As sea levels rise and saltwater seeps into freshwater, stressed aquatic populations may retain overall growth even as diversity declines, MIT scientists find. As sea levels rise and saltwater seeps into freshwater, stressed aquatic populations may retain overall growth even as diversity declines, MIT scientists find. As sea levels rise due to climate change, encroaching sea water will likely make freshwater environments saltier. In a new study, MIT researchers have shown how that increase in salinity might affect microbial ecosystems found in environments such as rivers and estuaries. The MIT team found that when salt levels rise, these populations lose diversity as faster-growing strains tend to take over the community, but they maintain their overall growth rate.