In contrast to the shallow subsurface “soil” environment, the microbial ecology of deeper subsurface aquifers is relatively poorly understood as this environment not easily amenable to study. In subsurface porous media that form aquifers the physical environment exerts major controls on microbial function; it imposes physical limitations on microbes (“size exclusion”) as well as restricting diffusional/dispersive supply of electron donors and electron acceptors that micro-organisms require for respiration. Furthermore, before now many modelling approaches have ignored the effect of pore throats, the restrictive effects of which will have an increasingly large impact at smaller length scales (i.e. in finer-grained or more compacted sediments). Via this research we aim to improve understanding of microbial colonization and function in the deeper subsurface by experimental testing of the effects of different variables on microbial activity and hence validate model descriptions of these processes.
There is a major pragmatic driver to this work. In situ microbial processes in the subsurface can drive the bioremediation of contaminated soils and groundwater via “Natural Attenuation (NA)”. NA is a management option for contaminated soils and groundwater recognized by both the UK Environment Agency and US Environmental Protection Agency and has the advantages of being minimally invasive and having a low carbon footprint compared to engineered interventions. However, it is a risk-based approach and implementation can be unnecessarily impeded by uncertainties in predicting outcomes. There are instances where degradable groundwater contaminants fail to degrade because of restriction of subsurface microbial activity. One of the major gaps in our knowledge for predicting the NA capacity of microbial communities is a lack of models to predict the ability of microbes to colonize and function in subsurface media. This project will address this uncertainty by using model experimental systems to validate mathematical descriptions of microbial colonization and function in subsurface environments.