Diversity and abundance of soil macroinvertebrates along a contamination gradient in the Central Urals, Russia

Study Extent

Study sites were located on gentle slopes of ridges in spruce-fir forest. A total of nine study sites (=locationID) were established, corresponding to areas with different pollution levels. The number of sampling plots within each study site ranged from one to three; 20 samples were collected from each sampling plot. The study of soil macrofauna is part of an ongoing long-term monitoring project; the dataset covers the period from July 03, 2004, to August 16, 2004.

Sampling

Soil macroinvertebrates were collected in July and August of 2004. Sampling plots 10 × 10 m in size were established in nine study sites. Soil macrofauna was hand-sorted out of soil monoliths 20 × 20 cm in area and 25–30 cm in depth depending on the presence of macroinvertebrates. A total of 340 samples and 8 430 individuals of soil macroinvertebrates were collected over 2004 year.

Quality Control

All soil macrofauna specimens were stored in the depository of the Laboratory of Population and Community Ecotoxicology of the Institute of Plant and Animal Ecology, Ural Branch, Russian Academy of Sciences (IPAE UB RAS). The specialists of the IPAE also performed species identification of most of the taxa: arachnids, chilopods, and diplopods were identified by Maxim P. Zolotarev; carabids and elaterids were identified by Alexander I. Ermakov; gastropods were identified by Maxim E. Grebennikov. Species identification of the staphylinids was carried out by Viktor B. Semenov from the Institute of Medical Parasitology, Tropical and Vector-borne Diseases named after E.I. Martsinovsky, Moscow. Earthworm species were identified by Elena V. Golovanova from the Laboratory of Invertebrate Systematics and Ecology of Omsk State Pedagogical University, Omsk.

Method steps

1. Fieldwork and processing of soil monoliths. Soil macroinvertebrates were collected in July and August of 2004. Sampling plots 10 × 10 m in size were established in nine study sites. Soil macrofauna was hand-sorted out of soil monoliths 20 × 20 cm in area and 25–30 cm in depth depending on the presence of macroinvertebrates. The sampling effort (time interval for extracting one soil monolith from the sampling plot) was approximately 5 minutes. Ten monoliths were collected from each plot randomly, excluding nearby trunk areas with a radius of 0.5–1 m around large trees (more than 30 cm in diameter) and any visible pedoturbations. During sampling, monoliths were divided into two layers: the O horizon (organic) and A horizon (organic-mineral). Monoliths were placed in plastic bags (separately for the layers), delivered to the laboratory, and stored before processing at 12°C for no more than five days (as a rule, 1–2 days). The collected invertebrates were wet-preserved in 70% ethanol; earthworms were carefully washed with water, fixed with 10% formalin, and then wet-preserved in 70% ethanol. Ants and relatively large microarthropods (springtails, oribatid mites) were left out of account. A total of 340 samples and 8 430 individuals of soil macroinvertebrates were collected over 2004 year.

General taxonomic coverage is 4 phyli, 7 classes, 16 orders, 39 families, 115 genera, 142 species of soil macroinvertebrates.

1. Annelida
   rank: phylum
2. Clitellata
   rank: class
3. Crassiclitellata
   rank: order
4. Enchytraeida
   rank: order
5. Arthropoda
   rank: phylum
6. Arachnida
   rank: class
7. Araneae
   rank: order
8. Opiliones
   rank: order
9. Chilopoda
   rank: class
10. Geophilomorpha
    rank: order
11. Lithobiomorpha
    rank: order
12. Diplopoda
    rank: class
13. Chordeumatida
    rank: order
14. Polyzoniida
    rank: order
15. Insecta
    rank: class
16. Coleoptera
    rank: order
17. Diptera
    rank: order
18. Hemiptera
    rank: order
19. Hymenoptera
    rank: order
20. Lepidoptera
    rank: order
21. Mollusca
    rank: phylum
22. Gastropoda
    rank: class
23. Ellobiida
    rank: order
24. Stylommatophora
    rank: order
25. Nematoda
    rank: phylum
26. Enoplea
    rank: class
27. Mermithida
    rank: order

