Rivers play a significant role in the global C cycle . Inland waters return to the atmosphere >40% of C received from terrestrial sources [2,3], and global CO2 emission rates for rivers are an estimated 1.8 Pg C/yr. Recent upwards revisions of these numbers follow discoveries that biological processes can influence river C cycling substantially, because dissolved organic matter (DOM) is not always as refractory as previously thought [3-6]. Despite these major breakthroughs, we still need to develop a detailed understanding of DOM processing in rivers which are sourced from headwater catchments with significant organic soil cover. Peatlands store ~1/2 global soil C and have particularly high rates of greenhouse gas release and dissolved/particulate C export [7-9] but there remains a need to constrain considerable uncertainty around biological processes vs. physicochemical influences on river C budgets [10,11] so we can predict accurately the effects of environmental change and land management interventions [e.g 12,13].
This project will seek to understand the processes controlling the removal of organic carbon in freshwaters and the subsequent fate of that carbon. The PhD student will test i) whether alteration of C by photo-oxidation is a pre-requisite for biological processing; ii) establish the relative importance of organic C source (soil leachates, leaf litter, in-stream production/particulates) and nutrient supply on the extent and rates of photo-oxidative and microbial degradation; iii) elucidate and quantify the effects of temperature via measurements of respiration across thermal gradients.
Research will involve field observation, and in-situ and laboratory experiments to monitor C cycling in river catchments with peatland headwaters and multiple downstream land uses. In addition, controlled experiments will be conducted using outdoor stream mesocosm facilities and in new temperature controlled environment facilities in the School of Geography. The project will capitalise on recent advances in the use of smart-tracers to measure respiration in rivers [e.g. 14]. The student will be trained in the use of state-of-the-art dataloggers and environmental sensors, water chemistry analysis, advanced data analysis techniques and scientific writing for publication. There will be opportunities to present work at international conferences. The student will benefit further from advice and support by being a member of the River Basin Processes and Management research group, which is a key group in the [email protected]
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