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Abstract

Large-scale hydrotechnical works were carried out in the estuary of the Pregolya River in 2014-2018. The structural changes in the summer zooplankton in the river mouth in 2019 were revealed in comparison with the data before the transformation of the riverbed. The total abundance and biomass of zooplankton was 136±111 thous. ind.·m-3, 860± 840 mg·m-3 in June 2019, this is comparable with average annual data 1996-2006: 71±66 thous. ind.·m-3 and 664±337 mg·m-3. In the summer of 2019, the euryhaline species Еurythemora affinis, inhabiting the Vistula Lagoon, was first recorded in the Novaya Pregolya branch, where it was not previously present according to 1996-2014 data. The presence of this species in the branches of the river, as well as indicators of water salinity, may be a consequence of an increase in the frequency or intensity of water surges into the river from the Vistula Lagoon. In this regard, the wind conditions in the periods of 1998-2006 and 2011-2019 have been analyzed. Increase in the frequency of winds acting along the effective surge direction (south-west, west) in 2011-2019 was not found. However, an increase in the frequency of storms was noted, including summer. Westerly storm winds cause inflow of water with zooplankton from the lagoon and channel upstream of the river. Probably, the reduction of plant communities and concreting of embankments, a change in the configuration of the channel bottom, favorably influenced the passage of waters from the lagoon in the river branches during surges and became the main factor influencing the spread of euryhaline species from the lagoon in the river branches.

Authors

Ju. Polunina

senior researcher, PhD

https://orcid.org/0000-0002-8157-9522

https://elibrary.ru/author_items.asp?id=910405

Zh. Stont

senior researcher, PhD

https://orcid.org/0000-0002-1315-6018

https://www.elibrary.ru/author_items.asp?authorid=724557