Detecting the Lasting Effects of Water Level Drawdown on Aquatic Vegetation in a Impounded Stretch of the Upper Mississippi River near La Crosse, Wisconsin

A series of locks and dams were constructed in the 1930s in the upper Mississippi River to sustain a 9-ft channel for waterway transportation.  Reducing water depth in the impounded region above the dam below the mandated level while still maintaining a 9-ft channel was conducted to promote aquatic vegetation in the reach near La Cross, Wisconsin during the summers of 2001 and 2002.   Aquatic vegetation data collected annually under the Upper Mississippi River Restoration – Environmental Management Program were analyzed to detect the lasting effects of the experiment.  Drawdown stimulated vegetation growth had been detected with varied durations post experiment: 1 year for Leersia oryzoides (L.) Sw.; 6 years for Schoenoplectus tabernaemontani (K.C. Gmel.) Palla; and >= than 7 years for Sagittaria rigida Pursh. And S. latifolia Willd..  The information is useful for scheduling future water level drawdowns to sustain healthy aquatic vegetation in the upper Mississippi River.