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

Abstract

Abstract.Recent research has shown inland water may play some role in carbon cycling, although the extent of its contribution has remained uncertain due to limited amount of reliable data available. In this study, the author applied an advanced model coupling eco-hydrology and biogeochemical cycle (NICE-BGC) to regional-continental scales, which incorporates complex coupling of hydrologic-carbon cycle and interplay between inorganic and organic carbon. The author evaluates latitudinal 10 effect and human impact on hydrologic and carbon cycles between boreal Ob River, temperate Yangtze River, and subtropical Mekong River basins in Asia by using different resolutions of river network data. The model simulated more heterogenous distributions of water and carbon flux in the finer river network data in these regions, and helped to identify some hot spots on a regional scale. Then, the model was extended to continental scale at 1°x1° resolution with a time step of t = 1 day to evaluate seasonal and diurnal variations in carbon flux parameters. The model result showed there is a seasonal variability of horizontal 15 transport and vertical fluxes among boreal, temperate, and tropical regions and among each continent, which reflects seasonal variations of biologic and hydrologic processes there. The result showed CO2 evasion increases and sediment storage decreases in nighttime, particularly clearly seen temporarily in summer in Yangtze River, which implied some hot spots and hot moments in the day-night difference of vertical fluxes in regional scale. These results emphasize the important role of Asian river systems on global carbon cycle, and the further need to improve the resolution of simulation, to implement carbon observation network, 20 and to apply satellite data in the higher-resolution.

Impact of anthropogenic disturbances on carbon cycle changes in terrestrial‐aquatic‐estuarine continuum by using an advanced process‐based model

“…Sensitivity analyses also predicted that CO 2 evasion would be reduced by an average of 15% in major estuaries despite the uncertainty of the simulated value (shown as the standard deviation in the figure), due mainly to increases in inland nutrient flux and sea level. However, the possibility of larger CO 2 flux during synoptic weather events (extremes such as flooding) needs to be considered (Aho & Raymond, 2019; Borges & Abril, 2011; Liu et al, 2016; Nakayama, 2017c), as this would be expected to increase due to climate variability in the future. It is also expected that biogeochemical cycling of nutrient, DOM, and POM would become more complicated in estuaries (Bianchi & Bauer, 2011; Canuel & Hardison, 2016; Hutchings et al, 2020).…”

“…To separate the effects of climatic change on spatio-temporal changes in CO 2 evasion in global major estuaries, the model simulation examined changes in inland nutrient flux, and ocean boundaries in terms of seawater temperature, ocean acidification, sea level, and total changes (Moss et al, 2010), respectively (Figure 7). However, the possibility of larger CO 2 flux during synoptic weather events (extremes such as flooding) needs to be considered (Aho & Raymond, 2019;Borges & Abril, 2011;Liu et al, 2016;Nakayama, 2017c), as this would be expected to increase due to climate variability in the future. It is also expected that biogeochemical cycling of nutrient, DOM, and POM would become more complicated in estuaries Canuel & Hardison, 2016;Hutchings et al, 2020).…”

bg-2017-447-RC1

“…He gathered and added more literature about time-series and seasonal variations of DOC fluxes as much as possible to compare seasonal changes of these quantities in different Asian Rivers in the revised Figure 4. In particular, he compared the available literature with the simulated result in Ob River (Kohler et al, 2003;Gebhadrt et al, 2004;McClelland et al, 2016), Yangtze River (Wang et al, 2012Shi et al, 2016;Ran et al, 2017), andMekong River (Li andBush, 2015;Borges et al, 2017) as much as possible though there were not so many available data except DOC yet. This validation also improved the accuracy of carbon flux in the revised Figure 5, as described in the following comment.…”