1. ¹Center for Environmental Diagnostics and Bioremediation, University of West Florida, Pensacola, FL, USA
2. ²Department of Marine Science, University of Georgia, Athens, GA, USA

Correspondence: JM Caffrey, Center for Environmental Diagnostics and Bioremediation, University of West Florida, 11000 University Parkway, Pensacola, FL 32514, USA. E-mail: jcaffrey@uwf.edu

³Current address: Department of Public Health Sciences, University of California, Davis, CA 95616, USA.

Received 22 May 2007; Revised 3 September 2007; Accepted 4 September 2007; Published online 4 October 2007.

Abstract

Nitrification, the oxidation of NH₄⁺ to NO₂^- and subsequently to NO₃^-, plays a central role in the nitrogen cycle and is often a critical first step in nitrogen removal from estuarine and coastal environments. The first and rate-limiting step in nitrification is catalyzed by the enzyme ammonia monooxygenase (AmoA). We evaluate the relationships between the abundance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) amoA genes; potential nitrification rates and environmental variables to identify factors influencing AOA abundance and nitrifier activity in estuarine sediments. Our results showed that potential nitrification rates increased as abundance of AOA amoA increased. In contrast, there was no relationship between potential nitrification rates and AOB amoA abundance. This suggests that AOA are significant in estuarine nitrogen cycling. Surprisingly, more of the variability in potential nitrification rates was predicted by salinity and pore water sulfide than by dissolved oxygen history.