$4)20*103$ m$3/$day of used water of a city is discharged into a river after passing through the treatment plant. And this river flows into a lake right after its discharge point. The P $($phosphorus$)$ concentration of purified used water is $7$ mg$/$L and the N $($nitrogen$)$ concentration is $18$ mg$/$L$.$ The flow rate of the river in the section where it flows into the lake is $6$ m$3/$s$,$ N conc $0\mathrm{.}2$ mg$/$L$,$ P conc. $0\mathrm{.}02$mg$/$L$.$

The lake waters will be used for water supply and listening purposes, and the first signs of eutrophication have begun to appear in the lake. The surface of the lake is $130$ m$2$ and the average depth is $10$ m$.$ Annually, $2000$ kg P and $12000$ kg N enter the lake from the lake surroundings.

What are the total nitrogen and phosphorus loads entering the lake?

What precautions should be taken to prevent eutrophication from progressing?

$($permissible nitrogen and phosphorus loads are $1\mathrm{.}5$ and $0\mathrm{.}1$ g$/$m$2.$year, respectively$)$