Spatio Temporal Heterogeneity PDF Download

The subsurface compartment of the Earth's Critical Zone is one of the biggest stores of carbon and nitrogen, and provides habitat for 95% of the global estimates of microbial biomass. These microbes mediate the transformation of carbon and nitrogen in the subsurface. But, their contribution to biogeochemical cycles is not yet estimated on a global scale due to the inaccessibility and the spatio-temporal heterogeneity of the subsurface. The relevance of these sub-scale spatio-temporal heterogeneities with respect to carbon and nitrogen cycling rates is not understood. This in turn affects interpretation of field data and formulation of suitable modelling studies. In this work, I addressed this gap by assessing the effect of spatio-temporal heterogeneities on microbial mediated transformation of carbon and nitrogen using a numerical modeling approach. I set up spatially heterogeneous simulation domains representative of the subsurface and introduced a network of microbial mediated reactions in these domains. I subjected these domains to temporal dynamics. I, then, quantified the impact of spatial heterogeneity on microbial mediated nutrient cycling in the subsurface and quantified the impact of temporal dynamics in the saturated zone of the subsurface. Consolidating the results, I proposed that indicators such as travel time of conservative solutes can be used to identify four types of reactive systems that respond to spatio-temporal heterogeneities in the subsurface: Reaction dominated systems, reaction influenced systems, transport influenced systems and transport dominated systems. The approach used in this thesis is applicable, transferrable, and suitably scalable across different sites. It can, thus, be used to fill a critical gap in the global biogeochemical budgets. It can also assist in forming a predictive understanding of the behavior of heterogeneous reactive systems in temporally dynamic conditions, resulting in secured access to groundwater.