Windermere Science Project stakeholder meeting presentations. Jones on changes to the lake physical structure with increasing temperature and the consequences for algal biomass

1. Responses of phytoplankton to a
changing climate
Ian Jones, Ellie Mackay, Steve Thackeray
Lake Ecosystems Group
Centre for Ecology & Hydrology
ianj@ceh.ac.uk

2. The project hypotheses:

3. Climate and lakes
Alter grazing potential
Warming climate
Warmer water
Shallower mixed layers
Longer stratification
Stronger stratification
More light in epilimnion
Increase internal loading
Phytoplankton changes

4. Climate and lakes
Alter grazing potential
Warming climate
Warmer water
Shallower mixed layers
Longer stratification
Stronger stratification
More light in epilimnion
Increase internal loading
Phytoplankton changes

5. Windermere South Basin (WSB) 2007
25
10m
13m
19m
22m
25m
30m
oC
)
7m
16m
15
2m
4m
20
1m
35m
(
u
t
a
r
p
m
e
T
10
5
0
Jan Feb Mar Apr May Jun
Jul Aug Sep Oct Nov Dec
2007

6. WSB: Start, end and duration of
stratification
330
270
s
y
a
D
210
150
90
30
1965 1975 1985 1995 2005 2015
Year
Start: slope = -0.4 days/yr, P < 0.01

7. WSB: Start, end and duration of
stratification
330
270
s
y
a
D
210
150
90
30
1965 1975 1985 1995 2005 2015
Year
End: slope = 0.3 days/year, P < 0.05

8. WSB: Start, end and duration of
stratification
330
270
s
y
a
D
210
150
90
30
1965 1975 1985 1995 2005 2015
Year
Duration: slope = 0.7 days/yr, P<0.001

9. 15
5 shallowest autumnal mixed layers
5 deepest autumnal mixed layers
-10
10
-20
-40
0
270
300
330
Day of Year
360
g
m
(
l
h
C
5
-30
)
m
(
h
t
p
D
d
e
x
i
M
-3
0
)
WSB Deep and Shallow years

10. WSB: ‘Deep’ and ‘Shallow’ years
15
-10
10
-20
-40
0
270
300
330
Day of Year
360
Chl in ‘shallow’ years; Chl in ‘deep’ years
g
m
(
l
h
C
5
-30
)
m
(
h
t
p
D
d
e
x
i
M
-3
)
0

11. Autumnal phytoplankton phenology
(last day chl > 6 mg m-3)
l
h
c
d
n
e
f
o
y
a
D
360
340
320
300
280
260
240
slope = 1.1; P<0.001
240 260 280 300 320 340 360
Day of overturn

12. WSB: Influence of more stratified days
280
240
slope = 0.6; P < 0.05
200
160
6
>
l
h
c
s
y
a
d
f
.
o
N
120
150 170 190 210 230 250
No. of stratified days

13. Influences of changing stratification
• There have been statistically significant delays in
overturn date and increases in total number of
stratified days
• Later overturn coincides with phytoplankton biomass
remaining higher for longer
• Years with more stratified days are years with more
days with higher phytoplankton biomass

14. 15.00
-3
)
WSB: Oct & Nov mixed depths and chl
10.00
slope = 0.3; P < 0.001
g
m
(
l
h
c
.
v
A
5.00
0.00
-40.0 -30.0 -20.0 -10.0
Mixed Depth (m)
0.0

15. WSB: Oct & Nov change of mixed depth
with air temperature
0.0
-10.0
slope = 1.9, P < 0.001
-20.0
)
m
(
h
t
p
d
e
x
i
M
-30.0
-40.0
4.00 6.00 8.00 10.00 12.00
Air temp (oC)

16. Change over time of Oct & Nov md
0.0
-10.0
-20.0
slope = 0.1; P < 0.05
d
e
x
i
M
m
(
h
t
p
e
d
)
-30.0
-40.0
1965 1975 1985 1995 2005 2015
Year

17. Autumnal mixed depths changes
• Shallower autumnal mixed depths coincide with
increased autumnal phytoplankton biomass
• Autumnal mixed depths are shallower in years which
have higher autumnal air temperatures
• Since 1967 there has been a statistically significant
shallowing of the autumnal mixed layer

18. WSB & WNB overturn
(Windermere South Basin & Windermere North Basin)
360
330
r
e
f
o
y
a
D
300
270
1965 1975 1985 1995 2005 2015
Year
WSB

19. WSB & WNB overturn
(Windermere South Basin & Windermere North Basin)
360
330
r
e
f
o
y
a
D
300
270
1965 1975 1985 1995 2005 2015
Year
WNB
WSB

20. Significance of relationships between
mixed depth and chl
0.80
0.60
0.40
P < 0.01
0.20
WSB
P < 0.001
P < 0.05
0.00
P < 0.05
-0.40
P < 0.01
-0.60
P < 0.001
e
u
l
a
v
R
'
-0.20
240
260
280
300
320
Day of year
340
360

21. Significance of relationships between
mixed depth and chl
WSB
P < 0.001
P < 0.01
P < 0.05
P < 0.05
P < 0.01
WNB
P < 0.001

22. WNB: Autumnal phytoplankton phenology
(last day chl > 3 mg m-3)
360
slope = 0.4; P < 0.05
330
300
3
>
l
h
c
f
o
y
d
t
s
a
L
270
270
300
330
Day of overturn
360

23. WNB: Influence of more stratified days
3
>
l
h
c
s
y
a
d
f
.
o
N
300
270
240
210
180
150
slope = 0.6; P < 0.001
180
210 240 270
No. of stratified days
300

24. -3
)
WNB: Mixed depths and chl
(days 312-342)
8.00
6.00
slope = 0.05, P < 0.05
4.00
g
m
(
l
h
c
.
v
A
2.00
0.00
-60.00
-40.00 -20.00
Mixed depth (m)
0.00

25. Summary
• Later overturn coincides with delayed seasonal decline
of phytoplankton biomass
• More stratified days coincides with more days with
high phytoplankton biomass
• Shallower autumnal mixed layers coincide with
increased autumnal phytoplankton biomass
• More pronounced effects in WSB than WNB (WNB
overturns later, when light availability is reduced)
• Longer stratification and shallower mixed depths
related to warmer air temperature
• Significant trends since 1967

26. Forward look
• Extend examination to include other available longterm data sets (such as Esthwaite Water)
• Examination of effects on individual phytoplankton
species
• Interrogation with process-based model