Characterization of Brazilian coastal waters biogeochemical quality evolution over the last two decades from satellite observation: impact of natural and anthropogenic forcings

Abstract

Coastal/shelf ecosystems represent areas of high ecological, societal and economical importance. The 8000 km long coast of Brazil hosts a mosaic of contrasted ecosystems (large estuaries, bays, lagoons, coastal and shelf waters) and habitats (mangroves, coral reefs, salt marches, seagrass) showing extremely heterogeneous dynamics. These ecosystems are diversely vulnerable to environmental changes of natural and anthropogenic origin acting on both continental and oceanic geosystems. Besides their vulnerability to climate induced variations of land/sea interaction and ocean dynamics, these ecosystems are also submitted to a variety of direct human pressures (urbanization, deforestation, intensive agriculture, dam installation) which significantly alter their biogeochemical quality. Monitoring the Brazilian marine waters thus represents a pressing need, being a crucial prerequisite for supporting the recent national initiatives related to the development of sustainable, ecosystem-based environmental policies. Besides the necessity to hold observations able to depict coastal/shelf waters spatio-temporal dynamics, an efficient scientific support to a sustainable management of marine environments rely on our capacity to deliver a clear diagnostic of the preservation or alteration of these ecosystems as well as an unequivocal identification of the natural or human related processes responsible for the observed changes. This represents one of biggest societal and scientific challenges of the next decades. The lack of long lasting and spatially representative observations over Brazil represents a strong limitation for achieving the latter objective. In that respect, ocean color remote sensing, which now allows the description of a variety of key biogeochemical descriptors, represents an alternative powerful and cost-effective tool for monitoring Brazilian waters. However, the full exploitation of the potential offered by this tool requires the use of adapted methods for interpreting the ocean color signal and extracting relevant information from the generated data sets. The COCOBRAZ project, which brings together French (LOG) and Brazilian (INPE, USP) partners holding complementary expertise (ocean color remote sensing, statistics, physical and biological oceanography) and existing collaboration, has been built in this context and aims at providing an overall diagnostic on the evolution over almost the last three decades of the biogeochemical quality of the Brazilian coastal and shelf waters. This will be based on the exploitation of an unprecedent ocean color data set generated in continuous from 1997 using the most adapted up-to-date methods for mapping the distribution of key water quality descriptors (phytoplankton biomass, dissolved-particulate matter, organic carbon stocks) over the whole Brazilian marine domain at a 1 km spatial resolution. This innovative optimization of ocean color satellite observation will be supported by an extensive in situ data set. The generated ocean color archives, together with data translating evolution of land/ocean environmental conditions, will be statistically analyzed using advanced methods in order 1) to identify changes in water quality in response to environmental variation at different timescales (interannual trends, evolution of the seasonality, episodic events) and 2) to demonstrate, for the first time, the potential of exploiting the 28yr long-lasting ocean color time series to identify and hierarchize the relative importance of natural and anthropogenic pressures responsible for the observed changes. A third objective will be to promote and facilitate the use of OCR observations for non-specialist researchers, students and young scientists. This will be performed through the dissemination of the results of the project towards Brazilian institutions, research networks, as well as long (PhD), medium (Masters) and short (summer school, workshops) terms advanced students training. (AU)