Fig. 2. Rate of input + diffusion - decay (red lines) for three values of pollutant discharge in region 1, M1 (0.9, 1.5, and 2.1), and the rate of loss from the saturating sink (blue line). For a given minimum pollution rate in region 1, M1, equilibria occur at the points at which the red line crosses the blue line. The pollutant level in the other region was set at 1.6. Other parameters: M2 (pollution discharge rate in region 2) = 0.75; D (transport rate between regions) = 0.1; c (decay rate) = 0.05; s (maximum sequestration rate) = 0.5; m (pollutant level at which sequestration is half the maximum rate) = 5; q, which determines the slope of f(P) near P = m, = 6. P stands for amount of pollutant, and f(P) scales the sequestration to the amount of pollutant.