Marine Geology, 40 (1981) 155-170 155 Elsevier Scientific Publishing Company, Amsterdam -Printed in The Netherlands VARIABILITY IN TOTAL MICROBIAL BIOMASS MEASUREMENTS MADE IN CROSSSECTIONS OF SALT-MARSH CREEKS THOMAS H. CHRZANOWSKI1, L. HAROLD STEVENSON1 and BJORN KJERFVE2 Departments o f Biology', and Geology2,and The Belle W. Baruch Institute for Marine Biology and Coastal Research, University o f South Carolina, Columbia, SC 29208 (U.S.A.) (Received June 10,1980) ABSTRACT Chrzanowski, T.H., Stevenson, L.H. and Kjerfve, B., 1981. Variability in e t a 1 microbial biomass measurements made in cross-sections of salt-marsh creeks. Mar. Geol., 40: 155-170. The temporal fluctuation and distribution of microbial biomass were studied at two salt-marsh creeks having different salinities and hydrographic features. One creek, North Jones Creek, is adjacent to the marsh inlet, while the second creek, South Jones Creek, interfaces with a brackish-water embayment. Samples for analysis of microbial biomass, measured as adenosine 5'-triphosphate (ATP), were collected synoptically for 25 h from three depths at each of three sites within each creek cross-section. The temporal fluctua- tion pattern of ATP at North Jones Creek followed a tidal rhythm with maximum con- centrations occurring at high tide. The temporal fluctuation pattern at South Jones Creek was somewhat erratic with highest concentrations of ATP recovered from samples collected during flooding tides. The distribution of mean ATP densities as well as net flux through each interface proved to be complex which suggests that sampling depth and station placement are critical in determining net fluxes through marsh creeks. INTRODUCTION There is an almost dogmatic belief that salt-marshes are exporters of organic materials (Valiela et al., 1978), but only recently have studies rigor- ously attempted to assess the functional role of such systems in coastal-zone ecology. Classically, material transport between a marsh and estuary has been estimated from mass-balance studies. In such studies, investigators select a transect across a creek draining a system and attempt to monitor movements of materials through the transect (Woodwell et al., 1977; Valiela et al., 1978; Rkenbrecher and Stevenson, 1978). Even though the body of literature dealing with material fluxes is developing rapidly, many studies lack sound baseline measurements and the absence of standardized techniques disallows meaningful comparisons among studies. Thus, one finds that the creeks monitored have ranged in width from 6 m to approximately 50 m, the number of sampling stations have been limited to one (Erkenbrecher and Stevenson, 1975; ~ einle and Flemer, 1976; Settlemyre and Gardner, 1977; 0025-3227/8l/OOOO-0000/$02.50 @ 1981 Elsevier Scientific Publishing Company