TEMPORAL AND SPATIAL VARIATION IN ZOOPLANKTON FLUX RATES IN THE OHIO RIVER.	

Debbie L. Guelda 1,2, Richard W. Koch 3,2, Jeff D. Jack 2, and Paul A. 
Bukaveckas 2.  1 Bemidji State University, Bemidji, MN  56601.  2 Department of 
Biology and Center for Watershed Research, University of Louisville, Louisville, 
KY 40292.  3 North Central Research Station, USDA Forestry Service, Grand Rapids 
MN 55744.

We conducted a 3 year survey in the lower Ohio River (RKM 854-1500) assessing 
physiochemical and biological parameters such as zooplankton flux rates.  The 
portion of the Ohio River in the study receives inputs from five major 
tributaries which have unique chemical and biological properties reflective of 
their watersheds.  For 1998-2000, zooplankton species richness was inversely 
correlated with discharge and the tributaries differed in zooplankton species 
structure.  Zooplankton flux rates (as individuals second-1 or grams carbon 
second-1) also varied with discharge.  Budgets of zooplankton carbon provided 
input contribution of zooplankton from the upper Ohio River and tributaries.  
Inputs from the upper Ohio River provided 38% of zooplankton carbon and were not 
correlated with discharge.  Tributaries provided 63% of zooplankton inputs; the 
importance of which varied seasonally and temporally.  The most important 
tributaries contributing zooplankton carbon to the Ohio River were those 
draining reservoirs (Cumberland and Tennessee Rivers).  Zooplankton showed no 
relationship with chlorophyll a or POC.  The Ohio River acted as a net source of 
zooplankton carbon during 4 of our sampling times for groups such as 
Ceriodaphnia, Diphanosoma, and rotifers and often acted as a sink for Bosmina.   
Zooplankton flux differed depending on position in the basin; the upstream 
portion of the study area was a 'source' of zooplankton, while the downstream 
area upstream of the Ohio River's confluence with the Mississippi River acted as 
a 'sink' to zooplankton.  

Keywords: zooplankton, Ohio River, budget, flux rates, discharge