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

Residence time (days)
Chlorophyll (ug l -1 )
140
120
100
80
60
40
20
0 2 4 6 8 10
20
The winter characteristics of the lake
(a) (b)
Rainfall (mm day -1 )
Since Esthwaite Water has a relatively short residence time, the year-to-year
variations in the flushing rate are quite pronounced (Figure VI.A.5). The method used
to estimate the residence time was that described by George and Hurley (2003).
This is based on the amount of rain falling on the catchment in the first ten weeks of
each year, a time when the lake is particularly sensitive to interannual variations in
the rainfall. Since winters in the area are projected to become wetter in the coming
decades the residence time of the lake will continue to decrease and have a major
effect on its winter chemistry and biology. In Esthwaite Water, as in other lakes in
the area, the quantity of nitrate leached from the catchment decreases during mild
winters (Figure VI.A.5). The factors responsible for this trend have been discussed by
George (2000b) and appear to match those reported by Monteith et al. (2000) in a
number of upland sites.
157
De-trended nitrate
(c) (d)
0
0 2 4 6 8 10 12
Rainfall (mm day -1 )
Daphnia / Eudiaptomus ratio
400
300
200
100
0
-100
-200
6
5
4
3
2
1
0 2 4 6 8
Air temperature ( o C)
0
1955 1960 1965 1970
Year
Figure VI.A.5 (a) The inter-annual variation in the residence time of the lake in
relation the average rainfall. (b) The inter-annual variation in de-trended
concentration of nitrate in relation the average air temperature. (c) The interannual
variation in the chlorophyll concentration in relation the average rainfall.
(d) The inter-annual variability in relative abundance of Daphnia and
Eudiatoptomus in relation to the water temperature.
0
2
4
6
8
Surface temperature ( o C)