Some parts of the Upper Mississippi River are easily observed to be more productive than others, yet there are no obvious features which distinguish them from other broad, shallow river flats. Large scale eddies may offer one explanation.
For example, such an eddy is associated with high production of fingernail clams (Musculium) and mayflies (Hexagenia) near Keokuk, Iowa, a site where diving ducks have congregated since the 1960’s to feed on these invertebrates. The eddy provides slow circulation which prevents stagnation and may transport detritus generated in plant beds to the invertebrate filterers and collectors. The eddy is 4.8 km long and 1.2 km wide and is relatively persistent. At a minimum, the travel time for water is 3 times that in the main channel, and the maximum replacement time could be as long as 20 days. Fifty-eight similar eddies are predicted for the 1078 km of the river between St. Louis and Minneapolis, based on analysis of river morphometry ---- approximately 1 per 20 km. The formation or loss of eddies and other secondary circulation patterns in response to variation in discharge and channel morphometry (either natural or man-induced) may help explain yearly and longer term variations in biological production.
The Mississippi River is such a large system that collaboration is necessary to sample the entire river adequately. Richard Sparks collaborated, with John Day and Robert Costanza from Louisiana State University in a special symposium, “The Mississippi River as an Integrated System”, at a Coastal Society meeting in New Orleans, 12-15 October 1986 which brought together scientists from the upper and lower Mississippi. There are shared concerns about problems created by man’s redirection and redistribution of sediment in the system.
Positions available include an ecosystem modeler and data base manager/analyst, both for 8 to 15 months, on the LR LTER project, and 2 aquatic ecologists on permanent hard money at the Natural History Survey (one to be a lotlc ecologist). For more information regarding these positions contact:
- (aquatic ecologists) Dr. Phil Ross (217) 333-6897)
- (data base manager/analyst) Dr. Peter Bayley (217) 333-6889/6890
- (modeler) Dr. Richard Sparks (309) 543-3105/3950.
Publications:
Adams, J. Rodger. 1986. Mechanics of a large eddy in the Mississippi River. Pages 645-652. In R.E.A. Arndt, H.G. Stefan, C. Farell, and S.M. Peterson (eds.), Proceedings of the Specialty Conference sponsored by the Aerospace Division, Engineering Mechanics Division, and Hydraulics Division of the Am. Soc. Civil Engineers, 3-6 June 1986, Minneapolis, MN.