Origin, Composition, and Flux of Dissolved Organic Carbon in the Hubbard Brook Valley

The concentration, composition, and flux of dissolved organic carbon (DOC) were measured in the Hubbard Brook Valley, New Hampshire. Data on precipitation, throughfall, soil solution, streamside seeps, stream water, and lake water are presented for 1976—1980. Characterization of DOC included analysis of phenolics, monomeric and polymeric carbohydrates, carboxylic acids, primary amines, and aldehydes. DOC concentrations increased with passage of water through the forest canopy and forest floor, decreased due to abiotic sorption in the mineral soil, and remained relatively low in most "downstream" ecosystems (streamside seeps, streams, and Mirror Lake). Average flux of DOC is estimated as 16, 47, 263, 54, 23, and 20 kg · ha — 1 · yr — 1 in precipitation, throughfall, soil solution (E, upper B, and B horizons), and streamflow, respectively. The composition of DOC, in particular the relative proportions of carbohydrates, appears to be related to the degree of biological activity at a given site in the landscape. Carbohydrates are particularly high in both absolute and relative terms in throughfall and lake water, which are the areas of highest photosynthetic activity within the terrestrial and aquatic ecosystems, respectively.