Using CDOM optical properties for estimating DOC concentrations and pCO₂ in the Lower Amazon River

Journal Article · Mon Jan 01 04:00:00 EST 2018 · Optics Express

DOI:https://doi.org/10.1364/OE.26.00A657· OSTI ID:1455302

Valerio, Aline de Matos; Kampel, Milton; Vantrepotte, Vincent; Ward, Nicholas D.; Sawakuchi, Henrique Oliveira; Less, Diani Fernanda Da Silva; Neu, Vania; Cunha, Alan; Richey, Jeffrey

Colored dissolved organic matter (CDOM) is largely responsible for the optical properties of freshwaters and coastal areas and can be used as a proxy to assess the non-optical carbon content as the dissolved organic carbon (DOC) and the partial pressure of carbon dioxide (pCO₂). Nevertheless, riverine studies that explores the former relationship are more challenging due to the spectral mixture caused by the high content of inorganic materials in the suspended sediment. Here we evaluate the spatial-temporal variability of CDOM, DOC and pCO₂, as well as the potential of CDOM absorption coefficient (aCDOM(412)) for estimating DOC concentration and pCO₂ along the lower Amazon River. Our results revealed differences in the dissolved organic matter (DOM) quality between clear water (CW) tributaries and the Amazon River mainstem. A linear relationship between DOC and CDOM was observed when tributaries and mainstem are evaluated separately (Amazon waters: N=42, R2=0.74; CW: N= 13, R2 = 0.57). However, this linear relationship was not observed during periods of higher rainfall and river discharge, requiring a model specific to these time periods to be developed (N = 25, R2 = 0.58). A strong linear positive relation was found between aCDOM(412) and pCO₂( N=69, R2=0.65) along the lower river. pCO₂ was less affected by the optical difference between tributaries and mainstem water or by the presence of higher hygrometric conditions when compared to CDOM to DOC relationships. Including the river water temperature in the model improves our ability to estimate pCO₂ (N=69; R2 = 0.80). Our results also illustrate the complexity of DOM temporal dynamics in the lower Amazon River where the occurrence of extreme high and low discharge due to factors such as El Niño, can significantly alter the expected seasonal oscillation, as was the case during this study period. The ability to remotely assess both DOC and pCO₂ from CDOM optical properties highlight the importance of using remote sensing data for monitoring carbon dynamics in large running water systems worldwide.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1455302
• Report Number(s): PNNL-SA-131638
• Journal Information: Optics Express, Journal Name: Optics Express Journal Issue: 14 Vol. 26; ISSN 1094-4087; ISSN OPEXFF
• Publisher: Optical Society of America (OSA)
• Country of Publication: United States
• Language: English

Related Subjects

Amazon
CDOM
aquatic
biogeochemistry
carbon cycling
carbon dioxide
chlorophyll
chromophoric
climate change
coastal
continuum
dissolved organic carbon
ecosystem
emissions
exchange
flux
greenhouse gas
interface
optical
organic matter
outgassing
remote sensing
river
satellite
terrestial aquatic interface
tidal
tidal river