Corrigendum: Carbon Dioxide Emissions along the Lower Amazon River

A Corrigendum on
Carbon Dioxide Emissions along the Lower Amazon River

by Sawakuchi, H. O., Neu, V., Ward, N. D., Barros, M. d. L. C., Valerio, A. M., Gagne-Maynard, W., et al. (2017). Front. Mar. Sci. 4:76. doi: 10.3389/fmars.2017.00076

In the original article, there was an error in the upscaling of site-specific flux rates to local emissions for the different areas considered in the paper for the lower Amazon River. Hence, the error propagated throughout our local and global estimates presented in different sections of the paper and Tables 3, 4. Minor mistakes were also in the discharge values for lower and rising sampling season for IDs 5 (South Macapá) and 6 (North Macapá), which are switched in Table 1 and the values of Areas 1 and 2 presented in the Methods.

TABLE 1

Table 1. CO₂ fluxes to atmosphere (FCO₂), partial pressure of CO₂ in the water (pCO₂), gas transfer velocity (k₆₀₀) measurements according to site and season (mean ± SD) and measurements of mean depth (z), water velocity (w), discharge (Q) and wind speed (U₁₀).

TABLE 3

Table 3. Seasonal CO₂ emissions in the Amazon River channel considering different areas.

TABLE 4

Table 4. CO₂ emission estimates for rivers and streams in the Amazon.

Several corrections have been made to the text of the article and the updated sections are as follows:

Abstract: “We estimate that the lower Amazon River mainstem emits 20 Tg C year⁻¹ within our study boundaries, or as much as 48 Tg C year⁻¹ if the entire spatial extent to the geographical mouth is considered. Emissions from the Xingu and Tapajós lower tributaries contribute an additional 2.3 Tg C year⁻¹. Including these values with updated basin scale estimates and estimates of CO2 outgassing from small streams we estimate that the Amazon running waters outgasses as much as 0.95 Pg C year⁻¹, increasing the global emissions from inland waters by 15% for a total of 2.45 Pg C year⁻¹. These results highlight the lower reaches of large rivers as a missing gap in basin-scale and global carbon budgets. In the case of the Amazon River, the previously unstudied tidally-influenced reaches contribute to 5% of CO2 emissions from the entire basin.”

Methods section, subsection Annual CO₂ Emissions from the Lower Amazon River, the first paragraph:

“We divided the main channel into two zones: (Area 1) our study boundaries from Óbidos to Macapá, which has a surface area of 7,118 km², and (Area 2) the region extending from Macapá to the geographical river mouth, which has an additional surface area of 11,261 km² (Figure 1).”

Results section, subsection Upscaling CO₂ Emissions from the Lower Amazon River:

“The total flux of CO₂ from the main channel of the lower Amazon River was calculated for two zones (Figure 1) for each 3-month hydrologic period and annually (Table 3). The most conservative estimates (Area 1) only included the boundaries of this study, from Óbidos to Macapá, which had an average wetted surface area of 7,118 km². The flux of CO₂ from Area 1 was 20 Tg C year⁻¹. Area 2 extends from Macapá to the region of the mouth where the connection to land terminates, which had an additional surface area of 11,261 km². Area 2 had a total CO₂ flux of 28 Tg C year⁻¹, based on an extrapolation of average values measured across the north and south Macapá channels (Table 3). The sum of fluxes for these two zones, or the total emissions from Óbidos to the actual river mouth was 48 Tg C year⁻¹. The emissions from the lower Tapajós and Xingu rivers were 1.40 and 0.86 Tg C year⁻¹, respectively. Including these two tributaries to the budget would add more 2.26 Tg C year⁻¹.”

Discussion section, the eighth paragraph:

“Here we considered two different areas for upscaling annual CO₂ emissions from the lower Amazon River. Our most conservative estimate, including the area from Óbidos to Macapá (Area 1), was 20 Tg C year⁻¹. Area 2, which extends to the geographic terminus of the river, is a relatively short distance compared to Area 1, but covers 58% more surface area than the Óbidos to Macapá reach (Table 3). Applying the average FCO₂ observed near Macapá, we estimate Area 2 to emit 28 Tg C year⁻¹, which combined with the upstream section totalize 48 Tg C year⁻¹. Emissions from the Xingu and Tapajós tributaries contribute an additional 2.3 Tg C year⁻¹, resulting in a total flux of 51 Tg C year⁻¹ from the lower Amazon River basin. This estimate for the lower Amazon River, alone, is roughly 53% in magnitude compared to CO₂ emissions from all rivers in the conterminous United States (97 Tg C year⁻¹; Butman and Raymond, 2011) and ~12% of past estimates of basin-scale emissions from the Amazon (0.47 Pg C year⁻¹; Richey et al., 2002).”

