IDENTIFICATION OF THE RIPARIAN SOURCES OF AQUATIC DISSOLVED ORGANIC-CARBON

The riparian zone has been suggested by several researchers as the place where organic-rich runoff acquires much of its disserved organic carbon (DOC). The great variation in the hydrochemical environments within the riparian zone, however, makes quantification of the contribution from specific source areas within the riparian zone desirable. This paper explores the feasibility of identifying those sources by comparing the quality of DOC and other chemical parameters of runoff with soil solutions from different locations within the catchment. The study was located on the Svartberget Catchment in northern Sweden. Two soil profiles, one a riparian pear and the other an iron podzol, as well as streambank moss, were sampled as potential sources of aquatic DOC. Soil solutions in these samples and runoff were characterized by their inorganic chemistry, separation of the humic/fulvic component of DOC, and gel filtration to determine the molecular size distribution of DOC. The results show that the superficial organic horizons differ markedly in a variety of ways from the chemistry of runoff. The most likely origin of runoff is a mixture of upslope water from the B horizon with subsurface soil solution from the riparian zone. This is in agreement with what is known about flow pathways at Svartberget, but the information collected in this initial study was insufficient to quantify the contribution from specific sources. Potential, however, is seen to increase the power of this approach by using more techniques to differentiate the chemistry of specific source areas and exploit information provided by both seasonal and flow-related variations in the chemistry of runoff.