Variability of riparian soil diatom communities and their potential as indicators of anthropogenic disturbances

Riparian soils are affected by both natural and anthropogenic disturbances occurring in the water bodies and on the catchment area. These riparian areas are also rich in microhabitats and therefore host various soil biota, including diatoms. Diatoms are known for their bioindication abilities in water and could potentially be used in that context in the riparian zone. Therefore the possibility of riparian soil diatoms acting as indicators of both terrestrial and aquatic disturbances is worth discussion. We analysed diatom community structure and their variability between different study areas and sites. We also quantified diatom species diversity and richness and evenness of the riparian topsoils. Possible effects of various anthropogenic disturbances on diatom communities, alkaline air pollution, and the effects of mining waters pumped into the area were studied in north-eastern Estonia. These results were compared with results from an area with low human influence in south-eastern Estonia. Additionally, we evaluated the potential of diatoms as indicators of various anthropogenic disturbance levels and a water contamination gradient based on sulphate concentrations. Community parameters, including species richness, diversity, and evenness, indicated some differences between the studied communities both when the separate study sites and distinguishable anthropogenic disturbance levels were compared. Diatom assemblages also showed moderate variability between the study sites, which could be influenced by variable moisture conditions, variable organic matter content, and the trophic level of the water body. Despite the variable levels of human influence the two compared areas shared about 51.4% of the species. Our findings show that the diatom community composition of riparian soils could potentially indicate anthropogenic disturbance levels, especially through the abundance, absence, or presence of specific species (e.g. Hantzschia amphioxys, Fragilaria zeilleri var. elliptica, Pinnularia lata). Key words: diatoms, soil, riparian zone, bioindicators, human influence, disturbances.