RESOURCE LIMITATION IN RIVERINE BACTERIOPLANKTON: INTERACTIONS OF TEMPERATURE 
AND DISCHARGE

Richard W. Koch1 and Paul A. Bukaveckas2.  1North Central Research Station, USDA 
Forest Service, Grand Rapids, MN  55744, 2Department of Biology, University of 
Louisville, Louisville, KY  45292.

The flux of nutrients and organic matter from riverine systems is largely 
influenced by production and respiration of heterotrophic bacteria, yet the 
factors regulating riverine bacteria are poorly understood.  We used dilution 
bioassays to assess the interactions of temperature, carbon and nutrient 
availability on bacterial growth and respiration across a range of hydrological 
conditions in the Ohio River and two tributary reservoirs, Kentucky Lake and 
Lake Barkley.  Bacterial growth rates under ambient field conditions ranged from 
0.02 to 1.1 d-1 and were 5 to 90% of maximal rates found in resource amended 
treatments.  Temperature was the main factor limiting bacterial growth when 
water temperatures were below 20oC.  At temperatures >20oC, inorganic nutrients 
were especially important in the low nutrient environment of the reservoirs, 
while carbon most frequently limited bacterial growth in the Ohio River.  
Respiratory rates were generally higher in the Ohio River (mean 350 µg O2 L-1 d-
1) than in the reservoirs (150 µg O2 L-1 d-1), suggesting use of lower quality 
organic matter by riverine bacteria.  Bacterial respiration responded mainly to 
glucose additions, but N and P were intermittently important co-variables.  
Respiration rates were directly correlated with temperature, which caused 
bacterial growth efficiencies to decrease with rising temperatures.  Our 
findings indicate that multiple factors regulate phytoplankton and 
bacterioplankton and that spatial complexity may arise from differences in 
discharge.

Keywords: heterotrophic bacteria, bacterial production, bacterial respiration, 
resource limitation, regulated rivers