How does a river respond to perturbations caused by artificially enhanced silicate weathering?

The introduction of vast quantities of CO2 into the earth's atmosphere as a result of human activities is having a major, and currently unchecked, impact on our climate. To limit damaging environmental and societal impacts, the latest Intergovernmental Panel for Climate Change report (2018) advised that global warming should not exceed 1.5oC above pre-industrial levels. To achieve this target, not only must global greenhouse gas emissions be radically cut, but it is likely we will need to scrub an unknown quantity of CO2 out of the atmosphere. It is imperative therefore, that we continue to explore and adequately understand negative emissions technologies.The dissolution of silicate minerals by carbonic acid sequesters CO2 from the atmosphere and, over geological timescales, maintains climate equilibrium. Collaborating with the Leverhume Centre for Climate Change Mitigation (LCCCM), my proposed project will look at the potential of artificially enhancing this process to counteract anthropogenic climate change.Artificially enhanced silicate weathering (ESW) is still in its early stages of development. Until recently, the effects of ESW have only been tested under laboratory conditions or through numerical models5.The LCCCM is in preparatory stages of commencing a novel field experiment, which will add crushed basalts to farmland of approximately one hectare in Plynlimon, Wales. They will examine variations in the soil and groundwater chemistry to gain an insight into how ESW will respond within natural environmental conditions. My proposed project will work alongside this experiment, and will aim to monitor a nearby river's response to the perturbation.Previous research of natural silicate weathering has yet to determine the fate of sequestered CO2 in riverine systems. The current estimates for the total global carbon flux are highly heterogeneous, and rarely include undefined parameters, such as the role of sulphuric acid weathering, which leads to the re-release of carbon2, fluxes due to groundwater flow, or the effect of anthropogenic influences, such as fertilisers4.Perhaps most importantly, it is still uncertain what inhibits calcite precipitation in rivers- an important control for overall pCO2 concentrations.My project will focus on the riverine fate of sequestered CO2, and will observe changes in a river's chemistry before and during the field experiment, using observational and computationally modelled approaches to consider CO2 fluxes in natural and perturbed environments. The results of the project will potentially provide new scope to the geoengineering technique, helping policy makers make better decisions to best tackle one of the biggest issues of the 21st century. Professor Gideon Henderson will supervise the project, with Dr David Hodkin helping with lab and PHREEQC analysis. Further, there is scope to work with Professor David Beerling, Head of the LCCCM team at Sheffield University for soil and groundwater geochemistry, along with Professor Ed Tipper, Cambridge University, for help with river analysis.