In this study, we used moderate resolution imaging spectroradiometer (MODIS) satellite images to quantify the sedimentation processes in a cascade of six hydropower dams along a 700-km transect in the Paranapanema River in Brazil. Turbidity field measurement acquired over 10 years were used to calibrate a turbidity retrieval algorithm based on MODIS surface reflectance products. An independent field dataset was used to validate the remote sensing estimates showing fine accuracy (RMSE of 9.5 NTU, r = 0.75, N = 138). By processing 13 years of MODIS images since 2000, we showed that satellite data can provide robust turbidity monitoring over the entire transect and can identify extreme sediment discharge events occurring on daily to annual scales. We retrieved the decrease in the water turbidity as a function of distance within each reservoir that is related to sedimentation processes. The remote sensing-retrieved turbidity decrease within the reservoirs ranged from 2 to 62% making possible to infer the reservoir type and operation (storage versus run-of-river reservoirs). The reduction in turbidity assessed from space presented a good relationship with conventional sediment trapping efficiency calculations, demonstrating the potential use of this technology for monitoring the intensity of sedimentation processes within reservoirs and at large scale.

In the Amazon floodplains, hydrological variability plays a crucial role by shaping the habitat, offering shelter and feeding or breeding areas. During the dry season, some fresh water turtles such as the yellow-spotted turtle (Podocnemis unifilis Troschel, 1848) use the sand banks at point bar areas as breeding sites, which must be available in time for the start of oviposition. In this study, we used altimetry-derived water level data from radar satellites combined with in-situ hydrological measurements to evaluate water level variations and relate them to oviposition starting dates (2003-2012) from Pacaya-Samiria National Reserve, Peru. Synchronous hydrological behavior was found between the major river stems (Ucayali and Marañon) and the inner rivers (Pacaya and Samiria), thus enabling the utilization of water level in the main river stem to correlate with oviposition in the inner rivers. Mean oviposition date was July 23^nd with selection of a narrow water level range (92 masl ± 0.9 SD). Consistent shifts towards early/late oviposition were found for years with early/late dry season onset. Extreme biological shifts in terms of oviposition date onset, were identified for specific years (2004, 2010 and 2011) mainly for the extreme dry year of 2010.