Spatial and temporal variability of biogeochemical cycles at the sediment-water in Terminos lagoon, Mexico

L’objectif de cette thèse concerne la quantification des flux benthos-pélagiques dans une lagune soumise à un régime climatique tropical rythmé de périodes humides et périodes sèches. La lagune de Terminos, située au sud du golfe du Mexique est le plus vaste écosystème laguno-estuarien du Mexique (2000 km2). Du fait de sa faible profondeur (3.5 m en moyenne), les processus benthiques sont sensés participer activement à l’ensemble du cycle biogéochimique de cet Ecosystème. Les mesures de flux benthiques ont eu lieu au cours de un réseau de 13 stations pendant une saison sèche (mars 2009 et 2010) et une saison humide (octobre 2009 et novembre 2010). Quatre stations ont fait l’objet de mesures plus fréquentes du 2008 au 2010. Des incubations ex-situ de carottes de sédiment prélevées ont permis de mesurer la variabilité spatio-temporelle des taux de respiration benthique (SOD) et des flux de sels nutritifs. Les SOD sont significativement différents entre les périodes sèches et humides (1327±161 et 2248±359 µmol m-2 h-1 respectivement). Les flux de silicates sont significativement plus importants pendant la saison des pluies (89.4±15.9 µmol m-2 h-1) que pendant la saison sèche (46.5±11.4 µmol m-2 h-1). Les flux de phosphates, faibles tout au long des périodes étudiées, n’ont pas montré de différence significative. Les flux d’azote dissous (DIN) sont de même intensité mais de sens opposé (2.9±18.8 µmol m-2 h-1 et 24.3±7.3 µmol m-2 h-1). Ces flux caractérisés par un fort signal saisonnier sont fortement corrélés avec les caractéristiques biogéochimiques des sédiments (Corg, N et chloropigments) et contribuent significativement au bilan du carbone et des éléments associés.The goal of this study concerns the quantification of sediment-water fluxes in a tropical lagoon under climatic forcing regulated by successive dry and wet periods. Terminos lagoon on the South coast of Gulf of Mexico (Campeche sound) is a shallow (3.5 m) but vast estuarine system (2000 km2) where the sediments are supposed to contribute largely to the overall biogeochemical cycling. Benthic flux measurements were performed twice over a network of 13 stations during dry (March 2009 and 2010) and wet periods (October 2009 and November 2010). A selection of 4 stations from this network were visited more frequently between 2008 and 2010. Sediment Oxygen Demand (SOD) and nutrient fluxes were measured through ex-situ incubations of sediment cores sampled manually. SOD were significantly different between both dry and wet seasons (1327±161 and 2248±359 µmol m-2 h-1 respectively). Silicates fluxes were significantly more intense during the wet season (89.4±15.9 µmol m-2 h-1) than during the dry one (46.5±11.4 µmol m-2 h-1). Phosphate fluxes, low during all periods did not show a temporal trend. Finally DIN fluxes showed a net uptake during the wet season (2.9±18.8 µmol m-2 h-1) and conversely an efflux during the dry season (24.3±7.3 µmol m-2 h-1). These fluxes depicted a pronounced seasonal signal, showed a significant correlation to sediment characteristics (Corg, N and chloropigments) and finally contributed to the overall carbon and nutrient budget of the lagoon

Global climate change and local watershed management as potential drivers of salinity variation in a tropical coastal lagoon (Laguna de Terminos, Mexico)

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Spatiotemporal variability in Terminos Lagoon (Mexico) waters during the 2009–2010 drought reveals upcoming trophic status shift in response to climate change

International audienceThe 2009-2010 El Niño was accompanied by a severe drought strongly impacting Mexico as well as Central America, the Caribbean, and the southern USA. The present work aims at assessing how such a major climatic event impacted the hydrological typology of transitional waters in Terminos Lagoon, one of the largest shallow tropical lagoons fringing the Gulf of Mexico. Spatiotemporal inter-comparison of hydrological conditions was conducted by pairing a reference multiparametric dataset (14 hydrological parameters versus 34 sampling stations) averaged over the October 2008 to July 2010 period with each sampling occurrence dataset and running Principal Component Analyses (PCA), setting the reference-survey dataset as active variables and each sampling occurrence dataset as non-active (supplementary) variables. It revealed that the exceptional deficit in freshwater supply to the lagoon during the 2009-2010 El Niño drastically reduced hydrological diversity and lowered the trophic status of the lagoon. Short-term shifts in environmental status are common in transitional waters and responsible for temporary shifts in community structure but climate change projections show a significant long-term decrease in the freshwater discharge at the regional scale that will impact Terminos Lagoon as well as other coastal lagoons of Mexico and Central America. When combined with sea level rise, such a decrease will result in a long-term shift in hydrological conditions with a subsequent increase in salinity and a decrease in the diversity of environmental conditions affecting trophic status, will have a long-term impact on the biota

Benthic ecology of tropical coastal lagoons: Environmental changes over the last decades in the Términos Lagoon, Mexico

International audience21 Terminos Lagoon is a 2000 km 2 wide coastal lagoon linked to the largest river catchment in Mesoamerica. Economic 22 development, together with its ecological importance, led the Mexican government to pronounce Terminos Lagoon and 23 its surrounding wetlands as a Federal protected area for flora and fauna in 1994. It is characterized by small temperature 24 fluctuations but with two distinct seasons (wet and dry) that control the biological, geochemical and physical processes 25 and components. This paper presents a review of available information on Terminos Lagoon. The review shows that 26 diversity of benthic communities is structured by the balance between marine and riverine inputs and that this 27 structuration strongly influences the benthic metabolism and its coupling with the biogeochemistry of the water column. 28 The paper also presents a number of specific drivers and recommendations for a long term environmental survey strategy 29 in the context of expected Global Change in the Centro America region. 30 3