Light availability and growth of wildcelery (Vallisneria americana)

Kimber, A., J. L. Owens, and W. G. Crumpton.  1995.  Light availability and growth of
wildcelery (Vallisneria americana) in Upper Mississippi River backwaters.  Regulated
Rivers:  Research & Management 11:167 174. Reprinted by U.S. Geological Survey,
Environmental Management Technical Center, Onalaska, Wisconsin, November 1997.
LTRMP 97-R024. 8 pp. (NTIS # PB98-126436)


ABSTRACT

Large beds of Vallisneria americana declined in the backwaters of the Upper Mississippi
River after a drought that occurred between 1987 and 1989.  One hypothesis for this
decline is that low light availability may have decreased net photosynthesis to the extent
that overwintering tubers were not formed.  Following the decline, light availability
remained low.  To determine what light levels would be necessary for the re-establishment
of Vallisneria in the Upper Mississippi River, the long-term growth of
plants in a backwater lake and in an experimental pond was measured while the surface
and subsurface light were monitored continuously.  Plants grown from tubers
transplanted to 0ù5, 1ù0, and 1ù5 m depth in the lake grew and produced tubers only at 0ù5
m depth (9% of surface light).  At 1ù0 m, light availability was less than 1% of the
surface light.  Plants grown from tubers in experimental ponds with four shade treatments
(2, 5, 9, and 25% of surface light) for the same growing period produced
replacement-weight tubers in 9% light.  For a longer growing season, plants also
produced replacement-weight tubers in treatments with at least 5% of surface light.

An average light-extinction coefficient of 4ù64 m-1 was calculated for the backwater lake
based on continuous data collected during 94 days during the growing season from eight
widely separated sites.  Using equations based on the average extinction coefficient for
the lake and average leaf lengths of plants grown in experimental ponds, we predict that
in years with comparable turbidity, plants grown from locally collected tubers will grow
and produce replacement tubers only at depths of 0ù8 m or less.


 KEYWORDS

Light extinction, macrophyte growth, macrophyte restoration, Upper Mississippi River,
Vallisneria