A satellite view of riverine turbidity plumes on the NE-E Brazilian coastal zone

Turbidity plumes of São Francisco, Caravelas, Doce, and Paraiba do Sul river systems, located along the NE/E Brazilian coast, are analyzed for their dispersal patterns of Total Suspended Solids (TSS) concentration using Landsat images and a logarithmic algorithm proposed by Tassan (1987) to convert satellite reflectance values to TSS. The TSS results obtained were compared to in situ collected TSS data. The analysis of the satellite image data set revealed that each river system exhibits a distinct turbidity plume dispersal pattern. The behavior, dimension and degree of turbidity of the São Francisco River plume have been greatly altered by the construction of a cascade of hydroelectric dam reservoirs in its hydrological basin. The plume has lost its typical unimodal seasonal pattern of material dispersion and its turbidity has decreased due to the regulation of river flow by the dams and TSS retainance by the reservoirs. In contrast, the Doce and Paraíba do Sul river plumes are still subject to seasonal pulsations and show more turbid conditions than the SF plume, as dams are less numerous, set in the middle river sections and the natural river flow has been maintained. The Caravelas Coastal System river plume is restricted to near shore shallow waters dominated by resuspension processes. During austral spring and summer when NE-E winds prevail, all plumes generally disperse southward. Short-term northward reversals may occur in winter with the passage of atmospheric cold fronts. The São Francisco and Doce river plumes tend to disperse obliquely to the coast and transport materials further offshore, while the Caravelas and Paraíba do Sul plumes tend to disperse mainly parallel to the coast, enhancing TSS retention nearshore.<br>O presente estudo analisa as plumas de turbidez dos sistemas dos rios São Francisco, Caravelas, Doce, e Paraiba do Sul localizados na costa NE/E do Brasil utilizando imagens Landsat e o algoritmo logarítmico para Total de Sólidos em Suspensão (TSS) proposto por Tassan (1987). Os resultados obtidos foram comparados com Total de Sólidos em Suspensão medidos in situ. A pluma de turbidez de cada sistema mostra padrões de dispersão distintos. O comportamento, a dimensão e o grau de turbidez da pluma do Rio São Francisco têm sido drasticamente alterados devido à cascata de barragens e seus reservatórios presentes em sua bacia de drenagem. Já as plumas dos rios Doce e Paraíba do Sul apresentam pulsações sazonais e maior turbidez, uma vez que as barragens nesses rios localizam-se no setor médio e mantiveram a pulsação sazonal da vazão. A pluma do sistema costeiro de caravelas permanece restrita às águas rasas dominadas por processos de ressuspensão. Durante a primavera e verão, quando os ventos de NE-E prevalecem, as plumas dos quatro sistemas se dispersam na direção sul. Durante o inverno, inversões do padrão de dispersão podem ocorrer com a passagem de frentes frias. As plumas dos sistemas São Francisco e Doce tendem a se dispersar obliquamente à costa, favorecendo o transporte de material para regiões oceânicas, enquanto que as plumas dos sistemas Caravelas e Paraíba do Sul se dispersam paralelamente à costa, favorecendo a retenção de TSS