Influences of dissolved organic carbon on stream water chemistry in two forested catchments in central Sweden

Stream water chemistry in two headwater streams draining two small, adjacent catchments in Bispgården, central Sweden was studied during the 2003 and 2004 growing seasons. The two catchments closely resemble each other in regard to size, shape and drainage density, with the major difference found in the area of wetland lining the streambeds. The emphasis of the study was to investigate the stream water chemistry of these closely resembling catchments, regarding the quality and quantity of dissolved organic carbon (DOC) and its influence on the concentrations of di- and trivalent cations. The streams showed significant differences in the content and size distribution of DOC and in the distribution of cations between the different size fractions. For both streams the high flow events induced by precipitation influenced the chemistry of the streams through increase of organic matter and its associated cations. Fanbergsbäcken, with relatively low pH and high DOC concentration, had a greater amount of high molecular mass (HMM) DOC to which approximately 75% of Al and Fe and about 50% of Ca and Mg were associated. Gråbergsbäcken, with a higher pH and lower DOC level, had approximately 65% of Al, 40% of Fe and 30% of Ca and Mg associated to its HMM DOC fraction. Sixteen different low molecular mass organic acids were found in the stream water, of which oxalic and lactic acid were present in the highest concentrations.