Abstract
Aulacoseira ambigua abundance and filament length were measured weekly during spring and autumn bloom periods in Trout Lake, Wisconsin, USA. In addition, several chemical and biological variables thought to influence A. ambigua growth were assessed. Results of the field-based observations were complimented with controlled laboratory experiments to evaluate the effects of phosphorus availability on A. ambigua growth. Relative to the autumn bloom period, A. ambigua colonies were generally larger and more abundant in spring prior to the termination of the bloom in June. Chlorophyll-a concentrations indicated that other phytoplankton were also more abundant during the spring bloom. Batch culture experiments indicated that increased phosphorus availability during the spring bloom contributed to the seasonal increase in A. ambigua filament length and abundance. Increase in A. ambigua filament length in response to increased phosphorus availability is discussed as a mechanism that may increase nutrient removal through sedimentation and subsequently decrease the efficiency of nutrient regeneration in higher productivity lakes.
