Extending Apex to Model Microorganism Fate and Transport.

The Agricultural Policy/Environmental eXtender (APEX) model is a whole farm to small watershed scale continuous simulation model developed for evaluating various land management strategies. The current version, APEX0806, does not have the modeling capacity for bacteria fate and transport (F&T), which limits the usability of APEX in many environmental assessments. This study aims to build bacteria F&T modules in APEX in three modeling domains: 1) agricultural fields and pastures, 2) streams and reservoirs, and 3) vegetated buffers and riparian areas. This paper presents the details of the field and pasture F&T submodel. APEX provides essential inputs for the bacteria F&T subroutines including manure and animal waste loads and erosion rates, incorporation scheduling, runoff and infiltration rates, sediment transport, retention in vegetated buffer strips, and soil and air temperature time series. APEX bacteria F&T processes include aboveground survival, survival in soil, distribution between suspended and sediment-associated in runoff bacteria fractions after rainfall-induced release, mobilization from soil to runoff, and distribution between runoff and infiltration. Published data on the above processes were compiled to specialized databases to (a) determine a process model that is both simple in its structure and reasonably accurate, (b) determine default model parameters and their associated uncertainty, and (c) identify any contradiction that may preclude integrating multiple processes into a model structure. The data were collected using the multi-database search engine NAVIGATOR, available at the National Agricultural Library. Preliminary results of the loosely connected field and pasture bacteria F&T model in APEX implemented as the FiBFaT subroutine indicate reasonable prediction of bacteria processes in APEX when compared with experimental data and simulation results from the event-based KINEROS2/STWIR model. Results of the sensitivity analysis will be reported and discussed.