Although stream ecosystems are recognized as an important component of the global carbon cycle, the impact of climate-induced hydrological changes on carbon fluxes in stream networks remain unclear. We will discuss the effects of changes in snowmelt hydrology during the anomalously warm winter of 2013/2014 on gross primary production (GPP), ecosystem respiration (ER) and net ecosystem production (NEP) in an Alpine stream network. We estimated ecosystem metabolism across 12 study reaches of a 254 km2 subalpine catchment located in the Ybbs River Network (YRN), Austria, for 18 months. GPP peaked in 10 of our 12 study reaches during spring snowmelt, regardless of the amount of snow the previous winter. However, the shift from snow to rain precipitation following the low snow winter in 2013/2014 increased spring ER in upper elevation catchments, thereby shifting spring NEP from autotrophy to heterotrophy. Our findings suggest that the YRN evolved from transient sinks to sources of carbon dioxide (CO2) in spring as snowmelt hydrology differed following the high snow versus low snow winter. This shift towards increased heterotrophy during spring snowmelt following a warm winter has potential consequences towards annual ecosystem metabolism, as spring GPP contributed on average 33% to annual GPP fluxes compared to spring ER, which averaged 21% of annual ER fluxes. We propose that Alpine headwaters shunt less organic carbon to downstream ecosystems, but will emit more within-stream respiratory CO2 to the atmosphere annually, as the climate gets warmer.