Abstract
Submergent macrophyte distribution in lakes is usually related to depth. At lower depths (downslope on the littoral lake bed), macrophyte distribution and growth have been related to light (Spence 1982), substrate texture, nutrient status (Carpenter and Adams 1977), and lake morphometry (Duarte and Kalff 1986). Factors limiting distribution and growth at shallower depths (upslope on the littoral shore) are not as well understood. Meaningful descriptions of plant distributions in reservoirs are problematic because water levels vary through the course of a year (Brewer and Rerslett 1987). Water level fluctuations are a challenge to plant growth. A plant which begins the growing season at a depth of 3 m may be under 6 m of water after spring runoff fills the reservoir. Later in the summer, the same plant may be left at a depth of only 1 m as water is removed from the reservoir during summer drawdown. In reservoirs, where lake levels fluctuate substantially durin_g the growing season, the physical environment is characterized by increased spatial and temporal heterogeneity. Disturbances associated with changing water levels include ice scour during winter drawdown, abrasion due to increased erosion along the lake shore and wave action. Recent work suggests that the magnitude and timing of water level fluctuations may be the most important factor regulating macrophyte community processes at shallower depths in reservoirs (Gasith and Gafny 1990; Brewer and Parker 1990; Rorslett 1984). The status of the aquatic plant community in Jackson Lake was re-evaluated from June - August, 1995. During this time, we compiled a species list and mapped the distribution of macrophyte species.