The aquatic macrophyte seed bank in Lake Onalaska, Wisconsin

McFarland, D. G., and S. J. Rogers. 1998. The aquatic macrophyte seed bank in Lake
Onalaska, Wisconsin. Journal of Aquatic Plant Management 36:33 39. Reprinted by
U.S. Geological Survey, Environmental Management Technical Center, Onalaska,
Wisconsin, November 1998. LTRMP 98-R015. 7 pp. (NTIS #PB99-119596)


ABSTRACT:

Submersed aquatic vegetation, dominated by Vallisneria americana Michx., declined
dramatically in Lake Onalaska (Navigation Pool 7, on the Upper Mississippi River)
following drought conditions in the late 1980s.  Coinciding with the decline were marked
increases in the abundance of Myriophyllum spicatum L., particularly in areas vacated by
V. americana.  Recent evidence indicates that much of the lake has remained
unvegetated, but that since 1994, beds of V. americana have made a partial recovery. 
While the production of vegetative propagules may largely account for increases in
populations of both species, the extent to which seed production may contribute to their
expansion in the lake is unknown.  To assess the germination potential and distribution
of the aquatic macrophyte seed bank in Lake Onalaska, sediment cores (5 cm deep) were
collected from 74 sampling sites in July 1996.  Seedling emergence from sediments was
observed in an environmental growth chamber operated at 25 C and a 14-hr photoperiod
over a period of eight weeks.  Fifteen species of aquatic macrophytes germinated in
sediments from 55 sites.  V. americana seedlings emerged from sediments from 36 sites
throughout the lake, but were most prevalent in sediments collected within or
downstream (within 250 m) of established V. americana beds.  Seedlings of M. spicatum
emerged from only two collected sediments that had supported this species in protected
areas.  These findings suggest that seed production may play a greater role in the
dispersal of V. americana than M. spicatum, and further emphasize basic differences in
their survival strategies, particularly in flowing water systems.


KEYWORDS:

Aquatic plants, germination, Myriophyllum spicatum, sexual reproduction, Vallisneria
americana