Relationships between Surface Sediment Diatom Assemblages and Lakewater Characteristics in Adirondack Lakes

Relationships between surface sediment diatom assemblages and lakewater characteristics were studied in 38 lakes in the Adirondack Mountains of northern New York. Most of the lakes are dilute, poorly buffered, and oligotrophic to mesotrophic. The diatom flora (240 taxa identified) is typical for circumneutral to acidic lakes. The purposes of this study were to identify the environmental factors most strongly related to the distributions of diatom taxa and the overall composition of diatom assemblages, and to derive equations to infer lakewater pH from diatom assemblage data. Relationships between diatom assemblages and environmental gradients were analyzed using reciprocal averaging ordination (RA). Correlations between RA axis 1 and pH—related factors were strong (pH, r² = 0.90; alkalinity, r² = 0.81; p(Ca positive charges), r² = 0.67; pMg, r² = 0.78; pNa, r² = 0.48; p—total Al, r² = 0.58; conductivity, r² = 0.47). Correlations were weaker (but still statistically significant) with elevation, epilimnion temperature, and concentrations of SO₄, Cl, and Si. Total P, chlorophyll a, water color, and mean depth were not important in explaining differences among assemblages. Cluster analysis of lakes and diatom taxa, multiple regression of taxon cluster groups with lakewater pH, and the occurrence patterns of individual taxa also indicated that pH—related factors are closely associated with diatom distributions. Euplanktonic taxa were present only rarely in surface sediments of lakes having a pH <5.8, alkalinity <20 μmol/L, and concentrations of Ca positive charges <100 μmol/L and total Al >60 mg/L. Predictive equations were derived for inferring lakewater pH from diatom assemblage data. Most were based on approaches of Hustedt (1939), Nygaard (1956), Merilainen (1967), and Renberg and Hellberg (1982). Agreement between predicted and measured pH was very good; r² values ranged from 0.61 to 0.94 and se from 0.28 to 0.60 pH units. These predictive relationships can be used to interpret stratigraphic diatom assemblages to reconstruct lake pH histories. No significant relationships existed between Araphidinae: Centrales ratios and measures of trophic status.