The dynamics of vertical chlorophyll distribution in an oligomesotrophic lake

The vertical distribution of chlorophyll was examined in relation to physical and chemical parameters in oligomesotrophic Lake Samish, Washington state, during the latter half of a growing season. A majority of chlorophyll resided in the metalimnion in late July, with metalimnetic populations dominated by diatoms (Cyclotella bodanica) and chrysophytes (Mallomonas caudata, Dinobryon sertularia). A silica gradient appeared to be most important in determining the vertical position of these populations. Later in the season, segregation of nutrients and light, in the face of a deepening epilimnion, led to transient accumulations of phytoplankton at the top of the metalimnion. It appeared that losses due to heterotrophic activities accentuated the lower boundary of this chlorophyll peak.