Modelling pathogen dispersal and distribution in estuarine systems under changing environment

Treated and untreated wastewater enters estuaries via point source discharges, after which complex estuarine hydrodynamics can retain high concentrations of pathogens in these systems for days to weeks, posing a serious risk to public health. Through comprehensive fine scale three-dimensional numerical modelling, this research aims to study drivers of pathogen dispersal in estuaries and pathways of pathogen distribution. An interdisciplinary approach, combining knowledge from numerical modelling with laboratory derived data on pathogen behaviour and interactions with sediments, has been taken to improve the reliability of the model: 1) key fine-scale estuarine processes, i.e. current (including density current), turbulent mixing, and sediment transport have been studied using a process-based numerical model; 2) decay curves of target pathogens obtained through laboratory experiments for different water temperature, salinity, UV radiation have been implemented in the model; 3) the model also aims to incorporate pathogen attachment to sediments, their deposition, resuspension and subsequently altered decay rates. The Conwy estuary in North Wales, UK, has been used as our case study. The estuary holds considerable historical and contemporary significance in terms of shellfishery and tourism. With a catchment area of 678 km2 supporting a population of ~80,000 and large pastures, the estuary is susceptible to a range of pathogens, posing a public health risk via ingestion of bathing waters and indirectly via sea food.  The transport of pathogens from point sources, including wastewater discharge and sewage overflow, into the coastal environment has been studied under both current and future climate conditions such as sea level rise, warmer coastal waters, stronger river flow and population growth drawn from climate projections. As a further aspect of this research, conceptual estuarine systems will also be used to study fate and transport of pathogens under common estuarine dynamics and under representative climate scenarios.  This integration will allow for a more holistic approach that widens the applicability of the findings. This research will provide improved understanding of pathogen dispersal in coastal waters and the impact of climate change on pathogen distribution and potential exposure to humans. It will also provide insights for the development of adaptation strategies to protect public health under changing environmental conditions.