Denitrification Potential of Log Jams on the Sandusky River, Ohio
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Civil and Environmental Engineering and Geodetic Science Honors Theses;2005
Nitrogen in its oxidized form, Nitrate (NO3-), is considered a major pollutant of rivers and lakes in the United States, particularly in areas of high agricultural use. Nitrate is a nutrient that causes excess algal growth which can effectively suffocate aquatic life through a high biological oxygen demand by bacteria that decompose the algae. The effect of higher BODs can be to reduce oxygen to low levels resulting in uninhabitable conditions for some aquatic life. In addition to being detrimental to the health of water systems, NO3- in drinking water can have adverse health effects on infants, a condition called Blue Baby Syndrome. The only way to prevent cycling of nitrate in aquatic systems is by denitrification, a biological process by which nitrate is converted to N2 gas under anaerobic conditions and in the presence of organic material. Denitrification is a natural process in all river and wetland ecosystems. In this study, the potential for denitrification (DNP) in log jams of the Sandusky River was examined from a restoration design perspective. If log jams are a good source of denitrification substrate, it can then be inferred that the presence of exposed log jams have a positive impact on the health of the river system in terms of denitrification. This can provide an additional tool for understanding how dam removal, as a river restoration technique, affects the denitrification process. Dam removal may promote the creation and stability of log jams, thereby enhancing denitrification if a relationship between log jams and increased denitrification potential is found. The primary hypothesis of this study is that log jams have an increased potential for denitrification with respect to its river, which is likely a result of reduced flow favoring build-up of sediments and organic material. Further, the potential for denitrification will increase in proportion to the size of the log jam. The results of the study indicated that denitrification potential did not increase due to log jams with respect to the river. Furthermore, there was no significant relation between denitrification potential and size of the log jams. The results indicated that denitrification potential of the river, which consisted of samples collected from the river as well as the mudflat and floodplain, averaged slightly higher values. The floodplain values were highest and contributed most to the river average. Stream velocities and sediment types were analyzed in relation to denitrification potential as well. An expected trend of reduced stream velocities with increase in size of the jam was observed. It was expected that the reduced stream velocities, which indicates an increases in hydraulic retention time, would deposit finer sediments thereby creating a denitrification environment. However, the sediments collected from the log jams varied from sands and larger sediments to clays and silts and a consistency of denitrification between sediment types was not observed. Overall, the results suggest that denitrification is not enhanced by the presence of log jams due to increase in deposition of finer sediments because varied types and denitrification potential was observed for sediments associated with the log jams. Furthermore, this result was observed over varying size classes. The results suggest that log jams are passive in there influence on denitrification potential.
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