The only unknown is N 2 . The continuity equation can be rearranged to solve for N 2 . The first step is calculation of Nitrate entering the wetland through precipitation or inflow. Note that we are neglecting bird poop. Also note that nitrate concentration in precipitation is not always zero.
Air pollution can lead to nitrate in rainfall.
It is convenient to calculate nitrate mass in the wetlands calculation in units of kg. The second step is calculation of nitrate mass leaving the wetland. Nitrate concentration in water evaporating from the wetland is zero. Nitrate concentration in outflow from the wetland is the same as nitrate concentration in water within the wetland. Nitrate concentration in seepage water is probably different from the nitrate concentration within the wetland, but in this case we assumed that seepage is zero so we can neglect seepage concentration.