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  • Amazon river  (2)
  • River  (2)
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  • 1
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    The pulse of the Amazon: fluxes of dissolved organic carbon, nutrients, and ions from the world's largest river (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-10-26
    Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 35(4), (2021): e2020GB006895, https://doi.org/10.1029/2020GB006895.
    Description: The Amazon River drains a diverse tropical landscape greater than 6 million km2, culminating in the world's largest export of freshwater and dissolved constituents to the ocean. Here, we present dissolved organic carbon (DOC), organic and inorganic nitrogen (DON, DIN), orthophosphate (PO43−), and major and trace ion concentrations and fluxes from the Amazon River using 26 samples collected over three annual hydrographs. Concentrations and fluxes were predominantly controlled by the annual wet season flood pulse. Average DOC, DON, DIN, and PO43− fluxes (±1 s.d.) were 25.5 (±1.0), 1.14 (±0.05), 0.82 (±0.03), and 0.063 (±0.003) Tg yr−1, respectively. Chromophoric dissolved organic matter absorption (at 350 nm) was strongly correlated with DOC concentrations, resulting in a flux of 74.8 × 106 m−2 yr−1. DOC and DON concentrations positively correlated with discharge while nitrate + nitrite concentrations negatively correlated, suggesting mobilization and dilution responses, respectively. Ammonium, PO43−, and silica concentrations displayed chemostatic responses to discharge. Major and trace ion concentrations displayed clockwise hysteresis (except for chloride, sodium, and rubidium) and exhibited either dilution or chemostatic responses. The sources of weathered cations also displayed seasonality, with the highest proportion of carbonate- and silicate-derived cations occurring during peak and baseflow, respectively. Finally, our seasonally resolved weathering model resulted in an average CO2 consumption yield of (3.55 ± 0.11) × 105 mol CO2 km−2 yr−1. These results represent an updated and temporally refined quantification of dissolved fluxes that highlight the strong seasonality of export from the world's largest river and set a robust baseline against which to gauge future change.
    Description: This work was supported by a grant from the Harbourton Foundation to R. G. M. Spencer and R. M. Holmes. T. W. Drake was supported by ETH Zurich core funding to J. Six. R. G. M. Spencer was additionally supported by NSF OCE-1333157.
    Description: 2021-09-15
    Keywords: Amazon river ; Dissolved organic carbon ; Fluxes ; Weathering ; Geochemistry
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Drivers of organic molecular signatures in the Amazon River (2021)
    American Geophysical Union
    Details
    Publication Date: 2022-05-27
    Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 35(6), (2021): e2021GB006938, https://doi.org/10.1029/2021GB006938.
    Description: As climate-driven El Niño Southern Oscillation (ENSO) events are projected to increase in frequency and severity, much attention has focused on impacts regarding ecosystem productivity and carbon balance in Amazonian rainforests, with comparatively little attention given to carbon dynamics in fluvial ecosystems. In this study, we compared the wet 2012 La Niña period to the following normal hydrologic period in the Amazon River. Elevated water flux during the La Niña period was accompanied by dilution of inorganic ion concentrations. Furthermore, the La Niña period exported 2.77 Tg C yr−1 more dissolved organic carbon (DOC) than the normal period, an increase greater than the annual amount of DOC exported by the Mississippi River. Using ultra-high-resolution mass spectrometry, we detected both intra- and interannual differences in dissolved organic matter (DOM) composition, revealing that DOM exported during the dry season and the normal period was more aliphatic, whereas compounds in the wet season and following the La Niña event were more aromatic, with ramifications for its environmental role. Furthermore, as this study has the highest temporal resolution DOM compositional data for the Amazon River to-date we showed that compounds were highly correlated to a 6-month lag in Pacific temperature and pressure anomalies, suggesting that ENSO events could impact DOM composition exported to the Atlantic Ocean. Therefore, as ENSO events increase in frequency and severity into the future it seems likely that there will be downstream consequences for the fate of Amazon Basin-derived DOM concurrent with lag periods as described here.
    Description: This work was partially supported by National Science Foundation grant OCE-1464396 to Robert G. M. Spencer and funding from the Harbourton Foundation to Robert G. M. Spencer, R. Max Holmes, and Bernhard Peucker-Ehrenbrink.
