pCO2 seasonal and spatial variability in a large mangrove-dominated delta
Tropical estuarine systems are a key component in the transport of carbon to the open ocean and important sources of carbon dioxide (CO2) to the atmosphere.
However, many large tropical estuaries are still unaccounted for regarding their carbon dynamics and, particularly, their water-atmosphere CO2 fluxes. In this study, we aimed to understand the seasonal and spatial variability of aquatic partial pressure of CO2 (pCO2) and water-atmosphere CO2 fluxes in the Parnaíba River Delta, the largest coastal delta in the Americas.
This tropical delta is a pristine environment dominated by dense mangrove forests located on a climatic transitional coast, between humid and semi-arid climates, with marked seasonality in rainfall and river discharge. Continuous measurements of pCO2, temperature, salinity, and wind velocity were taken, while subsurface water samples were collected in discrete stations to analyze for pH, total alkalinity, dissolved inorganic carbon, dissolved oxygen, and chlorophyll-a.
Our results indicated significant seasonal and spatial variability of pCO2 in the delta. The seasonal variability was mostly related to the intensity of the river discharge, while the high spatial variability indicated that the pCO2 is likely controlled by a combination of river and ocean water mixing, and biological processes (respiration and photosynthesis), in both seasons. The delta was a source of CO2, with averaged fluxes higher during the rainy season.
Our results suggest that large tropical river deltas surrounded by extensive mangrove forests are important sources do CO2 to the atmosphere and that the seasonal variability of fluxes is important in the estimation of the annual contribution of CO2 by this type of system.
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