Concentration vs. streamflow (C-Q) relationships of major ions in south-eastern Australian rivers: Sources and fluxes of inorganic ions and nutrients

Abstract

Documenting the processes that control the geochemistry of rivers at different streamflows is important for understanding catchment processes and calculating solute fluxes. The concentrations of most major ions (Na, Ca, K, Mg, HCO3, Cl, and SO4) in southeast Australia rivers vary little with streamflow and can be defined as being chemostatic or chemodynamic. By contrast, NO3 concentrations generally increase at higher streamflows and NO3 locally displays flushing behaviour. Catchments draining different landscapes, including cleared low-relief sedimentary basins and mountainous basement areas with high percentages of native vegetation show similar behaviour. Additionally, there is no significant difference in the geochemical behaviour of smaller tributaries and higher-order rivers. These geochemical relationships are best explained by an increased baseflow input augmented by water mobilised from soil water, water from the saturated zone, or shallow groundwater during times of higher streamflow. Solute fluxes are well correlated with streamflow allowing first-order calculation of net solute exports.