Characterization of microbial nitrification and denitrification in an urban Wisconsin marsh

Abstract

This thesis consists of an introduction and two manuscripts. The first manuscript concerns nitrification and the ammonia oxidizing communities found in ponds within an urban Wisconsin marsh. The second manuscript covers denitrification and the denitrifiers within these same ponds. Nitrogen can limit production in many ecosystems, and so this research covered two important processes of the nitrogen cycle. Little research has been done on characterizing nitrification and denitrification from freshwater urban marshes, which was the focus of this study. We measured water and sediment chemistries, process rates, ammonia-oxidizer and denitrifier abundance, and assessed diversity of ammonia-oxidizing community, seasonally, from two pond types (based on annual water cover) from Myrick Marsh, La Crosse, WI. Nitrification and denitrification process rates followed a seasonal pattern. Ammonia-oxidizer abundance correlated to nitrification rates during spring and summer months, whereas denitrifier abundance was not correlated to denitrification rates. Annual water cover did not affect denitrifier abundance or denitrification rates, but moist sample locations without overlying water had higher rates of denitrification compared to sample locations with overlying water. Our study suggests that there is a functional redundancy within the ammonia-oxidizing community maintaining a relatively consistent rate of nitrification and that denitrification thrived in moist, aerobic locations.