Climate Change and the European Water Dimension - Agri ...

The chlorophyll concentrations measured in the lake are substantially lower if
the winter is wet i.e. a greater proportion of the slow growing winter crop of
phytoplankton is flushed out of the lakes (Figure VI.A.5). These losses are likely
to increase in the coming decades and could have a major effect on the subsequent
growth of the spring phytoplankton.
Analyses have shown that cold winters favour the survival and growth of the
cladoceran herbivore Daphnia hyaline var lacustris. Daphnia is a filter feeder that
requires a relatively high food concentration whilst the calanoid Eudiaptomus can
survive in much less productive environments. When the winter is cold,
appreciable numbers of Daphnia survive in the open water even when their
supply of food from the phytoplankton is very low. When the winter is mild,
however, the Daphnia cannot ingest enough food to survive and the
Eudiaptomus then dominate the micro-crustacean community (see more details
in George & Hewitt, 1999). Here, the important point is that relatively small changes
in the winter water temperature can have a significant effect on the long-term
dynamics of a key planktonic species.
VI.A.2. Conclusions
The historical variations in the winter characteristics of Esthwaite Water show that
this lake is very sensitive to year-to-year variations in the weather. These weatherrelated
variations influence the physical, chemical and biological characteristics of
the lake. In some cases, the changes are modulated by a single climatic variable
while in others the lake responds to the combined effects of the prevailing wind, sun
and rain.
158