https://doi.org/10.1029/2019GB006222

Akbarzadeh, Z., Maavara, T., Slowinski, S., & Van Cappellen, P. (2019). Effects of damming on river nitrogen fluxes: a global analysis. Global Biogeochemical Cycles, 33(11), 1339-1357. https://doi.org/10.1029/2019GB006222

Damming creates biogeochemical hotspots along rivers that modify the riverine flow of nutrients, including nitrogen (N). Here, we quantify the impact of dams on global riverine N fluxes using a reservoir N mass balance model. In-reservoir processes represented in the model include primary production, mineralization of organic N, denitrification, and sedimentary burial. In addition, we explicitly account for N fixation as a source of N, assuming that the N to phosphorus (P) ratio of the inflow regulates the magnitude of N fixation in reservoirs. The model is scaled up via a Monte Carlo analysis that yields global relationships between N elimination in reservoirs, either by denitrification or burial, and the hydraulic residence time. These relationships are then combined with N loads to the world's dam reservoirs generated by the Global-NEWS model and the estimated N fixation fluxes. According to the results, in year 2000, worldwide N fixation in reservoirs was on the order of 70 Gmol yr−1, while denitrification and burial in reservoirs eliminated around 270 Gmol yr−1, equal to 7% of N loading to the global river network. The latter is predicted to double to 14% by 2030, mainly as a result of the current boom in dam building. The results further imply that, largely due to N fixation in reservoirs, damming causes a global upward shift in riverine N:P ratios, thus lessening N limitation in receiving water bodies.

https://doi.org/10.1029/2019GB006222