Pathways of phosphorus, nitrogen, and carbon movement over and through texturally differentiated soils, South Australia

One method for preventing the degradation of water supplies through contami nation with phosphorus (P), nitrate (NO3), and dissolved organic carbon (DO C) is to restrict movement of these contaminants from the catchment into wa ter bodies. The purpose of the study was to quantify and characterise the p roportion of NO3, P, and DOC moving from duplex soils by overland flow and through-flow on a sub-catchment scale, and to characterise soil properties that influence their movement. Two sites in the Adelaide Hills (South Austr alia) with contrasting duplex soils were instrumented to collect overland f low and through-flow from the soils A and B horizon. Each site contained 2 sub-catchments in close proximity. Sub-catchments were well defined by the natural topography sloping from hillcrest to a stream headwater. Soil type, especially the degree of texture contrast, the macroporosity, and the prop ortion of clay in the B horizon, had a large influence on the pathways of w ater, and therefore P, DOC, and NO3 movement. Environmentally significant c oncentrations of P (>0.1 mg/L) and NO3-N (>0.5 mg/L) moved overland and thr ough these soils in 1997. High DOC loads (25 mg/L), which would also impact on water treatment costs, moved through some soils. Significant loading of P moved through and over soils in both dissolved (0.5 mg/L) and particulat e (0.3 mg/L) forms. Consequently, through-flow cannot be ignored as a contr ibutor to P in streams and both dissolved and particulate P must be measure d under these conditions to define the full impact of P. The findings from this research have implications for research on catchment management to res trict DOC and nutrient movement into waterways.