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 2016-0

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.