Calibration of diatoms along a nutrient gradient in Florida Everglades Water Conservation Area-2A, USA

The relationship between diatom taxa preserved in surface soils and environ mental variables at 31 sites in Water Conservation Area 2A (WCA-2A) of the Florida Everglades was explored using multivariate analyses. Surface soils were collected along a phosphorus (P) gradient and analyzed for diatoms, to tal P, % nitrogen (N), %carbon (C), calcium (Ca), and biogenic silica (BSi) . Phosphorus varied from 315-1781 mu g g(-1), and was not found to be corre lated with the other geochemical variables. Canonical correspondence analys is (CCA) was used to examine which environmental variables correlated most closely with the distributions in diatom taxa. Canonical correspondence ana lysis with forward selection, constrained and partial CCA, and Monte Carlo permutation tests of significance show the most significant changes in diat om assemblages along the P gradient (p < 0.01), with additional species dif ferences correlated with soil C, N, Ca, and BSi. Weighted-averaging (WA) regression and calibration models of diatom assembl ages to P and BSi were developed. The diatom-based inference model for soil [P] had a high apparent r(2) (0.86) with RMSEboot = 218 mu g g(-1). Indica tor diatom species identified by assessing species WA optima and WA toleran ce to [P], such as Nitzschia amphibia and N. palea for high [P] (similar to 1300-1400 mu g(-1)) and Achnanthes minutissima var. scotica and Mastogloia smithii for low [P] (similar to 400-600 mu g g(-1)), may be useful as moni toring tools for eutrophication in WCA-2A as well as other areas of the Eve rglades. Diatom assemblages analyzed by cluster analysis were related to lo cation within WCA-2A, and dominant taxa within clusters are discussed in re lation to the geochemical variables measured as well as hydrology and pH. D iversity of diatom assemblages and a 'Disturbance Index' based on diatom da ta are discussed in relation to the historically P-limited Everglades ecosy stem. Diatom assemblages should be very useful for reconstructions of [P] t hrough time in the Florida Everglades, provided diatoms are well preserved in soil cores.