A well-mixed lake with a surface area of 6.0 [Km^2] and an average depth of 10 m is fed by a stream and

rainfall. (Groundwater and runoff are insignificant inputs). The stream's flow rate is 1 [m^3/s], and the

concentration of phosphorous in the stream is 1 [mg/l]. Average rainfall is 1 [m/yr], and the rain has a

phosphorous concentration of 0.01 [mg/l]. Phosphorous removal by evaporation and by biological

processes is negligible. Phosphorous precipitates from the lake's water according to first-order kinetics,

with a rate constant of 0.005/d. The outlet stream has a flow rate of 0.2 [m^3/s], which keeps the

volume of water in the lake essentially constant.

The concentration of phosphorous in the lake is most nearly?