In this study, we concluded that the residence times of solutes and the Damköhler number (Da) of the biogeochemical reactions in the domain are governing factors for evaluating the impact of spatial heterogeneity of the domain on chemical (such as carbon and nitrogen compounds) removal. We thus proposed a relationship to scale this impact governed by Da. This relationship may be applied in larger domains, thereby resulting in more accurate modelling outcomes of nutrient removal in groundwater.

Our study generates information to aid policies and improve soil management practices for minimizing the negative impacts of forest conversion to rubber and oil palm plantations while maintaining production. Compared to forests, the fertilized areas of oil palm plantations had higher leaching of N, organic C, and base cations, whereas the unfertilized rubber plantations showed lower leaching of dissolved P and organic C. These signaled a decrease in extant soil fertility and groundwater quality.

Organic carbon in aquifer recharge waters and sediments can fuel microbial reactions that affect groundwater quality. We used high-resolution mass spectrometry to molecularly characterize organic carbon mobilized off sediment collected from a Bangladeshi aquifer, to reference its composition against dissolved organic carbon in aquifer recharge water, to track compositional changes during incubation, and to advance understanding of microbial processing of organic carbon in anaerobic environments.

The direct impact of rainfall on groundwater at Mt. Fuji, the largest volcanic mountain in Japan, was elucidated by multiple analyses including microbial DNA. Bacterial abundance and DNA not only supported the findings on the movement of groundwater obtained from chemical analyses but also elucidated chemically unseen flow. Evidence of piston flow in deep groundwater was first shown through changes in archaeal density and diversity. Microbial analysis extends our understanding of groundwater.

We used phospholipid fatty acids (PLFAs) to link specific microbial markers to the spatio-temporal changes of groundwater physico-chemistry. PLFA-based functional groups were directly supported by DNA/RNA results. O₂ resulted in increased eukaryotic biomass and abundance of nitrite-oxidizing bacteria but impeded anammox, sulphate-reducing and iron-reducing bacteria. Our study demonstrates the power of PLFA-based approaches to study the nature and activity of microorganisms in pristine aquifers.