Phosphorus transfer from land to water In pasture-based grazing systems

Deposited with permission of the author. © 2002 Dr. David Martin NashNutrient exports, in particular phosphorus, are a major problem for Gippsland and many other regions of the world. This thesis investigates the export of phosphorus in overland flow from pasture-based grazing systems in south-eastern Australia. Initially, field-scale monitoring is used to investigate the forms of phosphorus in overland flow with a view to identifying the primary mobilisation process. It is shown that from a well-managed pasture, phosphorus was primarily mobilised as a result of dissolution rather than physical detachment (erosion) processes. Phosphorus in the overland flow is shown to be predominantly in the dissolved reactive form (DRP). It follows that remedial strategies that rely on physically trapping phosphorus entrained in overland flow (i.e. buffer strips and riparian zones) are unlikely to be effective. The field-scale monitoring data are then used to investigate the structure of phosphorus exports. It is shown that the data conforms to a base-plus-increments model. It is proposed that phosphorus exports can be divided into a base or systematic component that results from a particular land use management system, and an incremental or incidental (preventable) component that is the result of particular management decisions, activities or incidents. (For complete abstract open document