Spatiotemporal patterns of nutrients’ diurnal variations in glacier-fed alpine streams: Insights from high-frequency observations in the Laohugou River, Qilian Mountains

The aquatic ecosystems of the alpine cryosphere have shown significant responses to climate change. While previous studies have primarily focused on long-term variations in alpine aquatic ecosystems, dramatic diurnal variations of nutrients and their relationships in alpine stream remain underexplored. This study employed high-frequency diurnal sampling along a glacier-fed alpine stream in the Qilian Mountains, from upstream to downstream, conducted monthly during the May–September melt period, to investigate the spatial and temporal variability of diurnal nutrient and environmental parameter variations. Turbidity increased sharply from 20 to over 2000 NTU in the afternoon as glacial melt intensified. Total phosphorus exhibited a similar trend to turbidity, whereas total nitrogen and dissolved organic carbon showed inverse trends. These coordinated variation patterns between nutrients and turbidity highlighted the role of diurnal glacial melt dynamics in driving nutrient variability. The influence of these variations diminished and delayed with increasing distance from the glacier. The diurnal variations of nutrients were intense in the early months of the melt and became weaker in the following months. This study emphasis the importance of examining the nutrient variations in glacier-fed streams at finer temporal scales and provide new insights into understanding the alpine aquatic ecosystems.