Oscillatory porewater bioadvection in marine sediments induced by hydraulic activities of Arenicola marina

We employed real-time pressure recording and high temporal resolution two-dimensional oxygen imaging to characterize the porewater bioadvection related to hydraulic activities of Arenicola marina, a widespread representative of benthic macrofauna. Behavior-specific positive and negative pressure oscillations and hydraulic pulses resulted in bidirectional porewater flow and highly dynamic redox oscillations on the scale of minutes. Pumping of water by the worm into its blind-ending burrow pressurized the sediment and caused sediment oxygenation at depth and the exit of anoxic porewater into the overlying water. The sediment volume that was affected by bioadvective transport of oxygen and the porewater flow patterns varied strongly among sediment types. In low-permeability sediments, localized plumes of anoxic porewater ascended from the sediment, presumably through sedimentary cracks, while porewater flowed evenly through highly permeable sediments. Hydraulic behaviors that moved water out through the open tail shaft caused a reduction of porewater pressures below the hydrostatic baseline which resulted in the collapse of plumes and enhanced oxygen penetration into the surficial sediments. Porewater bioadvection and the related perfusing and oscillatory phenomena will affect a variety of biogeochemical and ecological processes, including organic matter mineralization, benthic recruitment, and prey localization. We suggest that bidirectional porewater bioadvection and the associated transient geochemical conditions are prevalent features of biogenically active sediments.