A database of nutrients and dissolved oxygen for 2012-2022 was formed from long-term monitoring results of the hydrochemical indicators of the Yalta Port water area. The paper shows dynamics of nutrients for the studied water area and determines inorganic forms of nitrogen (nitrites, nitrates, ammonium) as priority pollutants in the port ecosystem. The self-purification capacity of the Yalta Port water ecosystem was assessed by calculating the specific assimilation capacity (AC_sp) in relation to nitrates, nitrites and ammonium using the balance method. The rates and times of removal of these inorganic nitrogen forms from the mentioned ecosystem were calculated. The paper analyses the obtained AC_sp values for the Yalta Port water ecosystem for two periods (2012-2017 and 2018-2022). The study shows that for nitrates, there is an increase in AC_sp from 31.49 to 36.07 μg/(L·day) for these periods, respectively. The same dependence was established for nitrites. For this nitrogen form, the change in AC_sp ranged from 0.08 to 0.1 μg/(L·day). As for ammonium, an inverse relationship was observed for these periods: a decrease in the AC_sp value from 8.67 to 7.56 μg/(L·day). The paper compares the obtained AC_sp values in relation to inorganic forms of nitrogen for the Yalta Port water ecosystem with similar values for the Sevastopol Bay ecosystem, which is under high anthropogenic load, affected by river runoff and has limited water exchange with the open sea. The more intensive hydrodynamic regime is suggested to account for the higher self-purification capacity in relation to inorganic forms of nitrogen in the Yalta Port ecosystem (as part of Yalta Bay) if compared with Sevastopol Bay.