Sizable carbon emission from the floodplain of Ob River

Ivan V Krickov,Svetlana Serikova,Oleg S Pokrovsky,Sergey N Vorobyev,Artem G Lim,Matthias B Siewert,Jan Karlsson

doi:10.1016/j.ecolind.2021.108164

Abstract

The Ob River floodplain is the second largest floodplain in the world. Despite its vast area, estimates of carbon (C) emissions from the Ob River floodplain are largely absent. Here we present seasonal C emission and water area extent from the main channel and the floodplain along a ~4 km reach in the boreal zone of the Ob River. We found strong seasonality in water area extent of the Ob main channel (~1.8 km2) and floodplain (~3 km2) with water covering 34% of land during flood and subsequently declining to ~16% and ~14% during summer and autumn baseflow, respectively. The C emissions also varied seasonally over the open water period, ranging from −0.1 to 0.6 g C m−2 d−1 for the Ob main channel and from 0 to 9 g C m−2 d−1 for the floodplain. The dissolved organic carbon positively affected CO2 concentrations and fluxes in the floodplain during all seasons, whereas pH and oxygen concentration negatively impacted CO2 concentrations and fluxes. Some nutrients (ammonia and phosphate) positively correlated with CO2 and CH4 concentrations in summer. The total C emission from the study reach (1.8 km2 main channel, 3 km2 floodplain) during moderate flooding was 236 ± 51 tons C yr−1 (>99% CO2, <1% CH4) with the floodplain accounting for ~65%. The contribution of the floodplain to the net river C evasion may be even greater during years of high flooding and in northern regions of the Ob River basin, where floodplain soils are more C-rich and are underlain by permafrost, and in years with more extensive flooding.

Highlights

Rivers and streams are known to be a major source of carbon (C) to the atmosphere with recent estimates (0.6–1.8 Pg C yr− 1, Lauerwald et al, 2015; Raymond et al, 2013) corresponding to ~1/8 to 1/4 of global anthropogenic emissions (Ciais et al, 2013)
The floodplains are known to provide the largest share of surface water C emission in lotic systems, Siberian rivers remained strongly understudied
The highest C emissions from the middle Ob River floodplain lakes occurred during late June and July, and largely exceeded the emissions from the main stem

Summary

Introduction

Rivers and streams are known to be a major source of carbon (C) to the atmosphere with recent estimates (0.6–1.8 Pg C yr− 1, Lauerwald et al, 2015; Raymond et al, 2013) corresponding to ~1/8 to 1/4 of global anthropogenic emissions (Ciais et al, 2013). Even for highlatitude regions where river and stream C flux measurements do exist (Campeau et al, 2014; Denfeld et al, 2013; Serikova et al, 2018; Striegl et al, 2012; Tranvik et al, 2018; Zolkos et al, 2019), they have been mainly carried out in the main channels, implying potential un certainties in extrapolation to the regional scales This is especially true for large Russian high-latitude rivers that are far less characterized than those of North America and Fennoscandia. A large body of research has compared C dy namics in floodplains/main channel of the Amazon River (Richey et al, 1988; Devol et al, 1990; Bartlett et al, 1990; Waichman, 1996; Bustillo et al, 2011; Rudorff et al, 2011; Scofield et al, 2016; Amaral et al, 2019, 2020; Hastie et al, 2019) and in other riverine systems across the world (Pulliam, 1993; Smith et al, 2000; Sun et al, 2013; Corson-Rikert et al, 2016; Peixoto et al, 2016; Geeraert et al, 2017; Zuijdgeest and Wehrli, 2017; Cunada et al, 2018; DelDuco and Xu, 2019; Gareis and Lesack, 2020; dos Santos et al, 2020; Barbosa et al, 2018, 2020; Bass et al, 2013, 2014)

Results

Discussion

Conclusion