A three dimensional model for Cryptosporidium dynamics in lakes and reservoirs

Abstract

A model of Cryptosporidium oocyst dynamics for lakes and reservoirs is presented. The model consists of a module that simulates oocyst inactivation, resuspension, settling and aggregation onto particles. This module was coupled to the three-dimensional Estuary Lake and Coastal Ocean Model (ELCOM), which was used to simulate lake hydrodynamics in addition to oocyst advection and turbulent diffusion. A field experiment that tracked the passage of a flood inflow throughout Myponga Reservoir, South Australia, was used to validate the coupled model. The model accurately captured the thermal dynamics, and the spatial and temporal distribution of different inorganic particle size classes and oocysts. The model and data indicate that oocysts do not readily attach to inorganic particles as other researchers have suggested but settle as free-floating oocysts according to Stoke’s sedimentation dynamics. The reduction in oocysts between the inflow and the offtake due to settling is therefore not as significant as previously thought. The potential for inactivation was also found to be small relative to the timescales for transport. The model is a useful tool to examine oocyst dynamics in lakes and reservoirs, to consider risk management assessments of different scenarios, and to assess the effectiveness of different sampling strategies.