Processes contributing to the maintenance of CO2 super-saturation in a large boreal river
Abstract
Large rivers play a significant role in the global carbon cycle as most are net CO2 sources to the atmosphere over long distances. However, the processes sustaining super-saturation of CO2 in large rivers are still not adequately understood. We address this issue in the 8th Strahler order river La Romaine in Eastern Canada, which is characterized by super-saturation of CO2 (median: 662 ppm, interquartile range: 563 to 747 ppm) along its entire lower portion (>300 km). The main objective of this study was to explore the relative contribution of tributaries, groundwater inputs, and in-stream metabolism to the sustained super-saturation of CO2 in this river. We measured the partial pressure of CO2 (pCO2) along the entire river main stem, tributaries and in groundwater within the watershed, and estimated river metabolism in the river. We further combined the ambient pCO2 with discharge measurements and estimates of lateral inputs within a mass balance approach to explore the drivers of the observed super-saturation in several ca. 50 km long river sections. Preliminary results show that groundwater has the highest relative contribution to the observed CO2 super-saturation, followed by river metabolism, while the contribution of tributaries is very minor. The major role played by groundwater inputs of soil-derived CO2 in driving the CO2 super-saturation within our study system is potentially transposable to other large boreal river systems. This emergent insight improves our fundamental understanding of how major river systems function within the carbon cycle, and our capacity to predict how this functioning may change in future scenarios of climate and hydrologic change.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMB047.0014B
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 0458 Limnology;
- BIOGEOSCIENCES;
- 0465 Microbiology: ecology;
- physiology and genomics;
- BIOGEOSCIENCES