Chlorophyll concentrations were determined by fluorescence after acetone
extraction (Holm-Hansen etai, 1965) and primary production was measured with
a modified version of the H14CO3 uptake method (Steemann Nielsen, 1952).
Alkaline phosphatase activity was measured from the increase in fluorescence,
when 4-methylumbelliferyl phosphate (MU-FP) substrate (Sigma) was
hydrolyzed to give the highly fluorescent product 4-methylumbelliferone (MU)
(Hoppe, 1983).