Addressing a significant knowledge gap in fluvial system atmospheric CO2 efflux: the contribution from karst landscapes

Karst landscapes cover a large proportion of the Earth's land surface: ~ 12% They represent an important C store on land, and also are considered to play an important role in climate regulation by consuming atmospheric CO2 during chemical weathering. However, we cannot be certain how effective this sink is if we do not know how efficiently the rivers draining karst landscapes remobilise weathered C to the atmosphere as CO2. Further, although there is a large body of research on how much C is carried away from weathered karst systems, researchers have not yet quantified by direct measurement the C return to the atmosphere from rivers. We propose to measure this CO2 degassing from rivers in karst systems and using chemical tracers that can distinguish between different source of carbon in the rivers, quantify how much C comes from the different sources and how these contributions change with different land use change, or as season and river flow change.
We will do this by undertaking measurements in a karst catchment in China. This field location is key to the research as there is much known about C loss by weathering and how different land use in the catchment (e.g. bare rock vs. paddy soils) affects the weathering process. In the first year of the research we will undertake fieldwork to measure CO2 efflux from springs and surface waters, ensuring we capture natural variation in efflux due to differences in river flow and seasonal temperature. In year 2 based on our detailed understanding of the catchment controls on CO2 efflux, we will use specialised tracers of the source of the C (isotopes) to quantify how much C in the CO2 degassed comes from the different sources. With this knowledge we will produce a quantitative process-based model to estimate CO2 efflux, that relies on descriptors of catchment and river characteristics. Finally we will test this model in other catchments to assess how well it describes more widely CO2 efflux from karst drainage systems, and from this testing refine the model / identify how it can be improved.
The model is important as it will support up-scaling of CO2 efflux from karst drainage systems and this information is valuable to those modelling the global C cycle and trying to understand how changes in atmospheric CO2 concentration are affected by fluxes to the atmosphere from the Earth's surface.

The following will benefit from this research:
1. By the end of the grant academic beneficiaries will have access to the first data set of direct measurements of CO2 efflux from karst drainage systems. This data set will be comprehensive capturing temporal and spatial variation and apportioning source contribution using isotope systematics. Of further academic benefit will be the process-based model and understanding of how generic this is to other karst fluvial systems. This will be of benefit to those whose research relies on accurate Earth surface CO2 fluxes to constrain atmospheric CO2 fluxes, and to C cycle modellers who wish to more accurately inform global C cycle research.
2. Through publication and conference activity, NERC National Capacity will receive publicity for innovation and excellence in novel 14C-dating approaches. They will benefit through enhanced international standing and resultant funded research collaboration. This will happen after year 2 and extend beyond the duration of the grant as the scientific community scrutinizes our publications and research findings are presented at conferences.
3. During and after the grant the UK science base will benefit as this research demonstrates we value sensitive environments internationally, and particularly international co-operation in research. The skill and information exchange that will occur during this research with Chinese colleagues will help consolidate the UK position as a key partner with the Chinese National Science Foundation and their investment in joint research activity.
4. Secondary school students and teachers will benefit by support in the learning and teaching of the geography curriculum through the development of exciting research-informed teaching materials and demonstrations. This will commence in year 2 of the grant, but extend beyond this period as once the material is developed as it is not time-limited (until replaced by an expanded understanding).
5. The wider public, and local communities hosting the research, will benefit during the research activity through research team communication activity that meets their passion for and excites them to understand the natural world more deeply. In turn if this encourages greater interest in STEM subjects, the relevant country science base will benefit.