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Water temperature was monitored from May to October 2016 in the Świder and Utrata rivers, two lowland tributaries of the Vistula River in central Poland. Seven temperature recorders were located along each river continuum to examine both anthropogenic and natural factors affecting spatial temperature variability. The results showed that water temperature patterns in quasi-natural sites were generally similar across the length of the rivers. The most pronounced temperature increases were found to be the result of reservoir releases, wastewater inflows, and channel regulations. Riparian shade changes have also been identified as the main driver of spatial temperature heterogeneity, while the impact of the tributaries was not clear and depended on the degree of their anthropogenic transformation. Linear regression performance was similar in the case of most quasi-natural sites in the Świder River, while in the case of the Utrata River differences were found in explanatory power, slopes, and intercepts. Such investigations of water temperature patterns indicate that in lowland rivers temperature variations can be spatially complex and significant in their magnitudes, thus current research could help in the context of riverine management – especially for fisheries and environmental protection.
Air temperature variability on the local scale is one of the most important elements of topoclimatic differentiation. The aim of this paper is to determine the seasonal variability of the thermal conditions of the downstream Świder River valley. The analysis was conducted from October 2011 until December 2014 using air temperature data from a measurement station in Adamówka (representative location for downstream Świder River valley) and from the reference meteorological station in Otwock-Świder, operated by the Institute of Geophysics of Polish Academy of Sciences. Differences of the average, maximum and minimum daily air temperature between the station in Adamówka and corresponding values under reference conditions (dTavg, dTmax, dTmin) were calculated for each season of the study period (spring, summer, autumn, winter). Only days with radiative type of weather were chosen to further analysis due to the greatest spatial diversity of climate elements within such periods. The differences found between air temperature values in Adamówka and Otwock-Świder were small, but stable during the year. Within the river valley, due to high heat capacity of the substrate and presence of forest complex, a reduction of thermal contrasts during the day was observed. Consequently, downstream Świder River valley was characteriszed by lower air temperature, both in terms of daily average and maximum values, compared to standard conditions at the reference meteorological station in Otwock-Świder. Opposite results were obtained only for minimum daily air temperature, which was higher in the river valley in autumn. This can be explained by the fact that at the end of the vegetation period the substrate with the higher heat capacity slowly emits energy, which resulted in an increase in the minimum daily temperature in this season. The authors suggest that further investigations should concentrate on determining the changes in differences between air temperature in reference station and many different stations representing the same type of topoclimate, and thus on the stability of those differences during the year. For this purposes long-term measurements of meteorological elements are required.
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