Seasonal variability of the spatial distribution of biogenic elements in the surface layer of the northwestern Black Sea

Based on the data of long-term (1970–2009) observations, the spatial distribution of seasonal concentrations of the main biogenic elements (phosphates, nitrates, ammonium nitrogen, silicic acid) were studied and the variability of their content in the surface layer of the northwestern part of the Black Sea (NWBS) was estimated. The seasonal concentrations of nutrients in the northern, western, southwestern and central regions, which differ in the degree of the influence of transformed river waters, were evaluated. It is shown that the seasonal variability of the content of nutrients in the indicated areas of the northwestern part of the Black Sea depends on the variability of the volume of river runoff and the spread of transformed river waters over the shelf, as well as on the regional hydrometeorological conditions and the intensity of the biotic cycle of nitrogen, phosphorus, and silicon. The detailed studies of the seasonal variability of the concentration of phosphates, nitrates and chlorophyll "a" and water salinity were carried out for the spring and summer seasons, which are the most provided with data on the alongshore and latitudinal (45°N) sections of the western region. The relationship between the seasonal values of the Danube runoff volume, water salinity, chlorophyll "a" concentration, phytoplankton biomass, and seasonal nutrient concentrations for the western region of the NWBS was assessed. The calculated multiple coefficients of correlation and determination showed that in the spring and summer periods the input of phosphates, nitrates and silicic acid with transformed river waters provided for about 20%, 36–50% and about 36% of their total dispersion, respectively. The assimilation of these biogenic elements by phytoplankton indicates that phosphates accounted for 10–23%, nitrates for 23–52% and silicic acid for 17–52% of their total dispersion, respectively. The obtained results indicate a relationship between the input of nutrients with transformed river waters and their output associated with the assimilation of nutrients by microplankton (phytoplankton and bacteria). Obviously, these fluxes could be regarded as the main components providing the annual balance of nutrients in the NWВS.

1. Berlinsky N., Bogatova Yu., Garkavaya G. Estuary of the Danube, The Handbook of Environmental Chemistry, vol. 5, Water Pollution Part H. Estuaries, Berlin, Springer, 2006, p. 233–264.

2. Black Sea Data base supplied with Ocean Base 3.07 DBMS. NATO SfP-971818 ODBMS Black Sea Project, 2003.

3. Bogatova Yu.I. Hydrochemical regime of the Ukrainian nearshore area, Water Resources, 2013, vol. 40, no. 3, p. 305–314.

4. Bol’shakov V.S. Transformaciya rechnyh vod v Chernom more [Transformation of river waters in the Black Sea], Kiev, Nauk. Dumka Publ., 1970, 328 p. (In Russian)

5. Cociasu A., Dorogan L., Humborg C., Popa L. Long term ecological changes of Romanian coastal waters of the Black Sea, Marine Pollution Bulletin, 1996, vol. 32, p. 32–38.

6. Erenberg A. Analiz i interpretaciya statisticheskih dannyh [Analysis and interpretation of statistical data], Moscow, Finansy i Statistika Publ., 1981, 406 p. (In Russian)

7. Friedel G., Dunkel Ch., Wehrli B. Benthic fluxes of nutrients in the northwestern Black Sea, Marine Chemistry, 1998, vol. 62, p. 77–88.

8. Garkavaya G.P., Bogatova Yu.I. [Hydrochemical survey]. Severo-zapadnaya chast’ Chernogo morya: biologiya i ekologiya [The northwestern Black Sea: biology and ecology], Kiev, Nauk. Dumka Publ., 2006, p. 60–83. (In Russian)

9. Gevorgiz N.S., Krivenko O.V., Kondrat’ev S.I. Obobshchenie dannyh mnogoletnih issledovanij soderzhaniya osnovnyh biogennyh elementov v severo-zapadnoj chasti Chernogo morya za period 1980–2002 gg. [Generalization of data from the long-term studies of the concentrations of main biogenic elements in the northwestern Black Sea during 1980– 2002], Ekologicheskaya bezopasnost’ pribrezhnoj i shel’fovoj zon i kompleksnoe ispol’zovanie resursov shel’fa, 2005, no. 12, p. 177–187. (In Russian)

10. Kondrat’ev S.I. Three typical hydrological-hydrochemical situations near the Danube River mouth based on the Marine Hydrophysical Institute research expeditions in 1997–2013, Physical Oceanography, 2019, vol. 26, no. 4, p. 326–340.

11. Kukushkin A.S. Seasonal changes of hydrobiological and bio-optical parameters in the coastal areas of the western part of the Black Sea, Diversity in Coastal Marine Sciences, vol. 23, C.W. Finkl, C. Makowski (eds.). Springer, 2018, p. 153–180.

12. Metody gidrochimicheskich issledovanij okeana [Methods of hydrochemical ocean studies], Moscow, Nauka Publ., 1978, 272 p. (In Russian)

13. Parkhomenko A.V., Kukushkin A.S. Evaluating mineral phosphorus fluxes in eutrophic waters of the northwestern Black Sea, Water resources, 2020, vol. 47, no. 1, p. 137–146.

14. Severo-zapadnaya chast’ Chernogo morya: biologiya i ekologiya [The northwestern Black Sea: biology and ecology], Kiev, Nauk. Dumka Publ., 2006, 701 p. (In Russian)