Dynamics of water temperature in a small mountain catchment

Water temperature has a significant effect on the river fauna and flora and changes the quality of the aquatic ecosystem. Water temperature similar to other physical and chemical indicators of water quality enters into the assessment of the ecological status of surface waters in accordance with the requirements of the framework directive on water (RSV EU). Therefore, it is important to monitor it and also to know to what extent it is influenced by other factors. The aim of this work was to evaluate the short-term water temperature development and also to analyse its regime with respect to influencing factors, especially air temperature and altitude. The study is conducted in the foreland and mountain part of the Jalovecký Creek catchment in Slovakia and uses hourly data from the hydrological year 2022 (November 1, 2021 – October 31, 2022). We performed field water temperature measurements along the entire Jalovecký creek (six sites at altitudes from 560 to 1,110 m a.s.l.) to better evaluate the water temperature regime. Seasonality of water temperature was analyzed by statistical analysis of time series. We used scatter-plots to assess the relationship among water temperature, air temperature and altitude. The analysis of the water temperature measurements showed that the highest mean hourly/daily water temperature was recorded at Ondrašová site (22.3°C/18.3°C), and the lowest was measured at the Hlboká valley (-1.2°C/-1.5°C). This fact resulted both from the altitude of the stations (Ondrašová 560 m a.s.l., Hlboká valley 1,110 m a.s.l.). The lowest mean monthly air temperature was measured in December (-0.2°C), while the highest was observed in July (15.7°C). The highest variations of the mean monthly water temperatures among the studied sites were observed during summer (June – August), when mean monthly temperature range reached even 8.0°C. The relationship between water and air temperature did not differ significantly among the investigated sites. However, the higher correlations were found for higher altitude (i.e., Hlboká valley). The results of the work could contribute to a better understanding of temperature conditions in high mountain streams.