On a global scale, intermittent rivers and ephemeral streams (IRES) constitute the majority of lotic networks by length but are relatively understudied despite serving as critical ecosystems in arid and semiarid regions. IRES are ecosystems where spatiotemporal variation in hydrologic regime can affect multiple functions, including nutrient cycling, decomposition, and ecosystem metabolism. Understanding how hydrological variation affects these functions is crucial for informing water resources management strategies. In this study, we examined the influence of seasonality, watershed position, and hydrologic regime on rates of gross primary production (GPP), ecosystem respiration (ER), and terrestrial leaf litter decomposition in the San Saba River (Texas, USA). This river exhibits substantial spatiotemporal variation in hydrologic regime along its upstream – downstream course: stable and consistent perennial flows, intermittent flows and drying in summer, and seasonally variable but perennial flows. We examined the above ecosystem processes at nine sites that represent these three flow regimes across seasons (Fall, Winter, Spring, and Summer). We hypothesized that light and temperature are principal drivers of GPP and ER, respectively, whereas hydrological characteristics, water temperature, and reach position strongly influence nutrient dynamics and litter decomposition rates. Preliminary analysis indicates the presence of substantial spatial variation in GPP and ER, but that ER and litter decomposition rates were strongly influenced by season. Overall, the results of our study indicate that different facets of ecosystem functioning are affected by diverse environmental drivers at various spatiotemporal scales. Findings from this study have implications for water resources management planning, especially under changing climates.