Abstract
Archaea are known to be dominant in extreme environments such as acid rock drainage (ARD), which occurs when iron-sulfur minerals react with water and air. Worldwide, the main reservoirs of ARD are open pit lakes that are produced at the end of open pit mining operations in iron sulfur rich mining areas. Archaea promote ARD production by accelerating iron oxidation and they are involved in the cycling of elements at ARD sites.
We studied the archaea in an ARD mining pit lake (Batman Pit) located in the wet dry tropical climate of north Australia. The Batman Pit was 90m deep at the time of sampling and located in an area where extensive wet season rains bring highly acidic drainage to the Pit. This wet season drainage can significantly influence the physicochemical character and microbial population of the Batman Pit. We measured community composition using next generation sequencing and we also measured pit lake physicochemistry and climatic variables to identify key drivers of community change. The community composition and chemistry was measured once in the dry season and then at the end of the wet season.
The wet season chemistry of the water column was significantly different from that of the dry season. Elemental concentration of arsenic, selenium, iron and sulfur was significantly higher in the wet season samples. In the wet season, water temperature was higher and pH was lower compared to the dry season. Despite these significant changes in physicochemical parameters, the archaeal community composition did not change with season or depth. In this iron-sulfur rich environment, we found the ammonia oxidiser Nitrosopumlis was the dominant archaeon at both wet and dry season sampling times. The results also suggest that the archaea population in Batman Pit does not play a significant role in iron cycling, however they may have a significant role in nitrogen cycling.