Climate change is causing increased fluctuations in water levels in many lakes, altering littoral habitats and affecting local biota. A dramatic example of such impacts occurred in Lake Kinneret, Israel, where a 5-year drought (2013-2018) led to an unprecedented water level decline. Dense forests of Tamarix jordanis, of exceptionally high tree density and spatial coverage, developed in the exposed shores. In 2019-2020, high rainfall and rapid refilling of the lake inundated these forests, creating a novel littoral environment that had never existed before.
We studied the temporal dynamics of Tamarix trees and the associated littoral habitat under continued inundation. We hypothesized that the physicochemical conditions and biota (phytoplankton, zooplankton) in the Tamarix-dominated habitat would differ significantly from unvegetated littoral habitats. We also examined how this habitat influenced cichlid fish that reproduce in the littoral zone. To address these issues, we applied remote sensing, a field study and ecosystem modelling. Using Sentinel-2 imagery, we mapped the spatial distribution of live, inundated vegetation and its decline over time under continuous flooding. We sampled monthly for chemical and biological determinations (2019-2021) along transects through two inundated forest sites and one control site without vegetation. We modelled the biomass and catch of cichlid fish under several Tamarix habitat scenarios.
Soon after inundation, the limnological conditions among the trees differed dramatically from those at the control site. The Tamarix habitats were characterized by minimal water circulation, low light intensity, hypoxia, low pH, and high concentrations of nutrients and particulate organic matter. The phytoplankton and zooplankton assemblages were unique, with species never previously recorded in over 50 years of Kinneret monitoring. Hypoxia prevented cichlid fish from utilizing this habitat. Over time, the Tamarix canopy withered, and the extreme habitat conditions dissipated. Differences in physicochemical conditions and biota between the inundated and control sites gradually diminished over time, with rates of change being influenced by tree density and wind exposure. Tamarix survived three years of continuous flooding, but died in the fourth year. Modeling results indicated that the impact on the fish population and commercial catch was minimal.
Understanding the dynamics of novel habitats emerging due to climate change is crucial for effective ecosystem management and conservation. Lake Kinneret serves as a valuable case study for addressing similar challenges in freshwater systems worldwide.