The ecology of testate amoebae (Protozoa:Rhizopoda) in oceanic peatlands in Newfoundland, Canada:: Modelling hydrological relationships for palaeoenvironmental reconstruction

Peatland testate amoebae are important indicators of hydrology in fossil studies. The direct quantitative application of this principle has been limited due to a lack of suitable modern data and statistical techniques. This study gives results on the ecological relationships of testate amoebae faunas from Newfoundland, Canada, and explores techniques for modelling the relationship with water table depth. Water table, soil moisture and pH are the dominant influences on species composition in 60 samples from 14 peatland areas. Forty species occurred in > 6 samples and these are used to model the relationship with water table depth. Several models were tested. Tolerance downweighted weighted averaging (WA-Tol), weighted averaging with partial least squares (WA-PLS) and partial least squares (PLS) were assessed by jack-knifed error estimates. WA-Tol out-performed all other models and had an RMSE of 6.32 cm with a maximum bias along the gradient of 5.20 cm. WA-Tol probably performs better because the relatively high tolerance values of some species have less influence on the reconstructed values. A series of good indicator species can be identified on the basis of their narrow tolerances. These are Arcella discoides, Difflugia bacillifera, Nebela carinata, Cryptodifflugia sacculus, Nebela griseola, Nebela marginata, Quadrulella symmetrica, Amphitrema stenostoma, and Sphenoderia lenta. The analyses suggest that accurate quantitative reconstructions of past water tables are possible using these techniques and that experimentation with different models is worthwhile to improve their predictive capacity. In order to avoid problems with poor analogues, reconstructions should be based on larger more comprehensive data sets of modern faunas from a wider region.