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Improved estimation of carbon fixation rates from active flourometryusing spectral fluorescence in light-limited environments
Silsbe, G.M.; Hecky, R.E.; Smith, R.E.H. (2012). Improved estimation of carbon fixation rates from active flourometryusing spectral fluorescence in light-limited environments. Limnol. Oceanogr., Methods 10: 736-751. dx.doi.org/10.4319/lom.2012.10.736
In: Limnology and Oceanography: Methods. American Society of Limnology and Oceanography: Waco, Tex.. ISSN 1541-5856, more
Peer reviewed article  

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  • Silsbe, G.M.
  • Hecky, R.E.
  • Smith, R.E.H.

Abstract
    Bio-optical models predict photosynthetic electron transport rates through photosystem II (ETRPSII) from measures of irradiance (E), the absorption coefficient of pigments associated with PSII (a(PSII)) that are spectrally scaled to E ((a) over bar (PSII)), and the quantum efficiency of PSII (phi'(PSII)). However bio-optical models currently suffer from methodological uncertainties in the quantification of (a) over bar (PSII), and variable stoichiometry between ETRPSII and the more ecologically-relevant carbon fixation (P-C), defined here as the quantum requirement for carbon fixation (Phi(e,C) = ETRPSII x P-C(-1)). Here we analyze measures of P-C, phi'(PSII), and (a) over bar (PSII) across optical, thermal, nutrient and phytoplankton composition gradients in Lake Erie. We show that phi'(PSII) in the light-limited portion of the water column is relatively constant despite the wide range of biological and environmental conditions, but that variations in (a) over bar (PSII) are large. Measures of (a) over bar (PSII) are shown to be highly influenced by methodology as different approaches significantly influence measures of ETRPSII and Phi(e,C). A new technique that derives (a) over bar (PSII) from in situ spectral fluorescence measures is introduced and shown to yield ETRPSII estimates that correlate well with independent measures of P-C under light limited conditions. The Phi(e,C) inferred from this new approach agreed well with independent assessments in the lake and demonstrates that bio-optical models with well-parameterized (a) over bar (PSII) can be usefully predictive of light-limited P-C across wide biological and chemical gradients in this great lake.

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