Modelling aggregated catchment-scale phosphorus transport over 200 years in the Peel Harvey catchment, Western Australia

A simulation model was developed using the STELLA dynamic modelling software package to model the transport of phosphorus (P) through major source, sink and flow sectors of the Peel-Harvey Catchment in South Western Australia. Phosphorus is the most important nutrient in this catchment for promotion of nuisance and toxic algal blooms and a greater understanding of farm and catchment P transport is essential to developing and assessing better P management strategies both now and into the future. The model attempts to track changes in stores and flows of P over a 200 year time horizon to match catchment development and associated nutrient inputs and outputs to the present day (100 years of development) and a further 100 years into the future assuming inputs and outputs remain constant from now onwards. The present catchment scenario produces model outputs which agree well with monitored water quality data, survey data of farm inputs and outputs, and soil P content data leading to confidence that modelling of further scenarios will produce meaningful output. The model’s dynamic nature lends itself to adaptation to other catchments of varying scales including small, and even farm-scale catchments, to obtain a better understanding of P dynamics and management strategies at this range of scales. This makes the model useful for testing catchment management and planning policies at the broadest scale as well as individual farm-management decisions at the small scale