Oribatid mite (Acari: Oribatida) and Chironomid (Diptera: Chironomidae) communities from a high-Andean cushion peatland in Peru (14°S) and their use for palaeoenvironmental reconstruction during the Nasca cultural period

The edaphic Oribatid mites and Chironomid larvae of five different successional stages of a high-Andean cushion peatland in southern Peru (14°S) were investigated. In total, 17 Oribatid mite taxa, belonging to eight families could be identified. Taxonomic remarks for the species found and an analysis of community structures are provided. The investigation shows significantly higher Oribatid mite densities in the early and medium successional stages in comparison to the successional climax ecotope. From the Chironomids, 11 taxa belonging to three subfamilies could be identified. For the taxa found, taxonomic descriptions and an analysis of community structures are also provided. Within the successional rank order of the peatland, the abundance of Chironomids is highest in pioneer soils, followed by mid-successional and degraded soils. Subsequently, a biogeographical investigation is presented of the Oribatid mite fauna from the high Andes is. Only 39 sampling sites, ranging from 3000-5200 m altitude from southern Ecuador (4°S) to mid-Argentina (34°S), have been sampled before. Only seven of these sampling sites can be assigned to cushion peatlands. For all available sampling sites, a diversity analysis was carried out, which revealed 219 species from 116 genera, comprising 51 families from the high Andes >3000 m a.s.l.. For cushion peatlands, 48 species from 34 genera, comprising 18 families were identified, of which only nine species were found in two or more sampling sites. In the high Andes, the γ-diversity of Oribatid mites shows evident fluctuations with latitude. At low latitudes 30 species. With increasing latitude, the richness declines to seven species at 19°S before it increases again to 14 species at >30°S. This fluctuation is probably associated with changes in precipitation. The analysis reveals that the high Andean Oribatid mite community is highly nested at both the genus- and species-level, and shows a zonal character for the community in contrast to the azonal occurrence of cushion peatlands; a significant change in the taxonomic composition of the community is indicated at about 4-7°S. In a subsequent geochemical investigation, the soil conditions (water content, C/N ratios, conductivity, pH and element content) of 38 samples from five ecotopes of the selected peatland in southern Peru were analysed. The data reveal the ecological heterogeneity of the peatland with strong variations in nutrient availability (very poorly oligotrophic - strongly mesotrophic), soil wetness (dry - saturated) and element content (e.g. in As, Cr, Cu, Fe, K, Pb and Rb). On the basis of these results, an advanced succession model is proposed for the different peatland ecotopes. Furthermore, the geochemical data were used to reveal microhabitat descriptions, community responses and the soil condition indicator potential of the Oribatid mite and Chironomid communities. From the Oribatid mites, seven indicators were assessed, with six species indicating low soil wetness 73%. From the Chironomids, five indicator taxa were revealed, with four taxa indicating soil wetness of 80-81%, and a single taxon indicating soil wetness >81%. Finally, to apply the autecological data to the palaeoecological record, the Oribatid mite and Chironomid subfossil assemblages were investigated in a 152 cm-long core, retrieved from the cushion peatland, which represents a record covering 1064 years (1924-860 cal yr BP; 26-1090 AD). 16 Oribatid mite species and 12 Chironomid taxa were identified, with five significant indicator taxa from each being used to reconstruct soil wetness quantitatively, by employing a modern analogue technique (MAT) model. The model predicts a humid period from 1924-1426±22 yr BP (26-524±22 AD) with a significant dry spell occurring from 1601±35-1543±24 yr BP (349±35-407±24 AD), and which was fully established by 1567 yr BP (383 AD). After 1426±22 yr BP (524±22 AD), the soil wetness shifted to drier conditions and remained stable until 860 yr BP (1090 AD). The reconstructed soil wetness fluctuations are supported by supra-regional signals revealed by other studies and coincide with migration movements and cultural changes of the Nasca people in the Peruvian costal area. This investigation confirms the sensitivity of the high-Andean cushion peatlands for climate fluctuations and highlights the strong dependency of the foothill region and the local population on the water supply from the high Andes. The water supply is essentially controlled by the peatlands in the headwaters, which basically act as water storages and drainage controllers. The results emphasise the need for a sustained conservation effort to protect the high-Andean cushion peatlands, which are nowadays endangered by mining activities and overgrazing.