Abstract:

This dataset was generated from a study to test the effects of crude oil on N cycling processes. We conducted a lab incubation study on salt marsh sediments from three sites subjected to differing amounts of hydrocarbon contamination following the 2010 Deepwater Horizon (DWH) oil spill. Of the three sites, the Chandeleur Islands were moderately oiled, while Dauphin Island and Dog River were not impacted by the DWH spill. Sediments were incubated with and without water accommodated fraction (WAF) of oil for 6 days, then potential rates of nitrification, denitrification, and DNRA were measured to determine if the addition of WAF impacted these pathways. The addition of WAF only impacted DNRA at Dauphin Island, in which potential rates were two-fold higher in 100% WAF than control samples (p < 0.05). In control samples, denitrification was four-fold higher at the Chandeleur Islands than Dauphin Island or Dog River (p < 0.05). There were no site differences or treatment effect on nitrification potential (p > 0.05).

Suggested Citation:

Tollette, Derek, Corianne Tatariw, Nikaela Flournoy, Patricia Sobecky, and Behzad Mortazavi. 2020. The effects of crude oil on nitrogen cycling in northern Gulf of Mexico salt marshes, 2018-01-10 to 2018-06-13. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/FA62KZ9A

Purpose:

The purpose of this dataset was to determine the impacts of oiling on salt marsh ecosystem function (i.e. denitrification, DNRA, and nitrification) and if the oiling histories of marshes influences these processes with the addition of new oil.

Data Parameters and Units:

Data sheet one—Process Rates Headers are: Sampling year (2018); Sampling Month; Site name: represents the three sites that were visited on each date; Latitude: represents the latitude of the sampling location; Longitude: represents the longitude of the sampling location; Treatment: water accommodated fraction (WAF) of oil. In multiple batches, 80 mg of Macondo 252 surrogate oil was added to 800 mL of 26 ppt artificial seawater to produce a loading rate of 0.1 g L-1. The solution was shaken outside for 72 h to mimic environmental conditions. WAF was separated and frozen until sediment was collected; Denitrification potential: measured in micromoles of nitrogen per kilogram dry sediment per hour (µmol N kg dry sediment-1 h-1); DNRA potential: measured in micromoles of nitrogen per kilogram dry sediment per hour (µmol N kg dry sediment-1 h-1); Nitrification potential: measured in micromoles of nitrogen per kilogram dry sediment per hour (µmol N kg dry sediment-1 h-1); Note: Nitrification Potential analysis was only performed for the April, May, June, 2018, samples from Dog River and Chandeleur Island. Data sheet two—Site Characteristics (Site Characteristics Data were collected for the Control Data) Headers are: Sampling Year (2018); Sampling Month; Site (Dauphin Island, Dog River, Chandeleur Islands); Latitude; Longitude; Treatment (Control); Porosity: fraction of void space in sediment (unitless); Loss-on-ignition (sediment organic matter as loss-on-ignition): measured in sediment percent mass lost from loss-on-ignition (%); Carbon content (sediment carbon content): measured in sediment percent carbon (%); C/N (sediment molar carbon to nitrogen ratio): (mol mol-1); Porewater NH4 (porewater ammonium): measured in micromoles of nitrogen per gram dry sediment (µmol N g sediment-1); Chlorophyll a (sediment chlorophyll a inventory): measured in milligrams of chlorophyll a per square meter dry sediment (mg m sediment-2); Aboveground biomass (plant aboveground biomass): measured in kilograms plant aboveground biomass per square meter (kg m-2); Belowground biomass (plant belowground biomass): measured in kilograms plant belowground biomass per square meter (kg m-2); Temperature: measured in degrees Celsius (°C); Salinity: measured in parts per thousand (ppt); DO (water column dissolved oxygen): measured in milligrams of oxygen per liter water (mg DO L-1); NO2+NO3 (water column nitrite plus nitrate): measured in micromoles of nitrogen per liter water (µmol N L-1); PO43- (water column phosphate): measured in micromoles of phosphorus per liter water (µmol P L-1); Note- Some values for NO2+3 (water column nitrite plus nitrate) were below detection, thus they were left blank.

