Seasonal snowmelt pulses are the dominant hydrologic feature of most alpine catchments. The majority of annual export of water, carbon and nitrogen occurs within a short window of only a few weeks. This observation has largely been based on relatively infrequent manual sampling, and our understanding of responses to finer-scale variation, “pulses within the pulse”, is critically incomplete. Here, we combine high-frequency sensor measurements of dissolved organic carbon (DOC) and nitrate (NO3-N) with historical grab sample data from a high altitude stream in the Rocky Mountains of Colorado. We characterize the linkages between precipitation, snowpack, streamflow, and solute export, over time scales ranging from decades to minutes. At all time scales, discharge (Q) variation was several orders of magnitude larger than concentration (C) variation, making it the dominant control on solute flux rates. Interannual variation in Q, and by extension solute export, appeared correlated to the depth of the winter snowpack, and how late into the spring the snowpack persisted. Seasonally, we observed clockwise C-Q hysteresis, with solute stores becoming depleted as the melt pulse proceeds. Using the sensor data however, we were able to observe individual events. In contrast to the seasonal patterns, these events enriched concentrations, suggesting the persistence of additional DOC and NO3-N stores which can be mobilized within, and even after the main seasonal snowmelt pulse. The historical data suggest that reduced snowpack and earlier snowmelt in the coming decades may result in reduced export of DOC and NO3-N. The sensor data however make this conclusion uncertain, as rain on snow events, which are expected to become more prevalent, appear equally capable of mobilizing solutes.
