Abstract:

This dataset contains potential denitrification and CH4 oxidation rates and concentrations of dissolved nutrients and greenhouse gases [nitrous oxide (N2O) and CH4] obtained in 2013, 2015, and 2016 during summer aboard the RV Pelican (PE1403, PE1601, PE1603, PE1605, and PE1703) in the northern Gulf of Mexico. Anthropogenic nutrient inputs fuel eutrophication and development of hypoxic conditions ([O2] < 2 mg L-), threatening coastal and near shore environments across the globe. The world’s second largest human-caused coastal hypoxic zone occurs annually along the Louisiana (LA) shelf. Springtime nitrogen (N) loading from the Mississippi River, combined with summertime stratification and increased water residence time on the shelf, promotes establishment of an extensive hypoxic zone that persists throughout the summer. The patterns of denitrification and methane (CH4) oxidation were investigated along the LA shelf. Denitrification rates up to 1,900 nmol N L-1 d-1 and CH4 oxidation rates as high as 192 nmol L-1 d-1 in hypoxic zone waters were documented. These zones were characterized by high concentrations of N2O (range: 1 to 102 nM) and CH4 (range: 3 to 641 nM). Ecosystem scaling estimates suggest that pelagic denitrification could remove between 0.1 and 47 % of the N input, whereas CH4 oxidation could remove between <1 and 16 % of the CH4 along the shelf over the summer hypoxic period. Denitrification and methane oxidizing bacteria within the LA shelf hypoxic zone were unable to keep up with the additional N and CH4 inputs to the water column. These rates are variable and physiochemical dynamics appear to regulate the microbial removal capacity for both reactive N species and CH4 in this ecosystem.

Suggested Citation:

Joye, Samantha and Mary-Kate Rogener. 2021. Potential denitrification and CH4 oxidation rates and concentrations of dissolved nutrients and greenhouse gases [nitrous oxide (N2O) and CH4] obtained aboard the RV Pelican (PE1403, PE1601, PE1603, PE1605, and PE1703) in the northern Gulf of Mexico during summer months between 2013-07-21 to 2016-07-31. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/SQNEJDPR

Purpose:

Determine the role of denitrification and methane oxidation in a Gulf of Mexico environment undergoing significant environmental shifts due to human fertilizer run off.

Data Parameters and Units:

The cruise documentation for the RV Pelican, (PE1403, PE1601, PE1603, PE1605, and PE1703) is attached and cruises were led by chief scientists Nancy Rabalais and Frank Stewart. Headers are: Site: Collection Type; Lat (latitude degree minutes seconds), Long (longitude degrees minutes seconds), Date (sampling date, dd/mm/yyy), Time (L) (local), Depth (Depth from surface in water, m); NH4 (ammonium μmol/L); NO2 (nitrite μmol/L); NOx (μmol/L); NO3 (nitrate μmol/L); DIN (dissolved inorganic nitrogen μmol/L); DON (dissolved organic nitrogen μmol/L); PO4 (phosphate μmol/L); DIN:DIP (dissolved inorganic nitrogen/dissolved inorganic phosphate molar ratio); DOC (dissolved organic carbon μmol/L); N2O (nitrous oxide nmol/L); CH4 (methane nmol/L); Methane oxidation (pmol L-1 d-1); Methane Oxidation st deviation (standard deviation, pmol L-1 d-1); Turnover Rate Constant (d-1); Turnover Rate Constant standard deviation (d-1); Denitrification rate (nmol L-1 d-1); Denitrification rate standard deviation (nmol L-1 d-1) All means and standard deviations are calculated from triplicate incubations.

Methods:

Potential denitrification rates were determined using stable isotope 15N tracer method. Methane oxidation rates were determined using radioactive tracer method. Experimental incubations were conducted at in situ temperature.

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