Soil invertebrates of coniferous forests along a gradient of air pollution (Komi Republic)

Abstract Background The role of soil invertebrates in the cycle of substances, soil-forming processes and the provision of ecosystem services is undeniable. Therefore, soil invertebrates are valuable in bioindication studies. Comprehensive research of soil invertebrates in the production area of Mondi Syktyvkar JSC as the largest pulp and paper enterprise in the European part of Russia was initiated in 2003. A huge amount of data about composition, abundance and structure of soil macro- and mesofauna along an impact gradient was accumulated during the period from 2003 to 2019 years. These data can be used to study local biodiversity, monitor the state of soil invertebrate communities and assess the impact of the pulp and paper industry on the environment. New information Datasets here presented include information from a monitoring programme for soil invertebrates that inhabit coniferous forests in the production area of Mondi Syktyvkar JSC (Komi Republic). The assemblages' structure of macrofauna, collembolans and nematodes are described. Information on the number of individuals of springtail species, nematodes genera and macrofauna taxa is given. A total of 11146 sampling events of macrofauna, 6673 sampling events of Collembola, and 2592 sampling events of Nematoda are recorded along a gradient of air pollution from pulp and paper industry emissions.


Introduction
Previously, we have already published data on the occurrence of soil invertebrates on the European North-East of Russia (Konakova et al. 2020a, Konakova et al. 2020b. It is shown that soil invertebrates are characterised by high abundance and diversity in the study area. The structure of invertebrate communities reflects changes in soil-ecological factors. The response of invertebrates to ecosystems changes under anthropogenic impact has importance for monitoring of the state of soils (Lavelle et al. 2006, Zvereva andKozlov 2010). Intensive industrial development in Europe has a significant effect on natural ecosystems. Although the main production centres of the pulp and paper industry are located in the countries of North America and Northern Europe, there areonly poor data about such anthropogenic effects on the soil invertebrate diversity in literature (Dolgin et al. 2012). It is shown that air pollution by emissions from chemical enterprises causes changes in the abundance, biomass, diversity, structure and spatial distribution of soil fauna (Rusek and Marshall 2000, Kuznetsova and Ivanova 2020, Nesterkov et al. 2020). The technologies used in the pulp and paper industry at the end of the 20 century have significantly changed today. New and more advanced technological processes have appeared (Jaworska et al. 2020). Works aimed at reducing of pollutants emissions into the environment have been carried out at the Mondi Syktyvkar JSC since 2002 (Baturina et al. 2020). An improvement in the vital state of forest stands was noted. There is no pronounced negative impact of the enterprise on the soils (Robakidze and Torlopova 2018). The ongoing reduction of emissions from the modernised enterprises makes it possible to analyse the natural recovery of soil fauna (Vorobeichik et al. 2019). There are practically no long-term observations of the soil invertebrates response to environmental changes under industrial impact. Dataset about nematodes is the initial study to understanding diversity and abundance of this group in the production area of pulp and paper industry enterprise. Datasets about large soil invertebrates and collembolans allow us to assess the changes that have occurred in the reduction of industrial emissions. 2021) in coniferous forests along a gradient of air pollution (Komi Republic). The objectives of this study are to include data of observations for the last 18 years and to provide a basis for monitoring research of soil invertebrate communities in impacted areas of aerotechnogenic emissions from the pulp and paper industry.
boundaries of the background zone. So, the absence of any emissions impact is allowed. The analysis of emissions dispersion from Mondi Syktyvkar JSC showed that the distribution of the main emissions components occurs at a distance of up to 18 km. Therefore, coniferous forests located at a distance of 22-50 km from the enterprise were chosen as sites of the background zone (Baturina et al. 2020 Monitoring plots (PP), with distance from the emission centre of Mondi Syktyvkar JSC.

Funding: This project was supported by The Ministry of Science and Education of Russian
Federation АААА-А17-117112850235-2 "Distribution, systematics and spatial organisation of fauna and animals population in taiga and tundra landscapes and ecosystems at the Northeast European Russia"; agreement with JSC "Mondi SLPK" № 45-2018/180405 "Assessment of long-term impact of Mondi Syktyvkar JSC on the biological diversity in the production area".

