Coastal water column ammonium and nitrite oxidation are decoupled in summer. (5th September 2016)

• Record Type: Journal Article
• Authors: Heiss, Elise M.; Fulweiler, Robinson W.
• Is Part Of: Estuarine, coastal and shelf science. Volume 178(2016)
• Page Start: 110
• Page End: 119
• Publication Date: 2016-09-05
• Subjects: Nitrification -- Nitrogen cycle -- Water column -- Environmental effects -- USA, Rhode Island, Narragansett Bay; Estuarine oceanography -- Periodicals; Coasts -- Periodicals; Estuarine biology -- Periodicals; Seashore biology -- Periodicals; Coasts; Estuarine biology; Estuarine oceanography; Seashore biology; Periodicals; 551.461805
• DOI: 10.1016/j.ecss.2016.06.002
• Languages: English
• ISSNs: 0272-7714

Abstract

Abstract: Water column nitrification is a key process in the nitrogen cycle as it links reduced and oxidized forms of nitrogen and also provides the substrate (nitrate) needed for reactive nitrogen removal by denitrification. We measured potential water column ammonium and nitrite oxidation rates at four sites along an estuary to continental shelf gradient over two summers. In most cases, nitrite oxidation rates outpaced ammonium oxidation rates. Overall, ammonium and nitrite oxidation rates were higher outside of the estuary, and this trend was primarily driven by higher oxidation rates in deeper waters. Additionally, both ammonium and nitrite oxidation rates were impacted by different in situ variables. Ammonium oxidation rates throughout the water column as a whole were most positively correlated to depth and salinity and negatively correlated to dissolved oxygen and light. In contrast, nitrite oxidation rates throughout the water column were negatively correlated with light and pH. Multivariate regression analysis revealed that while both surface (<20 m) and deep (>20 m) ammonium oxidation rates were most strongly predicted by depth and light, surface rates were also regulated by salinity and deep rates by temperature. Surface (<20 m) nitrite oxidation rates were best explained by [H + ] (i.e. pH) alone, while salinity, [H + ], temperature, and depth all played a role in predicting deep (>20 m) nitrite oxidation rates. These results support the growing body of evidence that ammonium oxidation and nitrite oxidation are not always coupled, should be measured separately, and are influenced by different environmental conditions. Highlights: Water column NH4 + and NO2 − oxidation rates increase along a shore to shelf transect. Oxidation rate differences across this gradient were driven by increasing rates with depth. NO2 − oxidation rates outpace NH4 + oxidation rates in the estuary and offshore. NH4 + and NO2 − oxidation rates are most impacted by different environmental variables.