Understanding how long water stays in the Earth's surface (from the moment it lands as precipitation until it reaches a stream or evaporates back to the atmosphere) is quite important for many Earth science investigations. However, its estimation is still in its infancy, and not many methods exist that allow for the direct observation of water ages within the subsurface. Antonio Meira developed an experiment that tried to directly observe water ages in a weighing lysimeter by combining two different methods: the first method uses information from chemically labeled water from influx and outflux. The second method uses electrical resistivity imaging of the soil, allowing for the observation of the internal distribution of water ages. We learned that our system tends to discharge older water from storage until it reaches its highest levels of storage, which is when greater portions of younger water start being released. This behavior can be explained by an upward movement of the water table that is able to reach the regions where younger water is located, allowing for its mobilization out of the system.
