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Title: Evaluation of Primary Production in the Lower Amazon River Based on a Dissolved Oxygen Stable Isotopic Mass Balance

Abstract

The Amazon River outgasses nearly an equivalent amount of CO 2 as the rainforest sequesters on an annual basis due to microbial decomposition of terrigenous and aquatic organic matter. Most research performed in the Amazon has been focused on unraveling the mechanisms driving CO 2 production since the recognition of a persistent state of CO 2 supersaturation. However, although the river system is clearly net heterotrophic, the interplay between primary production and respiration is an essential aspect to understanding the overall metabolism of the ecosystem and potential transfer of energy up trophic levels. For example, an efficient ecosystem is capable of both decomposing high amounts of organic matter at lower trophic levels, driving CO 2 emissions, and accumulating energy/biomass in higher trophic levels, stimulating fisheries production. Early studies found minimal evidence for primary production in the Amazon River mainstem and it has since been assumed that photosynthesis is strongly limited by low light penetration attributed to the high sediment load. Here, we test this assumption by measuring the stable isotopic composition of O 218O-O 2) and O 2 saturation levels in the lower Amazon River from Óbidos to the river mouth and its major tributaries, the Xingu andmore » Tapajós rivers, during high and low water periods. An oxygen mass balance model was developed to estimate the input of photosynthetic oxygen in the discrete reach from Óbidos to Almeirim, midway to the river mouth. Based on the oxygen mass balance we estimate that primary production occurred at a rate of 0.39 ± 0.24 g O m 3 d -1 at high water and 1.02 ± 0.55 g O m 3 d -1 at low water. This translates to 41 ± 24% of the rate of O 2 drawdown via respiration during high water and 67 ± 33% during low water. These primary production rates are 2-7 times higher than past estimates for the Amazon River mainstem. In conclusion, it is possible that at high water much of this productivity signal is the result of legacy advection from floodplains, whereas limited floodplain connectivity during low water implies that most of this signal is the result of in situ primary production in the Amazon River mainstem.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1342287
Report Number(s):
PNNL-SA-123464
Journal ID: ISSN 2296-7745
DOE Contract Number:
AC05-76RL01830; DGE-1258485; 1256724; 08/58089-9
Resource Type:
Journal Article
Resource Relation:
Journal Name: Frontiers in Marine Science; Journal Volume: 4
Country of Publication:
United States
Language:
English
Subject:
Photosynthesis; Respiration; metabolism; Aquatic; River; Amazon; carbon; oxygen; mass balance; tropical rivers

