MEPS 478:57-70 (2013)  -  DOI: https://doi.org/10.3354/meps10040

ABSTRACT: We provide the first reported estimates of anammox activity in tropical continental shelf sediments (southern section of the Great Barrier Reef lagoon; GBRL). The measured contribution of anammox to total N₂ production was up to 70% but restricted to only 1 of the 4 (2 inshore and 2 offshore) sites assayed. Sediment characteristics (contents of total organic carbon [TOC] and manganese [Mn], C:N ratio) at this site appeared to favour anammox activity and the estimated maximum rate was 4.9 µmol m^-2 h^-1. Anammox bacteria may be a significant contributor to N₂ production along the coastal zone of the GBRL. The availability of labile (low C:N) TOC seemed to drive denitrification to completion in the offshore sediments. However, rates of NO₃^- reduction to NH₄⁺ at the offshore sites were comparable to or higher than denitrification rates. It was unclear whether dissimilatory or assimilatory processes were responsible for the observed reduction of NO₃^- to NH₄⁺ at the offshore sites. At the 2 inshore sites, NO₃^- reduction to NH₄⁺ was a larger sink for NO₃^- than denitrification. Anammox does exist in the tropical continental shelf sediments of the GBRL and should be studied further to determine its role in larger scale N cycling. The roles of assimilatory and dissimilatory nitrate reduction to ammonium also need to be assessed within the GBRL.

KEY WORDS: Great Barrier Reef · Anammox · Dissimilatory/assimilatory nitrate reduction to ammonia · Denitrification