Integração de dados de campo e sensoriamento remoto no estudo do fluxo de água e matéria no Arquipélago de Anavilhanas, Rio Negro - Amazonas, Brasil

Abstract

Rio Negro is the sixth largest river in the world in water volume and the largest black water ecosystem in the Amazon basin. Its lower course is a unique and important region with hundreds of islands, lakes and channels, and include the second largest fluvial archipelago in the world, called Anavilhanas. This whole region is a global biodiversity hotspot, it supports the livelihood of hundreds of local communities and is a destination for ecotourists. Despite its importance, little is known about the water properties of this region and how human activities, such as the construction of dams, impact its properties and functioning of this ecosystem. The Rio Negro basin has the lowest density of hydrological monitoring stations among other large Amazon rivers. On the other hand, advances in remote sensing technology can fill gaps in hydrological and water quality data. Here I explore how we can use remote sensing data and methods to better understand the dynamic between water, matter and the use of natural resources in this region. Specifically, I aimed at understanding the spatial and temporal variability of water flows, suspended sediments concentration (SSC) and dissolved organic carbon (DOC) in the lower Rio Negro, especially in the channels of the Anavilhanas archipelago, through data integration hydrological and remote sensing data (field radiometry, Terra/Aqua, Sentinel-1, Sentinel-2 and Sentinel-3 satellites). The results indicate that in the 2016-2017 hydrological year the average SSC in Rio Negro was 3.06 mg L-1 and the average DOC concentration was 9.60 mg L-1. Suspended sediment flow between 1 and 9 million tons per year and flow of dissolved organic carbon in the order of 11 million tons per year were estimated for the Rio Negro basin. The flow of dissolved organic carbon was directly related to the Rio Negro liquid discharge, with higher and lower values occurring in the periods of high and low waters, respectively. The peak of discharge of suspended sediment near Manaus occurred in September, with a lag of two months in relation to that observed upstream of the Anavilhanas archipelago. It was identified retention of 60% of suspended sediment from the Rio Negro reaching the archipelago. Due to the high amount of DOC and low SSC load, Rio Negro has very low values of reflected energy (Rrs <0.018 sr-1 in the visible) and great light absorption (≈ 8.00 m-1 at 440 nm). The variability of the reflected energy throughout the hydrological year was controlled by the inflow of suspended sediment from the Rio Branco, (the major tributary of the Rio Negro basin) that changed the optical properties of the Rio Negro in Anavilhanas. Evaluations of multispectral satellites to estimate SSC in Anavilhanas showed better results with the red band (650–690 nm). Empirical models show that the green/red band ratio can be used as an indicator of the dissolved organic carbon of the Rio Negro. The hydrogeomorphological scenario characterized suggests a slow and continuous process of retention of the suspended solid load in Anavilhanas, with a sedimentation rate approximately eight times lower than those estimated during the archipelago's formation period. I conclude that the Anavilhanas fluvial system acts as a water reservoir and suspended sediment sink in the lower course of the Rio Negro, mainly the period of greatest influence of the Rio Solimões backwater effect. This study presents data on the lower course region of Rio Negro that can be used in future scientific studies and decision-making, for example to asses extreme weather events in the region or the impact the construction of Bem Querer hydroelectric power plant in the Rio Branco.