An assessment of a mesocosm approach to the study of microbial respiration in a sandy unsaturated zone

Hendry, M. (2001) An assessment of a mesocosm approach to the study of microbial respiration in a sandy unsaturated zone. Groundwater, 39(3), pp. 391-400. (doi: 10.1111/j.1745-6584.2001.tb02323.x)

Abstract

Microbial respiration rates were determined through a 3.2 m thick, sandy unsaturated zone in a 2.4 m diameter X 4.6 m high mesocosm. The mesocosm was maintained under near constant temperature (18° to 23°C) and reached steady moisture content conditions after several hundred days. Soil-gas CO2 concentrations in the mesocosm ranged from 0.09% to 3.31% and increased with depth. Respiration rates within the mesocosm were quantified over a 342–day period using measured CO2 concentrations and a transient, one-dimensional finite-element model. Microbial respiration rates were 2 × 10–1μg C·g−1·d−1 throughout most of the system, but decreased to 10–4 to 10–3μg C·g−1·d−1 within the capillary fringe. Microbial respiration rates were also determined in minicosms (500 g sample mass) over a range in temperatures (4° to 30°C) and volumetric moisture contents (0.044 to 0.37). The functional dependence of CO2 production on temperature and soil-moisture content was similar for the two scales of laboratory observation. Respiration rates in the minicosms, for temperatures and moisture contents in the mesocosm, were up to an order of magnitude greater than those determined for the mesocosm. The higher respiration rates in the minicosms, compared to the mesocosm, were attributed to greater disturbance of the samples and to shorter acclimation time in the minicosms. Extrapolating the laboratory respiration rates to field conditions yielded rates that were two to three orders of magnitude greater than rates previously determined in situ for C-horizon material. Results show that in situ microbial reaction rates determined using disturbed samples in minicosms and mesocosms yielded respiration rates that greatly exceeded field conditions. Mesocosms can, however, provide a useful environment for conducting process-related research in unsaturated environments.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Hendry, Professor Martin
• Authors: Hendry, M.
• College/School: College of Science and Engineering > School of Physics and Astronomy
• Journal Name: Groundwater
• Publisher: Wiley-Blackwell Publishing, Inc.
• ISSN: 0017-467X
• Published Online: 13 December 2005