CAREER: Predicting Biofilm-Bound Sediment Dynamics Through Multiscale Experiments

Sediment transport is a key process controlling coastal and riverine erosion, which costs the U.S. billions of dollars per year. Most natural sediment, such as mud and fine sand, inevitably harbors microbial biofilms. Biofilms have been shown to alter the threshold and rate of sediment transport by up to 40-fold. However, predictive sediment transport equations that account for the impacts of biofilms are lacking. A key challenge in developing such predictive equations is that the transport of sediment at macroscale (> 1 m) is controlled by biofilms at micro (10^-6 to 10^-3 m) to mesoscale (10^-3 to 10^-1 m). This study aims to combine micro- to mesoscale flow-cell and imaging technology with macroscale flume experiments to quantify the impacts of micro- to mesoscale biofilms on macroscale sediment transport. Predictive equations for biofilm-bound sediment transport will be developed. The results of this study will help improve predictions of coastal and riverine erosion, which will guide future coastal and riverine restoration projects, and support better predictions and control of the spread of biofilm-bound particulate contaminants. In addition, multiscale hands-on educational activities based on the proposed research will be developed and integrated into teaching, mentoring, K12 education, and public outreach. These activities will introduce the essence of the research to a diverse range of young learners, including female and Native American students. The goal of the proposed research is to (1) quantify the impacts of sediment size and hydrodynamic conditions on the properties of micro- to mesoscale biofilms on sediment surfaces; (2) predict the macroscale transport of suspended microscale biofilm-sediment aggregates; (3) predict the onset of bedload transport for sediment covered with mesoscale biofilm mats. Systematically controlled experiments with submicron resolution confocal microscopic imaging will be conducted in microfluidic flow cells to visualize and quantify the development of micro- to mesoscale biofilms on sediment surfaces and the formation of biofilm-sediment aggregates. Flume experiments combined with digital imaging, tensile tests, rheometer measurements, hydrodynamic measurements, and topographic measurements will be conducted to quantify the impacts of biofilms with varying morphological and rheological properties on macroscale sediment transport. The results from both microfluidic and flume experiments will be used to develop predictive equations for the transport of suspended biofilm-sediment aggregates and biofilm mat-covered bedload. 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.