Daily and other short-term changes in the ecosystem components of the world's largest hypersaline lagoon Bay Sivash (Crimea)

Abstract

The interrelationship between various processes and components in the daily cycle of water bodies has been little studied, especially in hypersaline water bodies. A three-day study was conducted in the world's largest hypersaline lagoon Bay Sivash (the Sea of Azov). 16 biotic and abiotic parameters were measured 21–80 times in the studied site (wind direction and speed, photosynthetically active radiation (PAR), temperature, oxygen content, pH, Eh, turbidity, chlorophyll a fluorescence, zooplankton abundance, and others). There was a clear daily rhythm of PAR in the surface layer of the water, however, the stochastic weather factor (cloudiness, wind speed and direction) influenced the quantitative expression of it. The proportion of PAR entering deeper layers as shown, depends on the height of the Sun, as well as intra-ecosystem factors, for example turbidity and the development of mats of filamentous algae. Fluctuating from 1.69 to 98.03 NTU, turbidity depended on the speed and direction of the wind with windward winds leading to the resuspension of bottom sediments to a greater extent than leeward ones. Wind speed and direction also significantly influenced the distribution of biotic components such as the filamentous green alga Cladophora and zooplankton. Oxygen content fluctuated from between 1.8 and 16.58 mg L−1. An increase in oxygen concentration was observed only at PAR above approximately 500–1000 μE m−2;s−1. The increase in temperature and the virtual absence of wind, which was observed on 05/28/2022 and 05/29/2022, contributed to an increase in the oxygen concentration in the water on these days and the formation of hyperoxic conditions in this hypersaline lagoon.