Background: Groundwater will off gas significant quantities of CO₂ to the atmosphere once it reaches a stream or a lake. This is because groundwater is typically at equilibrium with CO₂ in soil air, which can be much higher than atmospheric air, due to plant roots and microbes respiring. This is a major source of natural CO₂ to the atmosphere, and this process is called evasion of CO₂.

The pH of the surface ocean is 8.2. The concentration of carbonic acid (H₂CO₃*) is 0.0141 mM and is at equilibrium with respect to the atmosphere, which is at approximately .0415 mbar CO₂ (415 ppm). The following reactions obtain for ocean water:

H₂CO_3(aq)* HCO₃^-_(aq) + H⁺_(aq) K = 1.69 x 10^-7

HCO₃^-_(aq) CO₃^2-_(aq) + H⁺_(aq) K = 1.17 x 10^-10

[H₂CO_3(aq)*] = pCO₂ * .034

Question: This groundwater emerges into a lake with a pH of 6.6 that is at equilibrium with the atmosphere. Calculate the amount of CO₂ that is off gassed from this groundwater when it mixes into this lake and equilibrates with the atmosphere. You may assume that the groundwater seeping in does not alter the pH of the lake. Report your answer in units of milligrams of CO₂ evaded per liter of groundwater input.