Discussion section, the ninth paragraph:

“Adding our estimations of the fluxes estimated for Area 1 and the sum of Area 1 and 2 to estimations by Richey et al. (2002) increases basin-scale CO₂ outgassing to 0.49 and 0.52 Pg C year⁻¹, respectively. A recent re-evaluation of basin-wide outgassing estimates upstream of Óbidos was done using a combination of direct flux measurements and more detailed k-values calculations along with observations by Alin et al. (2011) for tributaries and streams. It was estimated that basin scale CO₂ outgassing upstream from Óbidos was roughly 0.8 Pg C year⁻¹ (Rasera et al., 2013). First order streams add an additional 0.1 Pg C year⁻¹ to basin scale CO₂ fluxes in the Amazon basin (Johnson et al., 2008). Adding our estimates for the lower river to these values results in basin-wide budgets of 0.92 Pg C year⁻¹ and 0.95 Pg C year⁻¹ for Area 1 and the sum of Area 1 and 2, respectively (Table 4). Replacing these new estimates for the Amazon in the global CO₂ budget by Raymond et al. (2013) increases the global budget by as much as 18% for a total of 2.48 Pg C year⁻¹.”

Discussion section, the tenth paragraph:

“In the case of this updated global budget, the Amazon River represents 38% of global CO₂ emissions. However, the contribution of other tropical rivers to the global budget are likely also underestimated considering that most tropical rivers are even less well-characterized than the Amazon, particularly in the lower reaches, where we've demonstrated that emissions can be high relative to the rest of the basin. Furthermore, we have not included the entirety of the Amazon in our newest budgets. For example, the Tapajós and Xingu rivers were not included due to their large spatial expanse and minimal data coverage. The lower portion of these tributaries, alone (Figure 1), emit roughly 2.3 Tg C year⁻¹, and these estimates do not encompass their entire surface area nor potentially elevated CO₂ concentrations closer to their headwaters.”

Discussion section, the eleventh paragraph:

“Another factor that can lead to an underestimation of basin-wide budgets is not including Amazon River water that travels further offshore from Area 2 and along the coastline. For example, the Amazon River can remain unmixed with the ocean as far as 60 km offshore from Area 2 (Molinas et al., 2014). Abril et al. (2014) estimated that only 18% of the CO₂ from a point source would be degassed in a stretch of approximately 150 km downstream in the Amazon River taking into account a k-value of 15 cm h⁻¹ and water current of 150 cm s⁻¹. Thus, it is reasonable to assume that the mouth of the Amazon is the last point source of CO₂ to the Amazon plume, sustaining significant emissions for a significant distance offshore. This region, along with near-shore coastal waters, is not included in any studies of CO₂ cycling in the Amazon River plume in the Atlantic Ocean due to a lack of sampling and terrestrial contamination of remote sensing products by adjacency effect near-shore (Cooley et al., 2007; Subramaniam et al., 2008). We estimate that Area 3 may emit up to an additional 31 Tg C year⁻¹, but note that this is a simple calculation based on measurements at Macapá. Further exploration of this offshore area is essential for constraining the total basin-wide CO₂ flux. Although it is too early to confidently incorporate this offshore freshwater region (Area 3) into basin-wide budgets, this rough estimation highlights that expansive regions of offshore freshwater plumes may be an important missing gap in aquatic carbon budgets.”

Concluding Remarks section, the first paragraph, the third sentence:

“Here we show that the lower reaches of the Amazon River are an active area in terms of freshwater CO₂ emissions from the Amazon, and perhaps the world, although, lower river reaches have yet to be adequately studied in other comparable tropical systems.”

