Investigating Environmental Controls on Temperature Dynamics in an Urban Stream

Abstract

Water temperature is a critical environmental variable influencing aquatic ecosystems. This study investigated the factors controlling stream temperature and thermal stratification in Rock Creek (RC) and Bethany Lake, an urbanized watershed featuring an in-line irrigation pond and buried wastewater infrastructure. Previous research suggested that subsurface water flow might drive temperature shifts in Rock Creek during summer periods when flow from Bethany Lake ceases. From 2023 to 2024, continuous temperature and stage monitoring, combined with statistical methods including principal component analysis and random forest regression, were used to evaluate seasonal temperature dynamics and their controlling factors. Results confirmed that seasonal reversals in temperature trends occurred within Rock Creek, though these may have been strongly influenced by monitoring techniques and thermal stratification. During summer periods, Bethany Lake did not flow into Rock Creek, and within Rock Creek above and below Bethany Lake there was negligible streamflow. Solar irradiance emerged as the most influential parameter for stream warming during these periods. Unexpectedly, lake elevation had a measurable influence on Upper RC stage, suggesting hydrologic interactions that are not yet fully understood. Piezometer data indicated that variability in subsurface water elevation was correlated with fluctuations in Bethany Lake elevation, but only within piezometers near the middle of the study reach. Despite this, there was no measurable fluctuation of stream temperature in relation to subsurface water elevation. This study underscores the importance of understanding interactions among anthropogenic modifications, hydrologic connectivity, and environmental controls on stream temperature. These findings have implications for urban stream restoration and management, particularly in mitigating thermal stress on aquatic species during low-flow summer periods. Furthermore, in these low-flow settings, commonly used hydrologic measurement techniques and instrumentation may lack precision to identify fine-scale processes and connections. Isotopic techniques (tracer or natural abundance studies) or other methods may need to be applied to have a more accurate understanding of surface-subsurface hydrologic exchange