Development of an in situ monitoring system for tracking solutes and gas emissions in soil

Soil is a complex medium that supports numerous biological and chemical processes across multiple phases. The transformation of inorganic and organic compounds can lead to the accumulation of harmful substances in soil and the emission of reactive gases that affect air quality and climate. However, quantitative measurements remain limited by the lack of methods for in situ monitoring of multiphase processes and by approaches restricted to one or a few compounds at a time, measured either in the liquid or the gas phase. Thus, gaps persist in quantifying and monitoring transformation processes occurring at the gas-liquid interface.

Here, we describe a newly developed method to continuously measure gas fluxes and solute concentrations in soil by coupling a dynamic gas flux chamber (DC) with an open-flow microperfusion (OFM) technique, hereafter termed OFM-DC. The latter OFM method had previously been applied in medicinal research for drug development, and we have optimized it for the utilization in soil. OFM enables the continuous sampling and concentration measurement of soil solutes (e.g., microbial metabolites) in both laboratory and field settings, whereas DC quantifies soil trace-gas emissions (e.g., CO_2, NO_x, and HONO) over time.

We will present first experiments using the novel setup with synthetic soil systems that have characterized microbial activity and chemical properties. Our case studies on in situ measurements of microbial nitrogen (N) processes and reactive N gas (NO, HONO) emissions reveal the effectiveness of our methods for investigating multiphase soil transformation mechanisms under dynamic soil water conditions.

The OFM–DC measurement setup demonstrates its potential for long-term field monitoring of soil–air quality and the related impacts on planetary health. The obtained data can support improved soil management, which in turn can minimize soil degradation and trace-gas emissions.