Responses of phytoplankton to a changing climate

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

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Responses of phytoplankton to a changing climate

  1. 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. 2. The project hypotheses:
  3. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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

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