SEDIMENTED DIATOMS IN NORTHERN NEW-ENGLAND LAKES AND THEIR USE AS PH AND ALKALINITY INDICATORS

Gradient analyses of 29 chemical and physical (C-P) variables and diat om remains in surface sediments of 63 New England lakes (pH 4.4-7.9) i ndicate a primary C-P gradient of pH, alkalinity, Ca, Mg, conductance, and Al; diatom distributions are most strongly related to that gradie nt (especially to pH and alkalinity) and also reflect secondary gradie nts (oceanic-inland, lake morphology, and regional chemistry). The pri mary relationship supports the calibration of regression models for pa leolimnological inference of pH and alkalinity based on diatoms. To op timize inference models for the region's most acidic lakes, a second s et of calibrations was run after culling the seven least acidic lakes. Diatom distributions on the restricted pH and alkalinity gradients ar e of two types: roughly uniclinal and variously unimodal. Models assum ing each type were calibrated: CLUSTER (linear), DCA (unimodal), and C CA (unimodal). Log-transformation of alkalinity improved the 63-lake D CA and CLUSTER regressions, but worsened or left the others unchanged. Postulated causes of incongruous diatom assemblages and outlier pH an d alkalinity inferences are sediment mixing, focusing time lag, growth of epipelic diatoms at the core site, and atypical lake morphology. C areful selection of calibration lakes is at least as important as the choice of regression models.