Role of rivers in exporting carbon from terrestrial ecosystems
Earth system models (ESMs) simulate the interaction between the C cycle and the climate system at the global scale. They can predict how carbon dioxide (CO2) emissions from human activities increase CO2 concentration in the atmosphere, and how this affects climate change. ESMs comprise multiple components for the atmosphere, the oceans and the terrestrial ecosystems. The land component of the ESM simulates the exchange of C, water and energy between the atmosphere and terrestrial ecosystems, but not lateral exports of C through the river network from land to ocean. This C exchange is important if scientists are to fully understand the effects of CO2 emissions from human activities on CO2 concentrations in the atmosphere, and thus on climate warming. Improved models As part of the Marie Skłodowska-Curie Individual Fellowships grant scheme, the EU-funded Horizon 2020 C-LEAK project addressed this gap. Researchers assessed the impact of lateral C fluxes on the anthropogenic CO2 budget using a mechanistic approach. Understanding estimated lateral C exports from terrestrial ecosystems is crucial as they are in the same order of magnitude as the estimated land C sink, and thus, an important process in the terrestrial C budget. “Lateral C exports must be considered if we want to project the future strength of the terrestrial C sink, which will determine how much of the anthropogenic CO2 emissions will actually accumulate in the atmosphere and contribute to global warming,” explains research fellow Dr Ronny Lauerwald. The C budget is the difference between inflows and outflows of C to and from a specific system. The terrestrial C budget is controlled by various factors impacting C uptake and outflows. For instance, the net CO2 uptake by terrestrial vegetation, the outflows of CO2 from the organic C decomposition, lateral exports of C through the river network and by the removal of C through the harvest of crops or wood from the forest are all components. Better climate predictions Researchers upgraded two existing land surface models to explicitly represent the lateral exports of C from terrestrial ecosystems through the inland water network. “The results of this model development are ORCHILEAK, a new version of the French land surface model ORCHIDEE, and JULES-DOCM, a new version of the British land surface model JULES,” Dr Ronny Lauerwald points out. Scientists used these models to analyse the effects of lateral C exports on the C budgets of terrestrial ecosystems. “The two models were used in addition to analyse the effects of direct (e.g. land use change) and indirect factors (e.g. climate change and increasing atmospheric CO2 concentrations) on these lateral C exports. For this, simulations were run at regional (Amazon Basin) and global scale,” Dr Lauerwald explains. C-LEAK has improved the representation of terrestrial C budgets and will improve the future projections on accumulation of anthropogenic CO2 emissions in biomass and soils as well as the atmosphere. Dr Lauerwald concludes: “In the long run, this work will help to improve climate projections.”
Keywords
C-LEAK], carbon (C), carbon dioxide (CO2), model, lateral C export, sink, Earth system models (ESMs), climate change
