Influence of Lake Morphometry on the Response of Submerged Macrophytes to Sediment Fertilization

The influence of lake morphometry on the growth of submerged macrophytes in response to sediment fertilization was studied at sites of varying bottom slope (steep to gentle), wave exposure (high to low), and depth (1.0 and 2.5 m) in Lake Memphremagog (Quebec–Vermont). The biomass increases were on average 2.1 times greater for fertilized plants than for the paired controls. The extent of the growth response was greatest at the 1.0-m sites. The smaller response at the 2.5-m sites was further decreased as exposure to waves increased. The smaller response at 2.5 m (depth of maximum biomass) suggests that factors such as light limitation, length of the growing season, and littoral slope, but not sediment nutrient levels, limit submerged biomass there. The importance of the physical factors appears to increase as the biomass increases. "Overwintering" plants showed greater response to fertilization than those growing from seeds. Overall, the extent of the growth response to sediment fertilization depends on the energy environment (i.e. depth, wave exposure, and slope) of the littoral. The influence of these physical factors explains previous difficulties in finding strong correlations between nutrient levels and the growth of submerged macrophytes.