Surface Chemical Reactivity and Metal Adsorptive Properties of Natural Microbial Mats, Iron Oxides, and Infaunal Mucus Secretions

Chemical adsorption reactions occurring at the solid-water interface play an important role in mineral nucleation, elemental mobility, and the geochemistry of natural waters in general. Chemical equilibrium surface complexation modeling (SCM) of adsorption reactions has been widely applied in recent years to better understand these roles. However, many important sorbents remain unevaluated for surface chemical reactivity, or have only been evaluated under artificial conditions such in laboratory microbial culture. This thesis expands current knowledge regarding the elemental adsorptive properties of organic matter (OM) and iron oxide sorbents in three independent but complimentary studies. In chapters 2 and 3, concentrated bacterial and algal biomass harvested directly from natural hydrothermal springs provide the first available data for the abundance and nature of microbial reactive functional groups in natural settings. Both studies demonstrate that natural microbial biomass is generally comparable with laboratory culture in terms of in overall surface reactivity. Metal desorption experiments and surface complexation modeling provide insight into in-situ adsorption reactions occurring from hydrothermal spring waters onto microbial mat and iron oxide substrates. Significant variation in adsorbed metal loads argues against a universal surface complexation model for bacteria, and points to a strong role for silica in natural iron oxide surface chemistry. Complimentary studies detailed in Appendices 1 and 2 further examine the relation of this finding to the iron oxide rock record.;Bioturbating animals may have a profound effect on the sediment-water interface. Mucus is secreted by a variety of infaunal animals but its geochemical properties are poorly understood. Chapter 4 details experiments where Terebellid polychaete burrow mucus was characterized by FTIR spectroscopy, acid-base titrations and cadmium adsorption experiments to understand the reactive site density and aqueous metal affinity of natural animal mucus. The data reveal that Terebellid mucus shows strong compositional similarity with mucus from distantly related organisms, and possesses proton-reactive surface site densities and cadmium stability constants that are relatively high, most likely stemming from mucin's extended conformation and abundance of chalcophilic thiol organic functional groups. These results provide insight into the nature and geochemical reactivity of animal mucus as it pertains to elemental mobility across the sediment-water interface.