| The leaching of dissolved organic matter (DOM) in forest ecosystems serves both to export organic matter and to redistribute it within the ecosystem. This dissertation is concerned with the role of DOM as a vehicle for the transport of the N and P atoms associated with the DOM. In a deciduous forest watershed in the Southern Appalachian Mountains, the average annual output from the forest floor in the form of dissolved organic matter was 21, 31, and 5.9% of the input in solid litterfall for C, N, and P, respectively. In solution percolating from the forest floor, 94% of the N and 64% of the P was organic. Leaching from the forest floor was not a source of inorganic N and P for the mineral soil. Instead, the forest floor was a sink for the removal of these inorganic nutrients delivered in the throughfall. In contrast, the forest floor was an abundant source to the mineral soil for N and P in the form of DOM.; The chemical properties and interactions of dissolved organic matter with soil surfaces are crucial in determining the mobility of these organic nutrients. Most of the dissolved organic carbon (DOC) was in the organic acid fractions with the hydrophobic acids composing 35 to 57% of the DOC in all samples except summer throughfall.; Over 95% of this DOM was removed as the water percolated through the soil profile and left the ecosystem in streamwater. We examined the importance of decomposition in the removal of DOC and DON. Samples of DOM from all ecosystem strata were adjusted to a common initial DOC concentration and incubated in solution for 134 days. Throughfall samples decomposed most rapidly. In general only 14 to 33% of the DOC in forest floor, soil solution, and stream samples decomposed during the incubation period. The relative order of average decomposition of DOC from the various strata was, from greatest to least: throughfall, Oi (forest floor) Oa (forest floor), B horizon, stream, AB horizon, and upper A horizon. (Abstract shortened with permission of author.)... |
