Fig. 1. Flow chart of simulation procedure for the spatial pattern of nitrifier microhabitats. The two examples represent a section of the three-dimensional simulation for one value of d. The letter d denotes density of units taking the value one (bold character for random distribution, noted as 1) or of size 50 elementary unit harboring at least one bacteria. The letter a denotes size of the aggregate side (number of size 50 elementary units) when Q = 1. The initial positive VU is the center of the aggregate (noted 1) (a = 3 or 5). Q: Probability that each adjacent unit in an aggregate belongs to same aggregate (Q = 0.3 or 0.7).