Abstract
Inland waters have an important role in the global carbon cycle, contributing significantly to terrestrial carbon fluxes through downstream export and exchange of CO2 with the atmosphere. However, large uncertainties in freshwater inorganic carbon fluxes remain. One contributing factor is uncertainty in carbonate system calculations for estimating the partial pressure of CO2 (pCO2) from pH and alkalinity in freshwater systems. The uncertainty stems largely from inaccurate pH values caused by glass pH electrode measurements in low ionic strength systems. This study compares indicator-based spectrophotometric and electrochemical pH measurements and their application for calculating freshwater pCO2. Our study found that, compared to a pCO2 reference method, pH electrode-based estimates of pCO2 were overestimated by 230 ± 200 μatm (n = 54) where indicator-based spectrophotometric pH estimates of pCO2 were 58 ± 33 μatm (n = 34) over the range of 100–1600 μatm. Furthermore, we found that when ionic strength was assumed to be zero, calculated pCO2 error was ~ 20% of the reference pCO2. A 19-d field study using autonomous spectrophotometric pH and pCO2 sensors found an average error in calculated pCO2 of −70 ± 57 μatm (n = 1685). Although, our focus is on riverine CO2, these findings and subsequent conclusions apply to all freshwater systems. Spectrophotometric pH measurements will improve future freshwater pCO2 calculations and better quantify inland waters' role in the global carbon budget.
| Original language | English |
|---|---|
| Pages (from-to) | 514-529 |
| Number of pages | 16 |
| Journal | Limnology and Oceanography: Methods |
| Volume | 20 |
| Issue number | 8 |
| DOIs | |
| State | Published - Aug 2022 |
Funding
The authors thank the H. M. Valett research group at the University of Montana for help with sample collection. The authors thank Venice Bayrd and Robert Payn for their help with data curation and to the anonymous reviewers for their constructive and valued feedback. This research was supported in part by the U.S. National Science Foundation Long Term Research in Environmental Biology program (DEB‐1655197), Montana NSF EPSCoR program (OIA‐1757351), and the University of Montana through a teaching assistantship to Fischer L. Young. The data and processing code underlying this manuscript provide laboratory and in situ sensor measurements of inorganic carbon parameters for the purpose of calculating freshwater CO. The data and code can be found on the Environmental Data Initiative (EDI) repository using the following DOI: 10.6073/pasta/c3bd7a65cfafa464b89857c5e375d20d . Registration with EDI is not required to access these data. All data and code are released with a public domain waiver, CC0 1.0 Universal (CC0 1.0), though attribution via citation is expected if the data or code are reused, as per scholarly convention. Preferred citation information can be found in the “References” section (Young et al. 2022 ). p 2 The authors thank the H. M. Valett research group at the University of Montana for help with sample collection. The authors thank Venice Bayrd and Robert Payn for their help with data curation and to the anonymous reviewers for their constructive and valued feedback. This research was supported in part by the U.S. National Science Foundation Long Term Research in Environmental Biology program (DEB-1655197), Montana NSF EPSCoR program (OIA-1757351), and the University of Montana through a teaching assistantship to Fischer L. Young. The data and processing code underlying this manuscript provide laboratory and in situ sensor measurements of inorganic carbon parameters for the purpose of calculating freshwater pCO2. The data and code can be found on the Environmental Data Initiative (EDI) repository using the following DOI: 10.6073/pasta/c3bd7a65cfafa464b89857c5e375d20d. Registration with EDI is not required to access these data. All data and code are released with a public domain waiver, CC0 1.0 Universal (CC0 1.0), though attribution via citation is expected if the data or code are reused, as per scholarly convention. Preferred citation information can be found in the “References” section (Young et al. 2022).
| Funder number |
|---|
| OIA‐1757351 |
| DEB‐1655197 |
| 2022, CC0 1.0 |