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What are the trends and drivers of riverine CO2 emissions in the Tibetan Plateau?

Iwan, Julia LU (2024) In Student thesis series INES NGEM01 20241
Dept of Physical Geography and Ecosystem Science
Abstract
The release of carbon dioxide (CO2) from inland waters plays an important role in the global carbon cycle. Yet, there are uncertainties related to estimating riverine CO2 evasion (FCO2), especially in data scarce regions such as the Tibetan Plateau. It is unclear how global change in the form of climate warming and anthropogenic disturbance affects emissions. This study reports annual CO2 fluxes as well as their change from 2000 to 2019 for streams and rivers across the Tibetan Plateau by comparing two representative but distinct approaches to calculate each of the commonly requested FCO2 modelling parameters, namely river surface area, gas transfer velocity, riverine partial pressure of CO2, and atmospheric CO2 concentration, yielding a... (More)
The release of carbon dioxide (CO2) from inland waters plays an important role in the global carbon cycle. Yet, there are uncertainties related to estimating riverine CO2 evasion (FCO2), especially in data scarce regions such as the Tibetan Plateau. It is unclear how global change in the form of climate warming and anthropogenic disturbance affects emissions. This study reports annual CO2 fluxes as well as their change from 2000 to 2019 for streams and rivers across the Tibetan Plateau by comparing two representative but distinct approaches to calculate each of the commonly requested FCO2 modelling parameters, namely river surface area, gas transfer velocity, riverine partial pressure of CO2, and atmospheric CO2 concentration, yielding a total of 16 combinations.
Across the Tibetan Plateau, the annual riverine CO2 emissions increased significantly from 2000 to 2019 for all model scenarios, with average values for the 16 scenarios ranging from 0.26 to 43.2 Tg C yr-1. The most realistic annual CO2 evasion was 37.7 ± 2.84 Tg C yr-1, based on the combination of a geometric equation for river surface area, energy-dissipation based gas transfer velocity, a machine learning model for aquatic partial pressure of CO2, and the local Tibetan Plateau-specific atmospheric CO2 concentration. The presented emissions were twice as high as the previous estimate, suggesting a serious underestimation of CO2 dynamics on the Tibetan Plateau.
The differences between the CO2 emission models were caused by the CO2 concentration gradient between atmosphere and water, as the interplay of global/local atmospheric CO2 concentrations and the two models for riverine CO2 concentrations (empirical/machine learning) determined the direction (i.e., whether there was CO2 release or uptake) and strength of the emissions, while effective river surface area and gas transfer velocity played a lesser role. There was a clear dichotomy between the low emissions/slight uptake in the central regions of the Tibetan Plateau and the high CO2 evasion in the southeastern parts. The trend in aquatic CO2 emissions was driven by the river surface area, in turn dependent on the discharge.
However, the combination of the large range of riverine CO2 emissions and the lack of direct pCO2 measurements in rivers and streams highlights the associated uncertainties in emission calculations, especially when estimating the riverine CO2 concentrations. With a changing climate, discharge might increase on the Tibetan Plateau, owed to the warming-induced melting of permafrost and glaciers, as well as the projected increase in precipitation. Following the connection between discharge and CO2 release, this might lead to higher CO2 emissions from the Tibetan Plateau. To improve the estimates of riverine CO2 dynamics on the Tibetan Plateau, the partial pressure of CO2 in rivers and streams needs to be modelled more accurately, using a refined model with higher temporal variation, as well as more direct observations. (Less)
Popular Abstract
The release of carbon dioxide (CO2) from inland waters plays an important role in the global carbon cycle. Yet, there are uncertainties related to estimating riverine CO2 evasion (FCO2), especially in data scarce regions such as the Tibetan Plateau. It is unclear how global change in the form of climate warming and anthropogenic disturbance affects emissions. This study reports annual CO2 fluxes as well as their change from 2000 to 2019 for streams and rivers across the Tibetan Plateau by comparing two representative but distinct approaches to calculate each of the commonly requested FCO2 modelling parameters, namely river surface area, gas transfer velocity, riverine partial pressure of CO2, and atmospheric CO2 concentration, yielding a... (More)
The release of carbon dioxide (CO2) from inland waters plays an important role in the global carbon cycle. Yet, there are uncertainties related to estimating riverine CO2 evasion (FCO2), especially in data scarce regions such as the Tibetan Plateau. It is unclear how global change in the form of climate warming and anthropogenic disturbance affects emissions. This study reports annual CO2 fluxes as well as their change from 2000 to 2019 for streams and rivers across the Tibetan Plateau by comparing two representative but distinct approaches to calculate each of the commonly requested FCO2 modelling parameters, namely river surface area, gas transfer velocity, riverine partial pressure of CO2, and atmospheric CO2 concentration, yielding a total of 16 combinations.
