Exploring Spatially Explicit Changes in Carbon Budgets of Global River Basins during the 20th Century

Abstract

Rivers play an important role in the global carbon (C) cycle. However, it remains unknown how long-term river C fluxes change because of climate, land-use, and other environmental changes. Here, we investigated the spatiotemporal variations in global freshwater C cycling in the 20th century using the mechanistic IMAGE-Dynamic Global Nutrient Model extended with the Dynamic In-Stream Chemistry Carbon module (DISC-CARBON) that couples river basin hydrology, environmental conditions, and C delivery with C flows from headwaters to mouths. The results show heterogeneous spatial distribution of dissolved inorganic carbon (DIC) concentrations in global inland waters with the lowest concentrations in the tropics and highest concentrations in the Arctic and semiarid and arid regions. Dissolved organic carbon (DOC) concentrations are less than 10 mg C/L in most global inland waters and are generally high in high-latitude basins. Increasing global C inputs, burial, and CO 2 emissions reported in the literature are confirmed by DISC-CARBON. Global river C export to oceans has been stable around 0.9 Pg yr –1 . The long-term changes and spatial patterns of concentrations and fluxes of different C forms in the global river network unfold the combined influence of the lithology, climate, and hydrology of river basins, terrestrial and biological C sources, in-stream C transformations, and human interferences such as damming.

Detrital Carbonate Minerals in Earth's Element Cycles

“…Such an increase in DIC fluxes would result in a 5.6% increase in TC, partially compensating the reduction of OC and PIC in terms of total carbon export (total disturbance: −2%). This is consistent with the estimation of a somewhat stable riverine TC export as a result of in-stream removal of anthropogenic carbon by POC deposition and respiration (Cole et al, 2007;Regnier et al, 2013;van Hoek et al, 2021).…”

“…An accurate and precise knowledge of the riverine carbon export is necessary to understand the distribution and fate of anthropogenic carbon perturbations (Friedlingstein et al., 2020 ; Resplandy et al., 2018 ). Over the past century, these riverine carbon fluxes have changed and continue doing so, likely in response to climate change and local human activities, such as industrialization, changes in land use, hydrology, and agricultural practices (Drake et al., 2018 ; Lambert et al., 2017 ; Li et al., 2019 ; Liu et al., 2020 ; Noacco et al., 2017 ; Raymond & Hamilton, 2018 ; van Hoek et al., 2021 ; Zeng et al., 2019 ).…”

“…The bulk anthropogenic effect on total global riverine DIC fluxes remains elusive (Raymond & Hamilton, 2018 ) and human activities other than dam‐building impact terrestrial and freshwater carbon cycling (van Hoek et al., 2021 ). Notably, humans also change conditions at the site of riverine PIC deposition: The current coastal ocean acidification in response to anthropogenic emissions and eutrophication (Borges & Gypens, 2010 ; Carstensen & Duarte, 2019 ) could enhance PIC dissolution, acting as a heterogeneous buffer (Middelburg et al., 2020 ).…”

“…The bulk anthropogenic effect on total global riverine DIC fluxes remains elusive (Raymond & Hamilton, 2018) and human activities other than dam-building impact terrestrial and freshwater carbon cycling (van Hoek et al, 2021). Notably, humans also change conditions at the site of riverine PIC deposition: The current coastal Ludwig et al (1996Ludwig et al ( , 1998; Meybeck (1982), DOC: (Aitkenhead and McDowell (2000); Dai et al (2012); Harrison et al (2005); Li et al (2019); Ludwig et al (1996Ludwig et al ( , 1998, POC: Beusen et al (2005); Galy et al (2015); Li et al (2017); Ludwig et al (1996Ludwig et al ( , 1998; Meybeck (1982), Superscripts: S : By changes in sediment flux only, D : By damming only (Maavara et al, 2017; This study); *: By climate change and land-use change for carbonate weathering only (Zeng et al, 2019).…”

Detrital carbonate minerals in Earth's element cycles

“…An accurate and precise knowledge of the riverine carbon export is necessary to understand the distribution and fate of anthropogenic carbon perturbations (Friedlingstein et al, 2020;Resplandy et al, 2018). Over the past century, these riverine carbon fluxes have changed and continue doing so, likely in response to climate change and local human activities, such as industrialization, changes in land use, hydrology, and agricultural practices (Drake et al, 2018;Lambert et al, 2017;Li et al, 2019;Liu et al, 2020;Noacco et al, 2017;Raymond & Hamilton, 2018;van Hoek et al, 2021;Zeng et al, 2019).…”