SMALL CHANGES IN SALINITY HAS MAJOR CONSEQUENCES FOR THE MICROBIOLOGY AND BIOGEOCHEMISTRY OF TEMPERATE FRESHWATERS

Freshwater salinization is widespread across the Unites States, resulting from a wide range of anthropogenic activities. The intensity of salinization can range from relatively small concentration increases to pulses of marine concentrations. The deleterious effects of the later on aquatic ecosystems and biota are relatively well understood; however, smaller increases in concentration and their effects on the primary ecosystem functions and the microbial populations that drive them have largely been ignored. Through watershed observations and a series of controlled lab experiments using temperate stream water, we have found that very small increases in salt concentrations and different ions can alter microbial community structure, the persistence and concentrations of fecal indicator bacteria, and lead to changes in ecosystem functions and greenhouse gas emissions. Furthermore, the effect size is moderated by the ionic composition, where different salt altered the trajectory of change. These results indicate that even mild freshwater salinization could alter ecosystem metabolism and the risk of microbial impairments.