Evaluation of the Growth of Vallisneria americana Michx. in Relation to Sediment Nutrient Availability

ABSTRACT

A recent (1988–1991) decline of Vallisneria americana Michx. (wildcelery) in Lake Onalaska, Wisconsin, prompted coordinated laboratory and field studies to evaluate die capacity of different sediments in die lake to support Vallisneria growth. Two sites were selected that formerly supported Vallisneria beds but differed in hydrologic patterns and sediment characteristics. SedimentfromSitel (die protectedsite) was predominandyfine-textured, with a silt-clay particle fraction of 77 percent; sediment from Site 2 (die unprotected/open water site) contained 79 percent coarse-grained sand. In die laboratory study, production and morphology of Vallisneria were examined on nonamended sediments from each site and on die same sediments amended by additions of N and P. In die field study, Vallisneria tubers were planted at die 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. Where growth was limited, N concentrations in aboveground plant tissues were below die critical N level established for this species. However, in all treatments of die study, aboveground tissue P concentrations were adequate for growth. In die field study, Vallisneria grew well at both sites and apparently was not limited by N or P. The only significant difference in growth between die two study sites was in maximum plant height (greater at site 2), probably a response by Vallisneria to differences in ambient light conditions between die 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 die 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.

Key Words:

• Vallisneria
• Lake Onalaska
• Upper Mississippi River
• sedimentfertility
• nitrogen
• phosphorus
• growth
• biomass production