The rapid proliferation of the nuclear industry after World War II resulted in the generation of substantial volumes of radioactive waste. This material was often buried in shallow trenches, a standard practice at the time, of which the Little Forest Legacy Site near Sydney (Australia) is an example. It has been reported that during heavy rain, the trenches exhibit an overflowing effect, analogous to a bathtub. The aim of this work was to test the hypothesis that intense rainfall events, are likely to introduce oxygen, and will therefore have an effect on the biology and chemistry inside the trenches during a fill-drain cycle.
Shotgun metagenomics was performed on water samples collected from a sample trench in triplicate across four time points during a 47-day period after a heavy rainfall event. (Radio-)chemical parameters were monitored as well. Functional analysis was performed with HUMAnN2 and taxonomy profiles obtained with GraftM.
Functional analysis of single reads shows clear differences between the initial sampling points characterised by higher relative gene frequencies related to aerobic heterotrophic metabolism such higher cytochrome-c oxidase and several sugar transporters. The maximum for these indicators is reached at day 4, matching a surge in the proportion of Proteobacteria (63.6% of the total prokaryotic community). Conversely, anaerobic metabolism genes such those specific of methanogenesis or dissimilatory sulfate reduction, and anaerobic taxa such Methanosaetaceae and ANME-2d, show a progressive increase over time with a maximum at the final sampling day. These changes coincided with an increased proportion in soluble Fe, Am, and Pu, supporting our hypothesis that rainfall events can induces transient aerobic conditions potentially altering radiochemical mobility.