Dynamics of Phytoplankton Distribution in Relation to Stratification and Winter Precipitation, Fallen Leaf Lake, California

Seasonal succession and interannual variation of modern diatom populations in Fallen Leaf Lake, Sierra Nevada, California, are characterized and discussed in relation to stratification, water quality, and inflow during spring runoff. Fallen Leaf Lake is a deep, transparent subalpine lake that undergoes a 5–6 month period of stratification and develops a deep chlorophyll maximum (DCM) dominated by diatoms. A seasonal succession was observed, where the early spring was dominated by Asterionella formosa, Fragilaria tenera-group (F. tenera and F. nanana), Tabellaria flocculosa strain IIIp, Aulacoseira subarctica, and Urosolenia eriensis. Asterionella formosa and T. flocculosa strain IIIp persisted into the summer, becoming dominant components of the DCM. In late summer, Cyclotella rossii succeeded the araphids in the DCM and persisted until deep mixing in the late fall. In winter, the lake is ice free and well mixed, and Au. subarctica was abundant in surface waters, along with Nitzschia and the oth...