Abstract
Lakes around the world are warming, but not all water layers are warming at the same rate, and some are even cooling. Most studies have focused on summer lake water surface temperatures or analyzed short-time series. Here, we analyze a 44-year time series of water temperature from nine depths in a small mountain lake using dynamic linear models and temporal trend decomposition. We observe a significant long-term warming trend, but this occurred only from August to December in all water layers. The lake warmed ca. twice as fast (0.23 °C decade−1) as the air, but warming of the epilimnion slowed down remarkably (from 0.65 to 0.10 °C per decade) after 1993, a consequence of changing stratification timing. Deeper water layers even cooled thereafter, pointing to a stronger isolation from surface layers, which were still warming over the whole study period. This differential warming of the lake was accompanied by significant shifts of lake freezing and thawing dates leading to shorter ice-cover periods (~ 5 days decade−1). As a result, the thermal Schmidt stability of the water column strengthened, but also temperature variance in the epilimnion increased significantly, together with increasing variance and extremes of local air temperature. Our results show a significant autumn/winter warming effect of lake water together with an increasing intensity of temperature fluctuations in this seasonally ice-covered mountain lake, suggesting that current broad scale estimates of climate change impacts on lakes, based on summer temperature measurements and surface layers, do not fully reflect the effect of climate change.
Highlights
Lakes around the world are affected by increasing air temperatures (O’Reilly et al 2015)
Mean lake surface water temperature (LSWT) have increased by 0.34 °C decade−1 from 1985 to 2009, i.e., at a rate similar to that of surface air temperature (IPCC 2014), but lake warming seems to be highly variable among lakes (O’Reilly et al 2015)
The overall objectives of this work were first, to assess patterns of lake water temperature in the epilimnion, metalimnion, and hypolimnion of the mountain lake Piburger See, Austria, over a time span of 44 years (1972–2015), second, to compare long-term temperature changes in these water layers, and third, to assess potential changes in the frequency of random and non-cyclic water temperature fluctuations that might have been caused by an increase in the frequency of extreme heat events in Europe and in the surrounding of the lake
Summary
Lakes around the world are affected by increasing air temperatures (O’Reilly et al 2015). In the Alps, air temperatures have increased twice as fast as the mean for the northern hemisphere and are expected to increase even faster during the remainder of the twentyfirst century (Gobiet et al 2014). In Central Europe, for example, in Austria, Germany, and in the western Carpathians, lake surface water temperature (LSWT) has increased rapidly (Novikmec et al 2013; Dokulil 2014a; Weckström et al 2016; Woolway et al 2017a). Mean LSWTs have increased by 0.34 °C decade−1 from 1985 to 2009, i.e., at a rate similar to that of surface air temperature (IPCC 2014), but lake warming seems to be highly variable among lakes (O’Reilly et al 2015). Despite the existence of lake-specific variability, annual mean deep-water lake temperatures are correlated to a certain extent within climatic regions (Dokulil et al 2006), suggesting a relatively high degree of correlation between lake-water temperatures and regional air temperatures (Livingstone et al 2010)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
