Using stable and radioisotopes to inform catchment dynamics in northern Australia

The tropical freshwater ecosystems of northern Australia (NA) hold immense ecological and cultural value (Ens et al., 2010; Jackson, 2012; Jackson et al., 2005). However, significant knowledge gaps remain regarding the origin and transit time distributions (TTDs) of water that sustains these ecosystems. In this study, TTD refers to the distribution of times it takes for water molecules to move through a catchment from precipitation until outflow (this is sometimes referred to as an age distribution). While some spring-fed rivers of the region are known to rely on deep, old groundwater (Gardner et al., 2011; Lamontagne et al., 2021) a comprehensive assessment of spring water origins is lacking (Duvert et al., 2022). As development pressures increase in NA (Australian Government, 2015a, 2015b; Hart et al., 2020), understanding how water sources respond to change is essential. Identifying the TTD and origin of water will help assess the vulnerability of these ecosystems to development and climate change.