Holden Laboratory

Vadose Zone Microbial Ecology

Sedgwick Natural Reserve
Soil horizons at Sedwick sampling site

Microbial processes in the unsaturated zone affect soil chemistry and chemical fates, with relevance to groundwater quality and atmospheric emissions. We examine microbial community composition, diversity, and processes in surface and deep soils, as related to C and N cycling and pollutant attenuation. Our field sites include locations within the UC Natural Reserve System (http://nrs.ucop.edu/), such as the Sedgwick Natural Reserve (https://sedgwick.nrs.ucsb.edu/).  We are interested in soil water as an environmental factor because it controls mass transfer in unsaturated porous media and imposes physiological stress on microbes under severely water-limited conditions. This interplay of physics and physiology has yet-to-be-defined controls on microbial processes under changing wetting and drying regimes.  

Related is our lab's long term interest in the microscale growth habits of bacteria in surface and deep soils.  We wish to understand the biofilm growth habit in the vadose zone, i.e., its prevalence and biophysical characteristics that affect pollutant biodegradation. While biofilms in wet environments are well-recognized as important growth modes for bacteria, less is known regarding biofilms in dry systems. Our work has been towards providing fundamental knowledge of unsaturated biofilm physiology, ecology, chemistry and physics.  This orientation towards biofilms cross cuts our work in all four main thrust areas of our funded research, and is a lens through which we plan and execute experiments, and analyze field samples.

This work was initially funded by the National Science Foundation (Microbial Observatories Program), and research continues via other related government-sponsored projects.

updated 12-31-19