Reconstructing past changes in wetland hydrology and carbon cycling

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Project Background Microbial processes in terrestrial settings are critical to governing greenhouse gas emissions. The modern carbon soil reservoir exceeds that of terrestrial vegetation and the atmosphere combined, and soil microorganisms annually cycle 1/3 of the carbon photosynthesised and account for the largest natural methane flux. In doing so, they govern the chemical and climatic state of our planet. And yet these processes remain poorly understood, mediated by a range of environmental factors. Insight can be derived from geological archives that document the responses of biogeochemical systems to past environmental perturbations. Our previous studies on peat and lignites provide tantalising insights into climate-driven disruption of the carbon cycle, but the underlying mechanisms remain unresolved. This project will address that by developing new approaches and records based on the isotopic composition of peat organic matter derived from plants and bacteria. Project Aims and Methods: Peat and lignite deposits have long been used to explore past changes in climate, especially changes in temperature and precipitation. What is much harder to ascertain are changes in biogeochemical processes. When it becomes warmer is organic matter (OM) preservation enhanced due to higher productivity or is that OM degraded due to enhanced microbial activity? If degraded, is that manifested as an increased flux of carbon dioxide? Or methane? Or neither because microorganisms also adapt to consume these greenhouse gases before they can escape from the wetland? We have obtained some insight by determining the carbon isotopic composition of individual compounds in the peat, some derived from plants and others derived from microorganisms, allowing us to probe the rebalancing of carbon flow during environmental disruption. However, our current investigations are limited, having focused primarily on temperate rather than tropical wetlands. We have also been unable to resolve, until now, more nuanced changes in microbial ecology. In this project, we will explore and compare environmental and biogeochemical disruptions in Welsh, English, Panamanian and Colombian peatland (the specific sites and time intervals developed in collaboration with the PhD student and the supervisory team). We will then refine and apply recent analytical innovations - the determination of bacterial hydrogen isotopic compositions - to ascertain the relationships between past changes in peatland hydrology, bacterial metabolism and carbon cycling.