Chrysophycean Microfossils Provide New Insight into the Recent History of a Naturally Acidic Lake (Cone Pond, New Hampshire)

Abstract

Cone Pond, New Hampshire, is an acidic (pH = 4.5) clearwater lake that is currently fishless. Historical records indicate declining fish populations between 1951 and 1966, but paleolimnological work using diatoms failed to find evidence for further recent acidification of this naturally acid site. We initiated new paleolimnological studies using mallomonadacean chrysophytes to further our understanding of Cone Pond's recent past. Our stratigraphic analyses indicate recent striking changes in the chrysophyte flora of this lake, with Mallomonas hindonii, a species only common in recently acidified lakes, replacing M. crassisquama, a cosmopolitan species that dominated the flora over the preceding 8000 yr; this recent change parallels the declines in fish populations. Because chrysophytes often bloom in early spring and are known, in other lakes, to experience changes in community composition before those expressed by the diatom community, a possibility is that chrysophytes track transient excursions of lake water chemistry associated with early snowmelt conditions. In this scenario, chrysophytes would respond to a constellation of specific short-term chemical changes including, but not restricted to, pH. Such pH associated changes could include changes in concentrations, speciation, or complexation of metals mobilized from the catchment or sediments, all of which are known to affect both chrysophytes and fish.