UNDERSTANDING SOIL RESPIRATION IN STORMWATER BASINS

Because of the nature of water recharge into a stormwater basin, it is possible to observe easily how the carbon dioxide respiration rate is affected as the soil becomes saturated from the bottom of the profile up. Specifically observed was a rapid increase and subsequent decrease of up to 9 times the previous flux rate, immediately before the soil reached its maximum saturation and leveled off. We attributed this to the carbon dioxide being stored within the pore space of the soil being forced out and replaced by water. This created a spike in the data that is clearly evident in both our data collected via deployment of the LICOR LI-8100 long term chambers at the stormwater basin and in an in-lab proof of concept experiment whereby a contained soil sample was wetted from the bottom in an attempt to replicate the conditions found in the stormwater basin. Because of the similar behavior in both conditions, the existence of this spike can be attributed to the saturation of the soil. The implications of this effect are key to understanding better the carbon balance of these basins. Certainly they exist as a carbon sink, but knowing how much carbon is lost to the atmosphere during respiration will help us better understand to what extent they are storing carbon.