TROPECOS News

7th Mangrove Macrobenthos and Management Conference (MMM7)

IMPROVING THE FINE-SCALE CHARACTERIZATION OF THE STRUCTURAL DIVERSITY OF MANGROVE FORESTS IN FRENCH GUIANA TO REFINE CARBON MAPPING

By Quentin Marsal (1,3), Christophe Proisy (1,2), Thibault Catry (3,4), Elodie Blanchard (3), Maxime Dutour (1,2) and Jean-Luc Maeght (1)

1: IRD UMR AMAP, Montpellier, France

2: IRD UMR AMAP, Cayenne, French Guiana, France

3: IRD UMR ESPACE-DEV, Montpellier, France

4: KHEOBS Laboratory, Phnom Penh, Cambodia

DOM quantity and quality were investigated in semi-arid mangroves with no external organic matter input, developing along an intertidal gradient: a salt-flat, an Avicennia marina stand, and a Rhizophora stylosa stand. Soil and porewater samples were collected during both wet and dry seasons, and analysed for physicochemical parameters, total and dissolved organic carbon (TOC, DOC), chromophoric and fluorescent dissolved organic matter (CDOM, FDOM), and mineralogical composition.

• Dissolved organic carbon content is higher in deeper soil layers.
• The deep dissolved organic matter is older and more humified than at the surface.
• The vertical gradients studied are amplified during neap tides.
• Cr and Mn follow the dissolved organic carbon vertical gradient.
• Ni and Mo follow an opposite vertical gradient to dissolved organic carbon.

Estuaries exchange greenhouse gases with the atmosphere and can either potentially warm or cool the climate. Most studies focus on CO2, but other gases such as CH4 and N2O can also be important. In several tropical deltas, mixing between river water and sea water can lower CO2 levels, leading these systems to act as CO2 sinks even without biological uptake. Here, we measured air‐water CH4 and N2O fluxes in a tropical estuarine delta in Brazil and combined these data with CO2 flux measurements collected at the same time and locations.

In June 2026, TROPECOS scientists from BOREA, iEES, UFF, MPEG and UFPA have sampled sediments cores, litters and litter bags in two Amazonian mangroves, Marapanim a preserved site and Salinopolis a site impacted by urbanization and sewage loads. In addition, forest inventories were performed in Marapanim.  

The third TROPECOS field work in mangroves of Marapanim Pará (19 Sep. 2025 – 3 Oct. 2025, involved 7 research scientists and students from BOREA, MPEG, UFF and UFPA. We measured gas fluxes in mangrove soils and waters, dissolved carbon concentrations and tidal exchanges, isotopic composition of dissolved inorganic carbon and methane, and litter fall. A world record of tidal variation of pCO2 in a mangrove tidal creek was obtained during equinox spring tides, with values lower than 900 ppmv at high tide and higher than 9 000 ppmv at low tide.