Diatom diversity and species composition in phytoplankton, sediment traps, and surface sediments from a warm monomictic tropical lake

Background: Diatom assemblages in sediments are frequently used as water quality and paleoenvironmental indicators. However, sedimentary diatom assemblages may present taphonomic biases due to processes occurring in the water column and water-sediment interface. Objective: The present study aimed to determine if in tropical deep lakes, the differences between water column, sediment trap and surface sediment samplings were large enough to provide antagonistic interpretations. It also aimed to determine if diversity metrics would be statistically different between the three kinds of samples. Methods: This study was performed in Lake Alberca de Tacambaro, Michoacan, Mexico, and involved the comparison of diatom species composition and diversity between phytoplankton, sediment trap and surface sediment samplings. Results: Nearly 80% of the diatom species, including the five most abundant taxa, were present in the three kinds of samples. Phytoplankton and sediment trap samplings documented the seasonal dynamics and indicated that the changes in species composition and diversity metrics were associated with the mixing and stratification processes of the water column. Unexpectedly, phytoplankton and sediment trap samples had relatively high percentages (ca. 20%) of benthic taxa (Achnanthidium minutissimum and Brachysira vitrea), which behaved as tychoplanktonic. Surface sediment samples showed a higher species richness and Simpson's diversity, but the three kinds of samples had similar Shannon diversities. Conclusions: In spite of the differences between the sampling methods, they did not provide antagonistic results on the condition of the lake. Surface sediment samples showed richer and more equitable assemblages, including diatoms from different habits, with an average-time window of about two years. The discrepancies between the phytoplankton and surface sediment diatom assemblages are an indication of recent changes in the diatom flora of this lake.