Microbial activity and bioturbation-induced oscillations in pore water chemistry of estuarine sediments in spring

Temperature increases occurring during the spring in temperate shallow-water marine sediments lead to increased microbial activity, oxygen removal and a decrease in redox potential1,2. These changes cause shifts in the relative importance of specific terminal electron acceptors used in bacterial respiration1. The decrease in redox potential affects the physiochemical state of redox-sensitive elements such as iron and sulphur2. In addition to changing sedimentary chemistry, these variations may affect the overlying water through changes in diffusional fluxes and other processes. Such biogeochemical processes are further complicated when the sediments are subjected to particle reworking and irrigation by bioturbating infauna3,4. In an attempt to clarify the chain of sedimentary events occurring between the relatively oxidizing, inactive winter and the highly reducing, active summer, we examined several chemical and biological parameters in samples of estuarine sediment collected from February to July of 1980. Some of those data are presented here, and we report that the combined effects of increasing microbial activity and the onset of rapid bioturbation produced oscillations in the concentrations of pore water constituents in these sediments