Spatial–temporal variations in riverine carbon strongly influenced by local hydrological events in an alpine catchment

Abstract

Abstract. Headwater streams drain >70 % of global land areas but are poorly monitored compared with large rivers. The small size and low water buffering capacity of headwater streams may result in a high sensitivity to local hydrological alterations and different carbon transport patterns from large rivers. Furthermore, alpine headwater streams on the “Asian water tower”, i.e., Qinghai–Tibetan Plateau, are heavily affected by thawing of frozen soils in spring as well as monsoonal precipitation in summer, which may present contrasting spatial–temporal variations in carbon transport compared to tropical and temperate streams and strongly influence the export of carbon locked in seasonally frozen soils. To illustrate the unique hydro-biogeochemistry of riverine carbon in Qinghai–Tibetan headwater streams, here we carry out a benchmark investigation on the riverine carbon transport in the Shaliu River (a small alpine river integrating headwater streams) based on annual flux monitoring, sampling at a high spatial resolution in two different seasons and hydrological event monitoring. We show that riverine carbon fluxes in the Shaliu River were dominated by dissolved inorganic carbon, peaking in the summer due to high discharge brought by the monsoon. Combining seasonal sampling along the river and monitoring of soil–river carbon transfer during spring thaw, we also show that both dissolved and particulate forms of riverine carbon increased downstream in the pre-monsoon season due to increasing contribution of organic matter derived from thawed soils along the river. By comparison, riverine carbon fluctuated in the summer, likely associated with sporadic inputs of organic matter supplied by local precipitation events during the monsoon season. Furthermore, using lignin phenol analysis for both riverine organic matter and soils in the basin, we show that the higher acid-to-aldehyde (Ad/Al) ratios of riverine lignin in the monsoon season reflect a larger contribution of topsoil likely via increased surface runoff compared with the pre-monsoon season when soil leachate lignin Ad/Al ratios were closer to those in the subsoil than topsoil solutions. Overall, these findings highlight the unique patterns and strong links of carbon transport in alpine headwater catchments with local hydrological events. Given the projected climate warming on the Qinghai–Tibetan Plateau, thawing of frozen soils and alterations of precipitation regimes may significantly influence the alpine headwater carbon transport, with critical effects on the biogeochemical cycles of the downstream rivers. The alpine headwater catchments may also be utilized as sentinels for climate-induced changes in the hydrological pathways and/or biogeochemistry of the small basin.

Groundwater Plays an Important Role in Controlling Riverine Dissolved Organic Matter in a Cold Alpine Catchment, the Qinghai–Tibet Plateau

“…Our work indicates that DOC flux is positively related to stream discharge, as illustrated in other major rivers and catchments on the QTP (Gao et al., 2019; Wang et al., 2021; Zhu et al., 2020). We also identified the differences in the DOM patterns between cold alpine and Arctic areas.…”

Global Riverine Export of Dissolved Lignin Constrained by Hydrology, Geomorphology, and Land‐Cover

“…Y. Bao et al, 2015;Benner & Kaiser, 2011;Besemer et al, 2009;Bouillon et al, 2012;Duan et al, 2007;Eckard et al, 2007Eckard et al, , 2017Fellman et al, 2014;Godin et al, 2017;Gonsior et al, 2011;Hedges et al, 2000;Hernes et al, 2008Hernes et al, , 2017Johnston et al, 2018Johnston et al, , 2021Liu et al, 2021;Mann et al, 2016;S. P. Opsahl & Zepp, 2001;Shen et al, 2012;Spencer et al, 2008Spencer et al, , 2012Spencer et al, , 2016Wang et al, 2021;Ward et al, 2012), see Section 2.4 for the data source of land-cover.…”

“… Locations of data. Red dots denote data from this study, and blue dots represent data from the literature (Aufdenkampe et al., 2007; H. Y. Bao et al., 2015; H. Bao et al., 2019; Benner & Kaiser, 2011; Besemer et al., 2009; Bouillon et al., 2012; Duan et al., 2007; Eckard et al., 2007, 2017; Fellman et al., 2014; Godin et al., 2017; Gonsior et al., 2011; Hedges et al., 2000; Hernes et al., 2008, 2017; Johnston et al., 2018, 2021; Liu et al., 2021; Mann et al., 2016; S. P. Opsahl & Zepp, 2001; Shen et al., 2012; Spencer, Hernes, et al., 2010; Spencer et al., 2008, 2012, 2016; Wang et al., 2021; Ward et al., 2012), see Section 2.4 for the data source of land‐cover. …”

Anthropogenic Disturbance Stimulates the Export of Dissolved Organic Carbon to Rivers on the Tibetan Plateau

“…The Tibetan Plateau (TP) is the highest and largest plateau in the world and contains numerous headwater streams for Asian rivers. , The TP where there are the most fragile and sensitive ecosystems on Earth , is suffering from the combined increasing pressure of global warming, extreme precipitation, and anthropogenic disturbance. , Despite the adverse natural environment resulting in a low population density in the TP (∼6.7 individuals km –2 in 2019), its population has doubled over the past five decades . Recent studies have highlighted the importance of DOC compositions or characteristics in glacier-fed streams responding to climate change on the TP. − Nonetheless, an extensive knowledge gap exists between how anthropogenic disturbances change the sources and fate of riverine DOC on the TP.…”