Microbial diversity and metabolic potential in siliciclastic ATES horizons

Microbial processes such as biofilm formation (clogging) and mineral precipitation (scaling) can affect the effectiveness of ATES systems. They can reduce the permeability of potential reservoirs and compromise the efficiency of ATES facilities on the long term. In addition, microbial processes can influence dynamics of toxic trace elements in the subsurface e.g. by releasing arsenic through iron mineral dissolution. Hence, it is crucial to identify microbial key players and metabolic processes to estimate the microbial impact on ATES and the clogging potential.

Here, we analyze the microbial abundance, community composition and their functional potential in relation to the thermo-hydrogeochemical conditions of bulk sediment and formation water of a Mesozoic sandstone aquifer of the North German Basin. The study focusses on the application of DNA-based approaches such as qPCR, high throughput sequencing and metagenomics. Bulk sediments and fluids were obtained from Jurassic sandstone in Berlin, Adlershof from a depth of 200-450 m.

The aquifer is characterized by an in-situ temperature of 17-22°C, Na and Cl dominated fluids (TDS ~20 g L^-1) and DOC including acetate (~3.5 mg L^-1), propionate and valerate. First results show that the fluid microbial community is adapted to saline and alkaline conditions. The community is highly dominated by the two taxa Alkaliflexus and Defluviitaleaceae UCG-011, but also contains sulfate reducing bacteria.

Results of this study together with a flow-through experiment analyzing geochemical, hydrochemical, mineralogical and microbiological processes under different conditions typical for ATES, will help to develop prediction tools for potential system operational failures and appropriate countermeasures.