Litter and nutrient flows in tropical upland forest flooded by a hydropower plant in the Amazonian basin

Extensive areas in the Brazilian Amazon have been flooded for the construction of hydroelectric dams. However, the water regime of these areas affects the dynamics of igarapés (streams) in adjacent terra firme (upland forests). When the reservoirs are filled, the water levels of streams rise above the normal levels and upland bank forests are flooded. We investigated how this flooding affects the litterfall and nutrient input in the upland forests upstream of a hydroelectric dam reservoir in the Central Amazonia. When the reservoir was filled, the forests were flooded and produced more than twice the litter (8.80Mg·ha−1yr−1), with three times more leaves (6.36Mg·ha−1yr−1) than when they were not flooded (4.20 and 1.92Mg·ha−1yr−1, respectively). During flooding, the decomposition rate was four times lower in flooded forests (0.328g·g−1yr−1) than in control forests (1.460g·g−1yr−1). Despite this, the flooding did not favor litter or nutrient accumulation. Therefore, dam construction changes the organic matter and nutrient cycling in upland Amazon rainforests. This may influence the important role that they play in organic matter dynamics and could have consequences for the regional carbon balance and, ultimately, global climate. [Display omitted] •Flooding by dams increases litter production in upland forests during dry seasons.•Flooding retards litter decomposition, but does not favor litter accumulation.•Upland forests double nutrient inputs when flooded, but reduce leaf concentration.•This is a forest strategy to prevent biomass nutrient depletion during flooding.•These alterations may have consequences for regional and global carbon balance.