How Simulations of the Land Carbon Sink Are Biased by Ignoring Fluvial Carbon Transfers: A Case Study for the Amazon Basin

Lauerwald, Ronny; Regnier, Pierre; Guenet, Bertrand; Friedlingstein, Pierre; Ciais, Philippe

doi:10.1016/j.oneear.2020.07.009

Cited by 42 publications

(61 citation statements)

References 60 publications

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“…GIEMS is also known to underestimate inundation under vegetated areas (Prigent et al, 2007;Papa et al, 2010) and has difficulties capturing small inundated areas (Prigent et al, 2007;Lauerwald et al, 2017). Indeed, with the GIEMS data we produce an overall flooded area for the Congo Basin of just 3 %, less than one-third of that produced with the Gumbricht dataset (Gumbricht et al, 2017) or the GLWD (Lehner and Döll, 2004). As such, it is to be expected that there is a large RMSE (272 %; Table 2) between simulated flooded area and GIEMS; more importantly, the seasonality of the two is highly correlated (R 2 = 0.67; Table 2).…”

Section: Simulation Of Hydrology and Aquatic Carbon Fluxesmentioning

confidence: 85%

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Historical and future contributions of inland waters to the Congo Basin carbon balance

et al. 2021

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Abstract. As the second largest area of contiguous tropical rainforest and second largest river basin in the world, the Congo Basin has a significant role to play in the global carbon (C) cycle. For the present day, it has been shown that a significant proportion of global terrestrial net primary productivity (NPP) is transferred laterally to the land–ocean aquatic continuum (LOAC) as dissolved CO2, dissolved organic carbon (DOC), and particulate organic carbon (POC). Whilst the importance of LOAC fluxes in the Congo Basin has been demonstrated for the present day, it is not known to what extent these fluxes have been perturbed historically, how they are likely to change under future climate change and land use scenarios, and in turn what impact these changes might have on the overall C cycle of the basin. Here we apply the ORCHILEAK model to the Congo Basin and estimate that 4 % of terrestrial NPP (NPP = 5800±166 Tg C yr−1) is currently exported from soils and vegetation to inland waters. Further, our results suggest that aquatic C fluxes may have undergone considerable perturbation since 1861 to the present day, with aquatic CO2 evasion and C export to the coast increasing by 26 % (186±41 to 235±54 Tg C yr−1) and 25 % (12±3 to 15±4 Tg C yr−1), respectively, largely because of rising atmospheric CO2 concentrations. Moreover, under climate scenario RCP6.0 we predict that this perturbation could continue; over the full simulation period (1861–2099), we estimate that aquatic CO2 evasion and C export to the coast could increase by 79 % and 67 %, respectively. Finally, we show that the proportion of terrestrial NPP lost to the LOAC could increase from approximately 3 % to 5 % from 1861–2099 as a result of increasing atmospheric CO2 concentrations and climate change. However, our future projections of the Congo Basin C fluxes in particular need to be interpreted with some caution due to model limitations. We discuss these limitations, including the wider challenges associated with applying the current generation of land surface models which ignore nutrient dynamics to make future projections of the tropical C cycle, along with potential next steps.

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Section: Simulation Of Hydrology and Aquatic Carbon Fluxesmentioning

confidence: 85%

“…a maximum of 10 % of the surface area of the Congo Basin can be inundated with water. This is identical to the mean MFF value of 10 % produced with the Global Lakes and Wetlands Database, GLWD (Lehner and Döll, 2004;Borges et al, 2015b). We also created an MFS forcing file from the same dataset ( Fig.…”

Section: Development Of Floodplain and Swamp Forcing Filesmentioning

confidence: 93%

Historical and future contributions of inland waters to the Congo Basin carbon balance

et al. 2021

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“…Anthropogenic perturbations of riverine C fluxes are manifold and comprise direct impacts through changing C and nutrient inputs following land-use change and agricultural activities, wastewater discharge, and hydraulic management (e.g. Tian et al, 2015;Lauerwald et al, 2020;Hastie et al, 2021;Maavara et al, 2017). There are also indirect impacts following climate change and changes in atmospheric composition.…”

Section: Introductionmentioning

confidence: 99%

“…Together, these perturbations have accelerated the turnover of C along the terrestrial-inland water continuum. The terrestrial C sink, which is classically estimated without taking into account the C exports through the river network, is thus generally overestimated (Regnier et al, 2013;Lauerwald et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

“…ORCHILEAK was previously parametrized and validated for the Amazon(Lauerwald et al, 2017;Hastie et al, 2019;Lauerwald et al, 2020), Congo(Hastie et al, 2021) and Lena(Bowring et al, 2020) basins. In our study of the European river network, we used the default parameter values ofLauerwald et al (2017) excepted for the surface roughness of the vegetation that was adjusted.…”

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confidence: 99%

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Spatio-temporal patterns and drivers of terrestrial Dissolved Organic Carbon (DOC) leaching to the European river network

Gommet

Lauerwald

Ciais

et al. 2021

Preprint

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Abstract. Leaching of dissolved organic carbon (DOC) from soils to the river network is an important component of the land carbon (C) budget. At regional to global scales, its significance has been estimated through simple mass budgets, often using multi-year averages of observed fluvial DOC fluxes as proxy of DOC leaching due to the limited availability of observations of the leaching flux itself. This procedure leads to a systematic underestimation of the leaching flux because of the reactivity of DOC during fluvial transport. Moreover, this procedure does not allow to reveal spatio-temporal variability in DOC leaching from soils, which is needed to better understand the drivers of DOC leaching and its impact on the local soil C budget. In this study, we use the land surface model ORCHILEAK to simulate the terrestrial C budget including leaching of DOC from the soil and its subsequent reactive transport through the river network of Europe. The model performance is not only evaluated against the sparse observations of DOC leaching, but also against the more abundant observations of fluxes and reactivity of DOC in rivers, providing further evidence that our simulated DOC leaching fluxes are realistic. The model is then used to simulate the spatio-temporal patterns of DOC leaching across Europe over the period 1972 to 2012, quantifying both the environmental drivers of these patterns as well as the impact of DOC leaching on the land C budget. Over the simulation period, we find that on average 14.3 TgC yr−1 of DOC is leached from land to European rivers, which is only about 0.6 % of the terrestrial net primary production, a fraction about one order of magnitude lower than reported for tropical river networks. Of the DOC leaching, on average 12.3 TgC yr−1 is exported to the coast via the river network, the rest being respired in transit. DOC leaching presents a large seasonal variability, with a maximum occurring in winter and a minimum in summer, except for the Northern most part of Europe where the maximum occurs in spring due to the snow melt. DOC leaching rate is generally lower in warm and dry regions, and higher in cold and wet regions of Europe. Furthermore, runoff, and the ratio between runoff from shallower flow paths vs. deep drainage and groundwater flow, is the main driver of the spatial variation of DOC leaching. Temperature, as a major control of DOC production and decomposition rates in the soils, plays only a secondary role.

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Wetland Carbon in the United States

Uhran

Zhu

Windham‐Myers

et al. 2021

Wetland Carbon and Environmental Management

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How Simulations of the Land Carbon Sink Are Biased by Ignoring Fluvial Carbon Transfers: A Case Study for the Amazon Basin

Cited by 42 publications

References 60 publications

Historical and future contributions of inland waters to the Congo Basin carbon balance

Historical and future contributions of inland waters to the Congo Basin carbon balance

Spatio-temporal patterns and drivers of terrestrial Dissolved Organic Carbon (DOC) leaching to the European river network

Wetland Carbon in the United States

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