Acknowledgements

1. Ultraviolet transparency as an indicator of lake metabolism in the Global Lake Ecological Observatory Network.Craig E. Williamson, Kevin C. RoseMiami University, Oxford, Ohio Fourth Global Lake Ecological Observatory Network (GLEON) Workshop March 2007, Lammi Biological Station, Finland.

2. Acknowledgements • Field Collection of Data: • Undergraduates and graduate students from multiple universities • Beartooth Lakes: • Jasmine Saros, Ryan Lockwood, Misa Saros • Pennsylvania Lakes: • Robert Moeller, Don Morris, Bruce Hargreaves • Work-up of UV-PAR Data: • Erin Overholt

3. Water Transparency • Most fundamental metric of water quality • Most fundamental driver of lake ecosystems • Highly responsive to environmental change

4. Water Transparency as a Metric:What wavelengths should we be using?

5. Water Transparency as a Metric:What wavelengths should we be using?

6. Importance of Water Transparency: • Controls Ecosystem Processes: • Mixing depth and heat budget in small lakes (DOC) • Lake autotrophy vs. heterotrophy (DOC) • Compensation depth – photosynthesis vs. respiration (DOC) • Vertical migration amplitude of zooplankton (DOC) • Responds to Environmental Change: • Autochthony vs. allochthony (DOC quality and quantity) • Eutrophication - nutrient overload (DOC quality) • Acidification increases transparency (DOC) • Climate change – flood, drought (DOC flux) • Land use, hydrology, forest fires (DOC flux) • Photobleaching - biolability of DOC • Phototoxicity – PAHs such as anthracene (DOC) • Zooplankton grazing – size distribution

7. DOC: 91% increase since 1988 in UK Lakes(similar in N. America, Scandinavia) Evans et al. 2006 Global Change Biology 12:2044

8. DOC Increases:What is going on? • Destabilization of peatlands that will increase decomposition, CO2 to atmosphere, and global warming? • Or restabilization and recovery from postindustrial acid deposition (SO4)?

9. Northern Peatlands Account for storage of 20-30% of global soil carbon Equivalent to about 60% of carbon in atmosphere

10. What Wavelengths to Use?PAR Has Low Absorbance vs. UV:

11. Limitations of PAR:“Noise” level near surface

12. Limitations of PAR: Spectral Shift Smith, Tyler, and Goldman 1973 Limnol. Oceanogr. 18:189

13. Selective absorption of red can cause shift in PAR attenuation at surface

14. UV Transparency Varies Among LakesKd = Slope of Semilog Plot: High Kd Low Kd

15. UV & PAR stimulate photochemical oxygen consumption 2-3 μmol L-1 h-1(note scaledifference) Reitner et al. 1997 L&O 42:950

16. Day-Night Photo-oxidative Oxygen Consumption:2-3 μmol L-1 h-1(Reitner et al. 1997 L&O 42:950) Hanson et a. 2003 L&O 48:1112

17. Photo-oxidation alters UV Transparency How did PAR Change?

18. Optical Change Index (OCI)Measures Relative Changes in Transparency Kd = Diffuse attenuation coefficient 0 = value at time zero T = value at time t

19. Positive OCI values = increasing transparency 4x change 2x change Negative OCI values = decreasing transparency The Optical Change Index (OCI) - Metric of change (+/-) in transparency - No bias toward waveband - Symmetric about zero

20. Multi-year Trends in Transparency • Lake Lacawac Lake Giles ~ 400 μmol L-1 DOC~ 100 μmol L-1 DOC

21. Multiyear Trends in UV Transparency: How did Visible (PAR) Change?

26. Seasonal Variation in UV Transparency How did PAR Change?

30. Alpine & Subalpine Lakes:Beartooth Mountains, MT/WY 2001-2006 UV & PAR Profiles Calculate OCI for each ordinal day (1-2 profiles/year)

31. Chl a = 1.6 μg/L DOC ~ 90 μmol/L

32. Chl a = 2.5 μg/L DOC ~ 50 μmol/L

33. Chl a = 9.5 μg/L DOC ~100 μmol/L

34. Alpine Lakes: Sentinels of Change

35. Agricultural Watershed: Acton Reservoir

36. Reservoir with Agricultural Watershed: OCI PAR > UV

37. Reservoir with Agricultural Watershed: OCI PAR Reflects Chlorophyll

38. Reservoir with Agricultural Watershed: OCI UV Does Not Reflect DOC

39. & UVR, PAR Conclusions: UVR vs. Visible? • Optical metrics of environmental change: • “Blue” lakes: UVR >>> Visible • “Brown” lakes: UVR > Visible • “Green” lakes: Visible > UVR • Use UVR & PAR as metrics of environmental change: Spectral data provide more information: • Need research into mechanisms; Possible signals: • Allochthony vs. Autochthony; color: chlorophyll ratio?

40. Limitations of UV: Attenuates rapidly DOC ~ 400 μmol L-1

41. BIC UV-PAR Radiometer(Biospherical Instruments Inc.)

42. Many Metrics of UV Transparency: 1) 1% 320 nm attenuation depth: • 1% to be consistent with 1% PAR (compensation depth) • 320 nm in region of maximum biological effectiveness: • Number of photons in solar radiation • Biological effectiveness per photon 2) DOC-specific absorbance • Measure of DOC quality and source: • allochthonous (more UV absorbing) • autochthonous (less UV-absorbing) • photobleaching (decreases DOC-specific absorbance) 3) UV:PAR ratio and spectral slope • Relative importance of dissolved versus particulate compounds • Dissolved components selectively absorb UV • Particulates are more wavelength independent • Example: Algal blooms versus allochthonous CDOM

43. THE END

44. Forested Watershed: Burr Oak Reservoir

45. Reservoir with Forested Watershed: OCI PAR > UV

46. Reservoir with Forested Watershed: OCI PAR Reflects Chlorophyll

47. Reservoir with Agricultural Watershed: OCI UV Does Not Reflect DOC

48. & UVR, PAR Conclusions: UVR vs. Visible? • Optical metrics of environmental change: • “Blue” lakes: UVR >>> Visible • “Brown” lakes: UVR > Visible • “Green” lakes: Visible > UVR • Use UVR & PAR as metrics of environmental change: Spectral data provide more information: • Need research into mechanisms; Possible signals: • Allochthony vs. Autochthony; color: chlorophyll ratio?

49. 0 200 400 600 800 1000 1200 Elevation m.A.S.L. Alpine Lakes: Sentinels of Change:Low DOC, low nutrients, high UV. Karlsson et al. 2005 Global Change Biology 11:710

50. Tahoe UV Transects 2006