Riverine and Estuarine Carbon Export to the Coastal Ocean (RECECO), Northern Gulf of Mexico
Rivers and estuaries are important carbon sources and sinks for the coastal ocean. The export of particulate and dissolved organic carbon from estuaries can be important to coastal food webs, and inorganic carbon exports from rivers control a significant part of the air-water CO2 fluxes related to the atmospheric and changing global carbon budgets. The Mississippi River (MR) exports a large carbon load to the Gulf of Mexico (GOM) and provides >95% of freshwater entering the Gulf. This river also supplies nutrients to local deltaic estuaries, such as Barataria Bay (BB), where phytoplankton growth may be very high due to river inputs at the mouth of the estuary. This 'new' phytoplankton production can mean that the estuary functions as a carbon sink, especially when new phytoplankton carbon is exported offshore. There are, however, few estimates of whether the northern GOM estuaries are a net carbon source or sink. We propose studying carbon export dynamics and transformations in the MR and BB, addressing three hypotheses:
1) The BB is a net sink for atmospheric CO2 on an annual basis, but may be a seasonal source of CO2 during some months.
2) The MR is a net source of atmospheric CO2 on an annual basis, with seasonal highs and lows that are related to fluctuations in temperature and turbidity.
3) The BB and the MR each export about the same amount of labile organic carbon to the coastal ocean.
Modeling. The modeling objectives are:
(1) to examine spatial and temporal changes in estuarine DOC, POC and DIC using a high resolution coupled 2-dimensional hydrodynamic-biological model, and
(2) to calculate DOC, POC and DIC fluxes through the BB passes. To accomplish the objectives, we will synthesize existing data within the first year to define DIC, DOC and POC gradients in the estuary and produce estimates of average C outwelling from BB and the MR. In year 2, we will parameterize and nest a carbon model within our hydrodynamic model to test effects of storms on outwelling.
Field work. The field work objectives are:
(1) to document CO2 source/sink relationships in different seasons for BB and the MR, and
(2) to document seasonal changes in organic matter production and lability. To accomplish these objectives, we will conduct 6 extended transect studies across the 2 years, with each extended transect encompassing 2 or more days of field work to measure C gradients and C process rates. Transect stations will be mostly the 18 long-term stations that start at Barataria Pass where 40-50% of water exchange occurs with the coastal ocean. Six to ten new stations will be added to the east of this transect to study marsh influences and outwelling at other important passes. The quarterly field studies in year 1 target known strong seasonal changes in the ecosystem; two additional extended transects will be done in year 2 to further study seasons (likely winter and summer) that show most contrast in C dynamics.
We have the following milestones, listed by quarter (Q1-8), for 2 years:
Q1: Initial winter transect; start lability experiments; first Annual Report due early May
Q2: Spring transect, synthesis of historical transect data, develop C model modules
Q3: Summer transect, synthesis continues as does development of C modules
Q4: Fall transect, synthesis continues, summary of 2010 water year and hydrology
Q5: Second winter transect, second Annual Report due in early May, Carbon Workshop hosted as part of 2011 Annual NGI meeting
Q6: Calculate export fluxes with calibrated model
Q7: Second summer transect, integrate carbon process modules with hydrology model, conclude carbon lability experiments
Q8: Write Manuscript(s)
Brian Fry, Department of Oceanography and Coastal Sciences, Louisiana State University
Dubravko Justic, Department of Oceanography and Coastal Sciences, Louisiana State University
Eugene Turner, Department of Oceanography and Coastal Sciences, Louisiana State University
Collaborators and Partners
Department of Oceanography and Coastal Sciences, Louisiana State University
AOML : Atlantic Oceanographic and Meteorological Laboratory, NOAA