Across the Tibetan Plateau, the annual riverine CO2 emissions increased from 2000 to 2019 for all model scenarios, while the actual emission values differed between the model combinations. The most realistic annual CO2 evasion was 37.7±1.80 Tg C yr-1, based on the combination of a river surface area using monthly discharge, gas transfer velocity highlighting the role of the river channel slope, a machine learning model for aquatic CO2 concentrations, and the local Tibetan Plateau-specific atmospheric CO2 concentration. The presented emissions were twice as high as previous estimates, suggesting a serious underestimation of CO2 dynamics on the Tibetan Plateau.
The differences between the CO2 emission models were caused by the difference between atmospheric and riverine CO2 concentrations, while effective river surface area and gas transfer velocity only slightly affected the magnitude of the emissions. The central Tibetan Plateau showed generally higher CO2 emissions in the east, and low emissions/slight uptake of CO2 in the west. The increase in riverine CO2 emissions was mainly driven by increasing discharge in the region.
The large range of riverine CO2 emissions suggested that the selection of the FCO2 parameters affected the reliability of the emission estimates. The riverine CO2 concentrations had the strongest effect on the magnitude of CO2 evasion, highlighting the importance of accurate modelling of riverine dissolved CO2. With a changing climate, discharge might increase on the Tibetan Plateau, due to the melting of permafrost and glaciers, as well as the projected increase in precipitation. Following the connection between discharge and CO2 release, this might lead to higher CO2 emissions from the Tibetan Plateau. To improve the estimates of riverine CO2 dynamics on the Tibetan Plateau, the model for riverine CO2 concentrations should be refined by including more direct measurements covering the Tibetan Plateau, as well as temporally varying model input data. (Less)
Please use this url to cite or link to this publication:
author
Iwan, Julia LU
supervisor
organization
course
NGEM01 20241
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Physical geography, carbon dioxide, hydrology, biogeochemistry, Tibetan Plateau, CO2 modelling
publication/series
Student thesis series INES
report number
660
language
English
id
9164794
date added to LUP
2024-06-17 16:49:26
date last changed
2024-06-17 16:49:26
@misc{9164794,
  abstract     = {{The release of carbon dioxide (CO2) from inland waters plays an important role in the global carbon cycle. Yet, there are uncertainties related to estimating riverine CO2 evasion (FCO2), especially in data scarce regions such as the Tibetan Plateau. It is unclear how global change in the form of climate warming and anthropogenic disturbance affects emissions. This study reports annual CO2 fluxes as well as their change from 2000 to 2019 for streams and rivers across the Tibetan Plateau by comparing two representative but distinct approaches to calculate each of the commonly requested FCO2 modelling parameters, namely river surface area, gas transfer velocity, riverine partial pressure of CO2, and atmospheric CO2 concentration, yielding a total of 16 combinations. 
Across the Tibetan Plateau, the annual riverine CO2 emissions increased significantly from 2000 to 2019 for all model scenarios, with average values for the 16 scenarios ranging from 0.26 to 43.2 Tg C yr-1. The most realistic annual CO2 evasion was 37.7 ± 2.84 Tg C yr-1, based on the combination of a geometric equation for river surface area, energy-dissipation based gas transfer velocity, a machine learning model for aquatic partial pressure of CO2, and the local Tibetan Plateau-specific atmospheric CO2 concentration. The presented emissions were twice as high as the previous estimate, suggesting a serious underestimation of CO2 dynamics on the Tibetan Plateau.
The differences between the CO2 emission models were caused by the CO2 concentration gradient between atmosphere and water, as the interplay of global/local atmospheric CO2 concentrations and the two models for riverine CO2 concentrations (empirical/machine learning) determined the direction (i.e., whether there was CO2 release or uptake) and strength of the emissions, while effective river surface area and gas transfer velocity played a lesser role. There was a clear dichotomy between the low emissions/slight uptake in the central regions of the Tibetan Plateau and the high CO2 evasion in the southeastern parts. The trend in aquatic CO2 emissions was driven by the river surface area, in turn dependent on the discharge. 
However, the combination of the large range of riverine CO2 emissions and the lack of direct pCO2 measurements in rivers and streams highlights the associated uncertainties in emission calculations, especially when estimating the riverine CO2 concentrations. With a changing climate, discharge might increase on the Tibetan Plateau, owed to the warming-induced melting of permafrost and glaciers, as well as the projected increase in precipitation. Following the connection between discharge and CO2 release, this might lead to higher CO2 emissions from the Tibetan Plateau. To improve the estimates of riverine CO2 dynamics on the Tibetan Plateau, the partial pressure of CO2 in rivers and streams needs to be modelled more accurately, using a refined model with higher temporal variation, as well as more direct observations.}},
  author       = {{Iwan, Julia}},
  language     = {{eng}},
  note         = {{Student Paper}},
  series       = {{Student thesis series INES}},
  title        = {{What are the trends and drivers of riverine CO2 emissions in the Tibetan Plateau?}},
  year         = {{2024}},
}