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Title: Representation of dissolved organic carbon from land to river system in JULES model
Author: Nakhavali, M.
ISNI:       0000 0004 7969 5297
Awarding Body: University of Exeter
Current Institution: University of Exeter
Date of Award: 2019
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The lateral transfer of organic carbon along the terrestrial-aquatic continuum is an important link in the global carbon (C) cycle and an important process which should not be ignored when assessing or modelling changes in terrestrial and aquatic C budgets. The amounts of C exported from terrestrial ecosystem into the inland water network have so far only coarsely been estimated by closing a budget based on observed fluvial C exports to the coast and the still poorly constrained estimates of inland water CO2 evasion and C burial in aquatic sediments. The representation of lateral C transfers in Earth System models (ESMs) will arguably help to improve the representation of soil C cycling and its response to climate change and atmospheric CO2 increase. A first and critical step in that direction is to include processes of production and export of dissolved organic carbon (DOC) in soils. Hence, in the first part of my thesis I developed an extension of the Joint UK Land Environment Simulator (JULES-DOCM) that integrates a representation of DOC production in terrestrial ecosystems based on incomplete decomposition of organic matter, DOC decomposition within the soil column, and DOC export to the river network via leaching. Our results showed that the model is able to reproduce the DOC concentration and controlling processes including leaching to the riverine system which is fundamental for integrating terrestrial and aquatic ecosystems. In the second part of my thesis, I optimized JULES-DOCM for global scale application by recalibrating two key processes controlling soil DOC concentrations: the rate of DOC production associated with soil organic carbon decomposition and the rate of DOC decomposition for the locations where observations were available. Then I used JULES-DOCM with these optimised parameters to simulate the global distribution of soil DOC concentrations and DOC leaching fluxes from soils to rivers. For the third part of my thesis, I used JULES-DOCM to simulate spatial-temporal trends in DOC inputs from soil to the river system from 1860 to 2010 at global scale, quantifying the impacts of major environmental drivers such as CO2 fertilization, climate and land use change. At the global scale, CO2 fertilization was identified as the main controller, followed by climate and land use change. Contrary to general assumptions, we find land use changes to only play a minor role in driving the changes in DOC leaching. In the last of my work I used JULES-DOCM and three representative concentration pathways (RCPs), RCP 2.6, RCP 4.5 and RCP 8.5 in order to estimate the future of terrestrial transported DOC flux to the river system. We find the increase of the atmospheric CO2 concentration as the main reason of the future increase of transported terrestrial DOC. In this thesis, I focussed on the detailed representation of soil DOC cycling and leaching, and simulated the historical and future trend of it. However, future work should include the fate of exported DOC in the river system as well as the exports of dissolved inorganic C and particulate organic C from soils to complete the representation of lateral C exports through the terrestrial aquatic continuum.
Supervisor: Friedlingstein, P. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available