Carbon (C) is a fundamental element of life and a key driver of metabolism in stream ecosystems. Much of the C processing in streams occurs through microbial activity within the sediments, where C is either assimilated into microbial biomass or respired as CO2. The proportion of C that is incorporated into microbial biomass, rather than respired, is known as carbon use efficiency (CUE). Higher microbial CUE could enhance the C sink capacity of stream ecosystems, potentially mitigating rising atmospheric CO2 levels. In this study, we investigate the effects of freshwater salinity on microbial CUE in stream sediments. As salinity has been increasing in many freshwater systems across the U.S. over recent decades, understanding its impact on microbial processes is critical. We collected stream sediments from the Logan River in Cache County, UT, for laboratory incubations at salinities varying from ambient to +100 uS. After 24 hours, we processed the sediments and microbes to estimate microbial CUE using two methods: stoichiometric modeling and 13C glucose tracing. Preliminary results from stoichiometric modeling suggest that CUE increases with salinity up to 75 uS above ambient, beyond which it declines. Statistical analyses and comparisons of CUE estimates from both methods are ongoing. These findings will provide insights into methodological differences in CUE estimation and shed light on how increasing salinity may affect microbial C processing in streams.