Stable isotope insights into arthropod food chains and nitrogen cycling in a rehabilitated tailings chronosequence

Field studies in post-mining sites on epigeic invertebrate groups are scarce despite their importance in pedogenesis and ecosystem multifunctionality. This research investigated the diversity, abundance and succession of aboveground invertebrates in a rehabilitated Pb/Zn tailings chronosequence of 5, 20 and 35 years. The study also explored the trophic relationship of selected arthropods and characterized the nitrogen (N) cycle using stable isotope measurements. The abundance and species richness in most investigated groups and the dominance index Berger-Parker (BP) of aboveground invertebrates increased with rehabilitation age from 0.17 BP in early to 0.31 BP in late stage. Elemental and stable isotope ratio analysis showed that N and C soil content increased and the C/N ratio decreased with age, yet despite this increased N availability in the system, the maturing N-cycle used N efficiently. The lack of large N losses from the system despite substantial atmospheric deposition inputs was indicated by the fact that N isotope ratios (delta 15N) in plants and animals became significantly more negative with rehabilitation age, -6.0 delta 15N for plants, -5.0 delta 15N for herbivores and 3.0 delta 15N for carnivores. The length of the invertebrate food chain expanded by more than half a trophic level (2.7 parts per thousand delta 15N) for top predator Coleoptera from early to late stage, probably reflecting more complex food webs including intra-guild predation in older communities. In conclusion, delta 15N measurements in plants and animals provided novel insights into the N-cycle, accumulative N flows and the trophic position in post-mining sites. It is proposed that isotope ratio measurements could be used as easy-to-measure, integrating indicators of nutrient cycling and the soil food web complexity of rehabilitated mine tailings and similar soil ecosystems.