Influence of Atmospheric Precipitation and Surface Runoff on Phytoplankton Characteristics in the Northern Part of the Black Sea

Abstract

The joint dynamics of the Black Sea phytoplankton parameters (primary production, specific growth rate, biomass) and the amount of precipitation over the period from 1998 to 2015 was studied in coastal areas and the open coast of the northern part of the Black Sea. The analysis used satellite data (SG) (GPCPMON) GPCP Version 3.2, TRMM TMPA (3B42RT), as well as SeaWiFS from 1998 to 2010, MODIS-Aqua from 2002 to 2015 and MODIS-Terra from 2000 to 2015. Phytoplankton indicators were calculated according to 46 КОВАЛЕВА, СУСЛИН LOMONOSOV GEOGRAPHY JOURNAL. 2023. VOL. 78. NO. 4 the models developed earlier by the authors. The average monthly values of all considered values were evaluated, as well as bi-weekly and daily values for atmospheric precipitation. As a result of the study, it was revealed that the role of atmospheric precipitation for the variability of phytoplankton characteristics is not significant in vast water areas over long time intervals, and it could be neglected. In some cases in the presence of large rivers and coastal runoff it increases up to 30% in the offshore areas. There was also a more noticeable effect of atmospheric precipitation on the biological productivity of phytoplankton in small, limited water areas over short time intervals. According to our data during the 18-year period there was a more noticeable correlation between the specific growth rate and precipitation in winter than in other seasons for the open coast of the Black Sea. The correlation of biomass and primary production with atmospheric precipitation is less pronounced. The specific growth rate correlated more than other studied phytoplankton indicators with the amount of precipitation. In three districts, an increase in the amount of precipitation relative to the previous level with monthly averages above 0,6 mm/day led to an increase in the specific growth rate, or maintained it at the same level. The increase in the specific growth rate was not the same everywhere and was not proportional to the amount of atmospheric precipitation. This indicates the influence of many factors on phytoplankton characteristics; however, precipitation could have an additional stimulating role.