The study area is situated in the lowest uplands of the Urals (altitudes are 150–400 m above sea level) and belongs to the southern taiga subzone. Primary coniferous forests (Picea abies, Abies sibirica, and Pinus sylvestris) and secondary deciduous forests (Betula pendula, Betula pubescens, and Populus tremula) prevail. Spruce and fir forests with nemoral flora on loam or heavy loam soils dominate on the western slope of the Urals, and pine forests on sandy loam or light loam soils prevail on the eastern side. Study areas are located in spruce-fir forests. The ground vegetation layer is dominated by Oxalis acetosella, Aegopodium podagraria, Gymnocarpium dryopteris, Dryopteris carthusiana, Asarum europaeum, Maianthemum bifolium, Cerastium pauciflorum, and Stellaria holostea. Soil formation occurs on eluvium and eluvium-diluvium of bedrock metamorphic rocks (shales, sandstones, quartzites, and silicified limestones). Soil cover is formed mainly by soddy-podzolic soils (Albic Retisols, Stagnic Retisols, and Leptic Retisols), burozems (Haplic Cambisols), and grey forest soils (Retic Phaeozems). Zoogenically active humus form (Dysmull) prevails (Korkina and Vorobeichik, 2021). The climate is warm-summer humid continental, Dfb according to Köppen-Geiger classification (Peel et al., 2007). The average annual air temperature is +2.0 °С; the average annual precipitation is 550 mm; the warmest month is July (+17.7 °С) and the coldest month is January (–14.2 °С) (mean values for the last 40 years, 1975–2015, according to the data of the nearest meteorological station in Revda). The snowless period is about 215 days (from April to October), the maximum height of the snow cover is about 40–60 cm. The Middle Ural Copper Smelter (MUCS), located in the suburbs of Revda, 50 km west of Yekaterinburg, has been in operation since 1940. The primary toxic emissions are gaseous compounds of sulfur, fluorine, and nitrogen and dust particles with adsorbed heavy metals (Cu, Pb, Zn, Cd, Fe, Hg) and metalloids (As). The annual amount of emissions in 1980 reached 225 × 103 t, being reduced to 148 × 103 t in 1990 and 106 × 103 t in 1991. The subsequent reduction was more significant: to 96 × 103 t in 1994, 63 × 103 t in 2000, 28 × 103 t in 2004, and, after an overhaul of the smelter in 2010, to only 3–5 × 103 t per year (Vorobeichik, Kaigorodova, 2017). Current concentrations of heavy metals in the forest litter near the MUCS are very high: Cu, 3500–5500 μg/g; Pb, 2500 μg/g; Cd, 17–20 μg/g; Zn, 600–900 μg/g; i.e., they exceed the background values by factors of 100, 40, 7, and 3, respectively (Vorobeichik, Pishchulin, 2016; Korkina, Vorobeichik, 2018). In the moderately polluted areas, exposure to emissions from MUCS has resulted in suppressed growth of trees (decrease in the height, diameter, and stock of tree stand) and ground vegetation (decrease in species diversity and productivity). Closer to the MUCS, in the heavily polluted area, the spruce-fir forest has survived in fragments with herbaceous communities of relatively poor species composition (Equisetum sylvaticum, Deschampsia caespitosa, Tussilago farfara, Agrostis capillaris) and a moss layer formed by Pohlia nutans. Despite the significant reduction of emissions in recent years, vegetation in the most polluted areas is not yet been recovered. However, some positive changes have already occurred in the moderately polluted zone (Vorobeichik et al., 2014). Apart from the metal accumulation and increased acidity, soil transformation manifests itself in the enhancement of the eluvial-gleying process, degradation of soil aggregates, decrease in exchangeable potassium and magnesium, increase in forest litter thickness, and shifts from zoogenically active Mull humus forms to Eumor humus forms without any signs of soil macrofauna activity (Kaigorodova, Vorobeichik, 1996; Korkina, Vorobeichik, 2016, 2018, 2021; Vorobeichik, Pishchulin, 2016).