An Investigation of Nutrient Transport Pathways From Agricultural Hillslopes to Stream and to Watershed.

Runoff from rainfed dairy systems is an important contributor to reduced water quality in streams and end of watershed environs (bays, estuaries and near-shore areas). Several relevant bodies of knowledge exist, namely: nutrient cycling at the point/field scale; in-stream nutrient processing and transport and; field scale runoff processes and pathways. However this knowledge tends to be poorly linked in the Australian context. The aims of this study are to undertake an integrated study of nutrient export to understand the interactions of different hydrological and biogeochemical processes, to examine the impact of time and space scales on these interactions and to further develop modelling approaches to represent these. A set of inter-linked studies will be undertaken in the Strzelecki ranges, south-east Victoria, using a nested monitoring design coupled with targeted process investigations. The catchment is steeply undulating with runoff mainly in the winter/spring season (due to seasonal excess of rain over PET) and a predominantly dairy landuse. Field studies will include the following: •Water discharge and quality (N, P, C) monitoring for events and baseflow at three scales (field, 1st order stream, 2nd/3rd order stream); •Runoff source area, process and flow pathway studies using physical (soil moisture, hillslope runoff pathways and groundwater) and hydrochemical tracing (isotopes, major ions); •Soil nutrient cycling and mobilisation studies at the field scale, including an assessment of the role of livestock in mobilising nutrients; •Riparian and in-stream nutrient cycling and transport studies using nutrient spiralling techniques and nitrogen isotope techniques; •Collection of supporting data on meteorology, landuse, vegetation cover, soil distributions and characteristics, roads, farm dams. Modelling will concentrate on: integration of the various sub-studies; assessment of the relative information content of various data for supporting modelling; the question of what is the appropriate level of model complexity; and ability to generalise the study results.