Terrestrial and aquatic ecosystems are linked through reciprocal exchanges of nutrients, energy, and organisms. Salinization is a large-scale global change impacting both aquatic and terrestrial ecosystems, yet how it affects the linkages between these systems remains poorly understood. Understanding how salinization alters ecosystem processes across the aquatic-terrestrial interface is critical for predicting responses to ongoing environmental change and informing conservation strategies. In this study, we tested the Sodium Subsidy-Stress (SSS) hypothesis, which predicts that moderate salinization subsidizes ecosystem processes while high salinization causes stress, resulting in a hump-shaped response. This talk will focus on organic matter decomposition to quantify the amount and rate that salinization alters decomposition in streams and adjacent riparian zones across an agriculturally and urban induced salinity gradient. We predict that the stress threshold will exist at a lower sodium (Na) level in streams than terrestrial riparia thus displaying a hump-shaped response across the two ecosystems. Using 30 stream sites across the central Shenandoah Valley in Virginia and West Virginia, spanning a gradient from reference conditions to highly salinized (50 to 900 uS/cm specific conductivity) streams. At each site, we deployed paired decomposition assays in the stream and terrestrial riparian zone consisting of red maple leaves and cotton fabric strips to quantify microbial and invertebrate-mediated decomposition. We also measured stream water chemistry and riparian soil ion concentrations to relate decomposition rates. We will present how decomposition responses to salinization differ between aquatic and terrestrial habitats, with potential decoupling of these linked processes under high salinity stress. Understanding how anthropogenic salinization affects carbon cycling and energy flow at ecosystem boundaries will allow managers to predict ecosystem responses and develop strategies to protect these important aquatic-terrestrial linkages in impacted watersheds.