Distinguishing salinization from desiccation induced salinity increases in shallow lakes affected by climate drying and land-use change

Global trends of increasing lake salinity stem from numerous mechanisms, including land use and climate change. As salinity varies inversely with water level in shallow lakes, the effects of a drying and warming climate can mimic salinization, the increased storage of dissolved salts. Even detecting trends in shallow lakes can be challenging due to large interannual variability. Here, I develop a new approach, based on a minimum of data, i.e. changing salinity–water level relationships, to identify and quantify salinization and disentangle mechanisms for rising salinity in warming and drying regions. The approach is applied to data from a long-term study of shallow lakes across south-west Australia, experiencing salinization due to land use change, and long-term climate drying and warming. Widespread desiccation or increasing salinity trends were found (58% of lakes), though only 18% of lakes had both trends. It is shown that 27% of the region’s lakes were salinizing and in these the average salt storage almost doubled in 20 years. Salinity trends are not reliable indicators of changing salt storage in shallow lakes. Salinity–water level relationships offer a physical basis with which to interpret changing lake hydrology, salinity and salinization in shallow lakes, even with poorly gauged inflows and outflows and an absence of bathymetry data. The approach gives new means to inform the conservation of shallow lake systems to maintain ecosystem services and aquatic biodiversity. • Widespread increases in salinity across south-west Australian lakes. • Desiccation impacts salinity distinctly from secondary salinization. • Upward shift in piecewise salinity-water level relationship quantifies salinization.