On the potential for terrestrial diatom communities and diatom indices to identify anthropic disturbance in soils

A large amount of studies focuses on aquatic diatoms’ ecology and their use in the assessment of water quality. Little is known about terrestrial diatoms’ ecological behaviour and sensitivity to environmental factors. We hypothesise that terrestrial diatom communities can serve as a proxy of anthropic disturbance levels in terrestrial sites. To test our hypothesis, we apply an aquatic index to soil communities that is to deliver new information on the physiographic controls on soil diatoms. Diatom and soil samples were collected in the Attert River basin in Luxembourg during three seasons, in sites characterised by different combinations of geological, soil (schist, marl and sandstone) and land use (forest, grassland and agriculture) features. We found an effect of seasonality on soil diatom communities, reflected by different species dominance and abundances in samples during the three seasons. Soil pH and land use (which translates in a different amount of total carbon and nitrogen in soil) were identified as the variables having the largest impact in structuring the communities and as among the features with the highest importance in defining the ecological status of the sites (i.e. disturbed farmlands having higher pH and lower carbon and nitrogen content). However, the lack of information about the sensitivity of some of the most abundant terrestrial species in our study area caused some discrepancies between the expected (i.e. forested areas with low anthropic disturbance) and the obtained results, with several forested sites classified as having high anthropic disturbance. These results suggest that soil communities are likely to contain information about soil ecological status and highlight the importance of a better characterisation of terrestrial diatom species for developing a quality index based on soil communities.