SS3.04 Biogeochemistry of DOC/DON in a Watershed Context
Date: Wednesday, June 12, 2002
Time: 4:00:00 PM
Location: Carson B
 
KaushalSS, University of Colorado, Boulder, USA, sujay.kaushal@colorado.edu
Lewis, W, M, University of Colorado, Boulder, USA, lewis@spot.colorado.edu
 
CHEMICAL COMPOSITION AND METABOLISM OF DISSOLVED ORGANIC NITROGEN AND CARBON IN MINIMALLY DISTURBED ROCKY MOUNTAIN STREAMS
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Seasonal changes in the chemical composition and metabolism of DON and DOC were investigated in two second-order streams draining watersheds with low rates of N deposition (ca. 3 kg/ha/yr). Over three years, concentrations of DON were related to discharge. Two DON fractions (humic and non-humic) differed considerably, in their seasonality, suggesting that treatment of DON as a single pool could be misleading. DON was primarily of non-humic origin whereas DOC was mainly derived from humic sources. Over an annual cycle, concentrations of both DON fractions increased linearly as nitrate declined. Non-humic DON showed a significantly greater rate of increase than humic DON, as nitrate was depleted, possibly due to differences in its production and turnover rate. The bioavailability of bulk DON and DOC was related to the C:N ratio of the non-humic fraction. Consumption of DON and DOC in incubations increased during snow melt, but was sometimes limited or co-limited by inorganic N and P during the growing season. The chemical composition and metabolism of DON in minimally disturbed streams may be influenced by the availability of inorganic nutrients.