Akademik Veri Yönetim Sistemi
PHYSICS AND CHEMISTRY OF THE EARTH, cilt.144, 2026 (SCI-Expanded, Scopus)
This study aimed to quantify diurnal (sunrise vs. midday) and spatial variations in electrical conductivity (EC) across the Degirmendere Stream Watershed, Eastern Black Sea Basin, Turkiye, and to evaluate the relative influences of daytime human activity, water temperature, discharge, and precipitation on EC dynamics. The study's value lies in its complete annual cycle of paired diurnal measurements, its four-station spatial network spanning a full land-use gradient, and its direct relevance to drinking water supply management for Trabzon Province via the Atasu Dam and Esiroglu Treatment Plant. EC is a widely used proxy for ionic loading in river systems, yet its diurnal behaviour in mixed-use watersheds supplying drinking water remains poorly documented. The Degirmendere Stream Watershed was selected because it combines a clear land-use gradient, a dam-controlled tributary providing an internal reference signal, and direct relevance to regional water supply management via the Atasu Dam and Esiroglu Treatment Plant. Weekly paired measurements were conducted across four monitoring stations (D1-D4) over a full annual cycle (December 2021 to November 2022; n = 43 events). Specific conductance standardised to 25 degrees C was back-calculated to in-situ EC to account for ambient thermal dynamics. Paired t-tests revealed that midday EC values were significantly higher than sunrise values at the downstream stations D3 and D4 (p < 0.01), indicating a detectable daytime anthropogenic signal in densely populated reaches, whereas no significant diurnal difference was observed at the upstream stations. A linear mixed-effects model identified station location (beta = 5.208), water temperature (beta = 3.946), and discharge (beta = -1.591) as the primary drivers of EC variability (p < 0.001 for all), while the period effect (sunrise vs. midday) was not significant after controlling for these predictors (p = 0.487). Correlation analysis confirmed a strong dilution effect driven by discharge (r = -0.830, p < 0.001), a moderate positive association with water temperature (r = 0.362, p < 0.001), and a weak but significant negative relationship with precipitation (r = -0.128, p = 0.018). The Atasu Dam tributary exerted a localised dilution effect at D2, interrupting the otherwise progressive downstream increase in EC. Despite measurable anthropogenic pressure at downstream reaches, all recorded EC values remained below 400 mu S/cm, classifying the watershed as Class I (very good) water quality under Turkish Surface Water Quality Regulations. These findings highlight the importance of diurnal sampling protocols and hydroclimatic controls in EC-based watershed monitoring.