Geomicrobial response to environmental stress-functional implications of identifying thresholds in anthropogenic gradients

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Agricultural land and urban pressures on the terrestrial-freshwater interface can lead to increased stress on biota, poor water quality and can be an impediment to ecosystem health. A long-standing approach to ecosystem assessment uses biological integrity (BI) measures contrasting biological attributes of degraded environments to those of more desirable, minimally impacted ones. However, anthropogenic activity produces diverse materials that stress biota, salts, nutrients, hydrocarbons, metals, and xenobiotics. A critical knowledge gap is to identify measures of BI diagnostic of the key microbially-mediated transformations of those materials in sediment and water and determining whether how these processes can ameliorate the stress. The sediment/water interface plays an important role in biogeochemical cycles (e.g., P, N, S, C, Fe and Si) and water quality. Although this ecotone harbors a vast array of microbial taxa, their dominant functional characteristics and resilience to increasing environmental stress e.g., anthropogenic pressures, environmental extremes are largely unknown. For example, studies of eutrophication involving P and N sediment dynamics have focused on adsorption/desorption mechanisms associated with metal oxides and their redox transformations (e.g., nitrogen fixation, mineralization (decay), nitrification and denitrification). However, these measures can be system specific as the essential microbial component is a black box in modelling and conceptual characterization. Our approach to understanding microbial functional expression coupled with geochemical methods show clear connections between microbial community response to redox fluctuations and mineral dissolution in the presence of bacteria, which can lead to specific pathways of metal and nutrient release and explain how the bacteria benefit from this electron exchange metabolism. Using microbial and analytic techniques in laboratory and field-based programs, this hypothesis driven research program will expand our understanding of bacterial response to anthropogenic pressure in aquatic freshwater sediments. We will identify the mechanistic and functional roles of bacteria at the sediment water interface in transforming key materials of concern that characterize classes of stressed habitats. Results will be shared in a new omics database and used to refine models of biogeochemical cycling in stress impacted ecosystems and improve understanding of microbial heterotopic function. Maintaining sustainable freshwater resources is essential to Canada's socio-economic sustainability through agriculture, industry, people, and tourism. This program will document the critical role that bacteria play in controlling metal and nutrient dynamics in natural freshwater ecosystems subject to anthropogenic stress. By identifying key biomarkers of gene expression, we will advance the application of tool based open arrays for assessing contaminants in terrestrial and aquatic ecosystems.