Long-term shifts in phytoplankton structure and functioning associated with water level fluctuations and salinity in Lake Kinneret

Human-induced changes in lake morphometry, particularly water level (WL) drawdown, together with increasing freshwater salinization, have stimulated interest in how these global threats affect aquatic ecosystems. The main objective of this study was to estimate the effects of two driving variables (DV): WL and salinity, expressed as total dissolved solids (TDS), on a set of state variables (StV) characterizing phytoplankton in Lake Kinneret. This lake represents a well-studied case of phytoplankton shifts associated with long-term WL fluctuations and increased TDS (from 630 to 930 mg L ^− 1 ₎ . The selected StV included structural variables (biomass of Cyanobacteria, Dinophyta, and total phytoplankton biomass) and functional variables (indices of taxonomic and functional diversity and an index of ecological stability). A long-term database was used to examine relationships between DV and StV over a 50-year period (1970–2019). Our results indicate that even small changes in salinity can produce significant shifts in the composition and dynamics of the phytoplankton community. The results of this study offer an approach to better understanding the mechanisms behind salinity effects on the algal community associated with a threefold increase in biomass of Cyanobacteria having relatively high halotolerance. This led to a gradual increase in taxonomic diversity relative to ecological stability and a steady rise in the biotic budget (Production/Destruction) of the community. These findings suggest that salinity regulation may be a controllable measure for managing freshwater resources. Overall, this study provides new insight into quantifying the effects of freshwater salinization on the structure and functioning of freshwater phytoplankton.