Evidence for flocculation in glacier-fed Lillooet Lake, British Columbia

This study provides evidence of in situ flocculation in a glacier-fed freshwater lake. Direct observation of flocculated particles using microscopy provides the strongest evidence to establish that clastic suspended sediment in Lillooet Lake is flocculated. Flocs in Lillooet Lake exhibit a hierarchical size structure, with primary particles (<4 μm) joining to create microflocs (10–35 μm), and both primary particles and microflocs joining to create macroflocs (200–280 μm). In situ laser particle sizing reveals primary particles and microflocs dominate in the epilimnion, a zone susceptible to shear induced by wind or inflow and exhibiting the highest suspended sediment loads. Macroflocs dominate in the hypolimnion, a more quiescent zone and exhibiting the lowest suspended sediment loads. Flocculated particles are invisible to traditional methods of sediment analysis in glaciolacustrine settings. Flocculation is a plausible explanation for accelerated sedimentation of the clay-sized sediments known to dominate the size distribution of varves in other glacier-fed lakes.