HYDROCHEMICAL MODELING OF DISSOLVED ORGANIC CARBON OF A SMALL, UNDISTURBED, OLD-GROWTH FORESTED WATERSHED IN SOUTHERN CHILE
Valdivia, Maria Vicenta
A simple, mechanistic hydrochemical model for DOC export was developed and tested for a small, old-growth forested watershed on the Chiloe island in southern Chile. Despite the important roles of DOC in both terrestrial and aquatic ecosystems, there are few tested watershed scale DOC models published to date and, in general, they have had modest success in reproducing observed stream DOC fluxes. The model developed here coupled a simple Boussinesq-type hydrological model of lateral subsurface flows from two soil layers and an Arrhenius-type model for DOC production in soil water. One unique aspect of this model is that DOC production is scaled to account for soil saturation. The streamflows were well simulated (r2=0.86). Simulated stream water DOC concentrations also agreed well with observed values (r2=0.80). Simulated soil water DOC concentrations were generally underestimated for the shallow soil layer and overestimated for the deep layer compared to observed values. Lysimeter sampling errors, lack of agreement between modeled and actual soil layers and the relative position of the lysimeters in the watershed are discussed as the possible causes of these deviations. In general, the model presented here captured the DOC stream water trends in this old-growth forest better than similar models used in other ecosystems. The simple structure of this DOC model may offer a good platform to gradually and accurately increase its intricacy, providing a better understanding of the inherent complexity of the processes regulating the carbon dynamics in forested ecosystems.
dissolved organic carbon; DOC model; hydrology model; hydrochemical modeling; forest soils; undisturbed ecosystems; Chiloe; Chile; Arrhenius; Van't Hoff; Lloyd and Taylor; Boussinesq; temperature; soil moisture