Mechanical imitation of bidirectional bioadvection in aquatic sediments

Abstract

Measuring the effects of bioirrigating infauna on sediment properties and geochemistry is often problematic due to the unpredictable nature of the animal activity. This can be overcome by the use of mechanical systems that allow mimicking of bioirrigation in a controlled and reproducible manner. A realistic mimic must allow both qualitative and quantitative imitation of the complex infaunal activities, i.e., be able to generate both positive and negative porewater pressure waveforms in a realistic range of amplitudes and frequencies using biologically realistic water volumes. We developed a mechanical irrigation system (Robolug) that meets these criteria and applied it to mimic a set of specific hydraulic behaviours of the common lugworm Arenicola marina. The resultant porewater pressure waveforms had realistic shapes and amplitudes and were realized by pumping biologically realistic volumes of water. The bidirectional bioadvection induced oxygen dynamics at depth and at the sediment water interface comparable to those observed with live lugworms. Additionally, we were able to reproduce the formation of sedimentary cracks, a phenomenon also observed with real lugworms. The Robolug irrigation system is a promising tool for a wide range of biogeochemical and ecological studies, as it allows the exploration of bio hydraulically induced transient geochemical conditions in a controllable and reproducible manner; avoids the uncertainties of animal performance; and permits manipulative experimental conditions that could potentially be harmful for organisms or alter their behaviors.