[L&O Featured Article] L&O Featured Article, Vol. 52 (4) July 2007

[L&O Feature Articles Announcements]

The Featured Article for the July 2007 issue of L&O is:

Hannig, M., G. Lavik, M. M. M. Kuypers, D. Woebken, W. Martens-Habbena, and
K. Jürgens. 2007. Shift from denitrification to anammox after inflow events
in the central Baltic Sea. Limnol. Oceanogr. 52(4): 1336-1345.

This article can be read at:

http://www.aslo.org/lo/toc/vol_52/issue_4/1336.pdf


Introductory comments by Mary Scranton (L&O Associate Editor) 

Hannig and his coauthors describe a study of the metabolic pathways
occurring in the Gotland Deep, an intermittently anoxic basin in the Baltic
Sea. By combining geochemical and microbial techniques, they demonstrate
that chemolithotrophic denitrification was most important in the redoxcline
prior to a major intrusion of oxic waters. No evidence for heterotrophic
denitrification was found, consistent with previous water column studies off
Namibia and Peru/Chile. They speculate, but do not demonstrate
experimentally, that sulfur species such as H2S, but possibly including
other compounds, act as the dominant electron donors for the
chemolithotrophic denitrification.

Following the intrusion, a suboxic zone was established where nitrate,
nitrite, and ammonium concentrations were all below detection limits. Under
these circumstances, manganese concentrations (both oxidized and reduced
forms) increased and anammox became the dominant pathway for nitrogen
removal. Apparently the intrusion of oxygenated water enhanced the formation
of manganese oxides, leading to the disappearance of the nitrate-sulfide
interface.

This paper is a very nice example of a well designed biogeochemical study in
which chemical analyses and isotope rate measurements have been combined
with microbial approaches (FISH and CARD-FISH) to convincingly demonstrate
shifts in activity associated with major physical perturbations. Fluctuating
oxygenated and reducing conditions exist in many environments ranging from
the Black Sea and Cariaco Basin to coastal hypoxic areas to mobile mud
belts, and thus results from studies of this type have broad implications.