Purpose. The work is aimed at assessing the temporal and spatial scales of variations in the physical and biological parameters of the seawater surface layer in the immediate vicinity of the urban rainwater drainage outlets in the Sevastopol Bay.

Methods and Results. The study area was limited to the Sevastopol Bay. Measurements were taken at the locations of the rainwater drainage outlets, namely in the Artilleriyskaya, Apollonova and Gollandiya bays. Temperature and salinity were measured by an unmanned surface vehicle (USV) using the TMA-21 sensor. The stations were located in a straight line normal to the coast from the rainwater drainage outlet. Quantitative and size composition of total suspended matter and bacterioplankton particles were determined using the Cytomics TM FC 500 flow cytometer. Water temperature was shown to vary within 1.5 °C and its horizontal gradient was weakly pronounced. In the salinity field, the gradient reached 0.5 m⁻¹. The maximum concentrations of suspended matter were revealed in the apical part of the Artilleriyskaya Bay (about 0.5 × 10⁶ particles mL⁻¹). The particle sizes of suspended matter ranged from 0.5 to 2.5 μm. Bacterial concentrations in the storm water corresponded to the summer maximums observed in the Sevastopol Bay (0.9 × 10⁶–2.8 × 10⁶ ppm). The storm water inflow into the bay resulted in changes of the picophytoplankton number (by 2–6 times).

Conclusions. The method of applying an unmanned surface vehicle for operative local monitoring of seawater state in the areas of the rainwater drainage outlets has been tested. The data on the salinity changes can serve as an indicator of the discharge intensity and can be used for forecasting the impact of storm water runoffs during reconstruction/relocation of the sewer network. The concentrations of suspended solids and microorganisms in the bay surface waters are restored one day after a heavy rain. Therefore, rapid assessment of the impact of potentially dangerous or accidental discharges requires application of the unmanned surface vehicles for conducting the operational measurements.

Sevastopol Bay, storm water runoff, unmanned surface vehicle, seston, bacterioplankton, temperature, salinity.

Expeditionary research, data accumulation, and data quality assessment were supported by the RFBR and Sevastopol Government grant No. 20-45-920019. Additional data processing, its visualization, and analysis were performed within the framework of the state assignment of FRC MHI on theme No. 555-2021-0005. Processing of the flow cytometer data and analysis of the results were done with a support of the state assignment of FRC ISS No. 121030300149-0. The authors are grateful to V. S. Mukhanov and E. O. Sakhon for their assistance in cytometry process.

Original Russian Text © A. V. Bagaev, V. V. Nikishin, T. V. Rauen, L. V. Verzhevskaya, S. V. Scherbachenko, 2022,
published in MORSKOY GIDROFIZICHESKIY ZHURNAL, Vol. 38, Iss. 2, pp. 165-184 (2022)

Bagaev, A.V., Nikishin, V.V., Rauen, T.V., Verzhevskaya, L.V. and Scherbachenko, S.V., 2022. Local Changes of Physical and Biological Parameters of the Sevastopol Bay Surface Waters under the Influence of Rain Drainage. Physical Oceanography, 29(2), pp. 152-171. doi:10.22449/1573-160X-2022-2-152-171

10.22449/1573-160X-2022-2-152-171

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