Text S1.

Ash leachates were performed following the United States Geological Survey Field Leach Test, which is a simple and cost-effective method to simulate leaching by water (Hageman, 2007). Deionised water was added to ash at a ratio of 20:1. Samples were mixed thoroughly and allowed to settle for ~10 minutes. Subsamples were collected and filtered with a 0.45 μm nitrocellulose filter. Filtered samples were then analysed and quantified using solution Inductively Coupled Plasma Atomic Emission Spectroscopy and Mass Spectrometry at the Isotope Tracing in Natural Systems laboratory ANSTO, Australia.