The Black Sea nitrogen budget revision in accordance with recent atmospheric deposition study

To date, most of published nitrogen (N) budget assessments for marine ecos ystems (particularly, the Black Sea) are, unfortunately, rather general and incomprehensive due to regular atmospheric load underestimation and frequent neglecting of some relevant N cycling constituents (e.g., N 2 fixation rate, dumping, shipping, gaseous emission, chemo denitrification). In this study it has been argued that atmospheric input was systematically underestimated in most of previous assessments of, since organic N constituents were not included. It has been experimentally found that organic pa rt in atmospheric deposition was dominant (~66% or 1777 ± 678 kg N km-2) N pollutant constituent, while DIN was ~34% (907 ± 361 kg N km-2) only during 2011 2012 campaign. Besides, contributions of water soluble (24.3%) and particulate (28.3%) organic N were distributed approximately equally in atmospheric deposition. Overall, an important role of atmospheric N organic pollutants in deposition, which was neglected before, has been proved. As a results, an average annual atmospheric bulk deposition rate of total N (TN) has been calculated as 2684±316 kg N km-2 based on long -term experimental dataset, thus atmospheric TN load for the whole Black Sea area has been estimated as 1159 ± 136 Gg N. During this study N budget for the Black Sea has been revised and its cons tituents have been amended. According to presented estimation of N balance the Black Sea is under strong pressure of anthropogenic N load (approximately 798 -1692 Gg N y -1), mainly from atmosphere and the north -western rivers. Weak understudied points and u ncertainties, to which the Black Sea countries research community should pay attention and focus its efforts immediately, have been highlighted.

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