topographically high dune crests and topographically low interdunes. The dunes remain relatively fixed in their position between major storm events, resulting in geographically stable subenvironments. Photogrammetric reconstructions of dune surfaces are used to characterize surface features and quantify invertebrate burrow openings along dune profiles. This is supplemented by X‐ray radiography and examinations of porewater and organic matter content from the two subenvironments. These results show a clear inverse relationship between burrow abundance and elevation at the dune scale, with the interdunes displaying significantly higher bioturbation intensities compared to dune crests. The burrow distributions appear to be strongly influenced by water saturation, presumably due to its role in controlling oxygen availability and preventing desiccation. This research provides insights into the local factors controlling infaunal distributions and the impact of palaeo‐topography on bioturbation, particularly in intertidal settings. Additionally, these data assist in interpreting heterogeneous bioturbation distributions in the sedimentary record, which are normally not interpreted due to a paucity of analogue models developed in modern environments.