Meeting Abstract

25.1  Wednesday, Jan. 4  Bioirrigation revisited: Infaunal hydraulic activities and porewater advection in marine sediments VOLKENBORN, N*; CHENNU, A; MATSUI, GYM; POLERECKY, L; WETHEY, DS; WOODIN, SA; University of South Carolina, Columbia; Max Planck for Marine Microbiology, Germany; University of South Carolina, Columbia; Max Planck for Marine Microbiology, Germany; University of South Carolina, Columbia; University of South Carolina, Columbia nils@biol.sc.edu

Marine sandy sediments, which cover the largest part of the Earth, are a mixture of sediment particles and interstitial porewater with a volumetric ratio of approximately 1:1. Over the last years we have documented substantial movement of porewater into, through, and out of the sediment due to hydraulic activities of various infaunal polychaete, bivalve and crustacean species. The magnitude and spatial extent of the biologically induced dynamic porewater pressure gradients are governed by the sediment's resistance to interstitial porewater flow, i.e., hydraulic conductivity (or permeability). In this talk we will present new insights into a range of physical aspects related to a life in porous media with permeabilities varying by 3-4 orders of magnitude. Based on porewater pressure time-series with live animals and artificial irrigation systems, and using oxygen as a reactive tracer for porewater transport, we show that many infaunal organisms are capable of increasing the local hydraulic conductivity of the sediment by means of hydraulic cracking. The formation of sedimentary cracks results in (i) a reduction of the energetic investment for ventilation/feeding on the individual level, and (ii) an extension of the suitable habitat towards low permeability muddy sand on the population level. Moreover, such biologically created “highways” of porewater transport may be one reason for the well-documented enormous small-scale variability of many benthic ecosystem functions, such as benthic productivity, organic mineralization, infaunal interactions and recruitment.