SS3.04 Biogeochemistry of DOC/DON in a Watershed Context
Date: Wednesday, June 12, 2002
Time: 4:30:00 PM
Location: Carson B
 
ZieglerSE, University of Arkansas, Fayettville, USA, susanz@uark.edu
Brisco, S, L, University of Arkansas, Fayetteville, USA, sbrisco@uark.edu
 
SOURCES AND BIOAVAILABILITY OF DISSOLVED ORGANIC MATTER (DOM) IN TWO OZARK STREAMS
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Seasonal and diel changes in the isotopic composition and bioavailability of DOM were observed in two small headwater streams. Dissolved organic carbon (DOC) concentrations ranged from 220 to 1176 mM in Moore Creek (MC), a stream with a watershed dominated by agriculture pasture, and from 46 to 264 mM in Huey Hollow (HH), a stream with a hardwood forested watershed. Stream water respiration was not clearly related to DOC concentration or temperature in either stream. The d13C of DOM ranged from 27.0 to 24.8 and 32.3 to 28.0 in MC and HH, respectively, and the isotopic composition of algae and leaf litter indicated that their importance as DOM sources varied seasonally. Stream water microbial activity was never N or P limited, and only C-limited during winter and spring in MC. In HH, microbial activity became colimited by C, N, and P during summer. During summer in MC, microbial activity was more C-limited at sunrise relative to sunset, suggesting the importance of algal exudates. In late summer microbial activity, although not limited at sunrise, became C-limited at sunset suggesting DOM became less bioavailable with exposure to sunlight.