Project: Collaborative Research: Megaripples as biocatalytical filters

NSF Award Abstract:
This project focuses on the role of large underwater sand formations, particularly at the mouths of estuaries, in the cycling of nutrients and organic materials. "Megaripples" are common features on marine sediments where bottom currents are rapid. In the northeastern Gulf of Mexico, these sand dune-like features are up to half a meter in height, with wavelengths reaching 20 meters. The investigators propose that megaripples act as large filter systems that rapidly convert dissolved and solid organic matter into inorganic carbon and nutrients, and thus influence the biological productivity of coastal waters. They propose to use a one-kilometer long megaripple field in the inlet of Chotawhatchee Bay, in the northeastern Gulf of Mexico, as a natural laboratory for studying these processes. In addition, they will conduct laboratory experiments to investigate the filter processes at a smaller scale. By producing data on the functioning of megaripples, the project addresses a knowledge gap that has implications on our understanding of the cycles of matter in coastal waters. The project offers opportunities for both graduate and undergraduate students in learning state-of-the-art techniques. The students will gain experience in working on high frequency data acquisition and analysis of 'big data'. To enhance outreach, the researchers will develop and teach two courses on Permeable Sediment Biogeochemistry and Aquatic Eddy Covariance Studies for the Saturday at the Sea program offered by Florida State University. Results will be disseminated via scientific journals, conference presentations and public lectures, and directly to the Apalachicola-National Estuarine Research Reserve (NERR), which will make the results available to the other 28 NERR sites.

The two main project objectives are: 1) demonstrate the general function of megaripples as biocatalytical filters, and 2) demonstrate that common inlet megaripples contribute to nutrient retention in coastal bays. A 1 km long megaripple field in the inlet of Chotawhatchee Bay (wavelengths: ~20 m, amplitudes: 20 to 40 cm) in the northeastern Gulf of Mexico will be used as an in-situ laboratory. Measurements will characterize megaripple topography and the water flowing over them. Salinity and suspended particles are utilized as natural tracers to quantify solute and particle entrainment into the megaripples. This project will deploy non-invasive aquatic eddy covariance instruments equipped with newly developed robust sensors to quantify sedimentary remineralization in the flushed megaripple bed. This technique integrates the benthic oxygen flux over a large section of the megaripple field, while including the natural dynamics of currents and light. Real-time water column measurements with a boat-mounted flow-through analyzer permit rapid quantification of large horizontal gradients of key water column parameters. The in-situ measurements will be combined with laboratory column reactor experiments that quantify nutrient re-mobilization through organic carbon mineralization in flushed megaripple sand. The megaripple field in the inlet of Chotawhatchee Bay is easily accessible from shore and by small boat, expediting instrument deployments and in-situ measurements while reducing project costs. Synthesis of all data will produce a conceptual and quantitative understanding of megaripples as natural biocatalytical filters. Because transport and reaction in megaripples are governed by basic physical and biogeochemical processes, these results will reveal information on the general biogeochemical functioning of megaripples that so far is not available.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.