Research and applications of ocean colour radiometry in the very turbid waters of the Río de la Plata river (Argentina)

DOGLIOTTI, A.I.

Encuentro; International Ocean Color Science Meeting 2017; 2017

Retrievinginformation from ocean colour radiometry in very turbid waters is highlychallenging. In particular the Río de la Plata (RdP) river, the widest river inthe world located in the eastern coast of South America at approximately 35 °S,carries high amounts of suspended particulate which are mainly provided by the Bermejo River, considered amongst the mostturbid rivers in the world. Very high concentrations of suspended particulatematter (SPM) have been reported ranging from 100 to 300 g m-3 and extremeconcentrations of around 1,000 g m-3. Interest in retrieving waterconstituents using remote sensing is mainly motivated by the environmental andeconomic importance of this estuary, specially for the countries on its shores,Argentina and Uruguay.One of the firstwork performed using remote sensing data in the turbid waters of RdP was a qualitativelyevaluation of atmospheric correction algorithm. However, at that time a direct validationof satellite-derived estimates could not be performed due to lack of in situreflectance measurements. After experiences gained in different renowninstitutions and in collaboration with the Argentine National Space Agency andthe University of Buenos Aires, fieldcampaigns have been performed and the first bio-optical data has been collectedin this region allowing a first evaluation of atmospheric correctionalgorithms. Since then, strong efforts have been put in collecting fieldmeasurements and in acquiring new instruments to improve our knowledge of this complexand interesting system. Given the high amount of suspended particulate matterthat the RdP exports to the adjacent shelf waters, directly affectingphytoplankton productivity, nutrient dynamics and transport of pollutants, thefocus has been put in retrieving SPM and in particular turbidity, an opticalproperty more related to reflectance than SPM. A general algorithm to retrieve turbidity from ocean color datahas been proposed and used to analyze 15 years of MODIS-derived turbidity maps.The seasonal and inter-annual variability of turbidity and its relation withOceanic Nino Index (ONI) and the water discharge of RdP tributaries were assessed.Given the highamount of sediments the availability of light is significantly reduced being notthe ideal condition for phytoplankton to grow, however intense blooms have beendetected in the estuary, like Microcystis sp. blooms in November 2012 in Buenos Aires and in February 2015 in Montevideo coasts. However, retrievingchlorophyll concentration in very turbid waters is highly challenging.More recently, atthe beginning of 2016, the city of Buenos Aires suffered a large invasion of floating aquatic Hyacinths(Eichhornia crassipes) whichcould be observed by different ocean colour sensors and for which a floatingvegetation index adapted for turbid waters has been developed and applied todetect and quantify them. This presentation draws mainlyon experiences gathered throughout the early and present stage of my research inthese extreme and optically complex waters which have been possible thanks tothe support of different institutions and successful collaborations withresearchers from different parts of the world.