Evolution of erosive and hydrodynamic impacts on water quality in tidal channels at the mouths of the Araguari and Amazon rivers

Abstract

An intense erosive process has recently caused progressive hydrogeomorphological changes in the mouths of two large rivers belonging to the Amazon River Delta, on the estuarine coast of Amapá State, namely: Araguari and Amazonas. Consequently, Araguari River was captured by the Amazon River and it influenced the sediment and water quality dynamics when two tidal channels expanded in opposite directions; this process affected both hydrographic basins and blocked Araguari River mouth. The aim of the current study is to analyze the space-seasonal variations of hydrodynamic and water quality parameters influenced by the following factors: location (channels connected to Araguari and Amazonas rivers), seasonality (dry/rainy) and spring tidal phase (flood/ebb). The herein adopted methodological stages comprised a) flow measurement with Doppler current profiler; b) water sampling (physicochemical and suspended sediments); c) suspended solids transport estimates; and d) multivariate statistical analysis of parameters. Results have indicated significant space-seasonal variation in these parameters (p<0.05). Water balance in the dry period has shown that Urucurituba Channel absorbs 100% of Araguari River flow, distributes 29% of it in the floodplain and discharges 71% of Araguari River flow into the Amazon River. This channel received 86% of Araguari River flow and absorbed 14% of the flow deriving from the floodplain in the rainy season, which totaled 100% of its flow at Amazon River mouth-solid discharge was proportional to 107,982 t of tidal cycle-1. Multivariate analyses have shown significant variations in 90% of the investigated parameters, which were influenced by such as location, seasonality and tidal phase (p<0.05). It was possible concluding that the recent channels have significantly affected the hydrodynamics, sediment transport processes and water quality of both basins. This phenomenon is currently in intense and irreversible hydrogeomorphological evolution, and it mainly affects the Araguari River estuary Evolution of erosive and hydrodynamic impacts on water quality in tidal channels at the mouths of the Araguari and Amazon rivers