The Effects of Ocean Tides on Suspended Surface Sediments in the Amazon River Using In-Situ Sampling and Satellite Imaging

Abstract

The Amazon tidal river consists of the lowermost 800 km of the Amazon River that is affected by tides. The effect of tides on surface suspended sediment concentration (SSC) in the Amazon has not yet been characterized, and may impact estimates of surface SSC as monitored through remote sensing. To assess potential tidal influence on surface SSC, water samples were collected and filtered in-situ and compared to published remote sensing maps. This comparison identified discrepancies between in-situ and remotely sensed estimates of surface SSC and constrained the influence of tides on the observed signals. Ocean tides have little effect on surface SSC throughout the Amazon tidal river, as reflected in in-situ average SSCs temporally and spatially. Surface SSC varies considerably over the course of the year, with the highest values coincident with rising water, and the lowest values associated with low-water conditions. Remotely-sensed estimates of surface SSC most closely match in-situ surface SSCs at sites located directly in the Amazon mainstem, while tributaries showed exaggerated differences in surface SSC. Since tides have minimal effects on surface SSC, it is reasonable to apply remote sensing for surface reflectance and SSC in the tidal Amazon’s mainstem route. With a better understanding of the effects of seasons and tides on surface SSC and how well remote sensing captures such variability, we can better monitor sediment discharge into the tropical Atlantic Ocean and improve sediment monitoring in the Amazon basin for future studies to come.