| |
Presented at the NABS Annual meeting, Vancouver, British Columbia, 2004
in Biogeochemistry 1
Spatio-temporal variation in benthic denitrification: does heterogeneity matter?
C.P. Arango, J.L. Tank, M.J. Bernot, and S.E. Inwood. Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556
Streams are heterogeneous ecosystems, but little is known about how heterogeneity influences nutrient transformations. We investigated heterogeneity in benthic denitrification in 2 forested streams with low nitrate concentrations and 3 agricultural streams with high nitrate concentrations in southwestern Michigan. Substrata were collected using stratified-random sampling, and associated denitrification rates were quantified using the chloramphenicol-amended acetylene inhibition method. Denitrification rates did not differ among substrata despite differences in land-use of surrounding watersheds (two-way ANOVA; p=0.01). However, when denitrification rates were weighted by substratum availability, there were differences among substrata (two-way ANOVA; p=0.01), indicating that spatial variability was important in whole-stream denitrification. There was also temporal heterogeneity in denitrification with mean rates being 6x higher in 2003 relative to 2002 (61.30 vs. 9.52 μg N2O/gAFDM/h; t-test, p<0.001), and the spatial distribution of substrata also varied between years. Our study identified multiple spatio-temporal scales of denitrification heterogeneity including: 1) within-reach substratum-specific rates, 2) between-reach substratum-specific rates, 3) temporal variability in denitrification rates, and 4) spatial variability of substratum abundance. In general, denitrification measures increased at least 10% when incorporating all substrata relative to estimates made with only the dominant substratum. Thus, recognizing heterogeneity provides a more complete understanding of whole-stream denitrification rates.
|
|
