Figure 4

CO2 production during microbial and substrate limitation zones. Through integration of the measured rate of carbon dioxide over time, the amount of gas produced during each limitation zone (see Figure 3) was calculated and reported as a fraction of total CO₂ produced. The substrate limitation zone dominates the overall metabolic activity output by up to 81% of total, a trend observed for all other substrate types tested. During this period, surface accessibility, rather than microbial colonization rate, is the major limiting factor.