VALLISNERIA AMERICANA MICHX DISTRIBUTION AND ABUNDANCE WITH A FEW CHEMICAL AND 
PHYSICAL PARAMETERS

Rebecca M. Thums 1, and Yao Yin2 
1River Studies Center, University of Wisconsin-La Crosse, La Crosse, WI 54601.  
2U.S. Geological Survey, Upper Midwest Environmental Sciences Center, Onalaska, 
WI 54650  

We conducted a field study of Vallisneria americana in August 2001 in an effort 
to better understand the distribution and abundance of this species in relation 
to a few selected chemical and physical parameters in Navigation Pool 8 of the 
Upper Mississippi River.  Our study plan was to investigate fifty-six sites, but 
we ended up with seventy-three sites investigated instead.  The seventeen extra 
sites were a result of an error of having selected a wrong navigation datum in 
the setting of the global position receiver used to locate sites during the 
earlier part of the investigation.  In selecting the fifty-six sites, we divided 
the sites that were sampled by the Long Term Resource Monitoring Program between 
1998 and 2001 into eight abundance categories of Vallisneria americana and 
randomly picked seven sites from each category.  At each site, we measured the 
velocity, turbidity, and water depth.  Six 1.5 x 0.32 m aluminum quadrats were 
strategically placed around the boat and the above-ground live biomass inside 
each quadrat was harvested and placed and sealed in plastic bags.  The harvested 
biomass were stored in a refrigerator until they were separated by species, 
oven-dried for 48 hours at 800 C, and weighed.  One sediment sample was 
collected from inside each quadrat using a 5-cm diameter Wilco sediment core 
sampler.  The top fifteen centimeters of the sediment core was extruded and 
placed in a plastic bag.  Within 24 hours after the collection of sediments, two 
solutions were prepared in laboratory using the sediments in the bags which were 
later analyzed for the concentrations of pore water ammonia, pore water nitrate 
and nitrite, extracted ammonia, and extracted nitrate and nitrite.  A portion of 
the remainder sediments was analyzed for moisture and organic contents.  The 
rest of the sediments is stored in a refrigerator and is being analyzed for 
particle size distribution.

We conducted a preliminary data analysis to correlate the biomass with the 
selected chemical and physical variables.  Our data reveal that Vallisneria 
americana was distributed within a narrow range of depth, flow velocity, and 
turbidity physical conditions, despite that the depth and velocity ranges of our 
data are larger than the ranges reported in literature.  The majority of the 
biomass was collected between a depth of 0.3 to 1.1 m, a velocity of 0 to 0.08 
m/s, and a turbidity reading of 2 to 18 Nephelometric Turbidity Units.  These 
readings are possibly more variable due to the atypical fluctuation in water 
level seen in 2001.  Both biomass displayed bell-shaped curves over carbon and 
moisture content gradients of the sediments, with concentration found between 20 
and 35% of moisture content and 0.5 and 4.5% of carbon content.  

Keywords:  aquatic macrophyte, Vallisneria americana, Upper Mississippi River, 
macrophyte distribution, abundance