Abstract
Carbon dioxide (CO2) can be either imported to streams through groundwater and subsurface inputs of soil-respired CO2 or produced internally through stream metabolism. The contribution of each source to the CO2 evasion flux from streams is not well quantified, especially in the tropics, an underrepresented region in carbon (C) cycling studies. We used high-frequency measurements of dissolved O2 and CO2 concentrations to estimate the potential contribution of stream metabolism to the CO2 evasion flux in a tropical lowland headwater stream. We found that the stream was heterotrophic all year round, with net ecosystem productivity (NEP) values ranging from 0.84 to 4.06 g C m−2 d−1 (median 1.29 g C m−2 d−1; here we expressed gross primary productivity (GPP) as a negative flux and ecosystem respiration (ER) as a positive flux). Positive NEP values were the result of a relatively low and stable GPP through the seasons, compared to a higher and more variable ER favored by the high temperatures and organic matter availability, particularly during the wet season. The CO2 evasion flux was relatively low due to low turbulence (median: 1.09 g C m−2 d−1). As a result, daily NEP rates exceeded the CO2 evasion flux with a potential contribution of 129% (median; 120–175% interquartile range), despite the strong seasonal changes in flow regime and landscape connectivity. The CO2 excess was likely transported downstream, where it was ultimately emitted to the atmosphere. Our results highlight the overwhelming importance of ER to the C cycle of low-energy, oligotrophic tropical streams.
| Original language | English |
|---|---|
| Pages (from-to) | 1132-1146 |
| Number of pages | 15 |
| Journal | Limnology and Oceanography |
| Volume | 68 |
| Issue number | 5 |
| Early online date | 2023 |
| DOIs | |
| Publication status | Published - May 2023 |
Bibliographical note
Funding Information:The authors would like to thank the Northern Territory Parks and Wildlife Commission, and Power and Water for access to the site. The authors acknowledge the help from field assistants and volunteers, particularly Diego Álvarez and Sydney Collet, and technical support from Matthew Northwood. Finally, the authors thank Bob Hall and two anonymous reviewers for their time and interest. Their feedback improved considerably this manuscript. V.S. was supported by an Australian Government Research Training Program Scholarship. C.D. was supported by the Australian Research Council (DE220100852). Open access publishing facilitated by Charles Darwin University, as part of the Wiley - Charles Darwin University agreement via the Council of Australian University Librarians.
Funding Information:
The authors would like to thank the Northern Territory Parks and Wildlife Commission, and Power and Water for access to the site. The authors acknowledge the help from field assistants and volunteers, particularly Diego Álvarez and Sydney Collet, and technical support from Matthew Northwood. Finally, the authors thank Bob Hall and two anonymous reviewers for their time and interest. Their feedback improved considerably this manuscript. V.S. was supported by an Australian Government Research Training Program Scholarship. C.D. was supported by the Australian Research Council (DE220100852). Open access publishing facilitated by Charles Darwin University, as part of the Wiley ‐ Charles Darwin University agreement via the Council of Australian University Librarians.
Publisher Copyright:
© 2023 The Authors. Limnology and Oceanography published by Wiley Periodicals LLC on behalf of Association for the Sciences of Limnology and Oceanography.