This study investigates the combined use of oribatid mites and diatoms in pine forest riparian zone soils. We focus on these organism groups as bioindicators of long-term anthropogenic disturbances of various origins categorized as two contamination levels: 1) moderate level that integrates the effects of sulphate-rich mining water contamination and alkaline air pollution that affected the area in the 1980s; 2) mild level that has been affected only by the alkaline air pollution. Additionally, the oribatid mite and diatom communities of these two groups of study sites were compared to another study area, which has similar natural conditions but is uninfluenced by these anthropogenic pollutants.

    Changes in oribatid mite abundance and the presence or absence of specific diatom species were the most significant differences in comparison of the two contamination levels and the area with very low human impact. Based on the community dissimilarities, both bioindicators had difficulty differentiating between the contamination levels when viewed separately. However, when the community data of the two groups were pooled, their ability to indicate the studied contami-nation levels improved noticeably. The sulphate-rich mining water contamination showed no strong influence on the communities, therefore the full indicative potential of these two groups may not have been reached. Nevertheless, this study provided new information about the soil communities inhabiting riparian areas and through that helped us understand some of the dynamics in diatom and oribatid mite communities brought on by long-term but weak disturbances. Some promising species were proposed from both groups that might help predict the effects of sulphate-rich mining water contamination or alkaline air pollution. Also, the taxonomic list of oribatid mites provides a valuable insight into the Estonian riparian forest soil oribatid fauna.

Keywords: oribatid mites, diatoms, riparian zone, disturbances, anthropogenic influence.