Spatial patterns in CO₂ evasion from the global river network

Abstract

CO 2 evasion from rivers (FCO 2 ) is an important component of the global carbon budget. Here we present the first global maps of CO 2 partial pressures (pCO 2 ) in rivers of stream orders 3 and higher and the resulting FCO 2 at 0.5°resolution constructed with a statistical model. A geographic information system based approach is used to derive a pCO 2 prediction function trained on data from 1182 sampling locations. While data from Asia and Africa are scarce and the training data set is dominated by sampling locations from the Americas, Europe, and Australia, the sampling locations cover the full spectrum from high to low latitudes. The predictors of pCO 2 are net primary production, population density, and slope gradient within the river catchment as well as mean air temperature at the sampling location (r 2 = 0.47). The predicted pCO 2 map was then combined with spatially explicit estimates of stream surface area A river and gas exchange velocity k calculated from published empirical equations and data sets to derive the FCO 2 map. Using Monte Carlo simulations, we assessed the uncertainties of our estimates. At the global scale, we estimate an average river pCO 2 of 2400 (2019-2826) μatm and a FCO 2 of 650 (483-846) Tg C yr À1 (5th and 95th percentiles of confidence interval). Our global CO 2 evasion is substantially lower than the recent estimate of 1800 Tg C yr À1 although the training set of pCO 2 is very similar in both studies, mainly due to lower tropical pCO 2 estimates in the present study. Our maps reveal strong latitudinal gradients in pCO 2 , A river , and FCO 2 . The zone between 10°N and 10°S contributes about half of the global CO 2 evasion. Collection of pCO 2 data in this zone, in particular, for African and Southeast Asian rivers is a high priority to reduce uncertainty on FCO 2 .

Effects of agricultural land use on fluvial carbon dioxide, methane and nitrous oxide concentrations in a large European river, the Meuse (Belgium)

“…Inland waters are important players in the global budgets of longlived green-house gases (GHGs), acting as vigorous sources to the atmosphere of carbon dioxide (CO 2 ) (Raymond et al, 2013;Lauerwald et al, 2015;Borges et al, 2015a), methane (CH 4 ) (Bastviken et al, 2011;Borges et al, 2015a;Stanley et al, 2016), and nitrous oxide (N 2 O) (Seitzinger and Kroeze, 1998;Hu et al, 2016). The largest fraction of global CO 2 and CH 4 emissions from riverine networks occurs at tropical and sub-tropical latitudes (Bloom et al, 2010;Raymond et al, 2013;Lauerwald et al, 2015;Borges et al, 2015b) that are in general more pristine than their temperate counter-parts.…”

“…The largest fraction of global CO 2 and CH 4 emissions from riverine networks occurs at tropical and sub-tropical latitudes (Bloom et al, 2010;Raymond et al, 2013;Lauerwald et al, 2015;Borges et al, 2015b) that are in general more pristine than their temperate counter-parts. Conversely, the largest fraction of global N 2 O emissions from riverine networks is assumed to occur in human impacted temperate rivers (Seitzinger and Kroeze, 1998;Hu et al, 2016).…”

Longitudinal discontinuities in riverine greenhouse gas dynamics generated by dams and urban wastewater

“…A growing body of research on greenhouse gas (GHG) emissions from inland waters has recently generated various global 35 syntheses of CO 2 and CH 4 data (Cole et al, 2007;Bastviken et al, 2011;Raymond et al, 2013;Lauerwald et al, 2015;Stanley et al, 2016;Marx et al, 2017) and conceptual frameworks incorporating anthropogenic perturbations as a critical driver of riverine biogeochemical processes in human-impacted river systems (Kaushal et al, 2012;Regnier et al, 2013;Park et al, 2018). However, these efforts have been hampered by data scarcity and inequality and inadequate consideration of multiple GHGs co-regulated by a wide range of concurrent environmental changes including anthropogenic perturbations.…”

“…However, these efforts have been hampered by data scarcity and inequality and inadequate consideration of multiple GHGs co-regulated by a wide range of concurrent environmental changes including anthropogenic perturbations. Above all, 40 recent global syntheses of CO 2 emissions from inland waters commonly emphasized the lack of reliable measurements of the surface water partial pressure of CO 2 (pCO 2 ) in many of large river systems across Asia and Africa Lauerwald et al, 2015). Furthermore, three major GHGs (CO 2 , CH 4 , and N 2 O) have rarely been measured simultaneously across different components of river systems except for a small number of large, 'natural' rivers such as the Amazon (Richey et al, 1988) and the Congo or highly human-impacted systems (Smith et al, 2017;Wang et al, 2017b).…”

Biogeochemical contrast between different latitudes and the effect of human activity on spatio-temporal carbon cycle change in Asian river systems

“…The model further clarified that these mechanisms are closely related to the slight increase in DIC and the decrease in POC in nighttime in three rivers. (Nakayama, 2017a(Nakayama, , 2017b in order to estimate the carbon cycle both in vertical flux such as CO2 evasion to the atmosphere and sediment storage, and in horizontal transport such as TOC, DOC, POC, DIC-flux to the ocean in previous data of these rivers (Schlunz and Schneider, 2000;Coynel et al, 2005;Rasera et al, 2008;Dubois et al, 2010;Alin et al, 2011;Butman and Raymond, 2011;Dai et al, 2012;10 Striegl et al, 2012;Abril et al, 2015;Lauerwald et al, 2015;Long et al, 2015). There are no data about CO2 evasion but only pCO2 and average efflux data in Mekong River Long et al, 2015), the author estimated CO2 evasion by multiplying the average efflux (gC/m 2 /yr) and water area (km 2 ).…”