Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Plant Science

First Advisor

Bruce H. Bleakley


Wetlands are an integral part of agricultural systems in the prairie pothole regions of the North Central United States and Canadian Provinces. Little research has been done on denitrification in prairie potholes, and a better understanding of their denitrifying capability could aide in optimizing management practices near pothole areas. Most probable number (MPN) and denitrifying enzyme activity (DEA or Phase I) assays were conducted. Most probable number (MPN) measures were used to give an estimate of dissimilatory nitrate reduction to ammonia (DNRA) and denitrifying populations present in the wetlands. This study involved 3 selected semi-permanent prairie pothole wetlands near Madison, South Dakota on farms with different farming practices which were conventional (CON), transitional no till (TNT) and organic (ORG). Phase I denitrifying enzyme activity assays were used to give an estimate of the soil's existing denitrifying enzymes, representing the denitrifying activity history of the soil. In addition to Phase I assays, an amendment-modified Phase I assay was used to test for whether carbon or nitrate was limiting to denitrification. Phase I assays by depth were done using soil from semi-permanent wetland 8 located on a farm using organic farm-management practices. In addition to the depth study, a natural denitrification rate potential study was done to examine natural denitrification rates without exogenous substrate addition. The effect of varying chloramphenicol concentrations on DEA assays was also examined. The original chloramphenicol concentration used in the study was 1. 0 g/L, as per recommendations in the literature. This concentration was later found to be inhibitory to existing denitrifying enzyme activity. Chloramphenicol concentrations for DEA assays in this study were then adjusted to a lower concentration of O.25 g/L. The MPN study showed DNRA bacteria to be more numerous in the wetlands than denitrifiers. DNRA populations dominated both the upland and lowland sites, and there were temporal variances for both DNRA bacteria and denitrifiers. Phase I rates for L V denitrifying bacteria were higher in the lowland and exhibited temporal variances. The Phase I rates-by-depth study showed much of the denitrification activity to be in the top 0-5 cm depth segment, and the 5-10 cm segment had higher rates than the 10-15 cm depth segment. Soil tests were completed for pH, nitrate, soluble salts, organic matter, potassium and phosphorus. Correlations between soil test and Phase I rates by depth were done and a model estimating 35% of the variance in N20 rates was proposed.

Library of Congress Subject Headings

Denitrification -- South Dakota
Wetlands -- South Dakota
Prairie Pothole -- South Dakota


Includes bibliographical references (pages 109-104)



Number of Pages



South Dakota State University


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