Effect of spatial heterogeneity on rate of sedimentary O2 consumption reaction

Soil is a complex natural system and exhibits heterogeneity both in space and time. In this study, we aim to investigate the effect of this spatially heterogeneous behavior of soil metabolic activity (measured as the rate of sedimentary O2 consumption) on the effective time-averaged rate constant. To meet this objective, we used a novel optical sensor plus imaging technology called VisiSens (PreSens Precision Sensing) that gave us a unique opportunity to obtain percentage air saturation of the sediment in time and space using the images of the surface of the sediment at a set interval (every 20 s for 40 min). Each of these series of images (each consisting of 120 images) were analyzed using an image analysis software (ImajeJ) to extract the spatial data of O2 saturation. For this study, we used fresh sediments collected from Llobregat (Barcelona, Spain) riverbed. The sediments were homogenized and monitored for percentage air upon addition of substrates containing glucose and humic substances. The results show that the rate of O2 consumption is heterogeneous in space and therefore should be considered in the computation of the effective rate of sedimentary O2 consumption for modeling purposes.