Seasonal Dynamics of Water Temperature and Dissolved Oxygen in Wular Lake, Kashmir: Evidence of Weak Dissolved Oxygen–Temperature Relationships in a Himalayan Wetland

Abstract

Wular Lake is a high-altitude freshwater wetland in the Kashmir Himalaya that experiences strong seasonal variation in physicochemical conditions. This study assessed seasonal changes in water temperature and dissolved oxygen across 20 sampling sites during summer, autumn, winter and spring, yielding 80 observations. Both variables were measured on site at each sampling location. Water temperature was recorded using a mercury-in-glass thermometer, and dissolved oxygen was measured using a portable dissolved oxygen meter. Seasonal differences were evaluated using one-way analysis of variance followed by Tukey post hoc comparisons, while Pearson correlation and simple linear regression were used to examine the relationship between water temperature and dissolved oxygen. Water temperature varied significantly among seasons, with the lowest mean value in winter (4.90 ± 1.62 °C) and the highest in summer (24.01 ± 2.70 °C). Dissolved oxygen also differed significantly among seasons, ranging from 7.31 ± 1.66 mg/L in autumn to 9.82 ± 1.19 mg/L in summer. The pooled temperature-dissolved oxygen relationship was weak and non-significant (r = 0.085, p = 0.452; R² = 0.007), indicating that temperature alone did not explain dissolved oxygen variability across the annual cycle. Seasonal analysis showed a significant negative relationship only in spring 2025 (r = -0.502, p = 0.024), while summer, autumn and winter showed no significant correlations. The relatively high summer dissolved oxygen values despite elevated temperature suggest that site-level oxygen dynamics may be influenced by processes other than solubility alone. One autumn observation of 4.20 mg/L fell below the 5.0 mg/L threshold recommended for sustaining aquatic life (USEPA, 1986), indicating a localised low-oxygen condition requiring attention. These findings demonstrate that the classical temperature-dissolved oxygen solubility relationship was weak in this biologically productive Himalayan wetland and support the need for direct seasonal dissolved oxygen monitoring rather than reliance on temperature as a proxy indicator in Ramsar-designated freshwater ecosystems of the Kashmir Himalaya.