Spatial, temporal, and vertical variability of nutrients in the Southeastern Black Sea

In this study, the nutrient concentrations along the coastal region of the Southeastern Black Sea were evaluated based on temporal, spatial, and vertical distributions. The water samples were collected seasonally in 2013 from 432 depths covering 55 stations. The nutrient concentrations showed significant spatial and temporal variations that declined abruptly from shore to offshore. The stations near the river discharge had the highest silicate, nitrate, and total dissolved inorganic nitrogen (DIN). The highest nitrate concentrations were determined within the oxycline layer and nitrite within the suboxic layer, while phosphate, ammonium, silicate, and DIN were within the anoxic layer. The findings of this study evinced that the Southeastern Black Sea possessed lower contents of nitrate (mean ± s.d., 0.58 ± 1.17 μM), phosphate (0.12 ± 1.00 μM), than the literature values reported for the western Black Sea, but consistent to the eastern Black Sea. However, the silicate concentrations of the study area were consistent with the western Black Sea while higher than the eastern Black Sea. The Trophic Index showed that two stations located on the coast of the Samsun and Giresun were at increased risk of eutrophication due to intensive urban and industrial inputs. This study provides detailed insights on the nutrient status of the coastal Southeastern Black Sea, which should facilitate the development of long-term monitoring programs concerning environmental aspects of marine and coastal planning. [Display omitted] •The decrease in nutrient concentrations from the shore to the offshore were evident.•Nutrient's maxima were observed at shallow depths in the west of the study area.•The highest NO3 and SiO4 recorded in winter, NH4, PO4 during summer.•The maximum PO4, SiO4, NO3, TIN, and Chl-a were found in stations from Samsun.•The NO3 was more abundant in oxycline, PO4, NH4, SiO4, TIN in anoxic layers.