Geological, Physical and Chemical Foundations

Abstract

Modern tidal flats are coastal geomorphological features with a recentgeologic history (Holocene period, 10,000 YBP) that are found globally, underdifferent climatic, hydrodynamic and sedimentological regimes. They are primarilycharacterized by fine-grained sedimentary deposits (silt and clay) that present uniquephysical and chemical properties, in comparison to other sediment types. The input ofsediments to mudflats can be either riverine, from offshore, and/or from the erosion ofcoastal sedimentary deposits. Tides and tidal currents are the dominant hydrodynamicforces shaping mudflats, with wave action playing a secondary role. Theoccurrence of intermittent or temporary flooding and the presence of variable redox(oxidation-reduction) conditions are typical features of mudflat sediments. Thetemporally and spatially variable changes from aerobic, oxidized states of mudflatsediment and porewater to anaerobic, reduced states drive particular redox reactionsthat govern the characteristic chemical processes and biogeochemical functioningthat distinguish mudflats from other coastal settings. Mudflat sediments are not inert;the high surface area:volume ratio of fine-grained sediment particles offers a vast andstructurally-complex landscape for colonization by microbes that rely on surfaceadhesionprocesses. Photosynthetic microalgae belonging to several taxonomicgroups (collectively known as microphytobenthos MPB) are the dominant microorganismsgrowing in association with sedimentary particles, and forming a biofilmlayer on top. In addition to physical forces, living benthic communities modifysediment properties as part of their normal physiology (micro- and macro-biota)and feeding, movement, and burrowing activity (meio- and macrofauna), especiallyin relation to stabilization and destabilization processes. These may ultimately havemarked effects on sediment stability and geomorphology. The interplay between suchbiological processes and sediments in mudflats is currently an active field of research.