SPATIOTEMPORAL DYNAMICS OF NITRIFYING MICROBIAL COMMUNITIES IN THE CAPE FEAR RIVER ESTUARY

Ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) play important roles in nitrification, a key process in the nitrogen cycle that contributes to the transformation of ammonium (NH₄⁺) into nitrite (NO₂⁻) and ultimately nitrate (NO₃⁻). Nitrification is particularly critical in estuarine environments as it can alter the composition of inorganic nitrogen exported to coastal waters. In the Cape Fear River Estuary (CFRE) near Wilmington, NC (southeastern USA), we conducted time-series sampling to assess spatiotemporal changes in abundance, diversity, and activity of nitrifying microbial communities, along with other environmental parameters such as temperature, salinity, dissolved oxygen, and nutrient concentrations. Using quantitative PCR (qPCR), we found that AOA exhibit an annual, recurrent ‘bloom’ each summer, with populations increasing 3-4 orders of magnitude above their typical abundance, aligned with previous work in coastal Georgia, USA. This AOA bloom coincided with a pronounced NO₂⁻peak, suggesting a decoupling of ammonia oxidation from subsequent nitrite oxidation processes. A strong and significant correlation between AOA gene abundance and NO₂⁻concentration was identified in the CFRE, whereas no correlation was found with AOB and NO₂⁻. These results suggest that AOA-mediated ammonia oxidation is a primary factor in the seasonally recurring NO₂⁻accumulation within the CFRE. Understanding these seasonal dynamics is critical for identifying the specific environmental triggers that drive AOA blooms, and any impacts they may have on coastal ecosystems.

Presentation Preference: Either

Primary Presenter: Parker Lawrence, University of North Carolina at Wilmington (pbl5777@uncw.edu)

Authors:

Parker Lawrence, University of North Carolina at Wilmington  (pbl5777@uncw.edu)

Bradley Tolar, University of North Carolina at Wilmington  (tolarb@uncw.edu)