Solve the following problems and show how you were able to arrive at the solutions. Describe and

justify the assumptions that were made to solve the problems, if all of the information is not provided

in the problem statement.

$(20$ points$)$ What is the flux density of the specified chemical in each situation? State all your

assumptions.

a$)$ Nitrogen ion $N{O}_3^{-}$into an anoxic lake sediment if rate is governed by a layer stagnant porewater

in the top $0\mathrm{.}5cm$ of sediment. Above this layer, $[N{O}_3^{-}]=6ppm$; below, its's zero. D is

$\frac{{10}^{-6}c{m}^2}{sec}(8pts)$

b$)$ Benzene from a lake surface, where the dissolved benzene concentration in lake water $700ppm$

and gas exchange coefficient for propane has been found to be $1\mathrm{.}7c\frac{m}{h}r.(12$ pts$)$