Continuous in-situ measurement of free extracellular enzyme activity as direct indicator for soil biological activity

Understanding the nature and extent of biological activity in soils is critical for characterizing transformation processes, such as those involved in nutrient cycles and pollutant biodegradation. Unlike monitoring chemical and hydrological parameters, the current methods for analyzing microbial processes typically rely on destructive sampling, thus limiting our understanding of biogeochemical dynamics under rapidly changing environmental parameters. Extracellular enzymes are excellent representatives of the soil micro-fauna's response to changing conditions. We hypothesized that it is possible to analyze the activity of free enzymes passing with the soil pore-water through a suction cup porous interface. Thus, specific enzymes activity in the soil pore-water can provide information on the biological activity in the soil and unsaturated zone in a simple, non-destructive, continuous manner. The current study examined free enzyme activity in pore-water samples, as obtained from a porous interface during soil column experiments, as compared to values measured directly from the soil. The results demonstrated a high correlation between the measured enzymatic activities of phosphatase, β-glucosidase, and fluorescein diacetate (FDA) in the pore-water and the soil samples. Additionally, a preliminary implementation of the method was tested in ongoing remediation in a contaminated site. The results showed a strong correlation between the in-situ measurement of enzyme activity and the pollutant's biodegradation rate in the soil.