Abstract:

We conducted seasonal (April, June, August, October 2015 and May, June, September, November 2016) measurements of net soil greenhouse gas (CO2, CH4, and N2O) fluxes at four locations (5, 10, 15, and 20m from the marsh edge) in four marsh sites in Terrebonne Bay, Louisiana. These sites include paired oiled and unoiled marshes in the Bay LaFleur and northern Lake Barre regions of Terrebonne Bay. Additionally, we collected 5-cm deep soil cores at the same 4 locations for a series of basic site characterizations: soil properties, soil extractable nutrients, porewater, overlying water and adjacent bay water depth, temperature, salinity, specific conductance and nutrients, when available. This dataset is a continuation of dataset R1.x139.143:0025 (2012) and dataset R1.x139.143:0027 (2013-2014).

Suggested Citation:

Roberts, Brian J.. 2019. Marsh soil net greenhouse gas fluxes and explanatory variables collected from marshes in Terrebonne Bay, Louisiana from April 2015 to November 2016. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/n7-tqpw-nq33

Purpose:

This dataset was developed as part of a research project investigating the effects of the Deepwater Horizon oil spill on salt marsh biogeochemistry. This component of the Coastal Waters Consortium (CWC) research effort addressed the following questions: 1) Do greenhouse gas fluxes vary seasonally and/or with marsh position?; 2) What are the primary drivers of net greenhouse gas fluxes?; 3) Are these results different between oiled and unoiled marshes?; and 4) Is there interannual variability in any of these patterns or responses to oiling?

Data Parameters and Units:

Region: User-defined identifier assigned to each sampling region (TB=Terrebonne Bay, WB= western Barataria Bay, EB=eastern Barataria Bay); Site: Site number designation; Latitude (decimal degrees); Longitude (decimal degrees); Oil status: Indicates whether the marsh received Macondo Oil (Oiled) or not (Unoiled); Plot: Plot identifier along the sampling transect; Distance (m): Distance from the marsh edge of the sampling plot (meters); Month-Year: Indicates the month and year that samples were collected or measurements made; net CO2 flux (micromol/m2/h): net carbon dioxide (CO2) flux from the soil to the atmosphere; net CH4 flux (micromol/m2/h): net methane (CH4) flux from the soil to the atmosphere; net N2O flux (micromol/m2/h): net nitrous oxide (N2O) flux from the soil to the atmosphere; Soil T: soil temperature at the plot, in degrees C; soil pH: pH of the top 5 cm of soil at the plot; soil Eh: soil redox potential (Eh) in the surface soil of the plot (units = mV); soil bulk density (g/cm3): bulk density of the top 5 cm of soil at the plot; soil organic C (%): organic carbon content of the top 5 cm of soil at the plot; soil total N (%): total nitrogen content of the top 5 cm of soil at the plot; soil total P (µg/g): total phosphorus content of the top 5 cm of soil at the plot; soil CN (mol:mol): organic carbon to total nitrogen ratio of the top 5 cm of soil at the plot; soil NP (mol:mol): total nitrogen to total phoshorus ratio of the top 5 cm of soil at the plot; soil CP (mol:mol): organic carbon to total phosphorus ratio of the top 5 cm of soil at the plot; soil water content (%): gravimetric water content of the top 5 cm of soil at the plot; soil extractable NO3 (micromols per grams dry weight of soil): extractable nitrate + nitrite concentration of the top 5 cm of soil at the plot; soil extractable NH4 (micromols per grams dry weight of soil): extractable ammonium concentration of the top 5 cm of soil at the plot; soil extractable PO4 (micromols per grams dry weight of soil): extractable orthophosphate concentration of the top 5 cm of soil at the plot; Porewater salinity (psu): salinity of porewater from the plot; Overlying water depth (cm): depth of overlying water at plot; Overlying water temp (°C): temperature of overlying water at plot; Overlying water salinity (psu): salinity of overlying water at plot; Overlying water specific conductance (mS): specific conductance of overlying water at plot; Baywater temp (°C): temperature of baywater adjacent to site; Baywater salinity (psu): salinity of baywater adjacent to site; Baywater specific conductance (mS): specific conductance of baywater adjacent to site; Baywater NO3-N + NO2-N (micromols per liter): dissolved nitrate + nitrite concentration of baywater adjacent to site; Baywater NH4-N (micromols per liter): dissolved ammonium concentration of baywater adjacent to site; Baywater PO4-P (micromols per liter): dissolved orthophosphate concentration of baywater adjacent to site; Baywater SiO2 (micromols per liter): dissolved silicate concentration of baywater adjacent to site.

