The seafloor plays a critical role in the elemental cycling within shallow water ecosystems. Although the coastal benthos has been relatively well studied, the quantitative role of infauna in modifying critical ecosystem services such as nutrient cycling remains still poorly constrained. This stems largely from difficulties in scaling biogeochemical dynamics observed at the plot ( In this collaborative project, researchers at the University of Georgia and the University of Maryland?s Chesapeake Biological Laboratory will quantify small-scale dynamics of infaunal activities and their ecological interactions under controlled conditions and incorporate these data into a novel modeling approach of sediment biogeochemistry. Specifically, they will carry out a series of experimental studies to 1) determine to what extent spatial arrangement of burrows in a complex 3-dimensional domain alters sediment biogeochemistry, 2) measure species-interaction effects and feedbacks on sediment biogeochemistry, and 3) use these findings to provide guidance on sampling the intrinsically heterogeneous coastal seafloor. Laboratory experiments will be developed using sediment microcosms with artificial burrows and real organisms ? the ubiquitous Arenicola cristata and Nereis diversicolor - in separate experiments. Fluxes between the sediment and the overlying water of several diagenetically and ecologically important solutes will be measured. Burrow mimic experiments will provide detailed empirical information on burrow irrigation and spatial orientation effects on sediment-seawater exchange. This information will be used to parameterize a three-dimensional reactive transport model. Microcosms containing different combinations of the two macrofaunal species distributed in even and clustered spatial arrangements will be used to determine species interaction effects on burrow geometry and irrigation, and consequences for solute fluxes. The experimental data will elucidate the response of infauna to spatial proximity as well as the interaction across and within species. Comparison of observational data to model simulations will be used to assess the impact of macrofaunal interactions on sediment biogeochemistry. Finally, reactive transport model simulations will be performed for scenarios differing in densities and spatial arrangement of macrofauna, as well as their interactions. Aggregate fluxes across the sediment water interface will be estimated by dividing the seafloor up into tiles for which model flux estimates can be obtained. This approach will be used to evaluate various possible sampling strategies, and determine how well a limited number of flux measurements can approximate the contribution of benthic infauna to coastal biogeochemical cycles. In terms of broader impacts, this study is expected to provide a framework for scaling individual flux measurements taken in coastal sediments to larger scale mass fluxes. The findings will broaden our understanding of nutrient dynamics in the coastal ocean and benefit the general experimental community by providing context for the interpretation of flux data and design of measurement campaigns. One graduate student will be trained in experimental and numerical methodology. In addition, development of outreach materials and exhibits about sediment biogeochemistry and benthic infauna for the CBL visitor center will expose roughly 3500 visitors per year to lesser known aspects of the marine environment.
