Abstract
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−1 a−1) were recorded in the late 1980s, after which N deposition decreased to more moderate, but still elevated levels till now (35 kg N ha−1 a−1). 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.
Highlights
Acidification is a natural process initiated by organic remnants from incomplete decomposition of lignin and hemicellulose compounds resulting in fulvo and humic acids that leach downward in soil and bind to iron and aluminum [1,2]
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
In 1959, a gradient study has been executed in the Hackfort forest on the influence of pH on soil microarthropods, of which at the time only the oribatid mites have been identified to the species level
Summary
Acidification is a natural process initiated by organic remnants from incomplete decomposition of lignin and hemicellulose compounds resulting in fulvo and humic acids that leach downward in soil and bind to iron and aluminum [1,2]. Acidity or pH is an important factor in soil, which to a large extend determines the abundance and species composition of soil microarthropods [4]. In 1959, a gradient study has been executed in the Hackfort forest on the influence of pH on soil microarthropods, of which at the time only the oribatid mites have been identified to the species level. It is expected that acidification will occur especially in the lower pH trajectory (plots III–V) due to high atmospheric acid deposition levels tipping mid-1980s. A single researcher samples the sites always following the same precise protocol (see for some other time series [17,18,19]). We can distinguish five crucial factors that must be kept constant for comparable results over the years of long-term time series: (1) exact sampling area,. For some of these steps, the magnitude of variation, even with important related deviations in the final results
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