Discrete water samples for nitrate (N-NO) analysis were collected at 0.5, 5, 10 and 15 meters in the Gulf of Trieste – time series station (station C1). The site is part of the LTER-North Adriatic site. Nitrite is measured colorimetrically after sample pre-filtration, using a segmented flow analyzer. Data are used to study biogeochemical nutrient cycles in the coastal Long Term Ecosystem Research station of the Gulf of Trieste, in the northernmost part of the Adriatic Sea and of the Mediterranean basin. Availability and partition of nitrogen in dissolved and particulate pools result from the concurrence of different forcing factors such as the general circulation, alternation between summer stratification and winter mixing, weather conditions, river discharge, diffuse and point-source continental inputs, sediment–water interactions and several biological processes. General information can be found at: http://nettuno.ogs.trieste.it/ilter/BIO/index.html"