Estimation of the microbial biomass in tidal flat sediment by fumigation-extraction

Abstract

A transect of ten profiles was laid out in 20 m intervals on a tidal sand flat approximately 100 m from the east shore of Sylt until the next tideway was reached. Sediment samples were taken from 0-2 cm depth (oxic layer) and 2-4 cm depth (anoxic layer). The average content of organic carbon (C) was 2.41 mg g-1 in the oxic layer and 1.86 mg g-1 in the anoxic layer. The organic C content correlated positively with non-biomass C, 0.5 M K2SO4 extractable C, total nitrogen (N), cation exchange capacity (CEC), and the textural classes <200 μm, and negatively correlated with the coarse sand fraction. The average total C:N ratio was 7.0 in the oxic layer and 6.7 in the anoxic layer, indicating that the C input comes entirely from the microflora. CHCl3-labile C was measured by the fumigation-extraction method and was converted to microbial biomass C (values in brackets). The average content of CHCl3-labile C was 407 μg g-1 (903 μg g-1) in the oxic layer and 214 μg g-1 (476 μg g-1) in the anoxic layer. CHCl3-labile C did not correlate with CEC and the textural classes <200 μm, indicating that conditions other than the physical environment determine this fraction (C input, grazing). © 1995 Biologische Anstalt Helgiland.