| Summary: | In 1959, a small forest lot has been investigated thoroughly by the former Dutch Institute of Applied Biological Research in Nature (ITBON). The site was selected because of the steep gradients found in soil pH and moisture content. We focus here on the pH gradient from 6.7 to 3.2 (pH-KCl) in 1959 over a distance of 20 m (five plots). The decades thereafter N deposition from industry, traffic and especially surrounding agriculture caused an acidification of soils. The highest N deposition values (up to 90 kg N ha<sup>−1</sup> a<sup>−1</sup>) were recorded in the late 1980s, after which N deposition decreased to more moderate, but still elevated levels till now (35 kg N ha<sup>−1</sup> a<sup>−1</sup>). The site was sampled again at the very precise gradient plots in 1987 and 2019. We present our findings on soil microarthropods on this small-scale pH gradient over time and discuss especially the problems we faced with this long-term monitoring taking into account exact sampling, constancy in mode of extraction, constancy in slide preparation, and identification and how to deal with changes in systematics as even a number of species were described new to science meanwhile.
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