Microbial marker for seawater intrusion in a costal Mediterranean shallow lake, Lake Vrana, Croatia

Climate change-induced pressures and increased water demand impose anadditional threat to the sustainability of coastal freshwater systems.The changes in precipitation patterns and quantity, rising seawaterlevel, and air temperature contributed to the irregularity of theavailable freshwater resources and even induced salinization of thepreviously freshwater systems. Lake Vrana is the largest surfacefreshwater resource in mid-Dalmatia, while the local springs are heavilyused in agriculture. The karstified carbonate ridge that separates thelake from the Adriatic Sea enables seawater intrusion if the lake'sprecipitation-evaporation balance is disturbed. The impact ofanthropogenic activities and drought exuberated salinization onmicrobial communities in Lake Vrana was tracked using 16S rRNA genesequencing. By monitoring changes in physio-chemical parameters andmicrobial communities, we studied the ecosystem response to salinizationand its recovery. The study aimed to determine how the spatio-temporalchanges in water ion content act as a selective force on microbialcommunity structure. Water column samples were sequentially filtered toseparate particle-associated and free-living microbes and determine thepotential differential salinity impact on microbial communities. Therelative abundance of halotolerant opportunistic taxa increased assalinization progressed. This study represents a valuable contributionto understanding the impact of the Freshwater Salinization Syndrome onthe Mediterranean lake microbial communities and the ecosystemresilience. Sequencing was performed at the Joint Microbiome Facility of the Medical University of Vienna and the University of Vienna under the project ID JMF-2112-11.