A simple, user friendly tool to readjust raw PAM data from field measurements to avoid over- or underestimating of microphytobenthos photosynthetic parameters

Intertidal mudflats are among the most productive ecosystems and microphytobenthic (MPB) biofilms play a key role in primary production. MPB primary production varies at short spatial and temporal scales. Accurate measurements thus require rapid non-intrusive methods like pulse amplitude modulate (PAM) fluorescence. However, the effect of granulometry and chl a concentration profile in light attenuation on irradiance and on fluorescence signal in the photic layer need to be taken into account when primary production is estimated using PAM. We propose a tool to readjust raw photosynthetic parameters (rETRmax, α, Ik) estimated from PAM measurements on the field, to avoid over- or underestimation. To develop the tool, we used models previously designed by Kühl and Jørgensen (1992), Serôdio (2004) and Forster and Kromkamp (2004) by integrating the chl a distribution profiles and sediment granulometry from pure sand to pure mud. The sensitivity of the correction to sediment granulometry and the shape of chl a profile were evaluated theoretically using a typical fluorescence data set obtained using PAM measurements. Our results confirm the importance of accounting for both the chl a profile and sediment granulometry when estimating a light attenuation coefficient. We show that, with the same chl a profile, the photosynthetic parameters are more underestimated in mud than in a sandy environment. Thus, granulometry and the chl a profile need to be systematically quantified and used to correct raw data measured in field studies using PAM before estimating photosynthetic parameters. The numerical tool is available as an e-document that is simple and easy to apply to any PAM data.