The Bioavailability of Dissolved, Particulate, and Adsorbed Organic Carbon in Groundwater Systems

Dissolved organic carbon (DOC) is the smallest amount of organic carbon present in aquifer systems and is typically dwarfed by amounts of particulate organic carbon (POC) and adsorbed organic carbon (AOC). Research conducted over the last half century, however, has shown that these dissolved, particulate, and adsorbed compartments interact dynamically with each other. That suggests the hypothesis that the bioavailability of DOC in groundwater may indicate the bioavailability of the associated POC and AOC compartments as well. If that proves to be the case, it would greatly simplify the process of evaluating the bioavailability of total organic carbon present in groundwater systems. That hypothesis was examined by (1) comparing DOC bioavailability between two aquifers receiving modern atmospheric recharge, but with the recharge passing through POC/AOC sources of substantially different geologic ages, and (2) measuring POC/AOC bioavailability in sediments in from two aquifers before and after injection with bioavailable DOC consisting of dissolved sugars and emulsified vegetable oil. The results of both comparisons are consistent with the hypothesis that DOC bioavailability in groundwater reflects the bioavailability of the associated POC and AOC compartments and vice versa. Thus, DOC bioavailability may be a useful indicator of an aquifer's potential to drive reduction/oxidation processes that affect the chemical quality of groundwater.