CHANGING LANDUSE: IMPACTS ON NUTRIENT EXPORT

Stream water chemistry is regulated by a suite of processes that operate at a variety of spatial and temporal scales occurring in both the landscape and within the stream. Considerable attention has been paid to determining nutrient outputs from agricultural land due to its potential for high anthropogenic nutrient losses and consequential ecological impacts in receiving water bodies. In Australia, plantation forestry is projected to significantly expand principally by conversion of pasture lands. While the long term hydrological impacts of conversion to plantation have been well documented, few studies have monitored the consequences for C, N, P and Si biogeochemistry and export. We will present results from a paired catchment study comparing native pasture with forestry land-use. In these systems soil nitrogen cycling has been particularly affected by land-use change. Nitrate concentrations as high as 20 mg l-1 have been observed during autumn runoff from the forested catchment compared to only 5 mg l-1 from the pastured catchment. Annual and interannual changes in stream nutrient concentrations will be discussed in terms of hydrology, plant uptake and soil microbial processes.