The temporal dynamics of benthic chlorophyll a (chl a) in the Ems estu
ary (The Netherlands, NW Europe) were studied over ca 3 yr at 6 statio
ns. The mean annual concentrations of chl a ranged from 28.6 to 247.0
mg m(-2) in the top 0.5 cm of sediment. The relative vertical distribu
tion of chl a in the sediment revealed a profile which was similar for
5 of the 6 stations. This distribution of chl a, representing vital c
ells, was reconstructed from typical vertical distributions of chl a i
ncluding the derivatives with an absorption peak at the same wavelengt
h. The graphs were converted and used to calculate the total biomass o
f the microphytobenthos expressed as organic carbon. The lowest value
of the mean annual biomass of microphytobenthos per station was 3.1 g
C m(-2), and the highest was 16.7 g C m(-2). Average values over the t
otal period investigated ranged from 3.2 to 11.0 g C m(-2). With one e
xception where a value of 0.6 was calculated, the ratio between the bi
omass from the 0.5 to 2.0 cm sediment layer and that from the 0 to 2 c
m sediment layer was fairly constant (0.40 to 0.47). This illustrates
that sampling only the top 0.5 cm of the sediment to determine the mic
rophytobenthos chl a and multiplying this value by the corresponding C
/chl a ratio results in the carbon biomass being grossly (40 to 60%) u
nderestimated. The use of an incorrect C/chl a ratio (which varied bet
ween 40 and 61 during the study period) in this calculation can increa
se this deviation by a further 50 %.