Abstract:
We examined marsh ecosystem processes in nine different marshes along the Mississippi coast (6 oiled and 3 unoiled marshes). At each site, we measured 24 hr soil CO2 fluxes on three separate dates (September, October, December, 2011). Fluxes were measured with a LI-8100 automated Soil CO2 Flux system. We measured soil CO2 fluxes at four subplots (two each in Juncus roemerianus and Spartina alterniflora vegetative zones) every 30 minutes during each 24 hr period. We used a cellulose strip bioassay as proxy for measuring microbial-mediated decomposition processes in oiled vs non-oiled sites.
Suggested Citation:
Davis, Michael. 2015. CO2 Efflux from Salt Marsh Sediments, Mississippi, August thru December 2011.. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N7RV0M3N
Purpose:
The overarching goal of this proposed task was to evaluate the extent, severity and potential duration of impacts from the Deepwater Horizon incident on ecosystem functions of Mississippi Gulf Coast salt marshes particularly carbon cycling functions.
Data Parameters and Units:
Site 1 = Heron Bay, Site 2 = Lower Point Clear, Site 3 = St. Joesph Point, Site 4 = Grand Bayou, Site 5 = Cat Island, Little Bay, Site 6 = Belle Fontaine, Site 7 = Graveline Bay, Site 8 = Chevron Refinery, Site 9 = Point Aux Chenes Bay, Site 10 = Petit Bois Island, Run A late summer (growing season), Run B fall (senescence), Run C late fall/early winter (dormant season),Tables -- IV Date: Date of Run (MM/DD/YY hh:mm CST), Port#: Port Number, Exp_Flux: CO2 flux LI-8100 exponential fit (umol CO2/m2/second), Temp: temperature(degrees Celsius), Moisture: soil moisture, VWC: volumetric water content (meter^3/meter^3) The tables "Spartina A", "Spartina B", "Spartina C", "Juncus A", "Juncus B", Juncus C", are raw data which were included to be transparent so you could see which values were eliminated. When the tide comes in during a run, flux values become unreliable so those values are discarded. That is when the sediment becomes inundated during high tide, sediment CO2 efflux stops and in some instances the equipment can pick CO2 going back into solution (some of the negative fluxes). “Spartina” is a dataset with the unreliable fluxes (i.e., inundated sediments) removed. Use Exp_FluxCV (see above) to make the determination of whether or not the data are reliable. If Exp_FluxCV is less than 2.0 we generally discard those data. The raw data have additional parameters: Obs#: Observation Number , #Raw: Reading taken before the chamber has equilibrated, Mean V1: gas flow from voltage channel 1 (umol CO2/m2/second), Mean V2: temperature from voltage channel 2 (degrees Celsius), Mean V3: moisture from voltage channel 3, Exp_FluxCV: coefficient of variance of Exp_Flux (%), Lin_Flux: CO2 flux LI-8100 linear fit (umol CO2/m2/second), Lin_FluxCV: coefficient of variance of Lin_Flux (%), CrvFitStatus (Curved fit solution type) "Exp" means the exponential fit was better than the linear fit (Exp_SSN less than Lin_SSN). "Lin" means the linear fit was still better after the maximum number of iterations, and the nonlinear coefficients have therefore been derived from the linear fit.
Methods:
We examined marsh ecosystem processes in nine different marshes along the Mississippi coast (6 oiled and 3 unoiled marshes). At each site, we measured 24 hr soil CO2 fluxes on three separate dates (September, October, December, 2011). Fluxes were measured with a LI-8100 automated Soil CO2 Flux system. We measured soil CO2 fluxes at four subplots (two each in Juncus roemerianus and Spartina alterniflora vegetative zones) every 30 minutes during each 24 hr period. This allowed us to examine diurnal effects due to both temperature and tides. Data were analyzed using soil temperature as a covariate. In addition, we used a cellulose strip bioassay as proxy for measuring microbial-mediated decomposition processes in oiled vs non-oiled sites. Cotton strips (2 x 8 cm) were placed into (12 x 6 cm) fiberglass fine mesh bags (1.0 mm). Sixty bags were randomly assigned to 1 of 9 study sites (total 540 bags). Bags were placed on either surface sediments just below the soil surface. At each site, bags were placed on both the Juncus roemerianus and Spartina alterniflora vegetative zones. At regular intercals, bags were collected and rates of microbial respiration (CO2 evolution) from surface sediment cotton strips was measured with a LiCor LI-6400 Infrared Gas Analyzer. Basic environmental data were also collected at each site during each visit, including salinity, dissolved oxygen, redox potential, temperature, pH, turbidity, and total dissolved solids.
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