Artificial flooding changes soil chemistry and carbon dynamics in upland forests next to hydropower plant in Amazon basin

Upland forest cover in the Amazon basin has been reduced by land use changes, e.g., the establishment of hydropower plants. Such plants cause permanent flooding and may produce periodic flooding in adjacent upland forests. We determined the short- and long-term effects of artificial flooding on the soil chemistry of upland forests adjacent to the Balbina Hydroelectric Reservoir, Amazonas State, Brazil. We randomized 20 sampling units in upland forests located on the banks of streams adjacent to the hydropower plant. Each sampling unit consisted of two paired forests: one artificial “flooded forest” near the stream and an unflooded “control forest.” We performed soil chemical analyses to determine the pH and total organic C, N, Al3+, and nutrient levels (P, Ca, Mg, and K). In the short term, flooding caused soil acidification, C loss, and increased soil nutrient availability, but this effect did not occur in the long term. In the long term, soil acidity decreased, C loss occurred, and available N cumulatively decreased because of annual flooding after the impoundment of the reservoir. These cumulative N losses, associated with high C emissions, may alter the regional climate and contribute to global climate change.