Tracing phosphorous transferred from grazing land to water

Abstract

Phosphorus transferred from land to water is a major problem across the world. Identifying the source of phosphorus in water is an important prerequisite to the development of remedial strategies. In this paper, key aspects of phosphorus transfer from grazing land to water are reviewed along with the techniques that may be used to trace its origin. Dissolution and erosion are the two processes that can mobilise phosphorus. Erosion is the physical transport of sediment, arbitrarily defined as materials that do not pass through a 0.45 μm filter, while dissolution is the transport of phosphorus either chemically dissolved in water or attached to colloidal material capable of passing through a 0.45 μm filter. Most phosphorus is transported from well managed pastures of southern Australia in a dissolved form (<0.45 μm) and the highest loads typically occur in surface runoff. Being monoisotopic in its natural state, phosphorus cannot be directly traced. However, a range of techniques have been used to identify the source of sediment, and by implication, the attached phosphorus mobilised by erosion processes. With minor exceptions no such techniques are available for tracing phosphorus mobilised by dissolution processes. Organic marker compounds (biomarkers) may have useful attributes for phosphorus tracing. There are a vast range of biomarker compounds including sterols, phospholipids and alkanes, that are specific to potential phosphorus sources at a farm scale, and specific to particular land uses at a catchment scale (e.g. faeces and both live and decaying vegetation). This paper investigates the use of biomarkers to augment the current suite of phosphorus tracing techniques at both farm and catchment scales.