Citation Formats

Gagne-Maynard, William C., Ward, Nicholas D., Keil, Richard G., Sawakuchi, Henrique O., Da Cunha, Alan C., Neu, Vania, Brito, Daimio C., Da Silva Less, Diani F., Diniz, Joel E. M., De Matos Valerio, Aline, Kampel, Milton, Krusche, Alex V., and Richey, Jeffrey E.. Evaluation of Primary Production in the Lower Amazon River Based on a Dissolved Oxygen Stable Isotopic Mass Balance. United States: N. p., 2017. Web. doi:10.3389/fmars.2017.00026.
Gagne-Maynard, William C., Ward, Nicholas D., Keil, Richard G., Sawakuchi, Henrique O., Da Cunha, Alan C., Neu, Vania, Brito, Daimio C., Da Silva Less, Diani F., Diniz, Joel E. M., De Matos Valerio, Aline, Kampel, Milton, Krusche, Alex V., & Richey, Jeffrey E.. Evaluation of Primary Production in the Lower Amazon River Based on a Dissolved Oxygen Stable Isotopic Mass Balance. United States. doi:10.3389/fmars.2017.00026.
Gagne-Maynard, William C., Ward, Nicholas D., Keil, Richard G., Sawakuchi, Henrique O., Da Cunha, Alan C., Neu, Vania, Brito, Daimio C., Da Silva Less, Diani F., Diniz, Joel E. M., De Matos Valerio, Aline, Kampel, Milton, Krusche, Alex V., and Richey, Jeffrey E.. Tue . "Evaluation of Primary Production in the Lower Amazon River Based on a Dissolved Oxygen Stable Isotopic Mass Balance". United States. doi:10.3389/fmars.2017.00026.
@article{osti_1342287,
title = {Evaluation of Primary Production in the Lower Amazon River Based on a Dissolved Oxygen Stable Isotopic Mass Balance},
author = {Gagne-Maynard, William C. and Ward, Nicholas D. and Keil, Richard G. and Sawakuchi, Henrique O. and Da Cunha, Alan C. and Neu, Vania and Brito, Daimio C. and Da Silva Less, Diani F. and Diniz, Joel E. M. and De Matos Valerio, Aline and Kampel, Milton and Krusche, Alex V. and Richey, Jeffrey E.},
abstractNote = {The Amazon River outgasses nearly an equivalent amount of CO2 as the rainforest sequesters on an annual basis due to microbial decomposition of terrigenous and aquatic organic matter. Most research performed in the Amazon has been focused on unraveling the mechanisms driving CO2 production since the recognition of a persistent state of CO2 supersaturation. However, although the river system is clearly net heterotrophic, the interplay between primary production and respiration is an essential aspect to understanding the overall metabolism of the ecosystem and potential transfer of energy up trophic levels. For example, an efficient ecosystem is capable of both decomposing high amounts of organic matter at lower trophic levels, driving CO2 emissions, and accumulating energy/biomass in higher trophic levels, stimulating fisheries production. Early studies found minimal evidence for primary production in the Amazon River mainstem and it has since been assumed that photosynthesis is strongly limited by low light penetration attributed to the high sediment load. Here, we test this assumption by measuring the stable isotopic composition of O2 (δ18O-O2) and O2 saturation levels in the lower Amazon River from Óbidos to the river mouth and its major tributaries, the Xingu and Tapajós rivers, during high and low water periods. An oxygen mass balance model was developed to estimate the input of photosynthetic oxygen in the discrete reach from Óbidos to Almeirim, midway to the river mouth. Based on the oxygen mass balance we estimate that primary production occurred at a rate of 0.39 ± 0.24 g O m3 d-1 at high water and 1.02 ± 0.55 g O m3 d-1 at low water. This translates to 41 ± 24% of the rate of O2 drawdown via respiration during high water and 67 ± 33% during low water. These primary production rates are 2-7 times higher than past estimates for the Amazon River mainstem. In conclusion, it is possible that at high water much of this productivity signal is the result of legacy advection from floodplains, whereas limited floodplain connectivity during low water implies that most of this signal is the result of in situ primary production in the Amazon River mainstem.},
doi = {10.3389/fmars.2017.00026},
journal = {Frontiers in Marine Science},
number = ,
volume = 4,
place = {United States},
year = {Tue Feb 07 00:00:00 EST 2017},
month = {Tue Feb 07 00:00:00 EST 2017}
}
  • Measurements of deltaD and some delta/sup 18/0 measurements were made on 36 rivers which drain the east coast of the United States. The data are consistent with the work of Friedman et al.(1964). The streamflow data of Bue (1970) were used to estimate the mean isotopic composition of runoff entering the Gulf of Maine, the Mid-Atlantic Bight, and the South Atlantic Bight. Assuming binary mixing between central Atlantic water and these fresh runoff waters, coastal water in the Gulf of Maine is isotopically indistinguishable from runoff into the Mid-Atlantic Bight and runoff from the St. Lawrence at salinities greater thanmore » 32%/sub 0/. However, up to salinities of 34%/sub 0/ the mean isotopic composition of runoff into the South Atlantic Bight is sufficiently different from the Mid-Atlantic Bight that the identification of coastal water masses in and around Cape Hatteras by deltaD and/or delta/sup 18/0 versus salinity plots should be possible.« less
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