Meteorological forcing at the air-water interface is the main determinant of the heat
balance of most lakes (Edinger et al., 1968; Sweers, 1976). Year-to-year changes
in the weather therefore have a major effect on the thermal characteristics of lakes.
However, lakes that differ with respect to their morphometry respond differently to
these changes (Gorham, 1964), with deeper lakes integrating the effects of meteorological
forcing over longer periods of time. Other important factors that can
influence the thermal characteristics of lakes include hydraulic residence time, optical
properties and landscape setting (e.g. Salonen et al., 1984; Fee et al., 1996;
Livingstone et al., 1999). These factors modify the thermal responses of the lake
to meteorological forcing (cf. Magnuson et al., 2004; Blenckner, 2005) and regulate
the patterns of spatial coherence (Chapter 17) observed in the different regions
(Livingstone, 1993; George et al., 2000; Livingstone and Dokulil, 2001; Järvinen
et al., 2002; Blenckner et al., 2004).
In this chapter, we summarise the long-term thermal changes observed in a number
of lakes distributed throughout Northern, Western and Central Europe. These
analyses complement the ice phenology results presented in Chapter 4, the ice modelling
results in Chapter 5 and the temperature modelling results in Chapter 7. Particular
attention is paid to the interannual and seasonal variations in the surface and
bottom temperatures of the lakes. In Europe, lake surface waters are typically at
their warmest in July or early August. Surface water temperatures in low-altitude
lakes in central Europe then often exceed 25¿C (Livingstone and Lotter, 1998;
Livingstone and Padisák, 2007), but are usually lower in lakes at high altitudes or
high latitudes (Livingstone et al., 1999; Korhonen, 2002; George et al., 2007b).
Long-term water temperature records are available from lakes in several different
regions (e.g. Livingstone, 1993; Bengtsson et al., 1996; George et al.,
2000; Livingstone and Dokulil, 2001; Nõges, 2004). These long-term data sets are
especially valuable for evaluating the thermal responses of lakes of varying size,
topography and geographical location to climate and climate change, making it possible
to detect gradual as well as abrupt shifts in their thermal characteristics. Where
these data sets include years with abnormal weather conditions, they are especially
valuable, since this information may help us evaluate the likely response of the
lakes to future extremes. Fritz (1996) postulated that lakes located in extreme habitats
or near an ecotone or climatic boundary will respond most sensitively to climate
change. In this respect, lakes located in the Alpine/perialpine region, on the Atlantic
coast, and at high latitudes are likely to respond most sensitively to the climatic
changes summarised in Chapter 2.
Ecologically, even relatively small changes in the thermal characteristics of lakes
¿ e.g. in their thermal stratification ¿ can cause major shifts in phytoplankton, bacterioplankton
and zooplankton populations as well as altering the rates of metabolic
processes (e.g. Steinberg and Tille-Backhaus, 1990; Tulonen et al.,1994; Weyhenmeyer
et al., 1999; Gerten and Adrian, 2000; Arvola et al., 2002; Jasser and Arvola,
2003). This is because organisms are often adapted to certain narrow temperature
ranges and because their life-cycle strategies can be highly sensitive to variations in
ambient water temperature (e.g. Chen and Folt, 1996).
ARVOLA Lauri;
GEORGE Glen D.;
LIVINGSTONE David;
JARVINEN Marko;
BLENCKNER Thorsten;
DOKULIL Martin;
JENNINGS Eleanor;
NIC AONGUSA Caitriona;
NOGES Peeter;
NOGES Tiina;
WEYHENMEYER Gesa;
2010-01-26
Springer Science+Business Media B.V.
JRC54770
978-90-481-2945-4,
https://publications.jrc.ec.europa.eu/repository/handle/JRC54770,
10.1007/978-90-481-2945-4_6,
