Influence of water-column depth and mixing on phytoplankton biomass, community composition, and nutrients
2008 (English)In: Limnology and Oceanography, ISSN 0024-3590, Vol. 53, no 6, 2361-2373 p.Article in journal (Refereed) Published
We independently manipulated mixing intensity (strong artificial mixing vs. background turbulence) andwater-column depth (2 m, 4 m, 8 m, and 12 m) in order to explore their separate and combined effects in a fieldenclosure experiment. To accentuate the vertical light gradient, enclosures had black walls, resulting in a euphoticdepth of only 3.7 m. All enclosures were placed in a well-mixed water bath to equalize temperature acrosstreatments. Phytoplankton responded to an initial phosphorus pulse with a transient increase in biomass, whichwas highest in the shallowest, least light-limited water columns where dissolved mineral phosphorus subsequentlybecame strongly limiting. As a consequence, the depth-averaged mineral phosphorus concentration increased andthe seston carbon (C) : phosphorous (P) ratio decreased with increasing water-column depth. Low turbulenceenclosures became quickly dominated by motile taxa (flagellates) in the upper water column, whereas mixedenclosures became gradually dominated by pennate diatoms, which resulted in higher average sedimentation ratesin the mixed enclosures over the 35-d experimental period. Low turbulence enclosures showed pronouncedvertical structure in water columns .4 m, where diversity was higher than in mixed enclosures, suggesting verticalniche partitioning. This interpretation is supported by a primary production assay, where phytoplanktonoriginating from different water depths in low-turbulence treatments had the relatively highest primaryproductivity when incubated at their respective depths of origin.
Place, publisher, year, edition, pages
2008. Vol. 53, no 6, 2361-2373 p.
IdentifiersURN: urn:nbn:se:umu:diva-20252OAI: oai:DiVA.org:umu-20252DiVA: diva2:208331