PHOTOAUTOTROPHS AND THE MICROAGGREGATION OF SAND IN A FRESH-WATER BEACH DUNE COMPLEX - IMPLICATIONS FOR SEDIMENT TRANSPORT BY WIND

A temporal investigation of sediments in a freshwater beach-dune complex on the northeastern shore of Lake Ontario shows that photoautotrophic microorganisms are important in particle aggregation and therefore, surface stabilization against wind erosion. The percentage of wind stable aggregates > 0.84 mm dia is greatest in panne areas, showing substantial increases in early spring. Considerable diversity of photoautotrophs is found in these moist, low lying areas with cyanobacteria, chlorophytes and diatoms present in an active state. Virtually no aggregation is observed in sediments from either the dune ridges or portions of the beach surface which are raked on a daily basis to remove detritus. These disturbed beach surfaces are mobilized by strong autumn winds. Although chlorophytes and cyanobacteria were cultured in the dune sediments, low chlorophyll a concentrations suggest that these microorganisms were not actively growing. In comparison, aggregation is evident in natural, undisturbed beach sediments, especially in midsummer. This increase is positively correlated with chlorophyll a concentration and number of genera. An exponential relationship is observed between chlorophyll a concentration and the percentage of aggregates (> 0.84 mm) in panne and natural beach samples. These aggregates contribute to the stability of these areas to wind transport.