Geomorphic controls on deposition of salt in the Greater Tamar Catchment, northeast Tasmania

Abstract

ABSTRACT In Tasmania, most salts in the landscape originate from rainfall and accumulate in landscapes after evaporation occurs. The distribution and quantity of salt in rainfall from an array of bulk deposition collectors in the Greater Tamar Catchment were assessed for the period September 2013 to August 2014. The bulk deposition samples were analysed for pH, electrical conductivity, major ions (Ca, Mg, Na, SO4 and Cl) and a selection of trace ions. The average salt flux across the study area was 79 ± 10 kg/ha/yr region, ranging from 170 ± 12 kg/ha/yr near the coast in the north to 42 ± 6 kg/ha/yr inland. Deposition of most ions decreased from the northwest to the south and east, and peaked in winter and spring. Geomorphic factors such as elevation and topography have an important effect on the volume of rainfall and flux of salt from windblown dust and oceanic aerosols. A comparison of measured chloride and salt deposition in Tasmania with other Australian atmospheric studies indicates that continental-scale models of salt flux are not appropriate for Tasmania. New models are proposed that take into account the influence of the Southern Ocean, Tasman Sea and topographic variation in the study area. The results provide improved estimates of rainfall-derived salt inputs to catchments in northeast Tasmania and enable more accurate salt budget modelling. Improved understanding of volumes and distribution of salts has implications for the management of soils and infrastructure that degrade as a result of dryland salinity in Tasmania.