Alpine lakes, snow cover and fish production
Snow depth
anomaly (cm)
Climate warming means that lowland lakes typically are ex-
periencing longer ice-free periods, promoting greater bio-
150
logical productivity. However, despite this warming trend,
100
biological productivity may be reduced, at least temporarily,
in alpine areas with increased winter precipitation.
50
0
During years with high winter precipitation in alpine areas of
-50
western Norway, in spite of higher temperatures, fish growth
and recruitment were lower than in low-snowfall years (Figure
-100
8.8). Annual fish growth rates were negatively correlated with
-150
spring snow depth – the greater the snow depth, the less the
fish grew
23
. During the years 1992 to 1995, a period with mean
1970 1975 1980 1985 1990 1995 2000
spring snow depth of 275 cm, fish growth was reduced by 50%
compared to years with much less spring snow accumulation
Temperature
(1991 and 1996). A further increase in winter snowfall in these
anomaly (°C)
regions, as projected by climatic scenarios, would be expected
4
to result in further reductions in biological production.
2
Figure 8.8: Strong interannual changes in snow depth and ice
0
cover may occur in some mountain areas due to increased
-2
winter precipitation (as snow). Photos show an alpine lake at
the Hardangervidda plateau, western Norway, in early July, for
-4
years of high and low winter precipitation. High snowfall years
-6
are associated with a strong North Atlantic Oscillation. The
charts show that snow cover is not related to temperature. 1970 1975 1980 1985 1990 1995 2000
Source: Based on Borgström and Museth 2005
39
Photos: R. Borgström
CHAPTER 8 RIVER AND LAKE ICE 209
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