Ultraviolet transparency as an indicator of lake metabolism in the Global Lake Ecological Observatory Network. Craig E. Williamson, Kevin C. Rose Miami University, Oxford, Ohio

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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.

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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

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Water Transparency

1. Most fundamental metric of water quality
2. Most fundamental driver of lake ecosystems
3. Highly responsive to environmental change

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Water Transparency as a MetricWhat wavelengths
should we be using?
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Water Transparency as a MetricWhat wavelengths
should we be using?
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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

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DOC 91 increase since 1988 in UK Lakes(similar
in N. America, Scandinavia)
Evans et al. 2006 Global Change Biology 122044
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DOC IncreasesWhat is going on?

1. Destabilization of peatlands that will increase
   decomposition, CO2 to atmosphere, and global
   warming?
2. Or restabilization and recovery from
   postindustrial acid deposition (SO4)?

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Northern Peatlands
Account for storage of 20-30 of global soil
carbon Equivalent to about 60 of carbon in
atmosphere
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What Wavelengths to Use?PAR Has Low Absorbance
vs. UV
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Limitations of PARNoise level near surface
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Limitations of PAR Spectral Shift
Smith, Tyler, and Goldman 1973 Limnol. Oceanogr.
18189
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Selective absorption of red can cause shift in
PAR attenuation at surface
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UV Transparency Varies Among LakesKd Slope of
Semilog Plot
High Kd
Low Kd
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UV PAR stimulate photochemical oxygen
consumption 2-3 µmol L-1 h-1 (note
scaledifference)
Reitner et al. 1997 LO 42950
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Photo-oxidative Oxygen Consumption2-3 µmol L-1
h-1(Reitner et al. 1997 LO 42950)
Hanson et a. 2003 LO 481112
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Photo-oxidation alters UV Transparency
How did PAR Change?
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Optical Change Index (OCI) Measures Relative
Changes in Transparency
Kd Diffuse attenuation coefficient 0 value at
time zero T value at time t
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The Optical Change Index (OCI) - Metric of
change (/-) in transparency - No bias toward
waveband - Symmetric about zero
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Multi-year Trends in Transparency

• Lake Lacawac Lake Giles
• 400 µmol L-1 DOC 100 µmol L-1 DOC

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Multiyear Trends in UV Transparency
How did Visible (PAR) Change?
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Seasonal Variation in UV Transparency
How did PAR Change?
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Alpine Subalpine LakesBeartooth Mountains,
MT/WY
2001-2006 UV PAR Profiles Calculate OCI for
each ordinal day (1-2 profiles/year)
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Chl a 1.6 µg/L DOC 90 µmol/L
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Chl a 2.5 µg/L DOC 50 µmol/L
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Chl a 9.5 µg/L DOC 100 µmol/L
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Alpine Lakes Sentinels of Change
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Agricultural Watershed Acton Reservoir
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Reservoir with Agricultural Watershed OCI PAR
gt UV
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Reservoir with Agricultural Watershed OCI PAR
Reflects Chlorophyll
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Reservoir with Agricultural Watershed OCI UV
Does Not Reflect DOC
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Conclusions UVR vs. Visible?

• Optical metrics of environmental change
• Blue lakes UVR gtgtgt Visible
• Brown lakes UVR gt Visible
• Green lakes Visible gt 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?

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Limitations of UV Attenuates rapidly
DOC 400 µmol L-1
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BIC UV-PAR Radiometer(Biospherical Instruments
Inc.)
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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) UVPAR 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

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THE END
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Forested Watershed Burr Oak Reservoir
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Reservoir with Forested Watershed OCI PAR gt UV
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Reservoir with Forested Watershed OCI PAR
Reflects Chlorophyll
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Reservoir with Agricultural Watershed OCI UV
Does Not Reflect DOC
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Conclusions UVR vs. Visible?

• Optical metrics of environmental change
• Blue lakes UVR gtgtgt Visible
• Brown lakes UVR gt Visible
• Green lakes Visible gt 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?

