Fig. 2. Rate of input + diffusion  decay (red lines) for three values of pollutant discharge in region 1, M_{1} (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, M_{1}, 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: M_{2} (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.
