Carbon Burial in Young Tropical Reservoirs Is Higher at Lower Latitudes*

Man-made environments such as tropical hydroelectric reservoirs alter the preexisting carbon (C) cycle and remove C from circulation through burial in sediments. Carbon burial (CB) was measured using the silica-tracer method during four field surveys in the less than six-year-old Belo Monte tropical reservoir. Fresh C sedimentation was also measured. Belo Monte’s CB median rate 276 (n = 84;min 0;max 352,625 mg C·m-2·d-1) is within the range (230 to 436 mg C·m-2·d-1) of CB rates measured further downstream at the Xingu Ria and higher than the averaged over 50 years oceanic rate 244 mg C·m-2·d-1 estimated for an increasingly deoxygenated ocean. Carbon burial median rates of tropical reservoirs with similar age and trophic state correlate inversely with latitude at a rate of 17.5 mg C·m-2·d-1 per degree. Carbon burial efficiency of these reservoirs correlates positively with latitude at a ratio of 0.22% per degree.

An Empirical Model for Dinitrogen Gas Emission from Inland Waters

The motivation to calculate this empirical model resulted from often observing—at the time disconcerting—excess dinitrogen gas (N2 concentration > background concentration) in bubble-gas emission samples, collected primarily for the purpose of carbon budget research, from Brazilian rivers and reservoirs sampled during roughly 100 field surveys lasting 4 days each on average and executed between years 2000 and 2012. We model the (serendipitously) measured dinitrogen gas above environmental concentration (N2aec) escaping in bubbles from Brazilian rivers as a function of dissolved nitrogen (N) in water. To this model, we mathematically add a pre-existing model of diffusively emitted denitrified dinitrogen (also as a function of dissolved N) from streams in the United States of America (USA). The resulting model predicts denitrified dinitrogen water-air emission from inland waters in the USA, China and Germany.