Synchrony dynamics of dissolved organic carbon in high‐mountain streams: Insights into scale‐dependent processes

In high‐mountain landscapes, organic carbon (OC) is 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. Dynamics 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 has become a reality with the advent of high‐resolution sensors. In this study, we applied wavelet analysis to high‐frequency discharge (Q) and dissolved organic carbon (DOC) measurements from nine streams in the Swiss Alps to investigate the persistence of synchrony in Q (SQ) and DOC (SDOC) among streams, and their response to drainage network position, climate, and land cover gradients across different time scales. Our findings revealed that SQ and SDOC decayed non‐linearly over the first ~ 5 km and stabilized from this point onwards, indicating that localized controls influenced synchrony within single basins, but drivers operating at regional scale acted as synchrony stabilizers. We also showed that short‐term (0–10 d) SQ and SDOC were strongly influenced by the distance between streams and network connectivity. In contrast, catchment‐related properties (i.e., altitude or land cover) were more important drivers of SQ and SDOC dynamics at longer time scales (> 50 d). However, the degree to which local catchment properties controlled synchrony patterns at the longest timescales depended both on response variables (i.e., Q vs. DOC) and 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.