Abstract

Lateral carbon transport from soils to the ocean through rivers has been acknowledged as a key component of global carbon cycle, but is still neglected in most global land surface models (LSMs). Fluvial transport of dissolved organic carbon (DOC) and CO2 has been implemented in the ORCHIDEE LSM, while erosion-induced delivery of sediment and particulate organic carbon (POC) from land to river was implemented in another version of the model. Based on these two developments, we take the final step towards the full representation of biospheric carbon transport through the land-river continuum. The newly developed model, called ORCHIDEE-Clateral, simulates the complete lateral transport of water, sediment, POC, DOC and CO2 from land to sea through the river network, the deposition of sediment and POC in the river channel and floodplains, and the decomposition of POC and DOC in transit. We parameterized and evaluated ORCHIDEE-Clateral using observation data in Europe. The model satisfactorily reproduces the observed riverine discharges of water and sediment, bankfull flows and sediment delivery rate from land to river, as well as the observed concentrations of organic carbon in rivers. Application of ORCHIDEE-Clateral for Europe reveals that the lateral carbon transfer affects land carbon dynamics in multiple ways and omission of this process in LSMs may result in significant biases in the simulated regional land carbon budgets. Overall, this study presents a useful tool for simulating large scale lateral carbon transfer and for predicting the feedbacks between lateral carbon transfer and future climate and land use changes.

Highlights

  • Lateral transfer of organic carbon along the land-river-ocean continuums, involving both spatial redistribution of terrestrial organic carbon and the vertical land-atmosphere carbon exchange, has been acknowledged as a key component of the global carbon cycle (Ciais et al, 2013; Ciais et al, 2021; Drake et al, 2018; Regnier et al, 2013)

  • Lateral transfer of dissolved organic carbon (DOC) and dissolved CO2 from land to ocean through river network has been implemented in the ORCHILEAK (Lauerwald et al, 2017), an ORCHIDEE branch developed from ORCHIDEE-SOM

  • Note that when the soil erosion rate of the floodplain soil is larger than the sediment deposition rate, sediment and organic carbon in Sdeep move up to replenish the stocks of the 11th soil layer

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Summary

Introduction

Lateral transfer of organic carbon along the land-river-ocean continuums, involving both spatial redistribution of terrestrial organic carbon and the vertical land-atmosphere carbon exchange, has been acknowledged as a key component of the global carbon cycle (Ciais et al, 2013; Ciais et al, 2021; Drake et al, 2018; Regnier et al, 2013). The erosioninduced transport of POC, which is maybe even more important than the DOC transport in terms of lateral carbon flux (Lal., 2003; Tian et al, 2015; Tan et al, 2017), is still not or poorly represented in LSMs. The explicit simulation of the complete transport process of POC at large spatial scales is still a major challenge, due to the complexity of the processes involved, including erosion-induced sediment and POC delivery to rivers, deposition of sediment and POC in river channels and floodplains, re-detachment of the previously deposited sediments and POC, decomposition and transformation of POC in riverine and flooding waters, as well as the changes of soil profile caused by erosion and deposition (Doetterl et al, 2016; Naipal et al., 2020; Zhang et al, 2020). We describe the development, application and evaluation of a new branch of the ORCHIDEE LSM (Krinner et al, 2005), hereafter ORCHIDEE-Clateral, that can be used to simulate the complete lateral transfer processes of water, sediment, POC and DOC along the land-river-ocean continuum at large spatial scale (e.g. continental and global scale). Comparing simulations results to those of an alternative simulation run with lateral displacement of C deactivated, we quantify the biases in simulated land C budgets that arise ignoring the lateral transfers of C along the land-river continuum

ORCHIDEE land surface model
Lateral transfer of DOC and CO2
Sediment and carbon delivery from upland soil to river network
Sediment and POC transport in inland water network
Sediment transport
POC transport and decomposition
Model application and evaluation
Stream water discharge and bankfull flow
Organic carbon transport
Lateral carbon transfers in Europe
Implications for the terrestrial C budget of Europe
Persisting short comings and future work
Conclusions
Code and data availability
Full Text
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