Stable Water Isotope Assessment of Tundra Wetland Hydrology as a Potential Source of Arctic Riverine Dissolved Organic Carbon in the Indigirka River Lowland, Northeastern Siberia

Shinya Takano,Youhei Yamashita,Shunsuke Tei,Atsuko Sugimoto,Maochang Liang,Tomoki Morozumi,Trofim C Maximov,Ryo Shingubara

doi:10.3389/feart.2021.699365

Abstract

Arctic tundra wetlands may be an important source of dissolved organic carbon (DOC) in Arctic rivers and the Arctic Ocean under global warming. We investigated stable water isotopes and DOC concentration in wetlands, tributaries, and the mainstream at the lower reaches of the Indigirka River in northeastern Siberia during the summers of 2010–2014 to assess the complex hydrology and role of wetlands as sources of riverine DOC. The wetlands had higher values of δ18O and DOC concentration than the tributaries and mainstream of the Indigirka River. A relationship between the two parameters was observed in the wetlands, tributaries, and mainstream, suggesting the wetlands can be a source of DOC for the mainstream through the tributaries. The combined temporal variations in riverine δ18O and DOC concentration indicate the mainstream water flowed into the tributaries during relatively high river-level periods in summer, whereas high DOC water in the downstream wetlands could be discharged to the mainstream through the tributaries during the low river-level periods. A minor fraction (7–13%) of riverine and wetland DOC was degraded during 40 days of dark incubation. Overall, the downstream wetlands potentially provide relatively less biodegradable DOC to the Arctic river and costal ecosystem during the low river-level periods—from late summer to autumn.

Highlights

The pedosphere of the Arctic has substantial stocks of organic carbon and plays an important role in the global carbon cycle as sources and sinks of CO2 and CH4, which are affected by global warming (McGuire et al, 2009; McGuire et al, 2010b)
We investigated the dissolved organic carbon (DOC) concentration and stable isotopes of water in the lower reaches of the Indigirka River in northeastern Siberia during summer to assess the complex hydrology and role of wetlands as a source of Arctic riverine DOC
The relationship between δ18O and DOC concentration indicated that the downstream wetland water could be a source of DOC in the Indigirka River mainstream through the tributaries

Summary

Introduction

The pedosphere of the Arctic has substantial stocks of organic carbon and plays an important role in the global carbon cycle as sources and sinks of CO2 and CH4, which are affected by global warming (McGuire et al, 2009; McGuire et al, 2010b). After the peak of river discharge, the DOC concentration generally decreases correspondingly with the decrease in discharge (Cooper et al, 2008; Prokushkin et al, 2009, 2011; Holmes et al, 2008, 2012), a phenomenon which can be attributed to the longer flow path of the infiltration water, created by seasonal deepening of the active layer. This longer flow path allows DOC decomposition and/or adsorption onto mineral particles in the soil before leaching into the stream (MacLean et al, 1999; Striegl et al, 2005; Petrone et al, 2006; Prokushkin et al, 2007)

Methods

Results

Conclusion