Comparison of Assimilative Capacity and Trophic Index for Various Parts of the Sevastopol Bay Water Area

Abstract

The ecological state of the marine shallow water ecosystem (the case of the Sevastopol Bay) is analyzed by the ratio of assimilative capacity and E-TRIX index depending on the anthropogenic load level for the whole bay ecosystem. As part of analysis, the eastern, central, western parts of the bay were distinguished as well as the Yuzhnaya Bay (southern part). Calculations of the assimilative capacity and E-TRIX index for ecosystems of different parts of the Sevastopol Bay were performed using the in situ data of inorganic nitrogen for the period 1998–2012 obtained from the MHI RAS oceanographic data bank. The paper compares values of ecosystem assimilative capacity calculated for inorganic nitrogen as a prevailing pollutant in municipal and storm wastewaters and E-TRIX trophic index of the sea ecosystem, with the technogenic load and biological process seasonality (warm and cold periods) of nutrient income taken into account. This allowed to properly distinguish water areas, which are most vulnerable in terms of formation of negative ecological events, up to disasters. According to the obtained data, such an area is that of the Yuzhnaya Bay. The second vulnerable water area is the eastern apex part of the Sevastopol bay exposed to the Chernaya River discharge. As the results showed, the situation worsens during winter and spring freshets due to increase in content of inorganic nitrogen forms in the Chernaya River runoff. The ecosystem of the western bay part adjoining the open sea is the safest in terms of nitrate nitrogen assimilative capacity, whereas the central part ecosystem appears to be the cleanest in terms of E-TRIX. The ecosystem most exposed to ecological risks in terms of both indices (assimilative capacity and E-TRIX) is that of the Yuzhnaya Bay (the southern part of the Sevastopol Bay). The observed imbalance of distribution of the calculated trophic index E-TRIX and assimilative capacity in different parts of the Sevastopol Bay is due to various nature of these quantities. The assimilative capacity of an ecosystem is defined by physical, chemical and biological processes given a dynamic removal of pollutants from the ecosystem, whereas E-TRIX is determined, in general, by seasonal variability of nutrient income into the ecosystem.

Intra-Decadal (2012–2021) Dynamics of Spatial Ichthyoplankton Distribution in Sevastopol Bay (Black Sea) Affected by Hydrometeorological Factors

“…We have identified four areas according to the distribution of the amount of ichthyoplankton: western (Ravelin), southern (Southern Bay), central (Avlita and Pavlovsky Cape) and eastern (Sukharnaya and Inkerman). According to the level of pollution of Sevastopol Bay, four areas were also distinguished [ 13 , 16 , 20 ]. It is known that the pollution of the water thickness of the southern part of Sevastopol Bay depends both on the intensity of the intake of pollutants and on the wind regime [ 16 ].…”

“…According to the level of pollution of Sevastopol Bay, four areas were also distinguished [ 13 , 16 , 20 ]. It is known that the pollution of the water thickness of the southern part of Sevastopol Bay depends both on the intensity of the intake of pollutants and on the wind regime [ 16 ]. The significance of the wind regime for the southern region is confirmed by the work on modeling the pollution spread in the Sevastopol Bay [ 21 ].…”

“…Numerical experiments on the contaminant spread from a possible release site in the central part (Gollandiya Bay, near Avlita) showed that the dependence of the direction/trajectory of the pollution spot on the type of water circulation was most evident in the Southern Bay, and to a lesser extent in the central part of Sevastopol Bay. Polluted water masses are retained in the southern part of the Bay with a predominance of northern winds; they are carried out with southern winds to the western part of Sevastopol Bay, affecting its ecological state [ 16 ]. This is consistent with the results of this work, since with the dominance of northern winds at one of the most polluted stations, the northern part of the Southern Bay, a fairly large average number of ichthyoplankton in 2012–2021 was recorded.…”

“…At the same time, significant data on the hydrodynamic and hydrochemical regimes of the bay have been collected [ 10 , 11 , 12 , 13 , 14 , 15 ]. Some previous works investigated the causes of pollution and their spatial distribution over the water area of the Sevastopol Bay [ 13 , 16 ]. The coastline of the Sevastopol Bay is characterized by significant indentation, due to the presence of bays and capes ( Figure 1 ), that affects the ichthyoplankton spatial distribution.…”