Help.Environmental..about Eutrophication?

4. It has been suggested that the limiting concentration of phosphorus for accelerated eutrophication is between 0.1 and 0.01 mg/L of P. Typical river water might contain 5 mg/L P, 50% of which comes from farm and urban runoff, and 50% from domestic and industrial wastes. Synthetic detergents contribute 50% of the P in municipal and industrial waste. If all phosphorus-based detergents are banned, what level of P would you expect in a typical river? If this river flows into a lake, would you expect the phosphate detergent ban to have much effect on the eutrophication potential of the lakewater? Why or why not?