Lluís Gómez-Gener, Nicola Deluigi, Tom Battin

In high-mountain landscapes, biological resources such as organic carbon (OC) are often limited and heterogeneously stored in poorly developed soils, snow, ground ice and glaciers. Climate change influences the dynamics of OC mobilization to- and processing into- the recipient streams. These patterns can vary from seasonal (e.g., snow melt in spring) to daily (e.g., ice melt in summer) depending on the location of the streams within the catchment. Capturing the temporal richness of stream biogeochemical signals is now a reality with the advent of high-resolution sensors. In this study, we used wavelet analysis on high-frequency discharge (Q) and dissolved organic carbon (DOC) measurements from nine streams in the Swiss Alps to investigate whether synchrony (S) of Q (SQ) and DOC (SDOC) persisted or collapsed among streams, and its response to the spatial position, climate, and land cover gradients across different time scales. Our findings reveal that short-term (0-10 days) SQ and SDOC were strongly influenced by distance between streams and network connectivity. In contrast, catchment-related properties (i.e., altitude or land cover) were more important in driving SQ and SDOC dynamics at longer time scales (>50 days). However, the degree to which local catchment properties controlled S patterns at the longest timescales depended both on the response variable (i.e., Q vs. DOC) as well on the main land cover (i.e., vegetation vs. glacier). Elucidating the most prominent timescales of SDOC is relevant given the hydrological alterations projected for high-mountain regions. We show that glaciers impose a unique seasonal regime on DOC concentration, potentially overriding the effects of other local hydrological or biogeochemical processes during downstream transport. Consequently, SDOC dynamics in high-mountain streams may change as glaciers shrink, thereby altering downstream opportunities for biogeochemical transformations.