A recent (1988-1991) decline of Vallisneria americana Michx. (wildcelery) in Lake
Onalaska, Wisconsin, prompted coordinated laboratory and field studies to evaluate the
capacity of different sediments in the lake to support Vallisneria growth. Two sites were
selected that formerly supported Vallisneria beds but differed in hydrologic patterns and
sediment characteristics. Sediment from Site 1 (the protected site) was predominantly
fine-textured, with a silt-clay particle fraction of 77 percent; sediment from Site 2 (the
unprotected/open water site) contained 79 percent coarse-grained sand. In the laboratory
study, production and morphology of Vallisneria were examined on nonamended
sediments from each site and on the same sediments amended by additions of N and P.
In the field study, Vallisneria tubers were planted at the two sites and harvested after 12
weeks of growth to compare morphology and tissue nutrient concentrations. In order to
account for local temperature and light conditions, surface water temperature, Secchi
depth, and light attenuation were monitored on a weekly basis. Laboratory study results
revealed that increased N availability (by N addition) generally increased total biomass
production and plant height, and to a lesser extent, tuber and seed pod production.
Additions of P had little overall positive effect on Vallisneria growth. Where growth was
limited, N concentrations in aboveground plant tissues were below the critical N level
established for this species. However, in all treatments of the study, aboveground tissue
P concentrations were adequate for growth. In the field study, Vallisneria grew well at
both sites and apparently was not limited by N or P. The only significant difference in
growth between the two study sites was in maximum plant height (greater at site 2),
probably a response by Vallisneria to differences in ambient light conditions between the
two sites. Marked differences between field and greenhouse study results suggest that
growth of Vallisneria on intrinsically infertile sediments may depend on a continuous N
supply to the sediments, most likely via sedimentation. Present (1992) conditions in
Lake Onalaska are suitable for growth; thus, reestablishment of Vallisneria in the lake is
likely, as long as conditions remain unchanged.
