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A multi-approach and multi-scale study on water quantity and quality changes in the Tapajós River basin, Amazon
We analyzed changes in water quantity and quality at different spatial scales within the Tapajós River
basin (Amazon) based on experimental fieldwork, hydrological modelling, and statistical time-trend analysis.
At a small scale, we compared the river discharge (Q) and suspended-sediment concentrations (SSC) of two
adjacent micro-catchments ( < 1 km2) with similar characteristics but contrasting land uses (forest vs. pasture)
using empirical data from field measurements. At an intermediary scale, we simulated the hydrological responses
of a sub-basin of the Tapajós (Jamanxim River basin, 37 400 km2), using a hydrological model (SWAT) and
land-use change scenario in order to quantify the changes in the water balance components due to deforestation.
At the Tapajós’ River basin scale, we investigated trends in Q, sediments, hydrochemistry, and geochemistry
in the river using available data from the HYBAM Observation Service. The results in the micro-catchments
showed a higher runoff coefficient in the pasture (0.67) than in the forest catchment (0.28). At this scale, the SSC
were also significantly greater during stormflows in the pasture than in the forest catchment. At the Jamanxim
watershed scale, the hydrological modelling results showed a 2 % increase in Q and a 5 % reduction of baseflow
contribution to total Q after a conversion of 22 % of forest to pasture. In the Tapajós River, however, trend
analysis did not show any significant trend in discharge and sediment concentration. However, we found upward
trends in dissolved organic carbon and NO− 3 over the last 20 years. Although the magnitude of anthropogenic
impact has shown be scale-dependent, we were able to find changes in the Tapajós River basin in streamflow,
sediment concentration, and water quality across all studied scales