The role of infauna on permeable sediment processes is poorly understood due to methodological limitations and a lack of empirical data. The interactions among porewater flows, sediments, and biogenic structures present a physically and biogeochemically complex sedimentary environment in which traditional measurement techniques and heuristic models are of minimal applicability. Chapter one provides an executive summary of this research. The second chapter describes a field investigation of the impact of the common lugworm and two species of thalassinid shrimp on porewater transport and chemistry in permeable sediments. In this work, novel experimental methods are employed to measure infaunal effects on porewater transport and chemistry. This experiment found differential effects of each taxon on porewater transport and solute chemistry that were highly related to infaunal functional characteristics, and independent of sediment properties.

Results from the field study prompted a laboratory microcosm study of lugworm effects on permeable sediment solute fluxes, presented in chapter three. Flow-through sediment microcosms mimicked tidal draining of intertidal flats and measured the effects of lugworms on sediment biogeochemistry. Lugworms were found to significantly alter solute fluxes as well as stoichiometric ratios from the microcosms. The potential ecosystem consequences of stoichiometric changes to regenerated solutes are explored with a new metric. Finally, chapter four presents a synthesis examination of the infaunal functional attributes important to permeable sediment processes with a multi-site, multi-species field investigation. Head-down deposit feeders were found to have similar effects on advection and chemistry, whereas other infauna had differential effects linked to the composition and morphology of the burrow/tube. The mechanisms by which different infauna may affect permeable sediment properties are discussed, and include consideration of covariates such as organism activity and density.

The results from this research highlight the importance of infauna to permeable sediment processes, while recognizing the limitations of their effects under different physical regimes. Benthic infauna play a significant role in the biogeochemistry of common permeable sediment habitats in coastal and near-shore environments. The results presented herein suggest the loss of large bioturbating infauna from permeable sediments due to human activities may result in significant changes to coastal biogeochemical cycles.