Minimising costs of environmental service provision: water-yield, salt-load and biodiversity targets with new tree planting in Simmons Creek Catchment, NSW, a dryland farming/grazing area

Although dryland farming and grazing have been practiced for over 130 years in the 17,000 ha Simmons Creek catchment without surface salinity problems, the area has been identified as a significant source of salt seepage to Billabong Creek in the NSW Murray catchment. Groundwater movement and salinity levels are spatially heterogenous at Simmons Creek. Groundwater of the upper catchment is relatively fresh and seemingly unconnected with the highly saline groundwater of the lower catchment. However, fresh surface water does flow from the upper to the lower catchment. This spatial diversity provokes the question of where high-water-use forest habitats might be placed to achieve different combinations of environmental services (greater water yield, lower stream salinity and greater biodiversity) at least cost. Agro-forestry and or carbon sequestration benefits are not considered here. This paper presents methods and preliminary calculations of land use changes for least-cost delivery of these environmental service targets.