SPREADING EUTROPHICATION AND CHANGING CO2 FLUXES IN THE TROPICAL COASTAL OCEAN: A FEW LESSONS FROM RIO DE JANEIRO

Authors

  • Gwenaël Abril Laboratoire de Biologie des Organismes et Ecosystèmes Aquatiques (Borea), Muséum National d’Histoire Naturelle, UMR 8067, CNRS, MNHN, IRD, SU, UCN, UA, Paris, France. Programa de Pós-Graduação em Biologia Marinha e Ambientes Costeiros, Universidade Federal Fluminense, Niterói, RJ, Brazil. Programa de Geoquímica, Universidade Federal Fluminense, Niterói, RJ, Brazil
  • Luiz C. Cotovicz Jr. Instituto de Ciências do Mar, Universidade Federal do Ceará, Fortaleza, Ceará, Brazil
  • Aguinaldo Nepomuceno Programa de Pós-Graduação em Biologia Marinha e Ambientes Costeiros, Universidade Federal Fluminense, Niterói, RJ, Brazil
  • Thais Erbas Programa de Pós-Graduação em Biologia Marinha e Ambientes Costeiros, Universidade Federal Fluminense, Niterói, RJ, Brazil
  • Suzan Costa Programa de Geoquímica, Universidade Federal Fluminense, Niterói, RJ, Brazil
  • Vinicius V. Ramos Programa de Pós-Graduação em Biologia Marinha e Ambientes Costeiros, Universidade Federal Fluminense, Niterói, RJ, Brazil
  • Gleyci Moser Faculdade de Oceanografia, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil
  • Alexandre Fernandes Faculdade de Oceanografia, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil
  • Eduardo Negri Faculdade de Oceanografia, Universidade do Estado do Rio de Janeiro, Rio de Janeiro, Brazil
  • Bastiaan A. Knoppers Programa de Geoquímica, Universidade Federal Fluminense, Niterói, RJ, Brazil
  • Nilva Brandini Programa de Geoquímica, Universidade Federal Fluminense, Niterói, RJ, Brazil
  • Wilson Machado Programa de Geoquímica, Universidade Federal Fluminense, Niterói, RJ, Brazil
  • Marcelo Bernardes Programa de Geoquímica, Universidade Federal Fluminense, Niterói, RJ, Brazil
  • Vincent Vantrepotte Laboratoire d’Océanologie et de Géosciences (LOG), Université de Lille, Université du Littoral Côte d’Opale, UMR 8187, Wimereux, France

DOI:

https://doi.org/10.32360/acmar.v55iEspecial.78518

Abstract

In Brazil and in many other tropical countries, large urban cities and populations are still growing on the coast and coverage in terms of sewage treatments is far from desirable. Cultural eutrophication is not solely a threat for the coastal ocean; it is now acting as one of its major biogeochemical and ecological driver. Along the littoral of the state of Rio de Janeiro, semi-enclosed marine bays and lagoons show clear spatial and temporal pattern of increasing concentrations of chlorophyll a (Chl a), organic carbon, and nutrients in their waters and sediments in urbanized regions. Acting as a buffer, the nearshore ecosystems have turned highly eutrophic and their autotrophic metabolism has been enhanced creating strong carbon dioxide (CO2) sinks. We compile here data of CO2
fluxes recently gathered in four coastal marine ecosystems in the state of Rio de Janeiro: the Guanabara Bay and the Araruama, Saquarema and Jacarepagua lagoons. We observed intense CO2 sources in restricted areas at the vicinity of sewage loads, where microbial degradation of organic matter predominates, and large CO2 sinks in confined and nearshore brackish, marine and hypersaline waters, where phytoplankton blooms occur. We also report a correlation
across the four ecosystems between the partial pressure of CO2 in waters and the Chl a concentration. Chl a satellite data all along the Brazilian coast suggest that the CO2 sink induced by eutrophication probably occurs in many coastal ecosystems including bays, lagoon and shelf waters, and could contribute to an additional blue carbon. Part of the additional organic carbon is stored in sediments, and part is exported offshore. However, this additional blue carbon has dramatic environment impacts as it would evolve toward the formation of marine dead zones, and could contribute to a production of methane (CH4) a more powerful greenhouse gas. We emphasize an urgent need for multidisciplinary research to promote simultaneously the storage of atmospheric carbon, and the preservation of biodiversity and socio-economic goods in the eutrophic tropical coastal ocean.

Keywords: tropical coastal ecosystems, cultural eutrophication, phytoplankton blooms, marine dead zones, blue carbon

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Published

2022-03-21