The phytoplankton of the Bay of Quinte, 1972–2008: point-source phosphorus loading control, dreissenid mussel establishment, and a proposed community reference

Abstract

The objective of this contribution is to further the understanding of long-term (37 years) changes in the composition and biomass of the phytoplankton of the Bay of Quinte (northeastern Lake Ontario), especially those changes associated with the simultaneous point-source phosphorus loading reduction/white perch winter kill of early 1978 and the establishment of dreissenid mussels in the mid-1990’s. The relatively shallow and polymictic upper bay has facilitated the ice-free period domination of the phytoplankton by meroplanktonic diatoms (especially Aulacoseira spp.); while a more balanced representation by several algal Divisions has characterized the thermally stratified, dimictic lower bay. At all three stations (upper bay, middle bay and lower bay), phytoplankton biomass declined and community similarity decreased after both the phosphorus loading and the Dreissena interventions, but the biomass changes associated with the P load reduction were greater than those associated with Dreissena establishment. Conversely, the loss of phytoplankton community similarity after Dreissena establishment was greater than that associated with P loading reduction at all three stations. The Remedial Action Plan phytoplankton objective of 4–5 mm3 l−1 (May-October mean) has been met inconsistently since the establishment of Dreissena. The post-Dreissena period, however, was also characterized by occasional very high biomass values for the potentially toxic cyanoprokaryote (blue-green alga) Microcystis, as well as by a dramatic decline in the bloom-forming blue-green Aphanizomenon, and the near extirpation of the diatoms, Tabellaria and Synedra spp. A partially synthetic phytoplankton community was constructed using data taken from three local aquatic systems (Trenton Bay, upper Hay Bay and West Lake). This might be used as a reference against which past and future changes in the upper Bay of Quinte phytoplankton can be compared and evaluated.