Concluding Remarks section, the second paragraph, the first and second sentences:

“The enormous surface area of the lower Amazon River (18,379 km²) is slightly less than half of the area of rivers and stream in the conterminous United States (Butman and Raymond, 2011), and similarly emits roughly half as much CO₂ to the atmosphere. This area alone releases an amount of CO₂ in the same order of magnitude than the uptake by the Amazon River plume in the Atlantic Ocean (Kortzinger, 2003; Cooley et al., 2007; Subramaniam et al., 2008).”

The authors apologize for these errors and state that they do not change the scientific conclusions of the article in any way. The original article has been updated.

References

Abril, G., Martinez, J. M., Artigas, L. F., Moreira-Turcq, P., Benedetti, M. F., Vidal, L., et al. (2014). Amazon River carbon dioxide outgassing fuelled by wetlands. Nature 505, 395–398. doi: 10.1038/nature12797

PubMed Abstract | CrossRef Full Text | Google Scholar

Alin, S. R., Rasera, M. F. F. L., Salimon, C. I., Richey, J. E., Holtgrieve, G. W., Krusche, A. V., et al. (2011). Physical controls on carbon dioxide transfer velocity and flux in low-gradient river systems and implications for regional carbon budgets. J. Geophys. Res. Biogeosci. 116:G01009. doi: 10.1029/2010jg001398

CrossRef Full Text | Google Scholar

Butman, D., and Raymond, P. A. (2011). Significant efflux of carbon dioxide from streams and rivers in the United States. Nat. Geosci. 4, 839–842. doi: 10.1038/ngeo1294

CrossRef Full Text | Google Scholar

Cooley, S. R., Coles, V. J., Subramaniam, A., and Yager, P. L. (2007). Seasonal variations in the Amazon plume-related atmospheric carbon sink. Glob. Biogeochem. Cycles 21:GB3014. doi: 10.1029/2006gb002831

CrossRef Full Text | Google Scholar

Johnson, M. S., Lehmann, J., Riha, S. J., Krusche, A. V., Richey, J. E., Ometto, J., et al. (2008). CO₂ efflux from Amazonian headwater streams represents a significant fate for deep soil respiration. Geophys. Res. Lett. 35:L17401. doi: 10.1029/2008gl034619

CrossRef Full Text | Google Scholar

Kortzinger, A. (2003). A significant CO₂ sink in the tropical Atlantic Ocean associated with the Amazon River plume. Geophys. Res. Lett. 30:2287. doi: 10.1029/2003gl018841

CrossRef Full Text | Google Scholar

Molinas, E., Vinzon, S. B., Vilela, C. D. X., and Gallo, M. N. (2014). Structure and position of the bottom salinity front in the Amazon Estuary. Ocean Dynamics 64, 1583–1599. doi: 10.1007/s10236-014-0763-0

CrossRef Full Text | Google Scholar

Rasera, M. F. F. L., Krusche, A. V., Richey, J. E., Ballester, M. V. R., and Victória, R. L. (2013). Spatial and temporal variability of pCO₂ and CO₂ efflux in seven Amazonian Rivers. Biogeochemistry 116, 241–259. doi: 10.1007/s10533-013-9854-0

CrossRef Full Text | Google Scholar

Raymond, P. A., Hartmann, J., Lauerwald, R., Sobek, S., McDonald, C., Hoover, M., et al. (2013). Global carbon dioxide emissions from inland waters. Nature 503, 355–359. doi: 10.1038/nature12760

PubMed Abstract | CrossRef Full Text | Google Scholar

Richey, J. E., Melack, J. M., Aufdenkampe, A. K., Ballester, V. M., and Hess, L. L. (2002). Outgassing from Amazonian rivers and wetlands as a large tropical source of atmospheric CO₂. Nature 416, 617–620. doi: 10.1038/416617a

PubMed Abstract | CrossRef Full Text | Google Scholar

Subramaniam, A., Yager, P. L., Carpenter, E. J., Mahaffey, C., Bjorkman, K., Cooley, S., et al. (2008). Amazon River enhances diazotrophy and carbon sequestration in the tropical North Atlantic Ocean. Proc. Natl. Acad. Sci. U.S.A. 105, 10460–10465. doi: 10.1073/pnas.0710279105

PubMed Abstract | CrossRef Full Text | Google Scholar