An interdisciplinary study of land-sea carbon coupling between the Penobscot River and Gulf of Maine

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An interdisciplinary study of land-sea carbon
coupling between thePenobscot River and Gulf of
Maine
William M. Balch Collin Roesler- Bigelow
Laboratory Andrew Barnard, WET Labs  Thomas G.
Huntington, USGS, Augusta, ME Huijie Xue,
University of Maine Orono  George R. Aiken, USGS
Boulder, CO
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Acknowledgements

• Respective lab groups
• Dave Drapeau, Bruce Bowler, Emily Booth, Laura
  Windecker, Heidi Franklin, Rois Langner, Dan
  Abraham, Kenna Butler, Yi Du
• NASA IDS

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Overview

• Introduce the study area
• Follow DOC from watershed to coastal sea
• Discuss quantity and quality of DOC
• Optical proxies for using remote sensing to
  estimate DOC concentrations
• 3-D circulation modeling results
• Summarize

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In a recent paper on the Gulf of Maines optical
properties, we showed that the Gulf is
CaseII-dissolved all the time and Case II
particulate about half the time
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The DOC Tea Bag Analogy

• Soil build-up of particulate organic carbon/leaf
  litter during growing season- the tea leaves
• Precipitation soaks POC- the steep
• DOC is extracted- the brew
• Transformations enroute- binds to other POC,
  mineral surfaces (i.e. stains your teeth), is
  metabolized (digested)
• Remaining DOC is carried downstream to the
  oceansome of which is visible, some not, but it
  is a large pool!

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But the plot thickens

• There are different ways to brew your tea
• The downstream ocean has its own source of DOC
  (some of which is colored)
• Which DOC dominates in river-impacted coastal
  waters?
• What is the fate of the terrestrial vs marine
  DOC? (fundamental to the Case II vs Case I
  distinction)

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The birth of terrestrially impacted, Case
II-dissolved waterWe start way upstream in the
Penobscot River
D
D
D
West Enfield
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Penobscot River empties into Penobscot Bay
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Penobscot Bay then empties into the Gulf of Maine
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Are the tributaries of the Penobscot equal in
their DOC concentration?
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When you brew your tea is everything
Summer tea
Iced tea
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Timing is everything

• Jan-May
• Frozen ground
• Fast runoff does not penetrate frozen
  sedimentspoor steep
• Temperature does affect the leaching cold water
  bad brew

• June-December
• End of growing season with lots of accumulated
  carbon
• Runoff percolates in earthgood steep
• Warm temperatures enhance microbial breakdown of
  leaf litter, good steep, good brew

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Put daily discharge, measured DOC concentration
as function of flow rate time of year, one can
model the daily DOC flux
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Optical proxies for DOC in the riverfluorescence
of DOC
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Penobscot River-seasonally variable relationship
between discharge and CDOM fluorescence
Eddington CDOM fluor Discharge W. Enfield
CDOM Fluor (ppb QS)
Discharge (cfs)
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CDOM Excitation/Emission fluorescence spectra
vary with land use
lEx(nm)
lEx(nm)
lEm(nm)
lEm(nm)
Passadumkeag Wetland
Pleasant River Agricultural watershed
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Ex/Em properties vary with the watershed
EX200EM300
F (QS eq)
peak ratio (Ex/Em 265/475 225/430)
Different Penobscot Watersheds
Aerial Coverage Wetland
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In line ferry data from Penobscot Baystrong
inverse relation between apg425 and salinity
S a 30 9 15 4.5 0 1
Salinity
apg425
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How much of the DOC that makes it down the river,
through the bay and into the Gulf of Maine?

• First two years of our IDS study we were very
  lucky
• 2004- Dry year
• 2005 THE wettest year on record
• Allowed a good contrast in the quantity and
  quality of the DOC that came out into the Gulf of
  Maine

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How much does the DOC change from Penobscot Bay
to the Gulf of Maine?
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How does the quality of the DOC change from Bay
to Gulf?
SUVA (10-3 m2 mgDOC-1 254nm)
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Space time plot for DOCin the Gulf of Maine
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SUVA (DOC specific absorption cross section)
x10-3 m2 (mg DOC)-1
Strong EW gradient
Sargasso Value0.8
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Going back 8 years with agp412 2004 and 2005
indeed were extraordinary years
05 04 03 02 01 00 99 98
Wettest
Dry
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They were extraordinary years for optical
scattering, too
05 04 03 02 01 00 99 98
Wettest
Dry
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Aqua estimates at the mouth of Penobscot Bay
Plt0.001
X
X
X
X
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We have combined the DOC Export along with 3d
circulation model of H. Xue to model the DOC
distribution
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It is clear that in the Gulf of Maine,
transformations are occurring in CDOM plotted
against salinity
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Summary

• The relation between discharge rate and DOC
  concentration shows two different relationships,
  a winter-spring and summer-fall pattern
• The fluorescence properties of CDOM provide
  information on watershed type
• DOC quantity drops gradually from the upper
  watershed through Penobscot Bay
• DOC quality (SUVA) is high throughout the Penn
  Bay and drops dramatically as water exits into
  the GoM suggesting a loss in aromaticity

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Summary

• During dry year (04) and wet year (05) no
  influence of Gulf of St. Lawrence water entering
  GOM and affecting CaseII dissolved conditions.
• Dry year (04) showed major loss of CDOM in mid
  Gulfphotooxidation?
• Aqua-derived DOC values look reasonable
• Clear evidence of nonconservative CDOM behavior
  in the Gulf
• Have modeled 3-D DOC flow. Future plans to
  incorporate DOC non-conservative transformations

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Thank you!
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How do three of the biggest watersheds compare in
the concentration of their DOC (tea)?