# Before and After: A Multiscale Remote Sensing Assessment of the Sinop Dam, Mato Grosso, Brazil
## 4 Discussion  
The Amazon Basin, roughly two-thirds of which is in Brazil, is the focus of a massive surge in hydroelectric dam construction, with plans that would eventually convert almost all Amazon tributaries into chains of reservoirs [49]. Greenhouse gas emissions from the lentic zones of hydropower dams have been intensively studied, with a focus on the high CH\({}_{4}\) emissions [42, 89, 90, 91]. Due to the increased global warming effect of CH\({}_{4}\) in the atmosphere, the proclaimed \"green\" energy generation from hydroelectricity has further been questioned [92]. For the HPPS, the estimate of yearly CH\({}_{4}\) emission from TROPOMI data (48-54 kt/yr) is within the range of reservoir emissions measured in eutrophic systems [90]. As more observations become available, the seasonal variability should be considered for a more accurate yearly estimate. For comparison, the CH\({}_{4}\) emission from biomass burning in the legal Amazon (1992-1993) ranged from \(<\)100 kt/yr (Amazonas, Roraima) to 1300 kt/yr (Mato Grosso) [93]. The greatest contributing factor to the amount of CH\({}_{4}\) emission from a reservoir is the amount of flooded vegetation that was not cleared prior to inundation, rather than reservoir age or location [90]. In the case of the HPPS lentic zone, flooded forest was the largest land cover class within the reservoir boundaries accounting for 75-78% (high and low water seasons, respectively). Canopy height data from GLAS indicated that the forest in the lentic zone was of reasonably tall stature (up to 30 m) (Figure 10) and biomass estimates indicated a combined AGB and BGB of 113.3 \(\pm\) 38.1 Mg/ha (Figure 11). [PERSON] et al. [43] estimate the 20- and 100-year C intensities of HPPS as 1052.6 and 358.3 kg CO\({}_{2}\) eq MMh\({}^{-1}\), respectively. The C intensity is the CO\({}_{2}\)-equivalent emissions produced per unit electricity generated [43]. The estimate for HPPS is considerably higher than the 20- and 100-year C intensities of the Belo Monte dam complex on the Xingu River, one of the largest run-of-the-river dams in the world [94] (62.2 and 37.9 kg CO\({}_{2}\) eq MMh\({}^{-1}\)) [43], but less than those of Balbina dam on the Uatuma River (12,004.5 and 3901.3 kg CO\({}_{2}\) eq MMh\({}^{-1}\)[43]. Under different global warming scenarios, [95] estimate that HPPS's 100 year C intensity could exceed 2000 kg CO\({}_{2}\) eq MMh\({}^{-1}\). For comparison, the C intensity of bituminous coal thermal plants is 792 kg CO\({}_{2}\) eq MMh\({}^{-1}\) and 348 kg CO\({}_{2}\) eq MMh\({}^{-1}\) for combined cycle gas thermal plants [92]. One hundred years after inundation, HPPS is estimated to approximate the C intensity of a natural gas thermal plant. While other studies have used pre-existing land cover datasets (e.g., [96]), to infer the impact of hydroelectric reservoirs on the landscape, there is substantial variability in the amount of forest and non-forest classes in both national and global datasets [5]. Hence, relying on such global datasets to assess the impact of hydroelectric reservoirs may not be adequate. In our study we generated a high spatial resolution classification of the land cover within the HPPS lentic zone leading to more precise estimates of inundated classes. This is of particular importance for the Riparian vegetation along the small creek tributaries of the Teles Pires. As shown by [41], fishes from small streams with Riparian forest depend on the aquatic-terrestrial linkage for survival. The assemblages of stream fish (taxonomic composition and trophic structure) in the small tributaries of the Teles Pires river vary according to the structural characteristics of the water bodies, including the depth, width, and speed of the current [97]. Changes that occur due to reservoir flooding can alter the assemblages of fish in these environments as species from the reservoir replace the stream fishes, now displaced to the very headwaters of the streams outside the lentic zone. Hydroelectric projects have major impacts on fish communities [38].