Methods:

Net soil-atmosphere and water-atmosphere greenhouse gas (CO2, CH4, and N2O) fluxes were measured using the static chamber method for soils (Livingston and Hutchinson 1995) and the floating chamber method when water depth exceeded 15 cm (MacIntyre et al. 1995). Gas samples were analyzed for CO2, CH4, and N2O concentrations on a ShimadzuGC-2014 gas chromatography equipped with a methanizer and both a flame ionization detector (FID) and a 63Ni electron capture detector. For extractable nutrient analyses, 2-3 g of soil was added to each of two 50-mL centrifuge tubes, one tube for extractable dissolved inorganic nitrogen (DIN), the other for dissolved inorganic phosphorus (DIP). 30 mL of 2N KCl was added to the DIN tube, and it was shaken at 250 rpm for 2 hours. The DIN tube was then centrifuged and the supernatant was 0.2 µm filtered and stored frozen until analysis. 30 mL of 0.5 M NaHCO3 was added to the DIP tube and it was shaken at 250 rpm for 16 hours. The DIP tube was then centrifuged, and the supernatant was 0.2 µm filtered and stored frozen until analysis. Dissolved inorganic nutrient concentrations were measured using a Lachat Instruments QuickChem® FIA+ 8000 Series Automated Ion Analyzer with an ASX‌-400 Series XYZ Autosampler. Samples were analyzed simultaneously for dissolved NOx (nitrate + nitrite) using Cu-Cd reduction followed by azo colorimetry and for PO4-P using the automated ascorbic acid reduction method. NH4-N was analyzed separately using phenate colorimetry to prevent contamination of the samples by fumes from the NH4Cl buffer used in NOxanalysis. Standard curves were prepared using standard PO4-P, NO3-N, and NH4-N stock solutions (Hach, Loveland CO) and yielded r2 values of ≥0.99. Soil properties were obtained following the procedures detailed in Marton and Roberts (2014) and Marton et al. (2015).

Instruments:

ShimadzuGC-2014 gas chromatography equipped with a methanizer and both a flame ionization detector (FID) and a 63Ni electron capture detector were used to determine CO2, CH4, and N2O concentrations. A Lachat Instruments QuickChem® FIA+ 8000 Series Automated Ion Analyzer with an ASX‌-400 Series XYZ Autosampler was used to measure dissolved inorganic nutrient concentrations.

Provenance and Historical References:

Livingston, G.P. and Hutchinson, G.L. (1995) Enclosure-based measurement of trace gas exchange: applications and sources of error. In: Matson, P.A. and Harris, R.C., Eds., Biogenic trace gases: measuring emissions from soil and water. Blackwell Science Ltd., Oxford, UK. 14–51. MacIntyre, S., Wanninkhof, R., and Chanton, J. P.: Trace gas exchange across the air-water interface in freshwater and coastal marine environments, 52–97, in: Biogenic Trace Gases: Measuring Emissions from Soil and Water, edited by: Matson, R. C. H. P. A., Blackwell Science Ltd., New York, 1995. Marton, J. M., & Roberts, B. J. (2014). Spatial variability of phosphorus sorption dynamics in Louisiana salt marshes. Journal of Geophysical Research: Biogeosciences 119(3), 451–465. doi:10.1002/2013jg002486 Marton, J. M., Roberts, B. J., Bernhard, A. E., & Giblin, A. E. (2015). Spatial and Temporal Variability of Nitrification Potential and Ammonia-Oxidizer Abundances in Louisiana Salt Marshes. Estuaries and Coasts 38: 1824-1837. doi:10.1007/s12237-015-9943-5

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