The effects of sediment drying and rewetting on nitrogen cycle processes in a 
small stream in the Kansas River watershed.

Bradley J. Austin
Department of Biological Sciences, Fort Hays State University
600 Park St. Hays, Kansas 67601

Eric A. Strauss
University of Wisconsin - La Crosse, River Studies Center 
1725 State Street La Crosse, Wisconsin 54601

      
Changing environmental conditions and increased water consumption has 
transformed many historically perennial stream systems into intermittent 
systems.  Multiple drying and wetting events throughout the year may impact 
many stream processes.  Two such processes, nitrification and 
denitrification, are also key components of the nitrogen cycle.  During 
summer 2007, an experimental stream constructed adjacent to the Saline River 
in Western Kansas was used to determine the effects of desiccation and 
rewetting of stream sediment on nitrification and denitrification potentials.  
Mean nitrification and denitrification rates in sediment not dried (controls) 
were 0.431 ± 0.017 µg NO3--N/cm2/h and 0.926 ± 0.106 µg N2O-N/cm2/h, 
respectively.  As sediment samples dried, nitrification rates decreased.  
Sediments dried less than seven days recovered within one day of being 
rewetted.  Denitrification rates were not negatively affected by one day of 
drying, while samples dried greater than one day experienced reduced rates of 
denitrification.  Denitrification in sediments dried seven days or less 
recovered by day seven of being rewetted.  Rates in sediments dried greater 
than seven days did not fully recover, for either process, even after 28 days 
of being rewetted.  These results demonstrate that alterations in stream's 
hydrology can significantly affect nitrogen cycle processes.