Effects of drought on waterchemistry in a boreal streamnetwork

Sammanfattning: Hydrological drought at high latitudes represents a rising environmental hazard induced byglobal climate change. Yet, we still know little about how drought events influence thebiogeochemistry of boreal streams. Here, I used 15 years of data from eight streams withinthe Krycklan Catchment to test how interannual variability in summer low flows influencesstream water chemistry. My analysis focused several key biogeochemical indicators in thesestreams, including concentrations of dissolved organic carbon (DOC), dissolved organicnitrogen (DON), nitrate (NO3) and ammonium (NH4), as well as the total C/N and NH4/NO3ratios. Overall, results revealed widespread declines in summer average DOC concentrationsand C/N ratios with greater drought severity. These responses likely reflect shifts in thebiogeochemical properties of soils that feed streams during high- versus low-flow summers.By comparison, nitrogen-based parameters were less clearly influenced by drought, exceptfor in mire-dominated headwaters, where NH4 and DON both increased during the lowestflow periods. Overall, the strong effects of flow variability drove a high degree of interannualsynchrony for DOC and C/N across all sites in the drainage system. This synchrony was morevariable overall for nitrogen-based parameters, with several sites having unique year-to-yearchanges in concentrations and ratios. However, strong temporal coherence for NH4 acrossforested streams suggest other broad-scale factors (e.g., related to forest processes) mayregulate interannual patterns for this nutrient. Collectively, results provide insight into howincreases in drought frequency and severity may alter boreal streams and rivers in the future.