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Alpine Lakes Sentinels of ChangeLow DOC, low
nutrients, high UV.
Karlsson et al. 2005 Global Change Biology 11710
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Lake Tahoe North TransectOCI May 3 July 24,
2006
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Lake Tahoe UV and PAR Vertical Profiles May
2006 July 2006 Calculate Optical Change May to
July
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Lake Tahoe, CA/NVDecrease in Secchi Transparency
Jassby et al. 1999. Limnol. Oceanogr. 44282
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Lake Tahoe, CA/NV 2006
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OCI in Emerald Bay, Lake TahoeMay 3 July 24,
2006
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Photobleaching Spectral Response
Moran et al. 2000. Limnol. Oceanogr. 451254
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Eutrophication Transparency Increased In Lake
Washington Following Sewage Diversion ASLO
Image Library Ray Drenner Redrawn from
Edmondson Litt. 1982. Limnol Oceanog 27
272-293.
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Yan 1999 Can. J. Fish. Aquat. Sci. 40621
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Zooplankton Grazing Increases Transparency
Clear-Water Phase
Lampert et al. 1986. Limnol. Oceanogr. 31478
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Zooplankton Size Related to Visible Transparency
Mazumder et al. 1990 Science 247312
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Transparency Regulates Mixing Depth in Small Lakes
Fee et al. 1996 Limnol. Oceanogr. 41912
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Zooplankton Vertical Migration Correlated with
Transparency
DVM amplitude is driven by fish predation
Dodson 1990 Limnol. Oceanogr 351195
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Fish Reduce Visible Transparency
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Zooplankton Species Diversity in 53 Patagonian
Lakes
OD Optical Depth Kd320 x Z Z lake
depth Marinone et al. 2006 Photochem Photobiol
82967
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DOC Regulates Transparency
Fee et al. 1996 Limnol. Oceanogr. 41912
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Zooplankton Species Diversity 320nm UV in 53
Patagonian Lakes
Marinone et al. 2006 Photochem Photobiol 82967
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Spectral Shift in 3 Lakes
Hutchinson, G.E. 1957. Treatise on Limnology Vol.
1
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DOC Seasonal Dynamics
Chapman et al. 2005 IAHS Publ 294
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Visible TransparencyControls Mixing Depth
Mazumder et al. 1990 Science 247312
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Modify this to better format to show how UV is
more responsive than PAR with solar
photobleaching but nutrient additions are not all
that different (do not show zooplankton data, and
mention Pats paper on how photobleaching depends
on spectral composition of bleaching solar.
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Instrument Needs and Costs

• Source Biospherical Instruments Inc.
• Medium bandwidth spectral radiometers
• Submersible and deck-cell units
• 8-10 nm bandwidth (FWHM)
• 305, 320, 380, PAR sensors, temperature
• Cost 5-6K per unit
• Additional 2K for antifouling

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Evans et al. 2006 full legend
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Ref for decrease in DOC in Alaskan rivers due to
increased microbial decomposition. Note - cant
get Geoph Res Let (off-campus at least)

• GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L21413,
  doi10.1029/2005GL024413, 2005
• A decrease in discharge-normalized DOC export by
  the Yukon River during summer through autumn
• Robert G. Striegl
• U.S. Geological Survey, Denver, Colorado, USA
• George R. Aiken
• U.S. Geological Survey, Boulder, Colorado, USA
• Mark M. Dornblaser
• U.S. Geological Survey, Boulder, Colorado, USA
• Peter A. Raymond
• School of Forestry and Environmental Studies,
  Yale University, New Haven, Connecticut, USA
• Kimberly P. Wickland
• U.S. Geological Survey, Boulder, Colorado, USA
• Abstract
• Climate warming is having a dramatic effect on
  the vegetation distribution and carbon cycling of
  terrestrial subarctic and arctic ecosystems.
  Here, we present hydrologic evidence that warming
  is also affecting the export of dissolved organic
  carbon and bicarbonate (DOC and HCO3 -) at the
  large basin scale. In the 831,400 km2 Yukon River
  basin, water discharge (Q) corrected DOC export
  significantly decreased during the growing season
  from 197880 to 200103, indicating a major shift
  in terrestrial to aquatic C transfer. We conclude
  that decreased DOC export, relative to total
  summer through autumn Q, results from increased
  flow path, residence time, and microbial
  mineralization of DOC in the soil active layer
  and groundwater. Counter to current predictions,
  we argue that continued warming could result in
  decreased DOC export to the Bering Sea and Arctic
  Ocean by major subarctic and arctic rivers, due
  to increased respiration of organic C on land.

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DOC Trends in Europe NA
SKjelkvale et al 2005. Env. Pollut. 137165
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Seasonal Variation in DOC
Clark et al. 2005 Global Change Biology 11791
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Optical Change Index (OCI) Measures Relative
Changes in Transparency
Estimate from diffuse attenuation coefficients
or
Estimate from 1 attenuation depths
0 value at time zero T value at time t
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DOM Spectral Slope Signatures
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Acidification Increases UV Transparency Little
Rock Lake
Williamson et al. 1996 Limnol. Oceanogr. 411024
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Remote Sensing CDOM

• UV transparency data may help ground-truth
  remotely sensed data on DOC concentrations.
• Use multispectral data for DOC and Chl

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Photochemical Oxygen Consumption
Reitner et al. 1997 LO 42950