Sampling methods
Study extent: We built our database by compiling sampling events of soil invertebrates, based on an exhaustive search in published and unpublished authors' sources, as well as from the Zoological Museum of the Institute of Biology Komi SC UB RAS. The data paper is based on three datasets. The datasets about macrofauna and collembolans provides temporal data on the number of their individuals in soil cores collected in pine and spruce forests of the production area of the pulp and paper industry enterprise. The dataset about macrofauna also contains the material collected by the pitfall traps and information on the age stages (larvae and imago) of invertebrates. Nematodes were collected in pine and spruce forests of the production area of Mondi Syktyvkar JSC only in 2018-2019, so these data are not temporal. The dataset about Nematoda provides information on the number of their individuals in soil cores. Three datasets have differences in data presentation. We The map-scheme of study area (lichen pine forest is marked orange, bilberry pine forestblue, bilbery spruce forest -yellow colour).
have combined them into one data paper, since a comprehensive study of the effect on soil invertebrates from the pulp and paper industry has not previously been carried out.

Sampling description:
The standard methods of soil zoology were applied. Sampling and pitfall trapping were carried out in pine and spruce forests of the impact, buffer and background zones of the enterprise production area.
Two sampling methods were used for collection of macrofauna at each site.
1. Soil sampling method. About 8-10 soil cores were randomly taken to a depth of 5-10 cm at each site. A quadrangular frame of 25 × 25 cm or 10 × 10 cm was used for sampling. Actively moving animals were placed into containers with 70% alcohol as a fixative. Further, in laboratory conditions, the extraction of invertebrates from soil cores into 70% alcohol was carried out in the funnels.
2. Pitfall trapping. Pitfall traps of the same type (plastic glasses, depth 10 cm, diameter 12.0 cm, salt water (30% vol.) and formalin (5% vol.) as a fixative) were used at each site. The traps were emptied once per 7-10 days; all collected invertebrates were preserved in 95% alcohol for subsequent identification with a binocular microscope.
One sampling method was used for Collembola collection. In each site, 10 soil samples were taken. Samples were taken to the full depth with division into two layers -litter and mineral horizons; in further analysis, the data on the layers were combined. Extraction was carried out according to the generally-accepted method using Berlese -Tulgren funnels in 96% alcohol for 7-10 days -the time sufficient to achieve an air-dry soil state. Collembolans from the samples were sorted under a binocular microscope. All individuals were mounted in slides in Phoera liquid according to a standard procedure (Potapov and Kuznetsova 2011).
The soil sampling method also used for Nematoda collection. Soil samples were collected from the organic and mineral soil horizons. In pine forests, eight soil cores (5 × 5 cm, 10 cm depth) were taken at each site. In spruce forests, five soil cores (5 × 5 cm, 10 cm depth) were taken at each site. Nematodes were extracted from 50 g of fresh soil using the modified Baermann Method (Ruess 1995). Extraction lasted for 48 h. Extracted nematodes were euthanised at 60°C and then preserved in 4% formaldehyde.
The material includes data collected during the period of modernisation and reduction of emissions of the enterprise. Thus, the real changes in soil invertebrate communities can be estimated.
Quality control: The data were collected by specialists from the Institute of Biology of the Komi Scientific Center of the Ural Branch of the Russian Academy of Sciences. Lumbricidae, Lithobiidae, Julidae, Polyzoniidae, Coleoptera (Carabidae, Staphylinidae, Elateridae, Curculionidae, Ostomatidae) and some Hemiptera were identified to species by specialists from the Institute of Biology. All specimens of Collembola and Nematoda were also identified to species and genera, respectively, by specialists from the Institute of Biology. Different taxonomic keys were used for identification of large soil invertebrates (Lohse 1964, Gurjeva and Kryzhanovskij 1965, Lohse 1974, Vsevolodova-Perel 1997, Andersson et al. 2005, Collembola (Fjellberg 1998, Potapov 2001, Fjellberg 2007 and Nematoda (Jairajpuri and Ahmad 1992, Bongers 1994, Brzeski 1998. The material (invertebrates fixed in alcohol and formalin, on preparations and in entomological collections) is kept in the Zoological Museum of the Institute of Biology. On each slide and/ or label, the following fields were filled out: "Collection date", "Locality" (with geographic coordinates), "Habitat", "Collector name" and "Determined by" (identification).

Geographic coverage
Description: The study area is located in the middle taiga zone of Komi Republic. The Mondi Syktyvkar JSC production area is located on the Vychegda River bank in the vicinity of Syktyvkar City. There are arrays of spruce and pine forests in the research area.

Taxonomic coverage
Description: The datasets contain all of the information obtained during the sampling for macrofauna, Collembola and Nematoda. A decrease of nematodes abundance (Fig. 3) and the decline in the species richness of macrofauna (Figs 4, 5) was noted in spruce and pine forests along the pollution gradient. There are changes in the abundance and number of Collembola species along the pollution gradient before and after emission reduction (  Table 2.
Abundance and species number of Collembola along the pollution gradient.
Soil invertebrates of coniferous forests along a gradient of air pollution ...