Hydrogeologic Controls on the Accumulation, Transport, and Discharge of Fecal Indicator Bacteria in Coastal Beaches

About This Grant

Coastal beaches are vital for recreation, tourism, and ecosystem health. However, they are increasingly threatened by fecal contaminants as indicated by high concentrations of fecal indicator bacteria (FIB). These bacteria can enter beach environments through human wastewater, stormwater runoff, and animal waste, accumulating in the sand and shallow groundwater. Natural coastal processes such as tides and waves can then mobilize and transport these contaminants across the land-sea boundary, posing risks to public health and marine ecosystems. This project will investigate how coastal hydrologic forces, including tidal fluctuations and wave action, influence the accumulation, movement, and discharge of FIB in beach aquifers. The research team will conduct fieldwork and groundwater sampling at two beaches in Hawaiʻi where FIB contamination is known to occur, and will develop advanced computer models to simulate how bacteria move through beach sediments. The findings will improve prediction and management of water quality risks in coastal zones. Broader benefits of the project include training two graduate students and engaging undergraduate students through the University of Hawaiʻi at Mānoa’s Undergraduate Research Opportunities Program. The team also plans to involve local communities through educational outreach and citizen science activities to support long-term coastal water stewardship in Hawaiʻi. Fecal contamination is an increasing concern in coastal beach environments, posing serious risks to public health and ecosystem integrity. Fecal indicator bacteria (FIB) are commonly used to detect and assess the extent of such contamination. These bacteria can enter the subsurface through various sources such as treated and untreated wastewater, stormwater runoff, and animal waste, and persist in beach aquifers where they interact with dynamic coastal hydrologic forces. However, a mechanistic understanding of how tide- and wave-driven seawater-groundwater interactions influence the fate and transport of FIB in coastal beach aquifers remains lacking. The project aims to fill that knowledge gap through a comprehensive approach that integrates state-of-the-art surface water, groundwater, and reactive transport modeling, along with field measurements. There are three objectives: (1) develop a state-of-the-art modeling framework that captures both surface and subsurface flow dynamics and simulates the accumulation, transport, and discharge of FIB within and through coastal beach aquifers; (2) conduct field studies at two fecal-contaminated Hawaiian beaches subjected to high and low wave energy, respectively, to quantify FIB distribution and transport under varying hydrodynamic conditions; and (3) analyze site-specific data and extend modeling efforts across a range of hydrogeological settings to identify the key controls on FIB exchange across the beach-sea interface. The successful completion of this project will advance understanding of coastal hydrogeological processes that govern bacterial transport, not only for FIB but also for other microbial groups such as pathogenic, sulfate-reducing, and nitrifying bacteria. The knowledge generated will support development of more effective coastal water quality management strategies and inform stakeholders and communities about the resilience and vulnerability of beach aquifer systems to fecal contamination in the face of changing coastal conditions. This project is jointly funded by Water, Landscape, and Critical Zone Processes (WaLCZ), the Established Program to Stimulate Competitive Research (EPSCoR), and the Earth Sciences Division (EAR). 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.