Methods:

Study Sites Samples were collected from smooth cordgrass (Spartina alterniflora) vegetated zones at three sites in the northern Gulf of Mexico. The Chandeleur Islands site is located off the coast of Louisiana (29.8954 N, -88.8278 W) and experienced moderate hydrocarbon contamination following the Deepwater Horizon (DWH) oil spill in 2010 (Michel et al., 2013). The Dauphin Island (30.2571 N, -88.1237 W) and Dog River (30.5705 N, -88.0854 W) sites are located off Mobile Bay, Alabama and do not have known histories of hydrocarbon contamination. Each site was sampled twice between 2018-01 to 2018-06. Dauphin Island was sampled 2018-01-10 and 2018-03-07, Dog River was sampled 2018-02-22 and 2018-04-24, and the Chandeleur Islands were sampled 2018-05-07 and 2018-06-13. Site Characteristics Point measurements of water column temperature, salinity, and dissolved oxygen were conducted at each site during each sampling period with a multiparameter meter (YSI Model 556). Water column nitrate-nitrite (NO2+3-) and phosphate (PO43-) concentrations were determined photometrically (Grasshoff et al., 1983) on a UV-Vis spectrophotometer (Genesys 10S, Thermo Scientific). Sediment organic matter was determined by loss-on-ignition. Cores (5 cm depth, 9.5 cm diameter, n = 3) were collected, sieved (2 mm), subsampled, and dried. In pre-weighed dishes, samples were ashed at 375 ºC for 1 h then at 600 ºC for 6 h and sediment weight differences pre- and post-ashing were used to determine percent organic matter. For percent C and C/N ratios, sediment cores (5 cm depth, 1.3 cm diameter, n = 3) were dried, ground, and carbonates were removed by acid fumigation (Harris et al., 2001). Sediment was dried again, reground, and carbon and nitrogen weights were measured using a Costech 4010 CHN elemental analyzer. Pore water extractable NH4+ concentrations were determined from sediment cores (5 cm depth, 1.3 cm diameter, n = 4). Sediment was weighed, 10 mL of 2N KCl was added, and slurries were shaken at 70 rpm at room temperature overnight. Slurries were centrifuged, 10 mL of the supernatant was centrifuged, and concentrations were determined fluorometrically (Holmes et al., 1999; Yates et al., 2015). The remaining sediment was dried to a constant weight and used to normalize NH4+ concentrations to per g dry weight. Sediment cores (1 cm depth, 1.3 cm diameter, n = 3) were collected for chlorophyll-a concentrations. Cores were freeze dried for 2 d, extracted in 10 mL of a 90% acetone solution for 24 h in the freezer, and chl-a was determined fluorometrically (Welschmeyer, 1994). Concentrations were normalized to per g dry weight. Aboveground biomass (n = 3) was harvested at each site during each sampling date by placing a 0.024 m2 quadrat over Spartina alterniflora and cutting at the base. Plant material was dried to a constant weight. Belowground biomass was measured in which sediment cores (5 cm depth, 9.5 cm diameter, n = 3) were sieved (2 mm) and the remaining plant material was dried to a constant weight. Experimental Design The effects of crude oil on nitrification, denitrification, and DNRA were determined by collecting sediment and conducting a lab incubation experiment. Sediment cores (5 cm depth, 9.5 cm diameter, n = 6) were collected, sieved (2 mm), subsampled into a 1 L beaker and stirred vigorously (between 300 and 700 rpm) for 30 min to homogenize the sediment. Sixty mL samples of the slurry were then transferred to 125 mL Erlenmeyer flasks (n = 12), allowed to settle overnight, and the overlying water was then replaced with artificial seawater (n = 4), 25% WAF (n = 4), or 100% WAF (n = 4). All treatments were prepared at a salinity of 26 ppt and flasks were shaken at 70 rpm in the dark and at room temperature for 6 d. Two days into the initial incubation of sediments from Dauphin Island, oxygen concentrations were measured in the water column, upper sediment, and lower sediment of control samples using a FireSting O2 fiber-optic oxygen sensor (PyroScience) to ensure the incubations were aerobic. The average oxygen concentrations in the water column, upper sediment, and lower sediment were 264.35 µmol L-1 (95.1% saturation), 56.25 µmol L-1 (20.2% saturation), and 8.50 µmol L-1 (3.1% saturation), respectively. Denitrification and DNRA After 6 d of incubation, 5 mL of homogenized sediment from each flask were transferred to exetainers (n = 8), four for denitrification analysis and four for DNRA. Exetainers were filled with 26 ppt artificial seawater, made anoxic by bubbling with 28N2 and capped with no headspace. Samples were shaken at 70 rpm at room temperature overnight in the dark to remove any residual oxygen or NO3-. Denitrification and DNRA potentials were determined with the isotope pairing technique (IPT; Nielsen 1992), where 15-labeled NO3- was added to sediment slurries and converted to 30N2 from denitrification or 15NH4+ from DNRA. For DNRA, sodium hypobromite (NaBrO) was added to oxidize 14+15NH4+ to 29+30N2 (Yin et al., 2014). Potential rates were measured using a membrane inlet mass spectrometer (MIMS) equipped with a copper reduction column (Eyre et al., 2002) for 29+30N2 signals. Following measurements on the MIMS, sediments were dried and rates were normalized to per kg of sediment per hour. Net Nitrification After 6 d of incubation, net nitrification was measured using methods modified from Henriksen et al. (1981) and Caffrey et al. (2010). Approximately 1 g of wet sediment was transferred to a new 125 mL Erlenmeyer flask and 50 mL of treatment water (control, 25% WAF, 100% WAF; n = 4 per treatment) was added. NH4Cl was added to bring the concentration to 100 µM of NH4+ and flasks were shaken at 130 rpm at room temperature in the dark for 24 hours. NO2+3- concentrations were determined photometrically (Grasshoff et al., 1983) on a UV-Vis spectrophotometer (Genesys 10S, Thermo Scientific) and normalized to per kg dry weight per hour.

