[L&O Featured Article] L&O Featured Article, Vol. 50 (6) November 2005

[lo-feature at aslo.org]

The Featured Article in the November 2005 issue of L&O is:

Gribsholt, Britta, Henricus T. S. Boschker, Eric Struyf, Maria Andersson,
Anton Tramper, Loreto De Brabandere, Stefan van Damme, Natacha Brion,
Patrick Meire, Frank Dehairs, Jack J. Middelburg, and Carlo H. R. Heip.
2005. Nitrogen processing in a tidal freshwater marsh: A whole ecosystem 15N
labeling study. Limnol. Oceanogr. 50(6): 1945-1959.

The article is freely available at:

http://aslo.org/lo/toc/vol_50/issue_6/1945.pdf

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Introductory comments by Stephen K. Hamilton (L&O Associate Editor) 

L&O Featured Article: 

Gribsholt, Britta, Henricus T. S. Boschker, Eric Struyf, Maria Andersson,
Anton Tramper, Loreto De Brabandere, Stefan van Damme, Natacha Brion,
Patrick Meire, Frank Dehairs, Jack J. Middelburg, and Carlo H. R. Heip.
2005. Nitrogen processing in a tidal freshwater marsh: A whole ecosystem 15N
labeling study. Limnol. Oceanogr. 50(6): 1945-1959. 

Stable isotopes have increasingly been employed in freshwater and marine
research during the past few decades, and novel applications and approaches
continue to be reported.  Most stable isotope studies can be grouped into
either studies of natural abundances or experimental tracer additions.
Natural abundance studies have yielded many insights, but the information
they provide can be limited.  Stable isotope additions offer many advantages
for tracing biogeochemical cycles and elemental flow through food webs, but
they can be expensive and complex to carry out, particularly when working in
situ or in large mesocosms.  Examples of experiments based on in-situ
isotope additions include the Lotic Intersite Nitrogen Experiment
(http://www.biol.vt.edu/faculty/webster/linx/), which has refined the
methods for the study of nitrogen cycling in small streams.  

Britta Gribsholt and coworkers have taken in-situ stable isotope additions
to a new level by performing a 15N-labelled ammonium addition at a tidal
freshwater marsh.  Nitrogen processing in these kinds of wetlands is of
interest because it bears on the problem of nitrogen pollution and
eutrophication of coastal waters, much of which derives from river inputs.
This experiment revealed the fate of ammonium as water entered and departed
the marsh over tidal cycles, and showed that a substantial fraction was
oxidized to nitrate (and some to nitrous oxide) at the sediment-water
interface, while relatively little nitrogen was retained in the ecosystem.
Such whole-ecosystem transformation rates would have been difficult to
obtain by traditional approaches.  The study had to surmount a number of
technical challenges, including the continually changing water inflow and
outflow rates and surface area of inundation.  Gribsholt's work joins a
handful of other pioneering studies (e.g., Holmes et al. 2000, Tobias et al.
2003) that have employed whole-ecosystem isotope additions to study
biogeochemical cycling in estuaries and tidal wetlands, and we can
anticipate more such studies in the future.  


References

Holmes, R. M., B. J. Peterson, L. A. Deegan, J. E. Hughes, and B. Fry. 2000.
Nitrogen biogeochemistry in the oligohaline zone of a New England estuary.
Ecology 81: 416-432. 

Tobias C. R., M. Cieri, B. J. Peterson, L. A. Deegan, J. Vallino, and J.
Hughes. 2003. Processing watershed-derived nitrogen in a well-flushed New
England estuary. Limnol. Oceanogr. 48: 1766-1778.