PARENT SESSION
Oral Session #35: Nitrogen cycling: Response to inputs, variation in time and space. Presiding: M. Fenn.
Tuesday, August 7, 2001. 1:00 PM to 5:00 PM. Hall of Ideas G.
Export of Humic and Non-Humic Dissolved Organic Nitrogen from Undisturbed Watersheds.
Kaushal, Sujay1, Lewis, William1, 1
ABSTRACT- Dissolved organic nitrogen comprises approximately 50% of the soluble fixed nitrogen exported from unaltered watersheds, yet little is known about its chemical composition, origin, and lability. Concentrations of dissolved organic nitrogen (DON), humic DON, and non-humic DON were determined over an annual period for two second-order streams draining subalpine watersheds that have been subjected to very low rates of N deposition (ca. 3 kg/ha/yr). Concentrations of DON and dissolved organic carbon (DOC) peaked sharply during early spring runoff. The C:N ratio of dissolved organic matter also increased at this time indicating seasonal changes in the chemical quality of DON. Non-humic substances were the predominant source of DON; they accounted for 60-90% of total DON but only 20-40% of total DOC exported from the watersheds. Non-humic organic matter typically had a lower C:N than humic substances suggesting that it was more labile. The pool of non-humic organic matter, which is the main source of DON in undisturbed watersheds, is likely to be affected in the future by increased atmospheric N deposition and subsequent increases in N availability and mineralization in soils.
KEY WORDS: dissolved organic nitrogen, dissolved organic carbon, nitrogen exports, nitrogen deposition