[L&O Featured Article] L&O Featured Article, Vol. 50 (1) January 2005

[lo-feature at aslo.org]

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

de Beer, Dirk, Frank Wenzhöfer, Timothy G. Ferdelman, Susan E. Boehme, Markus Huettel, Justus E. E. van Beusekom, Michael E. Böttcher, Niculina Musat, and Nicole Dubilier. 2005. Transport and mineralization rates in North Sea sandy intertidal sediments, Sylt-Rømø Basin, Waddensea. Limnol. Oceanogr. 50: 113-127.

The article is freely available at:

          http://aslo.org/lo/toc/vol_50/issue_1/0113.pdf

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

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

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Introductory Comments by Samantha Joye (L&O Associate Editor)

Permeable sandy sediments are an important habitat found in estuaries and along the continental shelf across the globe.  Such sediments were long assumed to play minor roles in coastal biogeochemical cycles because the low organic content and lower numbers of microbes observed in these sediments were assumed to equate with low (potential) rates of metabolism.  Recently, however, that view has changed and permeable sands are now viewed as dynamic environments that support high rates of metabolism.  We now realize that waves and tides accelerate flow through sandy sediments, providing a constant source of high-energy electron acceptors, such as oxygen and nitrate, as well as a steady input of reactive organic matter via sand filtration of material suspended in the circulating fluid.  

In permeable sediments, physical processes generate environmental complexity at multiple scales, making it necessary to conduct in situ studies in conjunction with laboratory studies in order to understand the dynamics of the system.  The featured L&O article by de Beer, Wenzhöfer, Ferdelman, Boehme, Huettel, van Beusekom, Böttcher, Musat, and Dubilier presents results from a comprehensive, interdisciplinary study of transport processes, geochemistry, microbial activity and microbial distributions in the sandy intertidal environments of the Sylt-Rømø Basin (North Sea).  de Beer et al. applied a diverse suite of tools from a variety of disciplines, including hydrodynamics, in situ sensor technology, ex situ rate measurements, geochemistry, and molecular biology, to provide important insight into the physical, geochemical and microbial dynamics of the habitat.  Using this approach, de Beer et al. estimated flow rates through the sediments of 160-500 L m-2 d 1 and concluded that the entire water body of the Wadden Sea can pass through can pass through the sandy sediments within 3-10 days.  These high rates of flow through the sediment result in high rates of aerobic respiration (~105-175 mmol O2 m-2 d 1), primary production (= 35 mmol O2 m-2 d 1), and sulfate reduction (~0.8-13.7 mmol m-2 d 1). Variation in the amount of microbial rRNA closely tracked patterns in activity.

This paper makes several significant contributions to our understanding of the biogeochemistry of sandy tidal flats. First, the paper documents the dynamic interplay between physical factors and the pore water oxygen regime.  The combination of in situ and ex situ O2 microprofiling provided a powerful method for determining rates of fluid flow through the sediments.  Second, advective inputs of oxygen and organic matter are shown to stimulate microbial activity significantly in these sandy sediments.  Third, high oxygen fluxes maintain the sandy sediments in a high-energy oxidizing state, preventing the accumulation of reduced metabolites like hydrogen sulfide despite high rates of microbial primary production.  Such interdisciplinary studies are required to advance our understanding dynamic sedimentary systems.