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 compl ex on the northeastern shore of Lake Ontario shows that photoautotroph ic microorganisms are important in particle aggregation and therefore, surface stabilization against wind erosion. The percentage of wind st able aggregates > 0.84 mm dia is greatest in panne areas, showing subs tantial increases in early spring. Considerable diversity of photoauto trophs is found in these moist, low lying areas with cyanobacteria, ch lorophytes and diatoms present in an active state. Virtually no aggreg ation is observed in sediments from either the dune ridges or portions of the beach surface which are raked on a daily basis to remove detri tus. These disturbed beach surfaces are mobilized by strong autumn win ds. Although chlorophytes and cyanobacteria were cultured in the dune sediments, low chlorophyll a concentrations suggest that these microor ganisms were not actively growing. In comparison, aggregation is evide nt in natural, undisturbed beach sediments, especially in midsummer. T his 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.