Installing water level recorder at Lake Louise to assess modern hydrologic controls on sedimentation (Photo by J. Tepper) 

 
Student Andrew Bearden sampling the "highway layer." 

Near-surface sediments within Lake Louise, Georgia, form a 15 to 20 cm thick layer of light gray sediment that is enriched relative to underlying sediment in inorganics (by a factor of 2.5) and trace metals (e.g. Ti by 28, Ba by 3, Pb by 36). This enrichment has previously been attributed to the influx of clastic sediments to the lake during construction of near-by interstate 75 in 1957. In this study we examine the spatial variability of inorganic sediment within this surface layer (SL). Our purposes are: (1) to infer controls on sedimentation, (2) to estimate how much sediment and metal has entered the lake because of highway construction, and (3) to discuss implications of observed spatial trends to trace metal loading in the lake. Sixteen Eckman grab samples of the SL were recovered at 10 m intervals across the lake. Volumetric subsamples from the top, middle, and bottom of the SL were analyzed to determine moisture content, dry bulk density, and inorganic content (by LOI). The middle (M) and top (T) sample groups are statistically indistinguishable from one another. However, the bottom sample group (B) has significantly higher inorganic sediment content, dry bulk density, and lower moisture content than the combined M-T sample group. In addition, simple linear regression indicates a statistically significant trend (r²=0.54, p<0.001) of increasing inorganic content with increasing water depth. This trend is strongest for B samples and likely reflects an initial focusing of construction-derived clastic sediment into the deepest parts of the lake by turbidity flows. Subsequent bioturbation and a diminished post-construction influx of sediment to the lake may be responsible for the reduced focussing trend apparent in the M-T sample group. Using these trends together with bathymetric data we estimate between 7.1 and 10.1 x 10⁵kg of dry sediment and ^{significant quantities of trace metals (e.g. 6540 kg Ti, 270 kb Ba, 60 kg Pb) were introduced to the lake by highway construction. In addition, sequential extractions performed on SL sediments indicate that the majority of trace metals reside within the inorganic sediment fraction. Consequently, the observed focussing of inorganic sediment to the deep parts of the lake basin implies a similar concentration in trace-metals within Lake Louise.} 
Reference: Hyatt, J. A., Ekstrom, N. F., and Tepper, J. H. 1997. Georgia Journal of Science, Vol 55, p. 82.