Instruments:

Costech CHN analyzer model 4010 was used to measure sediment molar C/N; Genesys 10S UV-Vis spectrophotometer was used to measure sitewater PO4; Membrane Inlet Mass Spectrometer (MIMS) was used to measure dissolved 29N, 30N, O2, Ar and N2; Tecan Sunrise absorbance microplate reader was used to measure sitewater NO2+3; Trilogy fluorometer outfitted with a CDOM/NH4 module was used to measure pore water NH4; YSI 556 multiprobe was used to take point measurements of water column temperature and salinity

Provenance and Historical References:

Caffrey, Jane M., James T. Hollibaugh, Nafisa Bano, and John Christopher Haskins. 2010. Effects of upwelling on short-term variability in microbial and biogeochemical processes in estuarine sediments from Elkhorn Slough, California, USA. Aquatic Microbial Ecology 58(3): 261–271. doi:10.3354/ame01387 Eyre, Bradley D., Soren Rysgaard, Tage Dalsgaard, and Peter Bondo Christensen. 2002. Comparison of isotope pairing and N2:Ar methods for measuring sediment denitrification: Assumptions, modifications, and implications. Estuaries 25, 1077-1087. Grasshoff, Klaus, 1983. Determination of nitrite. In: Grasshoff, Klaus, Manfred Ehrhardt, Klaus Kremling. (Eds.), Methods of Seawater Analysis. verlag chemie, pp. 139-142. Harris, David, William R. Horwath, and Chris van Kessel, 2001. Acid fumigation of soils to remove carbonates prior to total organic carbon or carbon-13 isotopic analysis. Soil Science Society of American Journal 65(6): 1853–1856. https://doi.org/10.2136/sssaj2001.1853 Henriksen, K., Hansen, J.I., and Blackburn, T.H., 1981. Rates of nitrification, distribution of nitrifying bacteria and nitrate fluxes in different types of sediment from Danish waters. Marine Biology 61, 299-304. Holmes, Robert M., Alain Aminot, Roger Kerouel, Bethanie A. Hooker, and Bruce J. Peterson. 1999. A simple and precise method for measuring ammonium in marine and freshwater ecosystems. Canadian Journal of Fisheries Aquatic Science 56, 1801–1808. https://doi.org/10.1139/f99-128 Michel, Jacqueline, Edward H. Owens, Scott Zengel, Andrew Graham, Zachary Nixon, Teresa Allard, William Holton, P. Doug Reimer, Alain Lamarche, Mark White, Nicolle Rutherford, Carl Childs, Gary Mauseth, Greg Challenger, and Elliot Taylor. 2013. Extent and degree of shoreline oiling: Deepwater Horizon oil spill, Gulf of Mexico, USA. PLoS One 8(6):e65087. doi:10.1371/journal.pone.0065087 Nielsen, Lars Peter. 1992. Denitrification in sediment determined from nitrogen isotope pairing. FEMS Microbiol. Ecol. 86(4), 357–362. Welschmeyer, Nicholas A. 1994. Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and pheopigments. Limnology Oceanography. 39(8), 1985–1992. doi:10.4319/lo.1994.39.8.1985 Yates, D.F., 2015. Standard protocol for fluorimetric analysis of ammonium in marine and freshwater samples. United States Environmental Protection Agency. Office of Research and Development. National Health and Environmental Effects Research Laboratory. Gulf Ecology Division. Guoyu, Yin, Lijun Hou, Min Liu, Zhanfei Liu, and Wayne S. Gardner. 2014. A novel membrane inlet mass spectrometer method to measure 15NH4+ for isotope-enrichment experiments in aquatic ecosystems. Environmental Science Technology 48(16): 9555–9562. doi:10.1021/es501261s

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