Relationship of intertidal surface sediment chlorophyll concentration to hyperspectral reflectance and chlorophyll fluorescence |
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| Authors: | Jacco C Kromkamp Edward P Morris Rodney M Forster Claire Honeywill Scott Hagerthey David M Paterson |
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| Institution: | 1. Centre for Estuarine and Coastal Ecology (NIOO-CEMO), Netherlands Institute of Ecology, P. O. Box 140, 4400 AC, Yerseke, The Netherlands
3. Sediment Ecology Research Group, Gatty Marine Laboratory, University of St. Andrews, KY16 8LB, St. Andrews, Fife, Scotland
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| Abstract: | Estimating biomass of microphytobenthos (MPB) on intertidal mud flats is extremely difficult due to their patchy occurrence,
especially at the scale of an entire mud flat. We tested two optical approaches that can be applied in situ: spectral reflectance
and chlorophyll fluorescence. These two approaches were applied in 4 European estuaries with different sediment characteristics.
At each site, paired replicate measurements of hyperspectral reflectance, chlorophyll fluorescence (after 15 min dark adaptation,
Fo
15), sediment water content, and chlorophylla concentrations were taken (including breakdown products: chla+phaeo]). Sediments were further characterized by grain size and organic content analysis. The spectral signatures of tidal
flats dominated by benthic microalgae, mainly diatoms, could be easily distinguished from sites dominated by macrophytes;
we present a 3 waveband algorithm that can be used to detect the presence of macrophytes. The normalized difference vegetation
index (NDVI) was found to be most strongly correlated to sediment chla+phaeo], except for the predominantly sandy Sylt stations. Fo
15 was also significantly correlated to sediment chla+phaeo] in all but one grid (Sylt grid A). Our results suggest that the functional relationships (i.e., the slopes) between
NDVI or fluorescence and chla+ phaeo] were not significantly different in the muddier grids, although the intercepts could differ significantly, especially
for Fo
15. This suggests a mismatch of the optical depth seen by the reflectometer or fluorometer and the depth sampled for pigment
analysis. NDVI appears to be a robust proxy for sediment chla+phaeo] and can be used to quantify MPB biomass in muddy sediments of mid latitude estuaries. |
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