Long-term measurements of dissolved organic nitrogen (DON) in atmospheric deposition in the Eastern Mediterranean: Fluxes, origin and biogeochemical implications

Atmospheric deposition of dissolved organic nitrogen (DON) was estimated in the Eastern Mediterranean by collecting and analyzing wet and dry deposition samples during a four year period (2003–2006). In wet deposition the annual volume weighted mean concentration of DON was estimated to be 23 μM and the annual mean flux was estimated to be 4.8 mmol/m2. The average contribution of DON, NO3− and NH4+ to total dissolved nitrogen (TDN) was 22.7%, 45.7% and 31.6% respectively. On the other hand during the dry season the average annual flux of DON was estimated to be of 17.4 mmol/m2 and those of NO3− and NH4+ were 25.3 mmol/m2 and 2.4 mmol/m2 respectively. The average contribution of DON, NO3− and NH4+ to TDN in dry deposition was 38.6%, 56.1% and 5.3 % respectively.The contribution of anthropogenic emissions on DON levels was found to be of comparable importance with that of natural sources i.e. dust. Atmospheric deposition of DON was mainly governed by dry deposition as 78% of total DON is deposited through this pathway. Finally, 20–30% of the new production which could be stimulated by the atmospheric TDN deposition in the Eastern Mediterranean basin can be attributed to DON.