Acid-Base Properties of Dissolved Organic Matter in the Estuarine Waters of Georgia, USA

Abstract

The contribution of dissolved organic matter (DOM) to alkalinity in estuarine waters and its relationship to CO 2 chemistry has not received much previous attention. In this paper, we present some of the first organic alkalinity measurements in the context of estuarine mixing, focusing on three rivers in the Southeastern US. The simple model presented here illustrates that the organic contribution to alkalinity in estuarine waters is largely controlled by the dramatic pH change in the early stage of the mixing. As mixing progresses, organic alkalinity becomes nearly conservative with respect to salinity change. Although no DOM removal during estuarine mixing was detected here, this work provides an alternative approach to evaluate the issues of colloid and small particle formation and coagulation during mixing. This paper demonstrates that a large fraction of the proton binding sites of humic substances is either completely protonated or deprotonated during the estuarine mixing processes and, therefore, that these sites contribute neither to alkalinity nor to proton transfer reactions. One class of chargeable sites may be adequate to model the acid-base properties of humic substances during the mixing process.