Loss of meltwater from glaciers and snowpack may increase synchrony of river habitats and resources in mountain watersheds.

Stream biogeochemical regimes can vary over short distances in heterogenous landscapes. In many mountainous and high-latitude watersheds, streams fed by rain and groundwater sources coexist with streams dominated by meltwater from melting glaciers, permafrost, and seasonal snowpack. The distinct physicochemical regimes of meltwater and non-meltwater fed streams can promote spatial and temporal asynchronies in biotic and abiotic environmental conditions within watersheds that promote ecological heterogeneity and stability. However, fading cryospheric inputs to watersheds threaten to homogenize and synchronize stream habitats and resources. Here, we compared the physicochemical conditions and biomass dynamics of stream food webs (course particulate detritus, periphyton, aquatic invertebrates, and fish) over a meltwater season from April to November in four streams with different predominant sources of runoff, one glacier-fed, one snow-fed, one rain-fed, and one stream transitioning from glacier- and snow-fed to a rain-fed. We then analyzed the temporal correlation ("synchrony") of the abiotic and biotic conditions in these streams and evaluated how synchrony might change if certain stream types were lost. We found that glacier-, snow-, and rain-fed streams had distinct temperature, flow, and water chemistry regimes and asynchronous seasonal patterns of detritus, biofilm, aquatic invertebrate, and fish biomass. The strongest differences were associated with the divergence of abiotic and biotic conditions in the glacier-fed stream relative to the other stream types. Synchrony analysis suggests that the climate-driven loss of meltwater contributions from the cryosphere may synchronize the seasonal resource dynamics of meltwater and non-meltwater streams during the primary growing season within and across watersheds. Increasing synchrony of abiotic processes that drive instream production could reduce ecological stability within watersheds as seasonal conditions converge, especially for mobile consumers that will lose the opportunity to integrate resource waves across complex landscapes.