Researchers at MIT examine how saltwater intrusion—driven by sea-level rise—may change microbial ecosystems in rivers, estuaries, and other coastal waters. As ocean salinity increases and sea levels rise, seawater seeps into freshwater systems, raising salt concentrations beyond historical ranges. The study indicates that this added salinity can stress microbial communities. Specifically, the researchers find that overall microbial growth may remain relatively strong even under these saltier conditions, while community diversity declines. In other words, the microbial ecosystem can shift toward a narrower set of salt-tolerant species rather than collapsing entirely. The findings connect climate-driven physical changes, such as saltwater encroachment into inland and nearshore habitats, to biological outcomes at the microbial level. The work therefore highlights that future salinity changes may not only alter how much microbial biomass is produced, but also how varied the microbial community remains across affected freshwater and transitional ecosystems.