Spatial and Temporal Variability of pCO2 in the Great Bay Estuary System

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Spatial and Temporal Variability of pCO2 in the
Great Bay Estuary System

• Chris Hunt, Joe Salisbury, Doug Vandemark, Janet
  Campbell
• University of New Hampshire
• Wade McGillis- Lamont-Doherty Earth Observatory
• ASLO Session SS07, Santa Fe
• February 5, 2007

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• 44 km2 of estuary, 230 km of shoreline
• Tidally dominated
• Freshwater typically represents only 2 of tidal
  prism
• Tidal height 2m
• Observed flushing time is 18 days from head of
  estuary (during high river flow)

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10 km to Gulf of Maine
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From Oczkowski, A. 2002, Riverine inputs of
nutrients to Great Bay, NH (USA), MS Thesis,
Department of Earth Science, UNH, Durham
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Fast equilibrator for continuous pCO2
measurements.
R/V Camden Belle
Flow-through system equipped to measure Fl-Chl,
Fl-CDOM, beam attenuation, DO, Temp, and
Salinity. Seawater is pumped through the system
at a rate of 20L/min.
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Apr 06
Oct 05
Salinity (psu)
Oct 06
Jun 06
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Oct 2005
Apr 2006
Oct 2006
Jun 2006
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Apr 06
Oct 05
pCO2 (uatm)
Oct 06
Jun 06
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K0
K1
H2CO3
HCO3- H
CO2(f) H2O
K2
CO3 H
Conservative pCO2 calculated using carbonate
equations from Pilson (1998) and K1 and K2 from
Cai and Wang (1998)
Conservative mixing line, using an
abiotic oceanic endmember
DIC (umol/kg)
Slope46.8
Int467.3
Cai W.-J. and Wang Y. (1998) The chemistry,
fluxes and source of carbon dioxide in the
estuarine waters of the Satilla and Altahama
Rivers, Georgia. Limnol. Oceanogr. 43,
657-668. Pilson, M.E.Q. (1998). An Introduction
to the Chemistry of the Sea. Prentice Hall,
Upper Saddle River, New Jersey.
Salinity (psu)
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Apr 06
Oct 05
pCO2 Anomaly pCO2conservative pCO2observed

• Values gt0 indicate
• less CO2 than predicted
• by conservative mixing
• Values lt0 indicate
• more CO2 than predicted
• by conservative mixing
• Values gt0 suggest
• autotrophy
• Values lt0 suggest
• heterotrophy

pCO2 Anomaly
Jun 06
Oct 06
(uatm)
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Apr 06
Oct 05
pCO2 Anomaly (pCO2conservative
pCO2observed) pCO2conservative

• Values gt0 indicate
• less CO2 than predicted
• by conservative mixing
• Values lt0 indicate
• more CO2 than predicted
• by conservative mixing
• Values gt0 suggest
• autotrophy
• Values lt0 suggest
• heterotrophy

pCO2 Anomaly
Jun 06
Oct 06
()
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Conclusions

• The Great Bay operates as a system of systems,
  with differing metabolic patterns
• We infer that seasonality and climatic events
  have a dramatic effect upon carbon processing
• Endmember contributions from rivers seem to
  strongly influence estuarine biogeochemistry
• General classification of estuaries as
  heterotrophic does not describe the Great Bay
  system, as well as other New England estuaries
  (e.g. Merrimack River)

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Speculations

• River-sourced nutrients, OC, and light limitation
  drive patterns of heterotrophy/autotrophy in
  Great Bay
• Precipitation events move terrestrial labile
  carbon to the estuary, promoting strong
  heterotrophy
• Inputs from municipal WWTF significantly affect
  estuarine carbon cycle, particularly during low
  river flow

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Oct 2006 Nitrate
Oct 2005 Nitrate
NO3 (umol/L)
NO3 (umol/L)
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Future Work

• Determine seasonal DIC and OC fluxes for system
  as a whole and individual rivers
• Calculate net CO2 exchange
• Use caffeine as an anthropogenic tracer
• Install continuous CO2 system in Great Bay?

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