ABSTRACT Direct and indirect anthropogenic influences, such as water resources management and land use change, can show local and regional effects on stream water temperature, which is increasingly exacerbated by climate change. Characterisation of these influences is important, for example, for assessing and managing aquatic habitats. However, this is often constrained not only by limited overall data availability but more critically by the coarse temporal and spatial resolution of the existing data. Here, we explored the use of a novel low‐cost, in situ 3D temperature sensor system and combined this with traditional stream water temperature loggers and remotely sensed thermal infrared (TIR) data to obtain insights into high‐resolution 3D spatial thermal patterns in river systems at different spatial and temporal scales. We applied this to the River Livet (104 km 2 ) in NE Scotland, which is influenced by the release of cooling‐water (thermal discharge) from a local distillery. We collected stream water temperature data under contrasting ambient conditions and explored the effects of the thermal discharge against the background of natural variability by comparing stream water temperature patterns at times with and without thermal discharge releases. Despite variations in natural background temperatures and flow, and with or without thermal discharge, we consistently observed a general water temperature increase from upstream to downstream along a 900 m reach. This means that the overall pattern in thermal variability in this river was not affected by the release of thermal discharge. However, results from this first multi‐method application in a complex river system also showed that a warm thermal plume related to the underwater release of thermal discharge obscured the natural thermal variability locally (across 30 m). These effects could be detected at the air‐water interface. The magnitude of these effects also appeared to depend on background conditions, with the largest noticeable impacts observed during relatively low flow (1.5 m 3 /s), with cold background air (1.7°C) and stream water temperatures (4.4°C). Our approach has enabled us to identify small‐scale thermal patterns in an anthropogenic‐influenced river. In the future, this approach could be used to determine thermal patterns in 3D in various natural and anthropogenically influenced hydrological environments.
Loerke et al. (Tue,) studied this question.