Subtle variability in water quality structures tropical diatom assemblages in streams of Cape York Peninsula, Australia

Contemporary benthic diatom assemblages were examined from 52 riverine and palustrine wetlands on Cape York Peninsula, Australia, to determine their environmental sensitivities and develop inference models. Multivariate analyses identified strong relationships between nine environmental variables and the diatom assemblage composition, with the aim to select variables for developing models. Total alkalinity, bicarbonate concentration, pH, electrical conductivity (EC) and latitude were most consistently and strongly correlated with diatom composition. The river basins sampled generally have an east-west orientation, so latitude potentially represents biogeographic differences between basins. Comparison of diatom assemblages between river basins showed significant differences, but substantial overlap in species. Diatom-based transfer functions were developed for each environmental variable and tested using the relationships between measured values and values predicted by the transfer functions. These were significant, and had low root mean square errors. An independent validation dataset for EC was analysed and applied to the EC transfer function. Results showed good predictions, giving confidence in its relevance beyond the training dataset. These understandings and models of the environmental effects on diatom assemblages allow for their application to future monitoring programs and reconstruction of past water quality conditions using fossilised diatoms in layered aquatic sediments of Cape York.