RELATIONSHIP BETWEEN DIATOM PRESENCE AND DISSOLVED SILICA IN THE FINGER LAKES, NY (USA)

Diatoms, a major group of algae in aquatic systems, are dependent on silica for the formation of their frustules. Thus, silica is fundamental to the growth of this group, as well as N & P. Textbooks state that 500 μg/L is the minimum concentration for sustained diatom growth. Earlier work indicated that silica concentration in the major tributaries and the Finger Lakes positively correlated to forested land use / land cover and water residence time but did not correlate to other factors like agricultural land use, productivity and bedrock geology. In this presentation, dissolved silica, diatom relative abundance, and other limnological data from the Finger Lakes of New York State are investigated to test the 500 μg/L limitation.

Since 2005, water samples from at least two sites in the eight easternmost Finger Lakes were collected on a weekly to monthly basis during the May – October field season, and analyzed for dissolved silica, plankton relative abundance, and other limnological data. Samples were filtered through a 0.45 μm Millipore filter, and the filtrate analyzed for dissolved silica using molybdic and ascorbic acid solutions with a trivalent antimony indicator by spectrophotometer. Plankton tows using an 80 μm mesh net integrated the plankton community through the epilimnion (upper 20 m). Each sample was preserved in a formalin/alcohol mixture, a minimum of 100 individuals identified to species, and relative percentage reported.

A complex response was observed between dissolved silica and diatom abundance. In Seneca and Cayuga Lakes, diatoms dominated the algal population during the early and late portion of the field season despite dissolved silica concentrations occasionally falling below the 500 μm/L threshold. In Owasco Lake, other species of algae dominated the flora during portions of the field season even though silica concentrations were almost always above 500 μm/L. In Canandaigua Lake, diatoms dominated the flora throughout the field season and silica concentrations were almost always above 500 mm/L. The variable response indicates that the 500 μm/L threshold should be used as a guideline. Other limnological variables like phosphorus scarcity, trophic status and/or watershed characteristics may also be important.