Reducing Sampling Bias Through Continuous Monitoring of Carbon Dioxide Efflux at NSZD Sites

INTRODUCTION

Recent research has shown that soil carbon dioxide (CO2) efflux can be used to quantify the rate of contaminant degradation – either natural or enhanced – occurring at petroleum hydrocarbon impacted sites. Point sampling programs with traditional flux chambers are currently the status quo for measuring carbon dioxide effluxes in the field, but this approach is problematic for gaining a thorough understanding of Natural Source Zone Depletion (NSZD) rates. In general, soil respiration rates can exhibit a large degree of daily and seasonal variation, potentially introducing biases to the measurements depending on the environmental conditions, the time of day or season during which sampling occurs. Point sampling programs fail to capture much of this natural variability in CO2 effluxes, which can inadvertently introduce biases when quantifying contaminant degradation rates using this method. Due to the spatial variability of CO2 effluxes observed at NSZD sites, an incomplete understanding of temporal variability further complicates data interpretation, reducing confidence in derived NSZD rates.

Using ecological models, we demonstrate the degree of natural variability in soil CO2 effluxes and highlight the biases introduced by point sampling to show that continuous monitoring helps eliminate these biases and allows for accurate quantification of contaminant degradation rates.

 

Inferred baseline soil efflux resulting from daily collection of samples at 8 am (Program A, dashed grey line with square markers) and 2 pm (Program B, dashed black line with circular markers) during a one week sampling program in May, compared to hourly efflux (light blue line) and the daily average efflux (bold blue line)

 

Differences between the average effluxes and efflux ranges derived from 1 week of continuous monitoring (hourly data) and 1 week of daily point sampling Program A and Program B.

 

 

To learn more, read the complete White Paper here: Reducing Sampling Bias Through Continuous Monitoring of CO2 Efflux at NSZD Sites

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