Methane and Nitrous Oxide Reshape the Air‐Water Greenhouse Gas Budget of a Tropical Estuarine Delta
Abstract
Estuaries are important sources and sinks of greenhouse gases (GHGs), yet assessments of their radiative balance often focus primarily on carbon dioxide (CO 2 ), with less attention given to methane (CH 4 ) and nitrous oxide (N 2 O). We combine measurements of CH 4 and N 2 O air‐water fluxes with concurrent CO 2 data in a tropical estuarine delta (Paraíba do Sul River, Brazil), based on three surveys under contrasting hydrological conditions. CH 4 concentrations were highest in freshwater‐dominated waters and mangrove creeks and decreased seaward, with greater values during high river discharge. Surface waters were supersaturated in CH 4 , indicating a permanent atmospheric source driven by freshwater inputs and organic matter degradation. In contrast, N 2 O exhibited weaker variability and alternated between source and sink, with concentrations linked to ammonium (NH 4 + ) and apparent oxygen utilization, suggesting nitrification as a dominant control. In CO 2 ‐equivalent terms, CH 4 emissions offset 30%–84% of the CO 2 sink during dry conditions and enhanced CO 2 emissions by 20%–44% during high discharge. N 2 O exerted a smaller but variable influence, either reinforcing or partially counterbalancing CO 2 fluxes. Together, CH 4 and N 2 O offset 10%–85% of the CO 2 sink in dry periods and added 18%–42% to CO 2 emissions during wet conditions. The relative influence of CH 4 and N 2 O was greatest where CO 2 fluxes were near equilibrium, particularly in the mixing and marine domains. Because many tropical deltas exhibit mixing‐driven CO 2 uptake of weak magnitude, CH 4 and N 2 O fluxes can reshape the radiative balance, underscoring the need for combined GHG assessments where CO 2 exchange is low or bidirectional.
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BibTeX
@article{cotovicz2026methane,
title = {{Methane and Nitrous Oxide Reshape the Air‐Water Greenhouse Gas Budget of a Tropical Estuarine Delta}},
author = {Luiz Cotovicz and Renato Ribeiro and Luciana Vidal and Marcelo Bernardes and Carlos de Rezende and Batiaan Knoppers and Gwenaël Abril},
journal = {Journal of Geophysical Research: Biogeosciences},
year = {2026},
month = jul,
doi = {10.1029/2026jg009956},
url = {https://hal.science/hal-05741237v1},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - JOUR
TI - Methane and Nitrous Oxide Reshape the Air‐Water Greenhouse Gas Budget of a Tropical Estuarine Delta
AU - Luiz Cotovicz
AU - Renato Ribeiro
AU - Luciana Vidal
AU - Marcelo Bernardes
AU - Carlos de Rezende
AU - Batiaan Knoppers
AU - Gwenaël Abril
PY - 2026
DA - 2026/07/14
JO - Journal of Geophysical Research: Biogeosciences
DO - 10.1029/2026jg009956
UR - https://hal.science/hal-05741237v1
AB - Estuaries are important sources and sinks of greenhouse gases (GHGs), yet assessments of their radiative balance often focus primarily on carbon dioxide (CO 2 ), with less attention given to methane (CH 4 ) and nitrous oxide (N 2 O). We combine measurements of CH 4 and N 2 O air‐water fluxes with concurrent CO 2 data in a tropical estuarine delta (Paraíba do Sul River, Brazil), based on three surveys under contrasting hydrological conditions. CH 4 concentrations were highest in freshwater‐dominated waters and mangrove creeks and decreased seaward, with greater values during high river discharge. Surface waters were supersaturated in CH 4 , indicating a permanent atmospheric source driven by freshwater inputs and organic matter degradation. In contrast, N 2 O exhibited weaker variability and alternated between source and sink, with concentrations linked to ammonium (NH 4 + ) and apparent oxygen utilization, suggesting nitrification as a dominant control. In CO 2 ‐equivalent terms, CH 4 emissions offset 30%–84% of the CO 2 sink during dry conditions and enhanced CO 2 emissions by 20%–44% during high discharge. N 2 O exerted a smaller but variable influence, either reinforcing or partially counterbalancing CO 2 fluxes. Together, CH 4 and N 2 O offset 10%–85% of the CO 2 sink in dry periods and added 18%–42% to CO 2 emissions during wet conditions. The relative influence of CH 4 and N 2 O was greatest where CO 2 fluxes were near equilibrium, particularly in the mixing and marine domains. Because many tropical deltas exhibit mixing‐driven CO 2 uptake of weak magnitude, CH 4 and N 2 O fluxes can reshape the radiative balance, underscoring the need for combined GHG assessments where CO 2 exchange is low or bidirectional.
SN - 2169-8953
ER -