Abstract for 40th annual meeting of MRRC, April 24-25, 2008, Dubuque


SURPRISES AND CHALLENGES: ALLOCHTHONOUS DRIFT AND HYPORHEIC MUSSELS.  

Jim Eckblad
Department of Biology, Luther College, Decorah, IA 52101

If one studies a dynamic system like the Upper Mississippi River for over 
three decades it’s probably not too unusual to have findings that were 
unexpected.  In my 35-years as a river biologist, there were two outcomes 
that stand out in this regard.  First, the magnitude of biotic transport out 
of backwater habitats into the main channel was greater than expected. This 
allochthonous drift, as has also been shown for drift within other streams, 
was quite different over a 24-hour day;  Hydra and Hyallela were in transport 
during day samples, while misc. fish fry and macroinvertebrates were in 
transport at night.  Second, both juvenile and adult mussels were found in a 
streams hyporheic zone (3 to 12 inches below the surface),  a region seldom 
sampled in quantitative mussel studies.  Both mussel numbers and species 
richness were greater in the hyporheic zone than in the upper 3 inches of the 
cobble substrate.  These two surprises suggest some challenges, both in terms 
of equipment and sampling schedules.   

Keyword:  drift, hyporheic zone,  macroinvertebrates,  mussels,  sampling