Changes in the yield of microphytobenthic chlorophyll from nutrients: Considering denitrification

The yield of microphytobenthic (MPB) chlorophyll from nitrogen expresses the relationship between chlorophyll formation and nutrient consumption within the surface sediment. In shallow coastal lagoons MPB have an important role in chlorophyll dynamics and may represent the majority of microalgal chlorophyll pigments. Given that chlorophyll has been used as an indicator of eutrophication, the yield is of utmost importance. Furthermore, the yield is a key parameter in models that aims at predicting eutrophication. Estimates of the MPB yield have been previously obtained from a series of microcosm experiments. However, discrepant results in nitrogen fluxes suggested the importance of other processes such as denitrification. Therefore, denitrification rates were used for the calculation of nutrient fluxes and new yield estimates were obtained for muddy sediments. Whereas the earlier estimate obtained was of 4.1 μg chl. (μmol N) ^-1, after including the denitrification rate in the calculation this value was reduced from 5 to 35%.