ORCHIDEE-SOM: modeling soil organic carbon (SOC) and dissolved organic carbon (DOC) dynamics along vertical soil profiles in Europe

Abstract

Abstract. Current land surface models (LSMs) typically represent soils in a very simplistic way, assuming soil organic carbon (SOC) as a bulk, and thus impeding a correct representation of deep soil carbon dynamics. Moreover, LSMs generally neglect the production and export of dissolved organic carbon (DOC) from soils to rivers, leading to overestimations of the potential carbon sequestration on land. This common oversimplified processing of SOC in LSMs is partly responsible for the large uncertainty in the predictions of the soil carbon response to climate change. In this study, we present a new soil carbon module called ORCHIDEE-SOM, embedded within the land surface model ORCHIDEE, which is able to reproduce the DOC and SOC dynamics in a vertically discretized soil to 2 m. The model includes processes of biological production and consumption of SOC and DOC, DOC adsorption on and desorption from soil minerals, diffusion of SOC and DOC, and DOC transport with water through and out of the soils to rivers. We evaluated ORCHIDEE-SOM against observations of DOC concentrations and SOC stocks from four European sites with different vegetation covers: a coniferous forest, a deciduous forest, a grassland, and a cropland. The model was able to reproduce the SOC stocks along their vertical profiles at the four sites and the DOC concentrations within the range of measurements, with the exception of the DOC concentrations in the upper soil horizon at the coniferous forest. However, the Published by Copernicus Publications on behalf of the European Geosciences Union. 938M. Camino-Serrano et al.: ORCHIDEE-SOM model was not able to fully capture the temporal dynamics of DOC concentrations. Further model improvements should focus on a plant-and depth-dependent parameterization of the new input model parameters, such as the turnover times of DOC and the microbial carbon use efficiency. We suggest that this new soil module, when parameterized for global simulations, will improve the representation of the global carbon cycle in LSMs, thus helping to constrain the predictions of the future SOC response to global warming.

The use of radiocarbon <sup>14</sup>C to constrain carbon dynamics in the soil module of the land surface model ORCHIDEE (SVN r5165)

“…Despite the importance of soils as a large component of the global carbon storage, soil compartments are not well represented in LSMs (Todd-Brown et al, 2013). Indeed, carbon dynamics in soil described in LSMs are based on the "Century" (Parton et al, 1987) or RothC models (Coleman et al, 1997) where soil carbon is represented as several pools with different turnover rates for each pool. Carbon is decomposed in each pool, one part of which is then transferred from one pool to another and the other part is lost through heterotrophic respiration.…”

ORCHIDEE MICT-LEAK (r5459), a global model for the production, transport, and transformation of dissolved organic carbon from Arctic permafrost regions – Part 1: Rationale, model description, and simulation protocol

“…from soils through the river network. Note that autochthonous primary production and derivative carbon transformations are ignored here, as they are considered relatively minor contributors in the Arctic lateral flux system (Cauwet and Sidorov, 1996;Sorokin and Sorokin, 1996).…”

KEYLINK: towards a more integrative soil representation for inclusion in ecosystem scale models. I. review and model concept

“…Ploughing, soil compaction, litter removal and obviously the use of insecticides are practices that are deleterious to the soil faunal community ( Yeates et al, 1997 ; Wardle et al, 1995 ), with repercussions for soil processes. Such major negative effects on soil organisms are ignored in the most widely used ecosystem models (ORCHIDEE— Camino-Serrano et al (2018) , PaSim and Biome-BGC— Sándor et al (2016) , ANAFORE— Deckmyn et al (2008) ) that thus cannot realistically simulate these management effects.…”