PARENT SESSION
Oral Session #7: Aquatic Ecology: Stream ecosystems. Presiding: T. Ehlinger.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas G.
The influence of ammonium, nitrate, and dissolved oxygen concentrations on nitrification rates associated with prairie stream substrata.
Kemp, Melody1, Dodds, Walter1, 1
ABSTRACT- Replicate substrate samples were collected from Konza Prairie Biological Station and incubated with varying levels of ammonium, nitrate and dissolved oxygen. Substrata included fine benthic organic matter (FBOM), coarse benthic organic matter (CBOM), filamentous green algae (FG), bryophytes (BRY), suspended particulate organic matter (SPOM), and epilithon (EP), and nitrification rates were determined by the N-serve method. Nitrification associated with FG and SPOM demonstrated an inhibition at high concentrations of ammonium, and rates associated with EP increased linearly with ammonium. Dense substrata responded to ammonium only at higher concentrations suggesting that diffusion plays a strong role. Uptake rates increased linearly with ammonium, but the percentage of uptake due to nitrification decreased. This may indicate that nitrifying bacteria have a higher affinity for ammonium than competitors. The second experiment addressed changes in nitrification rates with ammonium, nitrate, and oxygen additions. Nitrification rates were lowest when nitrogen gas was added, being undetectable when added with nitrate but not when added with ammonium, indicating that oxic micro-sites are likely to be utilized by nitrifiers when ammonium is plentiful. Nitrification rates were highest in the presence of ammonium and oxygen. Nitrate also stimulated nitrification rates, but to a lesser degree than ammonium.
KEY WORDS: nitrification, stream, ammonium, nitrate