Limnol. Oceanogr., 44(4), 1999, 1081–1090

This study quantifies the role of lake morphometry and submerged macrophyte beds on the accumulation of sediments in the littoral zone. Stable Pb, a historical marker of lacustrine sediments in southern Quebec, was used to date the sediments (;110 yr) and to calculate three long-term sediment accumulation rates (SARs) in Lake Memphremagog (located in Quebec and Vermont). The anthropogenic Pb burden in the littoral zone of Lake Memphremagog was found to be two to eight times greater (per m2) than the Pb burdens in the profundal zone of surrounding eastern township lakes. Pb concentrations were nearly fourfold higher than background Pb concentrations (115 and 31 mg g21, respectively), providing a reliable marker for littoral sediment core analysis. Lake morphometry is related to the three accumulation rates measured by providing distinct threshold limits (i.e., littoral slope, .10%; exposure, .10 km2) where sediments are unable to accumulate. Macrophyte beds are shown to disproportionately accumulate sediments at rates 2 to 20 times greater (per m2) than in the profundal zone. Linear regression models show that both the total SAR (mean, 1.7 mm yr21) and organic SAR (mean, 83.1 g m22 yr21) are best predicted by the biomass density of the macrophytes, closely followed by plant mean biomass. Bulk SAR, principally representing the larger, inorganic fraction of sediments, is least predictable. Biomass density, but not mean biomass, was related to the accumulation rate of stable Pb (mean, 37.7 mg m22 yr21), supporting empirical models that show growth form to be an important determinant of both sediment and plant tissue elemental concentrations. The variety of macrophyte communities sampled across Lake Memphremagog demonstrates that the conclusions drawn are not restricted to monospecific stands but to assemblages as a whole. It has long been recognized that the ultimate fate of sediments retained by lakes is deposition in the deep-water profundal zone. Paleolimnological sediment core analysis has benefited not only from uninterrupted long-term records of accumulation but also from a sedimentary environment that is both conducive to the preservation of sediments and resistant to disturbance and resuspension. Determining the fate of sediments in the near-shore region of lakes is more challenging, because the high-energy littoral environment and associated biotic communities are far more complex and dynamic. Identifying and quantifying the exchange of materials between the pelagic and littoral zones have been elusive goals, with some research identifying the littoral zone as a source of materials to the pelagic over the short term (Landers 1982; Pieczynska 1993; Kairesalo and Matilainen 1994; Schindler et al. 1996) and other research showing that the littoral zone is able to trap materials over longer time periods (Moeller and Wetzel 1988; Schröder 1988). Quantification of the effects of macrophytes and littoral morphometry on the distribution and accumulation of sediments is a prereq1 Present address: Department of Zoology, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.