Factors Controlling Sediment Denitrification in Midwestern Streams of Varying Land Use |
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Authors: | Sarah E Inwood Jennifer L Tank Melody J Bernot |
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Institution: | (1) Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556-0369, USA;(2) Present address: Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602-4712, USA;(3) Department of Biological Sciences, Murray State University, Murray, KY 42071, USA |
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Abstract: | We investigated controls on stream sediment denitrification in nine headwater streams in the Kalamazoo River Watershed, Michigan,
USA. Factors influencing denitrification were determined by using experimental assays based on the chloramphenicol-amended
acetylene inhibition technique. Using a coring technique, we found that sediment denitrification was highest in the top 5 cm
of the benthos and was positively related to sediment organic content. To determine the effect of overlying water quality
on sediment denitrification, first-order stream sediments were assayed with water from second- and third-order downstream
reaches, and often showed higher denitrification rates relative to assays using site-specific water from the first-order stream
reach. Denitrification was positively related to nitrate (NO3
−) concentration, suggesting that sediments may have been nutrient-limited. Using stream-incubated inorganic substrata of varying
size classes, we found that finer-grained sand showed higher rates of denitrification compared to large pebbles, likely due
to increased surface area per volume of substratum. Denitrification was measurable on both inorganic substrata and fine particulate
organic matter loosely associated with inorganic particles, and denitrification rates were related to organic content. Using
nutrient-amended denitrification assays, we found that sediment denitrification was limited by NO3
− or dissolved organic carbon (DOC, as dextrose) variably throughout the year. The frequency and type of limitation differed
with land use in the watershed: forested streams were NO3
−-limited or co-limited by both NO3
− and DOC 92% of the time, urban streams were more often NO3
−-limited than DOC-limited, whereas agricultural stream sediments were DOC-limited or co-limited but not frequently limited
by NO3
− alone. |
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