Microbial dynamics and human health risks at the beach – Will climate change matter?

Beaches provide recreational opportunities, relief from hot weather, and economic benefits to coastal communities. Visitors to the beach may be exposed to microbial contaminants and pathogens via water, sand, and aerosols. Water and sand coincide at the beach, providing an environment with unique advantages and challenges to pathogen introduction, growth and persistence, transport, and exchange among habitats. Advantages, such as refuge from predators in sand biofilms, and challenges, such as the relatively dry environment, may be both exacerbated and complicated by seasonal variability and predicted long-term anthropogenic climate change. Human exposure to waterborne pathogens will likely be amplified in the face of predicted extreme rain events, warming of water, and sea level rise, combined with urbanization and the popularity of beach activities. Such changes may also alter microbial dynamics at beaches, potentially impacting assumptions and population relationships used in mechanistic water quality and E. coli concentration models as well as quantitative microbial risk assessment frameworks. With model refinement and parameter development designed to fill critical knowledge gaps, predictive models of fecal indicator bacteria and pathogen fate and transport can help to characterize the risk of infectious disease from recreational water use. Here, we not only present a conceptual model that may serve as a first step toward inclusion of biofilm mechanics at beaches, but we also discuss potential approaches to incorporate sand-water interactions into hydrodynamic coastal models for enhanced beach health prediction. While beach health and water quality have long been active areas of research, the sand and sand-water interface habitats at beaches remain relatively unexplored. Recent work has shown that sand can be a reservoir of microbial contaminants at beaches, signaling a potential paradigm shift in both research and management of recreational water and beaches to a more holistic, beachshed-based model, as further detailed in Weiskerger et al. (doi: 10.20944/preprints201901.0225.v1).