[L&O Featured Article]May 2000 L&O Featured Article now available

[lo-feature-admin@aslo.org]

The featured article in the May issue of L&O is:

"Cyanobacterial blooms in the Baltic Sea: Natural or human-induced?" by
Bianchi, Thomas S., Erika Engelhaupt, Per Westman, Thomas Andr=E9n, Carl
Rolff, and Ragnar Elmgren. Limnol. Oceanogr. 45: 716-726.

This article is freely available at the Web address:

          http://aslo.org/lo/toc/vol_45/issue_3/0716.pdf

Instructions for reading PDF files are located on the ASLO web page:

          http://aslo.org/help/loonline.html

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Introductory comments by Jonathan Cole (L&O Associate Editor)

Featured article: "Cyanobacterial blooms in the Baltic Sea: Natural or
human-induced?" by Bianchi, Thomas S., Erika Engelhaupt, Per Westman,
Thomas Andrén, Carl Rolff, and Ragnar Elmgren. L&O 45(3): 716-726.

This month's Featured L&O paper is likely to be controversial. The
 question posed in the title is investigated by looking at the Baltic's long-term
sedimentary record. Sediments that have accumulated over 8000 years are
examined for algal pigments and a stable isotope of nitrogen (15-N),
interpreted as a signal for atmospherically fixed nitrogen. Results show
that blooms of nitrogen-fixing cyanobacteria have occurred regularly in the
Baltic for the past 7000 years, which is when saltwater intruded and turned
the previously freshwater "Ancylus Lake" into the brackish Baltic sea. The
authors conclude that cyanobacterial blooms are a natural and old
phenomenon in the Baltic rather than a recent and human-induced one.

This conclusion has serious implications for the management of
eutrophication in the Baltic. Baltic countries are presently trying to
reduce the inputs of both phosphorus and nitrogen by as much as 50%.
Critics of this expensive project suggest that removing phosphorus alone
would suffice since this would eliminate blooms of nitrogen-fixing
cyanobacteria. Bianchi et al. argue that phosphorus reduction alone would
in fact shift the Baltic to a new, man-induced state rather than restore it
to its natural state.

An intriguing result in this paper is that cyanobacterial blooms did not
occur in the Ancylus Lake freshwater period, i.e., prior to 7000 years ago.
The authors suggest that altered stratification and elevated sulfate
concentrations resulting from intrusion of seawater caused the sediments to
release previously accumulated phosphorus.