2.7 Concentration profiles. Figure 2.9 shows four concentration profiles measured very carefully at the bottom of four different lakes. For each profile, state whether the lake bottom is a no-flux or flux boundary and describe where you think the source is located and why. 2. Advective Diffusion Equation N Z De KWAWC Lake B Lake A Z 29 Lake C Lake D Fig. 2.9. Bottom concentration profiles for the four lakes in problem number 2.4