EVALUATION OF LIGHT PENETRATION ON NAVIGATION POOLS 8 AND 13 OF THE UPPER 
MISSISSIPPI RIVER

Shawn Giblin1, Kraig Hoff1, Jim Fischer2, Terry Dukerschein1
1Wisconsin Department of Natural Resources, Long Term Resource Monitoring 
Program, La Crosse, WI 54603 
2Wisconsin Department of Natural Resources, La Crosse, WI, 54601.

      The availability of light can have a dramatic affect on macrophyte and 
phytoplankton abundance in virtually all aquatic ecosystems.  The Long Term 
Resource Monitoring Program (LTRMP) and other monitoring programs often measure 
factors that influence light extinction (non-volatile suspended solids, volatile 
suspended solids, and chlorophyll) and correlates of light extinction (turbidity 
and Secchi depth), but rarely measure light extinction directly.  Light 
extinction, Secchi depth, transparency tube, turbidity, total suspended solids, 
and volatile suspended solids data were collected in 2003 on Pools 8 and 13 of 
the Upper Mississippi River.  Regressions were developed to predict light 
extinction based upon Secchi depth, transparency tube, turbidity, and total 
suspended solids.  Transparency tube, Secchi depth, and turbidity all show 
strong relationships with light extinction and can be used to effectively 
predict light extinction.  Total suspended solids do not show as strong a 
relationship to light extinction when tributaries are included, but the 
relationship improves when examining the main channel data only.  Volatile 
suspended solids were shown to have a greater influence on light extinction than 
non-volatile suspended solids.  The data were compared to recommended criteria 
established for light extinction, Secchi depth, total suspended solids, and 
turbidity by the Upper Mississippi River Conservation Committee to sustain 
submersed aquatic vegetation in the Upper Mississippi River.  During the study 
period, the average condition in Pool 8 met or exceeded all of the criteria and 
the average condition in Pool 13 failed to meet any of the criteria.    This 
report provides river managers with an effective tool to predict light 
extinction based upon readily available data.

Keywords:  Light extinction, Upper Mississippi River, transparency tube, Secchi 
depth, turbidity