Evaluation of salt sources and loads in the upland areas of the Murray-Darling Basin, Australia

Estimates of catchment salt balances throughout the Murray-Darling Basin (MDB) suggest mobilization of salt stores and generally increasing stream salinities. It is widely assumed these salts are rainfall-deposited cyclic salts of marine-aerosol origin, concentrated by evapotranspiration, stored in groundwaters and mobilized by clearing of native vegetation. In this paper, the assumptions about the sources of salts, in upland catchments in the south-eastern region of the MDB are re-evaluated. The estimation of dissolved salts is re-examined using electrical conductivity (EC), the assessment of stream salt loads from sporadic EC measurements and the sources of salts in upland catchments. It is concluded that, although evapotranspiration plays a significant role in the concentrations of salts in the lower MDB, mineral weathering is a major contributor to stream salt loads in upland rivers of the MDB that supply over 80% of surface runoff to the Murray River.