Water temperature in lowland streams: a preliminary study on its spatio-temporal variability and environmental dependence

The aim of the study was to evaluate the spatio-temporal dynamics of water temperature in the Wkra River catchment. Water temperature was monitored using digital recorders across 26 streams located in central Poland and representing small tributaries with variable catchment properties. On the basis of the measurement data collected during the hydrological year 2021, the spatial and seasonal variability of water temperature parameters was analyzed using statistical metrics and principal component analysis. Moreover, selected catchment and channel metrics in various spatial scales were combined with correlation analysis to assess their influence on monthly mean and maximum water temperature values. The results indicate significant spatial variability of water temperature in the Wkra River tributaries, creating a mosaic of thermal habitats. Seasonally, water temperature followed a sinusoidal pattern, while subdaily dynamics varied seasonally, with the highest values observed in spring and early summer.The mean and maximum water temperature values were related to environmental metrics mainly during the summer half-year; significant positive relationships were documented for the catchment area, whereas negative relationships were observed with channel gradient and riparian shade degree. In winter, only stream orientation demonstrated significant correlations. These findings are relevant in the context of anticipated changes in river thermal regime due to a climate warming effect, as well as setting new research issues; they also provide a unique basis in the context of fisheries management and land practices