[L&O Featured Article] L&O Featured Article, Vol. 49 (6) November 2004

[lo-feature at aslo.org]

The Featured Article in the November 2004 issue of L&O is:

Larned, Scott T., Vladimir I. Nikora, and Barry J.F. Biggs. 2004. Mass-transfer limited nitrogen and phosphorus uptake by stream periphyton: a conceptual model and experimental evidence.  Limnol. Oceanogr. 49:1992-2000.  

The article is freely available at:
          http://www.aslo.org/lo/pdf/vol_49/issue_6/1992.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 Joe Ackerman (L&O Associate Editor)

Benthic vegetation (ranging from periphyton, aquatic and wetland plants, seagrasses, and kelps) is attaining a more prominent position in limnological and oceanographic circles, as aquatic scientists have begun to realize the important roles that these attached algae and macrophytes play. In addition to being primary producers, these organisms modify local and regional flow, are sinks for nutrients, are locations of biogeochemical activity, trap and stabilize particulate matter, create important habitats for myriad other organisms, and among other things, are drivers of benthic environments. 

The featured L&O article by Larned, Nikora, and Biggs examines the processes that control nutrient acquisition by stream periphyton. Periphyton productivity is affected both by the mass transfer of nutrients from the surrounding fluid, and by the kinetics of cellular uptake. There has been considerable interest in the dichotomy between mass-transfer (and hence the role of fluid dynamics) versus kinetic control. The situation is complicated by the unfortunate tendency to view periphyton as a “thin layer” rather than a 3-dimensional “forest” of “filaments, diatom chains, and clusters [of algal cells]”. Hoping to resolve this dichotomy, Larned et al. studied the controls on the uptake of nitrate and dissolved reactive phosphorous both empirically and by using a conceptual model that incorporated the morphology and location of the “periphyton elements” within the periphyton canopy and benthic boundary layer (BBL). Their experimental results demonstrate that the periphyton canopy was as tall as or taller than the height of the diffusive sublayer of the BBL, even at the lowest velocities. Consequently, mass-transfer control occurs in the diffusive sublayer surrounding the individual periphyton elements. 

This research is important because it quantifies parameters that are used quite loosely in the literature. It also provides experimental evidence for mass-transfer control in oligotrophic periphyton systems, and provides a general conceptual framework for investigating nutrient uptake by benthic producers. It should serve as the basis for investigations of more complex stream periphyton systems, and may also prove useful for understanding similar issues in freshwater and marine macrophyte canopies.