Grant: Discovery Grants Program - Individual

Rivers provide numerous ecological services that support human well-being and biodiversity. The functioning of rivers is influenced by complex interactions between biotic and abiotic factors. Among these factors, microbial processes play a crucial role in driving nutrient cycling, organic matter (OM) decomposition, and ecosystem energy flux and health. Despite their significance, there remains a considerable knowledge gap regarding the specific contributions of microbial processes to river functioning. Research in this area is however critical, as river ecosystems worldwide are facing unprecedented threats due to human activities, such as water pollution, habitat destruction, and climate change. Human activities and their impacts vary in nature, intensity, and potential for downstream repercussions on microbial processes and river functions. This is particularly true for the St. Lawrence River landscape, where spatial differences in hydrodynamics and landscape heterogeneity together with anthropogenic forcing (e.g. agriculture, urban wastewaters, damming), create a complex mosaic of environmental gradients. The combination of changes in land-use and in the timing and intensity of precipitation events induced by climate change further influence patterns in OM delivery to microbial communities. Yet, there has been no systematic attempt to integrate microbial processes into river functioning and how they may evolve across a river landscape under human pressure. My research program aims to investigate the significance of microbial processes in river functioning and response to environmental changes. Over the next five years, my team aims to i) Identify how OM molecular composition and the abiotic environment (mineral adsorption) influence microbial C processing in rivers of different land use; ii) Assess the role of hydrology in regulating microbial processes in a changing landscape; and iii) Determine how features of the river landscape shape the response of microbial processes to environmental changes. I will combine large-scale field surveys with controlled laboratory experiments to test 1) if microbial processes will increase with agriculture and urbanization following an increased mobilization of bioavailable OM, but decrease with their adsorption to minerals, and 2) if microbial processes will be most relevant for ecosystem functioning during low flow conditions and in areas of decreased travel time as OM will not simply be shunted downstream. This research will improve biogeochemical and ecological predictions regarding the fate of OM in large river systems, and how hydrological controls associated to a changing climate may modulate this fate. The formalization of microbial processes as indicators of ecosystem integrity will help improve watershed management. Central to this research, HQP will acquire unique skills in environmental microbiology and develop multidisciplinary strategies to accelerate knowledge acquisition and transfert.