    Description: 2021-12-11
    Keywords: Amazon river ; carbon cycling ; dissolved organic carbon ; dissolved organic matter ; ENSO ; FT-ICR MS
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 3
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    Particulate organic carbon and nitrogen export from major Arctic rivers (2016)
    John Wiley & Sons
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    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 30 (2016): 629–643, doi:10.1002/2015GB005351.
    Description: Northern rivers connect a land area of approximately 20.5 million km2 to the Arctic Ocean and surrounding seas. These rivers account for ~10% of global river discharge and transport massive quantities of dissolved and particulate materials that reflect watershed sources and impact biogeochemical cycling in the ocean. In this paper, multiyear data sets from a coordinated sampling program are used to characterize particulate organic carbon (POC) and particulate nitrogen (PN) export from the six largest rivers within the pan-Arctic watershed (Yenisey, Lena, Ob', Mackenzie, Yukon, Kolyma). Together, these rivers export an average of 3055 × 109 g of POC and 368 × 109 g of PN each year. Scaled up to the pan-Arctic watershed as a whole, fluvial export estimates increase to 5767 × 109 g and 695 × 109 g of POC and PN per year, respectively. POC export is substantially lower than dissolved organic carbon export by these rivers, whereas PN export is roughly equal to dissolved nitrogen export. Seasonal patterns in concentrations and source/composition indicators (C:N, δ13C, Δ14C, δ15N) are broadly similar among rivers, but distinct regional differences are also evident. For example, average radiocarbon ages of POC range from ~2000 (Ob') to ~5500 (Mackenzie) years before present. Rapid changes within the Arctic system as a consequence of global warming make it challenging to establish a contemporary baseline of fluvial export, but the results presented in this paper capture variability and quantify average conditions for nearly a decade at the beginning of the 21st century.
    Description: National Science Foundation Grant Numbers: 0229302, 0732985; U.S. Geological Survey; Department of Indian and Northern Affairs
    Description: 2016-11-11
    Keywords: Arctic ; River ; Carbon ; Nitrogen ; Watershed ; Export
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 4
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    Isotopic evidence for sources of dissolved carbon and the role of organic matter respiration in the Fraser River basin, Canada (2022)
    Springer
    Details
    Publication Date: 2022-11-04
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Voss, B., Eglinton, T., Peucker-Ehrenbrink, B., Galy, V., Lang, S., McIntyre, C., Spencer, R., Bulygina, E., Wang, Z., & Guay, K. Isotopic evidence for sources of dissolved carbon and the role of organic matter respiration in the Fraser River basin, Canada. Biogeochemistry. (2022), https://doi.org/10.1007/s10533-022-00945-5.
    Description: Sources of dissolved and particulate carbon to the Fraser River system vary significantly in space and time. Tributaries in the northern interior of the basin consistently deliver higher concentrations of dissolved organic carbon (DOC) to the main stem than other tributaries. Based on samples collected near the Fraser River mouth throughout 2013, the radiocarbon age of DOC exported from the Fraser River does not change significantly across seasons despite a spike in DOC concentration during the freshet, suggesting modulation of heterogeneous upstream chemical and isotopic signals during transit through the river basin. Dissolved inorganic carbon (DIC) concentrations are highest in the Rocky Mountain headwater region where carbonate weathering is evident, but also in tributaries with high DOC concentrations, suggesting that DOC respiration may be responsible for a significant portion of DIC in this basin. Using an isotope and major ion mass balance approach to constrain the contributions of carbonate and silicate weathering and DOC respiration, we estimate that up to 33 ± 11% of DIC is derived from DOC respiration in some parts of the Fraser River basin. Overall, these results indicate close coupling between the cycling of DOC and DIC, and that carbon is actively processed and transformed during transport through the river network.
    Description: Open Access funding provided by the MIT Libraries. This work was supported by the WHOI Academic Programs Office, the MIT EAPS Department Student Assistance Fund, and the PAOC Houghton Fund to BMV; NSF-ETBC grants OCE-0851015 to BPE, VG, and TIE and OCE-0851101 to RGMS; NSF grant EAR-1226818 to BPE; NSF grant OCE-0928582 to TIE and VG; and a WHOI Arctic Research Initiative grant to ZAW.
    Keywords: River ; Carbon isotopes ; Radiocarbon ; Weathering ; Carbon cycle
    Repository Name: Woods Hole Open Access Server
    Type: Article
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