Benthic microbial response to a sedimentation event at low temperature in sediments of a eutrophic lake

Abstract

A laboratory study was performed in order to investigate the short-term response of a benthic microbial community to a spring bloom sedimentation event at low temperature. In the laboratory, organic material collected with phytoplankton nets was added to undisturbed sediment cores receiving the following four treatments: (1) addition of organic material and aeration of the water overlying the sediment, (2) only aeration, (3) only organic material addition, and (4) no organic material addition or aeration. Changes in microbial activity and biomass in the sediments were followed during six days at an experimental temperature of 4ºC by means of measurements of heat production, bacterial production ([³H]thymidine incorporation), oxygen consumption, bacterial biomass, ATP concentration and chlorophyll a concentration.

In treatments with organic material additions, a response in terms of simultaneously increasing heat production, bacterial production and oxygen consumption rates was observed. Microbial activity increased slowly during the first four days in cores with organic matter addition, and between Days 4 and 6 microbial activity approximately doubled in aerated cores and decreased in non-aerated cores. Mineralization rates calculated from heat production showed that a small proportion of the added organic matter was mineralized in the surface sediment during the experiment. The results of this study show that the benthic microbial community could respond to an input of organic material at low temperature within a few days. A well oxygenated overlying water phase was necessary for the response to proceed.