Dynamics of the Estuarine Turbidity Maximum Zone from Landsat-8 Data: The Case of the Maroni River Estuary, French Guiana

Noelia Abascal-Zorrilla,Vincent Vantrepotte,Dat Dinh Ngoc,Antoine Gardel,Edward J Anthony,Nicolas Huybrechts

doi:10.3390/rs12132173

Abstract

The estuarine turbidity maximum (ETM) zone occurs in river estuaries due to the effects of tidal dynamics, density-driven residual circulation and deposition/erosion of fine sediments. Even though tropical river estuaries contribute proportionally more to the sediment supply of coastal areas, the ETM in them has been hardly studied. In this study, surface suspended particulate matter (SPM) determined from OLI (Operational Land Imager)-Landsat 8images was used to gain a better understanding of the spatio-temporal dynamics of the ETM of the tropical Maroni estuary (located on the Guianas coast, South America). A method to estimate the remotely-sensed ETM location and its spatiotemporal evolution between 2013 and 2019 was developed. Each ETM was defined from an envelope of normalized SPM values > 0.6 calculated from images of the estuary. The results show the influence of the well-marked seasonal river discharge and of tides, especially during the dry season. The ETM is located in the middle estuary during low river-flow conditions, whereas it shifts towards the mouth during high river flow. Neap–spring tidal cycles result in a push of the ETM closer to the mouth under spring-tide conditions or even outside the mouth during the rainy season. An increase in SPM, especially since 2017, coincident with an extension of the ETM, is shown to reflect the periodic influence of mud banks originating from the mouth of the Amazon and migrating along the coast towards the Orinoco (Venezuela). These results demonstrate the advantages of ocean color data in an exploratory study of the spatio-temporal dynamics of the ETM of a tropical estuary, such as that of the Maroni.

Highlights

The trapping of suspended particles in river estuaries can often lead to the formation of highly turbid concentrations, sometimes culminating in the generation of an estuarine turbidity maximum (ETM)
Other points of discussion are the influence of river discharge on the ETM and of the presence of the mud bank in the study area since 2011 [36]
Understanding the spatial and temporal variability of the ETM is of primary importance in tropical estuaries where studies focusing on the sediment dynamics are rare, whereas development needs, including estuarine navigation, port development and monitoring of river-to-coast pollution, are rising with population increase

Summary

Introduction

The trapping of suspended particles in river estuaries can often lead to the formation of highly turbid concentrations, sometimes culminating in the generation of an estuarine turbidity maximum (ETM). Tropical rivers, located in areas of the world with high chemical weathering rates, between 30◦N and 30◦S, have been considered as contributing proportionally more fine-grained sediment to their estuaries than mid-latitude rivers [5]. Such tropical estuaries are commonly bordered by mangroves that trap sediments [6,7,8,9] and affect flushing rates [10,11], contributing to the dynamics of the ETM. Studies dealing with the ETM in tropical estuaries are relatively scarce when compared to those devoted to the study of estuarine hydrodynamics [12,13,14,15,16]

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Results

Conclusion