Consider three lakes in series with a pulse (instantaneous) input of a conservative contaminant into lake 1 that results in an initial concentration of 10 mg/l. lakes 2 and 3 initially have no contaminant initially. the inflow to lake 1 contains no contaminant. the hydraulic residence time of each lake is 3 months. write the appropriate mass balance equations and derive an equation (by solving the differential equations) for the concentration in each lake as a function of time. you can solve the mass balance equations sequentially. remember, the inflow concentration to the second lake is the outflow concentration from the first, and the inflow concentration to the third lake is the outflow concentration from the second.